How Body Works

198 199CHEMICAL BALANCE
Daily rhythms

4 Cortisol peaks JET LAG
After the morning
surge of cortisol, the body Air travel transports us into new
gets another dose around noon. time zones faster than the body can
From then on, cortisol plays adjust. It takes time for the new
a smaller role in the system. rhythm of daylight to reset the body
Melatonin is at its lowest level 5 Aldosterone surge clock. Some hormone cycles are
at this time. Midafternoon sees more flexible than others—cortisol
a peak in the hormone can take 5–10 days to adapt. While
aldosterone. This helps our rhythms adjust, the body feels
Cortisol keep the blood pressure hungry and sleepy at all the wrong
times—a phenomenon
steady by increasing water called jet lag. Shift
reabsorption in the kidneys. workers experience
this regularly, and
Melatonin the long-term
health consequences
12AM are not yet fully
understood.
3PM

6 Sleepy melatonin
Decreasing light
levels prompt the
6PM conversion of serotonin
into melatonin. This slowly
Thyroid gland prepares the body for
8PM sleep and finally causes
sleepiness itself.

9PM 7 Stimulating thyroid
In the evening, levels
of thyroid-stimulating
12PM hormone abruptly increase.
This stimulates growth and
Melatonin repair, but also inhibits
Cortisol neuronal activity, possibly

preparing the body
for sleep.

8 Growth hormone
The first two hours of sleep
see a burst in growth hormone,
which helps children grow and
adults regenerate. It’s also released
9 Melatonin peaks in the day, but more is produced
Melatonin levels in the blood A BRISK WALK AT
are highest around midnight. This is at night, when the body can LUNCHTIME HELPS BOOST
focus on repair. SEROTONIN LEVELS
also when cortisol levels are at their
lowest. This ensures that the body
rests completely overnight.

Diabetes MANAGING DIABETES

Insulin is the key that opens muscle and fat cells Sugary foods and certain carbohydrates
to receive glucose, which the body needs for cause fat to be laid down in the body’s
energy. Without insulin, glucose remains in the cells, and fat interferes with insulin. The
blood, and the cells don’t get the energy they more fat present, therefore, the greater the
need, which has serious health consequences. If risk of type 2 diabetes. A healthy, balanced
insulin fails to work, the result is diabetes, a diet not only reduces this risk, it is also
disease that has two forms—type 1 and type 2— a vital part of managing the disease once
and currently affects 382 million people globally. it develops. Generally, diabetic diets aim
at keeping blood glucose levels as normal
Muscle cell closed Glucose unable as possible, avoiding foods that cause
due to lack of insulin to enter closed sharp rises and falls
muscle cells in glucose. This also
helps in calculating
insulin dosages,
which may be a
part of treatment.

BLOODSTREAM 1 Glucose on the rise
During digestion, glucose is
Glucose but no insulin released into the bloodstream. The rise
in bloodstream in glucose levels triggers mechanisms
that will lower them—including the
release of insulin from the pancreas
(see pp.158–59).

3 No entry for glucose
Without insulin, glucose can’t enter the body’s cells.
Instead, it builds up in the blood, and the body reacts by
trying to get rid of it by other means, such as urination.
Glucose molecule

Type 1 diabetes 2 No insulin available PA N CRE AS
However, in type 1 diabetes,
In type 1 diabetes, the body’s immune system attacks the insulin-producing cells of the
the insulin-producing cells of the pancreas, leaving the pancreas have been destroyed by
pancreas unable to produce any insulin. The symptoms the body’s own immune cells. As a
emerge over a matter of weeks but can be reversed once consequence, no insulin is released
treated with insulin. Although people can develop type 1 to counter the rising glucose levels.
diabetes at any age, most are diagnosed before the age
of 40, particularly in childhood. Type 1 accounts for
10 percent of all diabetes cases.

200 201CHEMICAL BALANCE
Diabetes

The symptoms of diabetes Always feeling thirsty,
hungry, and tired
The symptoms of type 1 and type 2 diabetes are similar. Blurred vision caused by
The glucose that the kidneys can’t get rid of starts to buildup of glucose in the lenses
build up in the body, so the body tries to flush it out, so Bad breath caused by
thirst, water intake, and urination increase. Meanwhile, ketones being burned
the body’s cells are being starved of glucose, which instead of glucose (see p.159)
causes fatigue throughout the body. Weight loss also Hyperventilation caused
occurs, due to the body burning fat instead of glucose. by lack of energy
Weight loss
Nausea and vomiting
Frequent urination

Insulin molecule Glucose admitted by
opening muscle cell

insulin molecule Buildup of fat

3 Glucose barred entry
Due to a buildup of fat in
the cells, insulin is prevented
from doing its job of opening
STOMAC the body’s cells. Since the
cells are then starved of
glucose, they signal to
H the liver to release more

glucose, leading to a
further increase in
blood glucose levels.
Muscle cell BLOODSTREAM

1 Glucose in
During digestion,
glucose enters the
bloodstream as
normal.

4 Insulin overload
More and more insulin is
released in response to rising blood
glucose levels. This can cause the
pancreas to weaken and eventually
to stop functioning.

Insulin molecule Type 2 diabetes

2 Insulin out In type 2 diabetes, the body either isn’t producing enough
On detecting the presence insulin or its insulin isn’t working properly. It occurs more
of glucose in the bloodstream, the often in people with obesity, but it also occurs in people
pancreas releases insulin. of healthy weight. The symptoms emerge more gradually,
although some people may not show symptoms at all. In
fact, 175 million people globally are thought to be living
with undiagnosed type 2 diabetes. Type 2 accounts for
90 percent of all diabetes cases.



THE CIRCLE
OF LIFE

Sexual reproduction

You are driven by your genes to reproduce, so that your genes Seminal vesicle
continue to multiply in generations to come. Evolutionarily adds fluid to sperm
speaking, this is why we have sex. Millions of sperm compete
against one another to find one egg and begin the process
of creating a new individual.

Bringing sperm and egg together

The main aim of sex is to bring genes from the male and Prostate gland adds
the female together. The male inserts millions of packets further fluid to sperm
of genes in the form of sperm into the female in an attempt
to produce semen

to fertilize one of her eggs. If successful, the male’s and

female’s genes mix, generating a new, unique combination Bulbourethral gland
of genes in the offspring. To achieve this, both male and neutralizes acidity of
female individuals become sexually aroused by one
another, which causes some physical changes. Genital urine in urethra to
prevent harm
to sperm

organs in both genders enlarge due to increased blood WHY DO WOMEN
flow, the penis becomes erect, and the vagina secretes HAVE ORGASMS?
a lubricating fluid to aid the penis’s entry.
Sensitive nerve endings in the

clitoris send pleasurable signals

SEMEN NORMALLY CONTAINS to the brain, causing the vagina Sperm travels
1–8 BILLION SPERM PER FLUID to contract tightly around the through penis
OUNCE (140–300 MILLION penis, thus ensuring that the in the urethra

SPERM PER MILLILITER) male ejaculates as much
sperm as possible.

HOW DO ERECTIONS WORK? Closed veins prevent Artery
blood outflow transports
The penis contains two cylinders blood
of spongelike tissue, called the
corpora cavernosa. When small Sperm matures
arteries at the base of the penis in epididymis
dilate, or widen, blood flows into
the penis and the corpora cavernosa FLACCID Corpora ERECT
expand to form rigid cylinders. This cavernosa fill
compresses small drainage veins so
that blood cannot flow away and
the penis hardens. After ejaculation,
the pressure reduces and drainage
veins reopen, allowing blood to flow
out and the penis softens.

with blood

204 205THE CYCLE OF LIFE
Sexual reproduction

MALE BLADDER The perilous journey of sperm

During sex, the erect penis is inserted into the vagina. The penis
releases semen during orgasm and sperm start their journey to find
an egg. Millions of sperm, aided by whiplike movements of their tails,
swim up from the vagina, through the cervix, and into the uterus.
Sperm is carried in fluid currents caused by the movement of hairlike
cells lining the fallopian tubes. Only 150 or so sperm find their way to
the upper fallopian tubes, where fertilization usually occurs. The
remaining sperm are naturally flushed out of the vagina.

If sperm meets an egg, it FALLO
is usually here in upper
FEMALE BL fallopian tube
Vas deferens
carries sperm from
testis to penis
PIAN TUBE

ADDER
IS
CLITOR OVARY

UTERUS

PENIS

URETHRA Sperm travels
into the uterus
ERECTILE TISSUE Cervix
X100
TESTIS SCROTUM VAGINA X100

Penis ejaculates sperm ⁄1 500 IN (0.05 MM)
into the vagina

Scrotum contains both testes LARGEST CELL IN THE BODY
outside body, because sperm
production requires a cooler An egg (called an ovum) is the
temperature largest cell in the human body and
just visible to the naked eye. It is
protected by a thick, transparent LIFE SIZE
shell. Sperm cells are one of the
smallest types of cells in the body,
averaging about ⁄1 500 in (0.05 mm)
long, but most of this is its tail.

Monthly cycle

Every month, a woman’s body prepares for the possibility of pregnancy.
Stored in the ovaries, half a million dormant eggs await their turn for ovulation.
When hormone levels reach their peak, an egg bursts from an ovary, ready for
fertilization. Thick tissue in the uterus lining awaits the egg, if it is fertilized.

Menstrual cycle 1 ME2NST3RUATION
4
The menstrual cycle is controlled by the pituitary gland in the brain. Beginning at

puberty, follicle-stimulating hormone (FSH) is produced by the pituitary gland. 27 28

FSH prompts the production of estrogen and progesterone hormones in the 26
ovaries. The pituitary gland releases a monthly pulse of FSH and also
5
luteinising hormone (LH), triggering a monthly cycle. A single matured 25
6
egg is released from the ovary and the lining of the uterus—the 24 What happens when 7
endometrium—will thicken and then shed. If the egg is fertilized and 23 The first day of each menstrual 8
then implants into the endometrium, the cycle ceases. Later in life, period is labeled as Day 1. The
when the number of dormant eggs in the ovaries reaches a point length of the menstrual cycle
varies from woman to woman,
where they cannot produce enough hormones to regulate the 22 but between 21 and 35 days 9
menstrual cycle, menopause is triggered, and the cycle stops. is considered normal. The 10
21
MENSTRUAL CRAMPS 20 average length is 28 days.
19
11

The muscles in the lining of the 18 12
uterus naturally contract during 17 16 15 14 13
a menstrual period, constricting

tiny arteries to limit bleeding. If OVULATION
the contractions are intense or

prolonged, they press against Hormone surge
Estrogen is produced by cells in the
nearby nerves, causing pain. Muscles lining uterus 3
contract, causing pain
follicle that surrounds a maturing egg
in the ovary. When estrogen levels
peak, this causes a surge of FSH and
LH to be released from the
pituitary gland, which
1 Menstrual bleeding triggers ovulation. ESTROGEN
If a fertilized egg does not implant in the
endometrium, falling progesterone levels cut down
its blood supply, causing the outer layer to be
shed as menstrual bleeding. This can serve as an
indicator that pregnancy has not occured.
2 Endometrium grows
During the first 2 weeks
of the menstrual cycle, steadily
rising estrogen levels cause the
endometrium to grow.

Bleeding from vagina Slight rise in FSH levels
as endometrium sheds stimulates production of
estrogen and progesterone
FSH AND LH

206 207THE CIRCLE OF LIFE
Monthly cycle

3 Secondary Egg travels through
follicle develops fallopian tube, where it
Fluid-filled spaces form
may be fertilized, and
into uterus

4 Follicle matures FALLOPIAN TUBE within the dominant
The follicle grows follicle and the egg inside
continues to develop,
to about 0.8–1.2 in (2–3 cm) ready for ovulation.
across and may even bulge
from the ovary’s surface. UTERUS

Fluid-filled Dominant
space follicle enlarges

2 Fertilized egg
latches onto
Egg released OVARY One dominant follicle uterus lining
from ovary undergoes a growth spurt.
The other nondominant
Bursting follicle follicles stop growing.

5 Ovulation Egg
A surge of FSH and inside follicle
LH hormones from the
pituitary gland causes
ovulation. The follicle Primary
ruptures, releasing the egg 1 follicles form

through the ovary wall and FSH stimulates the
growth of several
into the fallopian tube. dormant follicles in the ENDOMETRIUM

ovaries, all of which begin
to release estrogen.

Fringe of tissue fingers 6 Degeneration 7 Scar forms
called fimbriae helps The empty follicle If pregnancy does
guide egg into collapses and forms a cyst
fallopian tube called the corpus luteum. not occur, the corpus luteum
stops making progesterone.
The corpus luteum produces The corpus luteum is then
more progesterone hormone
to keep the uterus lining replaced by scar tissue,
and the cycle restarts.
4 Further hormones thick and plump.
After ovulation,
progesterone is produced
by the dissolving corpus luteum
in the ovary. This hormone
prompts the growth of arteries PROGESTERONE Hormone patterns
into the endometrium. This makes Visualized here are the key hormones
the endometrium softer and that regulate the menstrual cycle.
spongier, ready to receive a
fertilized egg. Follicle-stimulating
hormone (FSH) and
ENDOMETRIUM luteinising hormone (LH)

Estrogen
Progesterone

One cell

Outer cell mass

One cell

Inner cell
mass
Outer Multiple
cell layer cells

Inner cavity filled
with fluid

4 2-CELL STAGE 5 BALL OF CELLS 6 HOLLOW BALL OF CELLS
The two cells within The dividing cells form a The blastula, or ball of cells,
has a fluid-filled cavity that will
the egg’s outer layer remain ball, called a morula, as it travels toward become the amniotic sac. Outer
attached. (But if they separate, the uterus. The morula is encapsulated in
identical twins may result.) an outer layer, so the dividing cells are cells will form the placenta when it
attaches to the uterus wall, and the
progressively smaller. inner cells will form the embryo.

Cell nucleus FALLOPIAN TUBE UTERU

Dividing cell

S

OVARY

3 FERTILIZED EGG Fertilized egg
The egg starts embedded on soft
to undergo the first of
many divisions. This is uterus lining

how an embryo grows EGG CELL
from a single cell.

VAGINA

2 FERTILIZATION 1 BURROWING IN
The sperm nucleus The sperm head
contains genes from the
father. When it merges Sperm uses enzymes to bore
genes through the egg’s outer
with the egg’s nucleus, layer. These enyzmes are
its genes join the egg’s Merging
genes, which come from nuclei similar to those used by
the intestines when they
the mother to complete Mixed digest food.
the genetic blueprint genes

for a new baby.

Sperm
head

Enzymes

208 209THE CIRCLE OF LIFE
Tiny beginnings

Tiny beginnings

An egg’s journey For some 48 hours after sex, around 300 million sperm race to
Each month, several fertilize an egg as it travels down one of the fallopian tubes.
eggs start to mature Sperm are chemically attracted to the egg, aiding them on
within the ovaries. their 6 in- (15 cm-) long journey. When a single sperm
Normally only one
developed egg is fertilizes the egg, a cascade of changes follows.
released at ovulation.
The released egg then Fertilization WHEN DOES
enters one of the PREGNANCY BEGIN?
fallopian tubes. If a woman has ovulated and has had sex, there
is a chance of fertilization—the joining of egg and Pregnancy does not start until
sperm to lay the foundation for pregnancy. The the fertilized egg successfully
embeds itself in the soft lining
moment the sperm penetrates the egg’s outer layer,
the egg undergoes a rapid chemical change and of the uterus—at this point,
hardens to prevent other sperm from burrowing new life has potentially
in. Now the combined egg and sperm is called a been conceived.

zygote. It begins to divide as it enters the womb
(uterus). Fertilization may have been achieved,
but there is a long way to go until birth.

THE ANSWER TO INFERTILITY

Infertility problems are common in IDENTICAL TWINS NONIDENTICAL TWINS
both genders, and affect one in six Single egg Two
couples. Some females may have cell egg cells
problems with ovulation, their
fallopian tubes may be blocked, SPERM EGG
or their eggs may be too old.
Alternatively, males can suffer from Shared
a low sperm count, or their sperm placenta
may swim poorly. Nevertheless,
there are a number of treatments Separate
available. One of these, in vitro placentas
fertilization, involves collecting
eggs and sperm and placing them How twins form
in a “test tube” for fertilization to
occur. The fertilized egg is then If two eggs are released at ovulation and both are
allowed to develop before it is fertilized, nonidentical twins result. These can be the
implanted back into the uterus same or different sexes and each has its own placenta.
to continue its development. When a single fertilized egg splits and each embryo
A more advanced procedure is continues to divide separately, identical twins results,
intracytoplasmic sperm injection, each with their own placenta. If the egg divides late,
in which a sperm nucleus is identical twins share a placenta.
injected directly into an egg.

The generation game

Although you are a unique individual, you may have familiar features that
are shared by your family. These traits are handed down from generation
to generation by genes carried by the mother’s eggs and father’s sperm.

Widow’s peak

Hereditary traits Freckles FATHER Pool of possible traits MOTHER
Father and mother can potentially
Genes instruct your body on how to pass any of their genes on to
contribute to their child’s physical
develop (see p.23). Structures called appearance and personality. This
example shows a possible way to
chromosomes carry multiple genes (see inherit three different traits: a
father’s widow’s peak and freckles,
p.16). Each sperm and egg cell from your and a mother’s roman nose. Roman nose

father and mother contains a random

selection of their genes. When these cells

merge during fertilization, the sets of genes

mix, forming a new and unique blueprint Father’s gene for Cell’s nucleus,
freckles does not where genes
that makes you “you.” If you have brothers pass onto first child are stored

or sisters, they inherit a similar selection

of genes to you, so you may resemble each

other in facial features or body shape and

may share similar personality traits or

mannerisms. Alternatively, siblings can Chromosomes in each
cell nucleus carry genes
inherit few of the same genes, and may
Mother’s gene for
not even look related at first glance. roman nose

RM EGG Other gene EGG
mother passes on

SP to second child

Father’s gene for SPE ERM
widow’s peak

Selected traits Father’s trait for
The combination of genes differs with widow’s peak is passed
each sperm and egg cell. In these instances,
for the first conception, the father’s gene for on to second child as
a widow’s peak is in the sperm cell that fertilizes well as the first
the mother’s egg cell with the roman nose gene.
However, the father’s gene for freckles is not
in the sperm cell that fertilizes the egg for the
first child, but is for the second.

Traits from both parents FIRST CHILD CHILD’S GENES SECOND CHILD CHILD’S GENES Shared traits
The sperm and egg that The second child
produced the first child has inherits the father’s
passed on the father’s gene genes for both a
for a widow’s peak and the widow’s peak and
mother’s gene for a roman freckles. These
nose. As a result, this child siblings share at
will share traits with both least one physical
parents. By chance, they characteristic—the
have not inherited their widow’s peak.
father’s freckles.

Dominant and recessive traits GENDER-LINKED INHERITANCE

Traits can be inherited in a dominant or recessive pattern. The dominant If a mother carries a faulty recessive gene for a vision
and recessive versions of a gene are called alleles and are found at the problem on one X chromosome, her body will use the fully
same place on a chromosome. A dominant allele usually shows its trait working gene on her other X chromosome. A daughter who
whenever it is present, while a recessive gene only shows its effects if a inherits the faulty gene will (like her mother) be a carrier
more dominant version is absent. If you have detached earlobes, you have and won’t be affected, as the dominant gene masks its
at least one dominant allele. Only if you have two copies of the recessive effects. However, as males have only one X chromosome,
version do you show the recessive trait—the rarer attached earlobe. any son with the faulty gene will have deficient vision.

FATHER MOTHER CARRIER UNAFFECTED
Dominant MOTHER FATHER
allele for
Recessive allele detached Recessive THE CIRCLE OF LIFE
for attached earlobes allele for vision
earlobes deficiency The generation 210 211game

DOUBLE DOMINANT- DOMINANT- DOUBLE UNAFFECTED UNAFFECTED CARRIER AFFECTED
DOMINANT RECESSIVE RECESSIVE RECESSIVE DAUGHTER SON DAUGHTER SON

DETACHED EARLOBES ATTACHED EARLOBE No vision No vision No vision Vision
deficiency deficiency deficiency deficiency

Growing life

The development of new life is a miraculous process Four–week embryo
in which a fertilized egg divides to form a full-grown The spine, eyes, limbs, and organs have
baby in just 9 months. Connecting the mother and started to form. The embryo is around 3⁄16 in
child is the placenta, a special organ that provides (5 mm) in length and weighs 1⁄32 oz (1 g).
the growing fetus with everything it needs.
Head
From cells to organs
Umbilical cord
During the first 8 weeks, the baby is known as an embryo.
Genes switching on and off instruct cells on how to develop.
Cells in the outer layer of the embryo form brain, nerve, and
skin cells. The inner layer becomes the main organs, such as
the intestines, while cells connecting the two layers develop
into the muscles, bones, blood vessels, and reproductive organs.
Once these main structures are laid down, the baby is called a
fetus until birth.

First heartbeat Leg bud Spine
Heart growth is almost Releases urine
complete by 6 weeks and
all four chambers beat Urine is released by the kidneys into the
rapidly at around 144 amniotic fluid every 30 minutes. It is
beats per minute. This
beating can be detected diluted in the fluid and can be swallowed
during an ultrasound scan. harmlessly by the fetus. Eventually, it
passes via the placenta to the mother

and she excretes it with her own urine.

Tiny limbs Lungs form
The upper limb buds will The two lungs begin to form
develop into the arms, around this time. They won’t
while the lower limb buds be ready to breathe air by
will form the legs. Fingers themselves until the baby
and toes begin fused is almost ready to be born.
together, then separate.

Fetal development PREGNANCY 1 2 3 4
Every fetus develops TIMELINE
at its own rate and the MONTH MONTHS MONTHS MONTHS
timing for key events
tends to vary.

MOTHER 212 213THE CIRCLE OF LIFE
EMBRYO Growing life

Mother’s blood vessel

Mother’s blood pools into space

Embryo’s Meeting point Support system
blood vessel The baby’s part of the
placenta ends in a fine The baby is supported by the placenta
network of blood —a unique organ that begins growing
vessels that extends into along with the embryo under the
the mother’s half of the control of both the mother’s and the
placenta—close to, but baby’s genes. In the placenta, blood
never mixing with, the vessels from both mother and fetus
mother’s blood. are intimately interwoven, but the
blood never mixes. If it did, the
PLACENTA mother’s immune system would reject
the fetus as “foreign.” The fetus gets
AMNIOTIC FLUID Umbilical its oxygen and nutrients from its
cord mother’s blood, via the placenta and
umbilical cord, and gets rid of wastes,
such as carbon dioxide.

Sense of smell
The fetus can recognise the

smell of its mother via the
amniotic fluid. After birth, the
baby is attracted to her smell.

Twitches and “kicking” Sensitive to noise First look
A baby’s “kick” can be any The baby is startled by The fetus’s eyelids do not
number of movements the loud noises. After birth, it open until around the
mother feels as her fetus will remember songs and seventh month. When
flexes its spine and learns voices it heard while the eyes first open, they
how to move its limbs. inside the womb. cannot form images—
they can sense only
light and dark.

5 6 7 8 9

MONTHS MONTHS MONTHS MONTHS MONTHS

Mother’s new body BRAIN

The growth of a baby inside a mother’s body
is an amazing feat—but also a demanding one.
The body undergoes an incredible amount of
changes and compromises during pregnancy.

Pregnancy transformation Draining brain SPINE
The brain recycles its fatty acids
Pregnancy is a time of great physical and in order to provide the baby’s LUNG
emotional change. These changes prepare brain with the fatty acids it needs.
the mother for the extra demands of pregnancy. This is a possible cause for the
The body must not only supply its own needs “wooly thinking” many women
but also provide the growing baby with all the
oxygen, protein, energy, fluid, vitamins, and experience toward the end
minerals it needs. The body also absorbs the of the pregnancy. Extra fatty acids
baby’s wastes, and processes them alongside
its own. Organs start to support both the body in the mother’s diet could
and the baby, so expectant women may tire easily; counteract this problem.
however, the wonder of pregnancy is a remarkable
example of the adaptability of the body. Breasts enlarge
The breasts and nipples
WHAT CAUSES ODD FOOD CRAVINGS? enlarge in response to rising levels
of the hormone estrogen. Milk-
Food cravings are undoubtedly one of the strangest producing glands in the breast
phenomena that accompany pregnancy. They mature in response to progesterone,
may be a symptom of nutritional deficiencies. another hormone. Breasts may
If the body or the baby is crying start to leak colostrum,
out for certain nutrients, this or “pre-milk,” at the end
could lead to desires for odd
food combinations, such as of pregnancy. .
gherkins with ice cream. Breathing and
Cravings for non-nutritive heart rates rise
items such as soil or coal are Blood volume increases by
rarer, but do sometimes occur. about one-third, so the heart
pumps harder. Pulse rates of the
mother rise, but veins dilate,
or widen, so blood pressure
naturally falls. Breathing is
quicker in order to obtain
the extra oxygen
the fetus needs.

DIAPHRAGM

LIVER

WHAT IS Squashed stomach STOMACH
MORNING SICKNESS? As the baby grows, so does
the uterus—this pushes the Estrogen release Pressure on spine
Early in pregnancy, hormone mother’s stomach up against As the uterus enlarges, the
changes in the inner ear disrupt the diaphragm. As a result, center of gravity of expectant
the balance of expectant mothers, women shifts forward so
many expectant women naturally they start to lean back.
inducing nausea and causing experience heartburn due This alters their posture and
dizziness similar to when drunk. to acid reflux, and they may puts extra strain on muscles,
ligaments, and small joints in the
Morning sickness can happen be afflicted with loud lower spine, causing backache.
at any time of day. burps too!

Hormone producer Progesterone release
As it forms, the placenta
THE UTERUS produces a hormone, human
EXPANDS TO chorionic gonadotropin (hCG),
500 TIMES ITS that is detected by pregnancy
NORMAL SIZE tests. The placenta then starts
BY THE END OF to produce estrogen and
PREGNANCY progesterone at an increasing
rate, causing physical changes
such as breast growth.

STRETCH MARKS Abdomen growth 214 215
As the uterus expands out
Stretch marks are a result of rapid weight of the pelvis, the distance
gain and stretching of the skin. Deeper in between the pubic bone and
the skin, elastic fibres and collagen that the top of the uterus (fundus)
normally keep skin firm helps doctors estimate the
and smooth wear thin stage of pregnancy. A fundal
over the course of height of 9 in (22 cm) suggests
pregnancy. Most women a pregnancy is at around
are left with stretch
marks – however, some 22 weeks.
lucky women go through Squashed bladder
pregnancy unscathed.
The bladder is squashed by
the rapidly growing uterus, so
it holds less urine, resulting in
frequent visits to the bathroom.
Late in pregnancy, the weight of the
uterus stretches the muscles that
support the bladder, which can lead

to unfortunate leaks when
coughing, laughing,
or sneezing.

The miracle of birth

Giving birth to a new life is a daunting and exciting experience.
Nine months of pregnancy have prepared mother and child for
labor—which can last from 30 minutes up to a few days.

Relaxin hormone Placenta DILATION

Relaxin CTION AND Cervix widens
softens The muscles in the
pelvic 2 uterus contract and push
ligaments

CONTRA the baby’s head against the cervix, which gradually dilates
UTERUS(widens) to around 4 in (10 cm) wide. Contractions are regular
and painful. Typically, this stage lasts about 10 hours, but
this can vary.

PLACENTA

Initiating birth Umbilical cord
Late in a pregnancy, the placenta will
produce a hormone called relaxin that CUOTNETRRUASCTING
relaxes the pelvic ligaments to widen
the pelvis, and softens and opens the Dilation of the
cervix and vagina, in preparation for birth. cervix begins
The exact trigger for labor is unknown.
Labor differences
WATER BREAKS
There are four stages to giving birth, but each
1 Amniotic fluid VAGINA stage may take a varying amount of time. Every
As the baby’s head VAGINAwoman has a different experience of labor, even
presses against the cervix, if they have multiple births during their life. These
the amniotic sac breaks. stages can happen in quick succession, or over
Usually less than 10 fl oz the course of a couple of days. During a second
(300 ml) of fluid leaks pregnancy, the time taken to get to the contraction
out. Unlike in the stage may be shorter than it was for the first.
movies, it may not all
come splashing out at
once—it could be
a steady trickle!

Amniotic Amniotic fluid
sac breaks released from body
through vagina

216 217THE CIRCLE OF LIFE
The miracle of birth

CROWNING 3 Time to push CARRYING TO FULL-TERM
After a pause, the contractions
become more powerful—this is when the Pregnancies can vary—only 1 in 20 babies are born
mother will feel the need to push. The baby is on the due date calculated at the beginning of
forced into the vagina (birth canal). Crowning
is when the baby’s head is first visible. pregnancy. Doctors consider forty weeks to be
full-term for a single pregnancy, give or take
2 weeks. For twins, doctors consider 37
weeks as full-term, and 34 weeks for a triplet
pregnancy. Twins and triplets are born at a
earlier stage of their development, so they
require extra medical attention.

TRIPLETS TWINS SINGLE

34 37 40
WEEKS

Baby starts to B
leave uterus
Placenta
Cervix fully dilated disconectsIRTH
from
4 Delivery uterus wall
Babies are Uterus
usually born head Baby now
What happens after birth first. This is so that fully born
the widest part of
After birth, the baby will take its first their body, the
breath. In doing so, the baby’s circulatory head, is in line
and respiratory systems begin to function with the widest part
independently from the mother for the first of the mother’s pelvis,
time. An instant rerouting of blood vessels allowing the rest of the
occurs in order to obtain oxygen from the baby to pass. The umbilical
lungs. The pressure of the blood flowing cord and placenta are
back to the heart closes a hole in the heart, delivered during the
afterbirth stage.

establishing a normal circulation.

BLOOD CAN BE COLLECTED Cord attached

FROM THE MOTHER’S PLACENTA
AND STORED AS A FUTURE SOURCE
OF STEM CELLS FOR THE BABY

Primed for life BABY REFLEXES rooting reflex
grasp reflex
Babies are born with features already in place Babies are born with over 70 survival reflexes. crawl reflex
that help them grow and develop. Between a Placing a finger next to a baby’s cheek will 0123456789
newborn’s skull bones are flexible, fibrous make them turn their head and open their
gaps that allow the head to expand as the mouth. This is the rooting reflex, and it helps Months
brain gets bigger. Babies grow fast in their them find their mother’s nipple
first year and triple their birthweight. when hungry. It fades when
regular feeding is established.
NTH MONTHS The grasp reflex helps stabilize
6 M 1 MO them if they
931Starting to smile2Trying to roll fall, and placing
During the first month At 3 months, babies can a baby on its
balance their head, kick and stomach will
of life, babies listen, watch, and wriggle, and try to roll over from initiate the
start to recognize people, objects, crawling reflex
and places. They will probably their back onto their front. Both of these
are needed for
smile for the first time at the age a longer period
of 4–6 weeks. of time.

ONTHS MONTHS Developmental milestones

3 Babbling begins 4 Sitting up During the first year of life, babies develop
At this point, babies At about 9 months, babies skills that help them explore the world
speak with babbles and coos. around them. Milestones of
They imitate sounds sit up and start to shuffle or crawl. development, such as
As motor functions develop, they their first smile and
and respond to are constantly moving. first steps, help
simple commands their caregivers
such as “yes” monitor their
and “no.” progress.

MONTHS MONTHS
10
12 Recognizing
Walking tall 6 themselves
5 Babies start

to walk most By the age of 12 months,
babies know their own name,
probably between and by 18 months, they start to
the ages of 10 and
18 months. Their recognize their own image.

first steps will occur
when holding
onto something.

219 219THE CIRCLE OF LIFE
Primed for life

A NEWBORN’S BRAIN IS ABOUT
ONE-QUARTER OF ITS ADULT SIZE

Focused senses 3 days
At first, a baby can
Newborns can focus on objects within 10in see only in black and
(25cm) and can distinguish shapes and patterns. white. A baby finds
They are familiar with their mother’s voice faces particularly
from the womb and they are soothed by gentle, fascinating.
rhythmic noises similar to those of their mother’s 1 month
heartbeat. Babies also recognize their Normal color and
mother’s smell. binocular vision start
to develop at the age
Improved dental health of about 1 month.
when breastfed
6 months
By 6 months, a
baby’s vision is
excellent. The baby
can now distinguish
between faces.

Fewer respiratory Importance of breastfeeding
problems when breastfed
Breast milk is the most important source of food for
Lower heart rate in a growing newborn. It is so nutritionally rich that
breastfed infants
Occurence of food allergies it provides all the energy, protein, fat, vitamins,
decreases when breastfed minerals, and fluids a baby needs during the
for 6 months first 4–6 months. Breast milk also supplies
friendly bacteria, conveys antibodies and
white blood cells that protect against
disease, and delivers essential fatty
acids that are vital for development of
the brain and eyes. The benefits of
breastfeeding are numerous, and
influence all of a baby’s bones and
tissues, and most of the organs.

Juvenile arthritis
is less common
when breastfed

Understanding others Thoughts BREAKER
and feelings OF TOY
Between the ages of 1 and 5,
most children develop an of person Toy owner
understanding that other people Child is aware is forgiving
have their own minds and their OWNER
own points of view. This is called of another’s OF TOY
the “theory of mind.” Once thoughts and
children realize that everyone
has their own thoughts and feelings
feelings, they can learn to take
turns, share toys, understand Toy owner
emotion, and enjoy increasingly is upset
complex pretend play as they act
out the roles they observe during Understanding others Resentment Forgiveness
everyday life. A child with theory of mind can Realizing a friend broke By recognizing that the
predict how others might feel in a toy on purpose causes break was accidental, the
a situation, can understand the upset, as the child child understands that
intentions behind someone else’s understands the the friend is sorry, and the
actions, and can judge how to respond. nefarious intention. friendship is secure.

Steady growth Childhood development
As you grow, your body proportions develop
Childhood is a time of rapid physical into a more adult pattern. Growth slows
between the ages of 5 and 8.
and emotional growth. Social skills

in adulthood are helpful, so it is

imperative that children spend

time with others of similar

ages in order to understand

themselves and each other, THEORY FIRST UNDERSTANDING
create boundaries, and OF MIND FRIEND RULES
establish social bonds. With
5
steady physical growth comes 3 4 YEARS
advanced language, emotional YEARS YEARS

awareness, and behavioral rules.

New nerve cell connections form in

the brain, laying the foundation for

mental development.

Growing up CHILDREN AGED
BETWEEN 2 AND
You are full of curiosity and energy as a child. 10 ASK ABOUT
During the key stages of childhood until puberty, 24 QUESTIONS
you gain a good grasp of language, understand EVERY HOUR
that others have minds of their own, learn about
the emotions of others, and actively start to
explore your environment.

221 221MIND MATTERS
Growing up

Forming friendships Understanding rules

Many children aged 4 and above build selective Rules-based games help children aged 5 and over
friendships with others who share similar interests to balance their desire to win with following the
and activities. They have a sense of future, so they can rules, which discourages cheating and bad
understand the value of a friendship with someone behavior. This helps them recognize right from
reliable with whom secrets can be shared. wrong and how society works later in life.

Rule-abiding behavior is BREAKING
rewarded THE RULES

FIRST FRIENDSHIP FIRST FALL OUT FIRST MAKE UP

First resolution FOLLOWING
Possessing a theory of mind helps friendships last. When they fall THE RULES
out, children can make up by reflecting on what made their friend
upset in order to resolve the conflict.

6 GENDER 8
YEARS DIFFERENCES YEARS

7
YEARS

Friendship groups Leader Popular girl,
Close or “queen bee”
Boys and girls have different types of friend
friendship groups by the age of 7, each Follower Popular girl’s
with their own hierarchy. Boys tend to best friends
form large groups of friends comprised of MALE FRIENDSHIPS FEMALE FRIENDSHIPS
a leader, an inner ring of close friends,
and peripheral followers. On the other
hand, girls usually have one or two close
friends with equal status. The most
popular girls are highly sought after
as “best” friends.

Hormonal teenagers

Puberty is the stage between childhood and adulthood, when the
sex organs mature and reproduction becomes possible. Fluctuating
hormone levels cause emotional and physical changes which can

make teenagers feel clumsy, moody, and self-conscious.

Hypothalamus

VOICE DEEPENS FAT CELLS Pituitary gland

Voice breaks Onset of puberty Female changes
Hormones cause the larynx
to enlarge and the vocal When body weight and leptin (a hormone made in fat Puberty generally starts a
cords to grow longer and cells) reach certain levels, the hypothalamus will year earlier in girls than in
thicker, deepening the voice. boys, between the ages of
release pulses of gonadotrophin-releasing hormone, 8 and 11. Puberty is completed
Male changes kickstarting changes in each gender. by the ages of 15 and 19.

Boys usually enter puberty TEENAGE BRAIN
between the ages of 9 and 12.
There is a wide variation in the The brain is undergoing its own
rate at which it progresses, and it changes, pruning old neural
completes by the ages of 17 and 18. connections and forming new ones,
and simply can’t keep up with
controlling the rapidly elongating
limbs, muscles, and nerves. That’s
why teenagers may feel less
coordinated than normal.

CHEST HAIR HAIR BREAST
BROADENS GROWTH
Breast buds
The ribcage grows develop and may
larger and some hair be tender. Nipples
may grow, but not all become more
males have hairy chests. pronounced.

Ovaries produce estrogen,
accelerating puberty changes

DURING A PUBERTY WHY DO TEENS Menstruation begins UTERUS AND
GROWTH SPURT, GET ACNE? The first period occurs OVARIES
HEIGHT MAY between the ages of 10 and
INCREASE BY AS The skin’s sebaceous, or oil, 16, at an average of 12 years.
MUCH AS 3½ IN glands are stimulated into action Ovulation occurs irregularly,
(9 CM) IN A YEAR! and the uterus grows to the
by the hormones of puberty. size of a clenched fist.
Testes produce When newly active, they take a
testosterone, while to settle down to a normal Vaginal secretion PUBIC HAIR
accelerating rate of oil secretion, so during The vagina lengthens and
puberty changes starts to secrete a clear or
puberty, many teens cream-white discharge—
PUBIC HAIR suffer from spots. one of the first signs of
puberty. The teenager's
SPERM PRODUCTION natural odor may also
IN TESTES become stronger.

First ejaculation EARLY AND LATE DEVELOPERS THE CIRCLE OF LIFE
The penis and testes grow
and sperm production Puberty starts at different Less developed than Hormonal 222 223teenagers
begins. The first ejaculation ages, so some friends of the her peers of same age
occurs, typically during sleep, same age may be taller and
as a "wet dream." seem more mature than 12-YEAR-OLD GIRLS
others. Therefore, three girls
at the age of 12 may differ
drastically in height and
weight. Girls tend to develop
earlier than boys because a
lower weight of around 105 lb
(47 kg) seems to be the key
to triggering female puberty.
A higher weight average of
around 120 lb (55 kg) appears
to be the trigger in boys.

Getting older

Aging is a slow and inevitable process. FREE RADICALS DNA
The rate at which you age depends on
interactions between your genes, diet, Premature aging can
lifestyle, and environment. result from genetic damage
caused by free radicals.
Why do you age? These molecular fragments
are produced by sunlight,
Why aging occurs is a mystery. We know that the cells in smoking, radiation, or
your body divide to renew themselves, but they can only pollution damaging your
do so a certain number of times. This limit is linked to DNA. Dietary antioxidants
the number of repeating units, called telomeres, found in fruit and vegetables
on the end of each of their chromosomes, the X-shaped help neutralize free radicals
packages of DNA in every cell’s nucleus. If you inherit and offer an increased
long telomeres, your cells can undergo more divisions, chance of living a longer life.
and as a result you may live longer.

TELOMERE TELOMERE
Chromosome

Telomere

CELL
NUCLEUS

Telomeres Duplicating cell Cell unable
to duplicate

At the end of each chromosome arm is 1 Cell renewal 2 Depleting telomeres
a telomere, a repeating section of DNA. The enzymes lock onto the Eventually, the telomere becomes
During cell division, enzymes attach to
the telomeres. These enzymes speed telomeres, ready to copy each cell. too short for enzymes to lock into place.
When an enzyme detaches, it takes a The cells with these short telomeres can
up the chemical reactions involved section of telomere, so chromosomes no longer duplicate or renew themselves.
in cell division.
shorten with each division. Cells run out of telomeres at different rates.

224 225THE CIRCLE OF LIFE
Getting older

Going bald MIDDLE AGE Fine hair Hair does not reach
Certain hair follicles become inactive, skin surface
reaching the end of their life cycle YOUTH OLD AGE Inactive hair follicle
quicker than others, resulting in different
patterns of baldness in men and women. Thinning
Even if you are bald, some of your hair hair
follicles contain hairs, but they do not
grow beyond the skin surface. follicle

OLD AGE Degeneration of hair
cells in ear
OL
Y AGE
YO
OLDMacula UTH

YOUT

Buildup of GE
waste products H

Deteriorating sight HABSENT TELOMERE Hearing loss
Light exposure can damage the macula, Tiny hair cells within the inner ear convert
a key region at the back of the eye, causing sound waves into nerve signals that your
a buildup of waste products that results brain interprets as sound. Damage or loss
in dark spots obscuring your vision. This is of these hair cells leads to increasing
known as age-related macular degeneration. age-related deafness.

Excess melanin OUTH YOUT
results in an
age spot Healthy
myelin sheath
D AGE
OLD A

Melanocyte cell that Decayed
produces the dark skin myelin sheath
pigment melanin Breakdown of nerves
The myelin sheaths that coat the nerve cells
Age spots Cell unable to in the brain can deteriorate, so traveling
Whenever your skin is exposed to duplicate electrical signals decelerate. This may
the sun, ultraviolet rays generate account for slower thoughts, poor
free radicals. These cause cells that 3 Unable to regenerate memory recall, and reduced sensation.
produce pigmentation to increase Only a few replicating cells remain in
their production, creating age spots. old age. When cells can no longer renew

themselves, they slowly deteriorate and the
signs of aging become clear. Cells may die
and be replaced with scar tissue or fat.

The end of life High blood
pressure—4%
Death is an inevitable part of the cycle of life. It occurs Unchecked and
when all the biological functions that sustain living uncorrected high
cells cease. Some deaths result from old age, while blood pressure can
some are due to disease and injury. be fatal late in life.

Leading causes of death What can kill us Diarrheal
Listed here are the leading causes of diseases—5%
death worldwide in 2012, provided by Noninfectious diseases, such as heart and lung Those suffering
WHO (World Health Organization). disease, cancer, and diabetes are most commonly from chronic
diarrhoea are at risk
Lung infections cited on death certificates. Many of these are of fatal dehydration
and failures—16% related to an unhealthy diet, lack of exercise, and and malnutrition.
Lung cancers and lower smoking, but some are due to nutrient deficiencies.
respiratory infections HIV—5%
together made the second- Deaths caused by
largest killer in 2012.
the Human
Immunodeficiency
Virus is decreasing

year by year.

HOW DOES WEALTH Heart and circulation Traffic accidents
AFFECT LIFESPAN? conditions—60% –5%

In high-income countries, Heart attacks and strokes are the Casualties on the
7 in every 10 deaths are among two leading causes of death road killed a large
people aged 70 years or older, worldwide. number of people
who’ve lived a good, long life.
1 PERCENT OF THE WORLD’S in 2012.
In the poorest countries, POPULATION DIES EVERY YEAR Diabetes—5%
1 in 10 children still die
Those with
in infancy. diabetes may die

due to heart
disease or stroke
because of their

condition.

226 227THE CIRCLE OF LIFE
The end of life

Brain activity Near-death experiences

One way to determine whether a person is dead is to scan People who almost die and are then
for brain activity. Brain death is diagnosed when electrical resuscitated often report experiencing
recordings (EEG) show an irreversible loss of all higher similar sensations, such as levitation,
and lower brain functions, so there is no spontaneous looking down on their body, and seeing
breathing or heartbeat. Someone who is “brainstem dead” a bright light at the end of a tunnel. Other
can only remain alive if artificial life support is in place. common descriptions of such near-death
experiences include having flashbacks,
No conscious brain or vivid memories, of their earlier life, and
activity detected being overcome by strong emotions, such
as joy and serenity. The cause of these
Brainstem active in experiences may be changing oxygen levels,
a coma and controls sudden release of brain chemicals, or surges
basic functions such of electrical activity—no one really knows.

as breathing
Comas
A coma is a state of
unconsciousness in which
someone cannot be woken,
makes no movements, and does
not respond to stimuli such as pain.
Despite this, the brainstem is still active
and can maintain some body processes.

YOUR BODY AFTER DEATH

When the heart stops pumping blood, the body’s cells no Rigor mortis
longer receive oxygen or have toxins removed. Chemical Rigor mortis starts in the eyelids and
changes in muscle cells and the overall cooling of the spreads to other muscles at a rate
body cause the limbs of a corpse to stiffen after an initial depending on surrounding temperature,
period of floppiness. This stiffening is called rigor mortis age, gender, and other factors.
and it wears off again after 2 days.

Blood pools Peak rigor Skin cells
In the hours following mortis Even after 24 hours, skin
death, blood pools in
your body’s lowest reached cells can be harvested
points, leaving a for medical use.
100 purple hue. °F (°C)

% of body in full rigor mortis 95 (35)
Temperature of body
Body reaches 86 (30)
room temperature 77 (25)

Odd noises Bacteria 68 (20)
A combination of internal gas release Organs and tissue 59 (15)
and stiffening muscles often causes are broken down by 50 (10)
strange, hair-raising noises. bacteria in the body. 41 (5)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 Hours



MIND
MATTERS

Second nerve cell
receiving neurotramsitter

Basis of learning Nerve cell

When we learn a new fact, gain a skill, or

react to stimuli, connections between

nerve cells form. Messages are passed from Vesicle containing Receptor on nerve cell
one cell to another by neurotransmitters neurotransmitters After learning
The nerve cell releases more
(chemicals that are released by nerve cells). Prelearning neurotransmitter and more receptors
The more frequently we remember what we Initially, when the nerve cell fires, a have formed on the second nerve cell,
have learned, the more messages the cells small amount of neurotransmitter is strengthening the connection.
send, and their connection becomes stronger. released, and there are only a few
receptors on the receiving nerve cell.

Types of learning Unimportant LEARNING WHAT
signals
We learn information in different ways, When a stimulus is new, we T
depending on what it is and how it is automatically pay attention to TO IGNORE
presented. For some abilities, we have a it. If it doesn’t signal anything
“critical period” during which we can fully important, we learn to ignore it.
master the skill. Adults who have
LEARNING BY ASSOCIATIONlearned a new language later in life, Startled at No response to RBeEwHaArVdIsOaRnRdEINFORCEMEN
have missed the critical period of sound sound reprimands
acquiring the basic sounds of the Getting rewarded for good
language, and therefore behavior and reprimanded f
may speak with or bad behavior can help
an accent. reinforce our concepts of what
is acceptable, and what isn’t.
Associative learning
When two events coincide on a regular Rewarded behavior
basis, we learn to associate them. If
you consistently eat when a bell rings,
hearing the bell may stir your appetite.

Hunger caused by
combined stimuli

Sound alone
causes hunger

Behavior leading to a
reprimand

Learning skills EXPLORING
A NEW CITY
Connections between nerve cells in our brains allow INCREASES
learning to happen constantly, often with no conscious YOUR BRAIN SIZE BY
effort from us—repetition helps retain these skills. FORMING NEW NERVE
CELL CONNECTIONS

230 231MIND MATTERS
Learning skills

AT WHAT AGE DO WE LEARNING W
LEARN THE MOST?
Fact stored in
When you are a child, memory
your cognitive, motor, and HAT IS IMPORTANT
language skills advance in (MOTOR SKILLS)Learning facts
leaps and bounds—at the When we come across information,
age of 2, you tend to learn pieces can be stored in our long–term
memory if we deem them worth
10–20 words per week! remembering. The judgment can be
either conscious or subconscious.

LEARNED MOVEMENT Fact accessed
Becoming automatic later when needed
When you learn to drive, you concentrate on Fact used in
your movements as well as the traffic. Through an exam
repetition, the driving body movements are
learned and become automatic, allowing you to EXAM REVISION
give attention to other things at the same time.

Fully focused Talking while
on driving driving

RESPONDING TO EVENTS When a memory starts to fade,
Episodic memory revising the information increases the
By reviewing our experiences we learn memory’s strength with each revision
to avoid undesirable situations, such as session—this ensures that the learned
forgetting our umbrellas on rainy days. information is stored in our long-term
memory. Revisiting information little
and often is best for retention. When
you cram for an exam or presentation,
you acquire a lot of information
quickly, but it is lost without revisiting
the information—this is why intense
study can be useful in the short-term.

STRENGTH OF MEMORY

Experience of Memory
getting wet of past
experience
changes
behavior

TIME

Making memories WHY DO WE
EXPERIENCE DÉJÀ VU?
Every time you experience something, your brain forms a memory.
Inconsequential moments and life-changing events are all stored, but A sense of familiarity in
how often you revisit the memory determines whether it is remembered unfamiliar situations may be
or forgotten. Memories are temporarily stored in your short-term because a similar memory is
memory, then, if important, are transferred to your long-term memory. recalled but is confused with

the present, so a sense
of recognition comes

without a concrete
memory.

1 Sensory memory TOUCH HEARING SMELL SIGHT TASTE
When you sense
something, you create a
transitory memory, even
if you are not conscious
of it. It is stored in your
sensory memory, and
unless transferred to
short-term memory, it
fades in less than a second.

2 Nerve signals ENCODING Short-term memory
Encoding is the process
by which a sensory memory CONSOLIDATION Our short-term memory can retain around
forms a true memory. When five to seven pieces of information. These
you pay attention to your memories, such as telephone numbers or
sensory memory, it enters directions, are stored only for as long as
your consciousness, and the Nerve cell you need them. Repeating it to yourself
helps prolong the memory, but if distracted,
nerve cells that encode the Previous ORMED you often forget it. Short-term memory is
memory fire more rapidly. memories thought to be based on temporary patterns
Nerve cell connections provide of activity in the brain’s prefrontal cortex.
strengthen temporarily to context
MEMORY IS F
form a short-term memory.
M
Final memory

3 Consolidation EMORY FORGOTT
New experiences are
compared against memories
to provide context for new EN

memories. Memories that Unimportant
have emotions and importance memories are lost
attached to them are stronger and
less likely to be lost. Sleep is vital for
consolidation to happen effectively.

Long-term memory ORY MONTHS 2 Storage
Y RECALL Months later, your
As far as we know, your long-term MORY FORGOTT
memory allows you to store unlimited ME nerve cell connections
amounts of information. Memories that may become permanent.
are most likely to be stored for life MEM
include those with a high emotional MIND MATTERS
impact, like a wedding, and that have Particularly memorable
a semantic value, such as your spouse’s Making 232 233memoriesexperiences can jump
name. These memories are connected to straight into long-term
growth in areas of the brain linked with EMORYstorage the same day.
memory, such as the hippocampus, so are
more stable than short-term memories. Revisiting a memoryEN S YEARS 3 Memory fades
When you recall a If months or years
MEMORY CONFABULATION 1 pass before you recall a

When you recall a memory, the memory, the nerve cells Nerve cell memory, it is more likely
memory enters a labile, or easily encoding it are reactivated. connection
altered, state. In a process called Each time this happens, more to fade. Specific details
confabulation, you may unintentionally about special events,
add new information to the labile nerve cell connections such as the food you
memory when it is reconsolidated are created and existing
by your subconscious. This new ones are strengthened, MEMOR ate at your wedding,
information will become an may be forgotten.
inseparable part of your memory. and the memory is less
likely to be forgotten.
If you don’t recall the DECADES
Losing a
memory frequently, 4 memory
it will be lost.
Eventually, memories
fade—even important
Nerve cell ones! It is not known
connection if the nerve cell
strengthening connections of a

memory disappear,
or whether they still
exist and you are
unable to access them.
STORED M
Real Fabricated HOME LIFE DATES VACATIONS
memory information

Recalled as
true memory

ELATIONSHIP JOURNEYS BIRTHDAYS

R

Falling asleep

Sleep is a curious phenomenon—we do 7 AM
6 AM
it every day, but we don’t know why. It

might allow your body and brain time

to repair themselves, flush out toxins Body paralysis
During REM sleep, muscles
that accumulate throughout the are paralyzed, so you don’t
act out your dreams. You
day, or strengthen memories. can wake in this stage.
During this scary
Depriving yourself of sleep experience, you are
semiconscious but
is taxing for your body. 5 AM unable to move.

After a good
night’s sleep, sleep
pressure is low

4 AM Adenosine hormone
broken down
Rapid eye movement sleep (REMs) during sleep
Most dreams occur during REM sleep. Sleep pressure
If woken in this stage, you are likely The longer you stay awake,
to remember dreaming. Your eyes the larger your sleep
move under your lids as you dream. pressure. This pressure is
comprised of rising levels
3 AM of chemicals such as
adenosine, which causes
fatigue by inhibiting
neurons in the brain. More
adenosine is produced if
you’ve had an active day.

2 AM Sleep
pressure peaks
at bedtime

Sleep walking 1 AM LE VEL 4 DEEP SLEEP
Sleep walking is most likely to occur LE
during deep sleep—but why it happens VEL 3
remains a mystery. You may walk L EVEL 2
around, eat, or even drive a car!

WE SPEND ONE-THIRD OF VEL 1LE
OUR LIVES ASLEEP, AND REM

WE DON’T KNOW WHY 12 PM AWAKE Unlikely to enter
REM sleep upon
LIGHT SLEEP falling asleep

AVOIDING SLEEP 234 235MIND MATTERS
Falling asleep
Many of us use caffeine to help
keep us awake. It makes us more Range of effects
alert by blocking a chemical in If you don’t sleep you will suffer from a
the brain called adenosine, range of physical and cognitive effects.
which is responsible for making Long-term sleep deprivation can even
us sleepy. After the effect wears cause hallucinations.
off, we suddenly feel very tired.
FORGETFULNESS
LOSS OF RATIONAL

THOUGHT

RISK OF ILLNESS

Stages of sleep HIGHER HEART
RATE
Each night you pass through
different sleep levels. Level 1 is MUSCLE
between sleep and wakefulness. TREMORS
In this stage, you may twitch as
muscle activity slows down. As If you don’t sleep
you enter true sleep, Level 2,
your heart rate and breathing Going without sleep for a long time
become even. During deep causes unpleasant symptoms. When
sleep, Levels 3 and 4, your brain you grow tired, your brain will
waves slow and become regular. steadily become unresponsive to
You tend to enter bouts of REM neurotransmitters (chemicals)
sleep once you have passed involved in regulating happiness.
through other sleep levels. In This is why tired people are often
REM sleep, your heart rate moody. When you sleep, your brain
increases and brain waves look resets itself, and becomes sensitive
similar to when you are awake. to these neurotransmitters
once again. The effects of sleep
A good night’s sleep deprivation become progressively
Illustrated here is a typical 8-hour night’s sleep. worse the longer you stay awake.
You climb and fall between different levels of
sleep in 90-minute bouts, interspersed with REM.

Awake Level 3 sleep

REM sleep Level 4 sleep

Level 1 sleep Sleep pressure

Level 2 sleep

Entering your dreams

Your brain draws on and remixes your memories of people, RATIONAL THOU
places, and emotions to create sometimes complex and NO
usually confusing virtual realities known as dreams. NTGHT UT

Creating dreams

During REM sleep, your brain is far from asleep. It is highly active

in this level of sleep, and this is when you do most of your

dreaming. Areas of the brain associated with sensation and

emotions are particularly active when you dream. Your heart and Logic impaired
breathing rates are high because your brain consumes oxygen at a The prefrontal cortex of your brain, where
similar pace as when you are awake. Dreaming is thought to be most of your rational thinking occurs, is
linked to how the brain processes memories. inactive. You tend to accept crazy events
in your dreams as if they are normal, because
Sleepwalking and talking Motor area your dreaming self is unable to process these
of brain events as anything else.
Sleepwalking occurs during slow-wave, is active
or deep, sleep. At this level of sleep, your NO SENSORY INP
muscles are not paralyzed, as they are
during REM. The brainstem sends nervous

signals to your brain’s motor cortex, causing

you to act out your dreams. It is more

common when people are sleep deprived.

Sleep talking occurs during REM sleep

if nerve signals that usually paralyze your

muscles are interrupted, temporarily

allowing you to vocalize in your dreams. Reliving sensations
It may also happen when you are moving Your brain receives little new sensory input when you
from one level of sleep to another. are asleep, so the part of your brain that processes
sensory signals is inactive. You do “sense” in your
Speech area dreams, but you are reexperiencing sensations
of brain is active you had at some point when you were awake.

SLEEPWALKING REM sleep RA PID EYE MOVEME
SLEEP TALKING Nervous signals in the
brainstem regulate brain
2 HOURS activity during REM sleep.
Interactions between
THE ESTIMATED TOTAL “REM-on” and “REM-off”
TIME YOU SPEND nerves control when and
DREAMING EACH NIGHT how often you pass into
REM sleep. The muscles that
move your eyes are the only
muscles that are active in
REM sleep, so your eyes
move when you dream.

236 237MIND MATTERS

Entering your dreams

BODY PARALYZED Inability to move MEMORY CONSOLIDATION
The motor cortex, which controls
conscious movement, is inactive. Sleep is important for memory storage.
The brainstem sends nerve signals
to the spinal cord, initiating You are more likely to retain new
muscle paralysis, which prevents
you from acting out your dreams. information after you have slept.
Production of neurotransmitters
that stimulate motor nerves is Dreams are thought to be a by-
completely shut down.
product of your brain processing and

shuffling new memories and forgetting

unimportant ones. Shuffled

Memory memory

forgotten

Emotions run wild
The emotional center in the middle
of your brain is highly active, which
explains the flurry of emotions you may
experience when dreaming. This area
encompasses the amygdala, which can
be active during nightmares because it
regulates your response to fear.

MOTIVE RESPONS
PR TORTREX
CE PATIAL AWARENES

EEFROORNTETXALCOMO Feeling of movement
Y SSEven though you don’t move when you dream, you may
feel as if you do. The cerebellum, which controls your
spatial awareness, may become active, resulting in the
feeling that you are running or falling in your dreams.

SENSORY EMOTIONAL VISUAL
AREA CORTEX CORTEX

CEREBELLUM

BRAINSTEM Remixed memories MENTAL IMAGER
The visual cortex at the rear
of your brain is active, because
it generates the imagery you
experience in your dreams from remembered events. This can
include places you’ve been, people you’ve met, and even
objects you’ve interacted with. They can either be things you
are emotionally attached to, or just completely random.

All emotional

Emotions influence our decisions and occupy much of our WHY DO WE CRY
waking lives. Social bonds were vital for our ancestors’ WHEN WE ARE SAD?
survival, so we have evolved to be able to read emotions
in others. Understanding how emotions work has led us When you are feeling sad or
to believe that we can influence how we feel. stressed, the tears you shed
secrete stress hormones such
Basic emotions
as cortisol, which is why
A few basic emotions are universally identified. Happiness, sadness, fear, we feel better after
and anger seem to have facial expressions that are recognizable to people a good cry!
in the most widely separated cultures. Combining these gives rise to the
huge number of complex emotions we experience.

Fear and anger Happiness and sadness
The body reactions for fear and anger are very similar, even Your brain and large intestine produce hormones, including
though they involve different hormones. It is mainly your brain’s serotonin, dopamine, oxytocin, and endorphins, that affect
interpretation that determines whether you feel angry or afraid. happiness. Lower levels of these hormones result in sadness.

Adrenal glands Testes or ovaries produce Brain produces majority of Large amount
produce ephinephrine testosterone during anger hormones relating to happiness of serotonin
when you are scared produced by
large intestine

EPINEPHRINE TESTOSTERONE SEROTONIN
Blood flows Eyes narrow
to brain Teeth causing crow’s feet
clenched
Heart rate Heart rate
increases Feeling of increases
well-being
reported all
over body

FEAR ANGER HAPPINESS SADNESS

Muscles Feeling emotion Reduced
tense A study documented feeling in
the physical sensations
people felt when legs
they experienced
certain emotions.
Feelings were either
heightened (positive)
or reduced (negative).

Reported feelings
Positive
Negative

Motor cortex 238 239MIND MATTERS
All emotional
Emotional center of brain

CONSCIOUS How emotions form FEELING
INTERVENTION SIGNALS
Emotions consist of feelings,
expressions, and body EXPRESSION

symptoms. It may seem like
your feelings come first, but
a feedback loop allows the

body to regulate your
emotions and vice versa. At a
certain point in this cycle you
are able to reinforce, inhibit, or
change emotions by altering
your response. For example,

if you are feeling happy,
continuing to smile will make

you feel even happier!

Conscious Motor Reflex Motor
smile neuron smile neuron

Conscious facial expressions Reflex facial expressions
After you have started to experience an emotion, you are able When you experience emotion, facial expressions appear without
to change your facial expression to hide or reinforce your true your control. For instance, when you hear good news, you cannot
emotion. This action is consciously controlled by neural help but smile. These reflex actions are thought to be due to
pathways from the motor cortex. signals from the amygdala, in the brain’s emotional center.

THE HAPPINESS WHY DO WE HAVE EMOTIONS?
YOU FEEL DURING
A “RUNNER’S Experts think that emotions evolved as
HIGH” IS CAUSED
BY NATURAL a preverbal way of communicating. By
CHEMICALS
IN THE BRAIN understanding emotional signals, we
CALLED OPIOIDS
can form stronger social bonds. Facial CRYING EMPATHY
expressions can demonstrate that FEAR

you are in need of help, are sorry for HAPPINESS

something you have done, or can warn

others to stay away if you are angry.

However, some scientists think there is
a simpler explanation: the widened eyes ANGER

of fear could help us see better, and the

wrinkling of the nose in an expression

of disgust could be a way of rejecting

harmful chemicals in the air.

HAPPINESS

EMOTIVE RESPONSES

Fight or flight CORTEX Visual cortex
processes the
When we are threatened, our body springs VISUAL CORTEXimage after
into action. Our brain sends signals to the automatic reaction
body causing a variety of physiological
changes that prepare us to face the Thalamus passes ALAMUS
challenge or to run away. sensory information

as nervous signals
to amygdala
AM
TH
YGDALA HIPPOCAMPUS

Amygdala activates
nervous response and
instructs pituitary gland

to release hormones

1 Brain activity Pituitary gland
The amygdala signals the body to releases epinephrine
and cortisol

take action before the fearful stimulus
has even been recognized by the visual
SNAKE cortex—this happens when you jump at
shadows. Then, the visual cortex fully
Activating a response analyzes the image to check if the threat
is real, and your physical reactions adjust
Have you ever been startled by a garden hose, only to realise accordingly. Your cortex also consults NERVOUS SIGNAL
it is not a snake and completely harmless? Before we are even memories stored in the hippocampus to EPINEPHRINE AND CORTISOL
consciously aware of a threat, our brain activates the nervous check if the threat was faced in the past.

system, which causes the release of hormones from the adrenal

glands. Meanwhile, the information also travels the longer route to

our cortex where conscious brain regions can analyze whether the

threat is genuine. If not, it will calm down the physical reaction.

IN TIMES OF HIGH 2 Alternative pathways
STRESS YOU MAY Signals from the brain are
EXPERIENCE TUNNEL sent to the body via nerves, and
VISION, IN WHICH YOU also by hormones released from the
DON’T NOTICE WHAT pituitary gland. The nervous signals
HAPPENS AROUND YOU travel faster than the hormones, so
they kickstart hormone production
in the adrenal glands.

BREA HE ART RATE INCREAS ES ASES MODERN STRESS IMMUNE SYSTEM ACTIVITY REDUCED
THING RATE INCRE T USED FOR ENERG
PUPILS DILATE Modern stress tends to be very different from the IGH BLOOD SUGAR
type encountered by our ancestors—our stressors
often overstay their welcome, and can’t be dealt
with by fighting or fleeing. Stress is helpful in the
short term, but continued stress negatively affects
your health, causing headaches and illness.

FA Y

IMMEDIATE STRESS PERSISTENT STRESS

3 Hormone producer
The adrenal glands that
sit on top of the kidneys produce
more epinephrine and cortisol in
response to the nervous signals
and hormones sent by the
pituitary gland. This heightens
H

the physical effects of stress.

4 Short-term effects 5 Long-term effects MIND MATTERS
Within seconds, Over minutes and
heart rate and breathing Fight or 240 241flight
increase to boost oxygen hours, signals from the
adrenal glands continue to
circulation. Blood vessels cause a cascade of reactions.
close to the skin constrict,
leaving you pale, and Blood sugar rises and fat
stores are metabolized for
your bladder muscles energy so your muscles
relax, possibly leading to
BLOO continue to work at their
BLO
embarrassing accidents! OD FLOWS TO MUSCLES full potential. Nonvital
RIC T
D VESSELS CONST ADRENAL GLANDS processes, such as immune
system activities, are shut
down to conserve energy.

Emotional problems

Our emotions are controlled by a balance of chemicals and circuitry in the
brain, so imbalances of certain chemicals can cause emotional disorders.
Experts once believed they were purely psychological, but they now
understand that physical changes underlie each illness.

Phobias Exposure can be either
gradual or sudden

A fear is classed as a phobia

if the fear outweighs 1 Fear 2 Exposure 3 Cured
the threat. It is logical Phobias are more common The only cure is to show When nothing bad
to be wary of snakes, happens, their emotions may
which can be deadly. toward evolutionary threats sufferers that the object of subside, and their bodies will
If that fear extends to (heights, spiders) than modern
pictures or toys and ones (guns, cars), suggesting we their fear isn’t harmful. learn not to fear that stimulus.

are primed to fear certain things.

begins to affect daily Acute anxiety

life, it becomes a

phobia. Phobias can

develop over time, be

learned at an early age, or be

associated with an incident

involving the stimulus. SYMPTOM TREATMENT CURE

Obsessive compulsive disorder 3 Cured
When nothing bad
Sufferers of obsessive compulsive disorder (OCD) experience intrusive happens, the patient’s anxiety
negative thoughts leading to compulsive behaviors, which they should decrease, breaking
incorrectly believe can relieve their anxiety. OCD is possibly caused the destructive cycle.
by overactivity in the areas connecting the brain’s frontal lobe to
deeper areas. Most cases are manageable with treatment.

1 Repetitive behavior 2 Reduced attention Disturbing
An uncomfortable, often irrational, Therapy prevents sufferers thought
thought will enter the mind and cause from performing their compulsions ceases
repetitive behavior to occur. Excessive when they have a negative thought.
handwashing or flipping switches a set The negative impact of the thought CURE
number of times are common examples. may begin to subside. Negative thought begins
to cease
Repetitive Repetitive behavior
behavior abolished

Source of
anxiety

SYMPTOM TREATMENT

242 243MIND MATTERS

Emotional problems

TRAUMATIC MEMORIES Thalamus active Emotional center
due to linking once- of the brain is
pleasant stimuli with highly active,
dealing with
negative emotions anger, sadness,
and pain
After trauma, some people experience
flashbacks, hypervigilance, anxiety, and BRAIN ACTIVITY Activity in the prefrontal cortex
depression—these are the symptoms reduced, affecting concentration,
of post traumatic stress disorder (PTSD). memory, and processing
When you are afflicted, recalling the
traumatic memory will trigger a “fight Depression
or flight” response, unlike ordinary
memories. Treatments can be provided The symptoms of depression include low mood,
through therapy or drugs. apathy, sleeping problems, and headaches. It is
thought to be caused by chemical imbalances in
PTSD Stress Non-PTSD the brain, leading to certain areas becoming
overactive or underactive. Antidepressants can
of event help reset this balance by raising levels of
chemicals, but they only address the symptoms,
Event
not the cause. Attitudes toward
Recall depression have progressed to
Recall understanding it as a condition,
Stress of not a state of mind.
event returns
Memory

Bipolar disorder of certain chemicals in the brain, including
norepinephrine and serotonin, and this causes the
Featuring changes in mood from mania to extreme brain’s synapses to become either overactive in
depression, bipolar disorder is highly genetic—it runs mania or underactive in depression.
in families—but it is often triggered by a stressful life
event. Bipolar disorder is a type of depression. It is
thought to be due to problems with the balance

Increased Decreased
chemical chemical
Manic phase Depression phase severe activity
Excessive energy, reduced activity Sufferers experience
sleep, and rapid speech are depression, including feelings
all common. Sufferers may
also have delusions, such as of hopelessness and fatigue.
They are more in touch with
thinking they are famous. reality than during mania.

SYMPTOM SYMPTOM

SYNAPSE Extreme SYNAPSE
sadness
Extreme
delight

Feeling attraction DOES CULTURE
AFFECT ATTRACTION?

Scientists are only just beginning to understand what Within a single culture, ideals
happens when we feel attracted to someone, why we are of beauty change over time.
attracted to certain people and not others, and why we In Europe, pale skin and a full
make our choices—and it is mostly to down to hormones. figure once indicated wealth and
was typically seen as attractive in a

woman. Now, a thinner, more

Chemical bond tanned figure is seen

When attraction begins, hormones play an important part as desirable.
in augmenting our romantic feelings. Levels of dopamine

in the brain increase, providing the familiar rush of pleasure.

A chemical that is converted into epinephrine is released, Ventromedial
causing a dry mouth and sweaty palms. It also causes your prefrontal
pupils to widen, which signals your desire to the other person, cortex
making you increasingly attractive. Serotonin levels change
and are believed to lead to obsessive, lustful thoughts. Arousal-
initiation
area

1 Immediate lust
Within moments of
seeing someone you are
attracted to, an area of the
brain called the ventro-
medial prefrontal cortex Dilated pupil

is activated to analyze E AND SPEED OF V ENSE OF HUMOR ACIAL SYMMETR
that person’s dating
potential. Testosterone is
Y
OICE

C
released in both genders, TON
stimulating feelings of lust. S
F

2 Contributing factors
Our attraction uses cues
such as facial symmetry and body
shape, because they signal good health
and fertility. Other cues, such as Heart rate increases as
similar interests, highlight whether attraction grows, so we may
we are compatible in the long term.
The color red ignites passion confuse the sensations of
in both sexes. OLOR OF CLOTHIN G love and fear, making a

scary film a great first date!

BODY SHAPE

3 Long-term pair bonding
After the initial attraction phase, relationships
change, and a different set of hormones become
important. Oxytocin is released after sex, and increases
feelings of trust and bonding, which aids in establishing
relationships. Another hormone, vasopressin, is equally PROLONGED EYE CONTACT
important. It is released when two people spend a great INCREASES THE MAGNETISM
deal of time together, promoting monogamy.
BETWEEN TWO PEOPLE
SEX
BODY ODOR
Subtle MENSTRUAL CY
signals Sweat can tell us how healthy
someone is, and even whether
we are genetically compatible.
People who have
an immune system
relatively different
from our own tend to
smell more attractive,
since a mixing of these
genes would encourage healthier
offspring. Generally, women prefer
the scent of men somewhat similar
to their own over the scent of those
who are either genetically identical
or completely dissimilar.
In many animals, it is obvious when MIND MATTERS

females are fertile, through bold signals Feeling 244 245attraction

such as brightly colored swellings on their OVULATION
CLE
body or pheromones in their urine. When it Changing signals
When women
comes to humans, ovulation isn’t as obvious— are ovulating,

and it’s not known why we evolved that way. there are subtle
changes that
Nevertheless, women do have subtle ways of indicate fertility;
voice pitch rises,
advertising their fertility, such as flirting more cheeks flush,
and you tend to
and dressing more attractively, and men seem flirt more and
dress more
subconsciously to be able to pick up on these attractively.

signals. One study showed that men release

more testosterone when reacting to the

scent of women who are ovulating

than those in a less fertile

phase of their cycle.

Extraordinary minds

Everyone’s brain is unique, but there are some people who can do
amazing things that most of us can only dream of. Slight changes
in the wiring of the brain, or the way we learn to use it, can give
rise to these incredible abilities.

Delayed language Socializing impaired Repetitive behavior Specific interests SOMETIMES AUTISM LEADS TO
Children with autism (but Reduced eye contact is an People with autism process Those who are autistic often
not Asperger’s) take longer early sign of autism. Autistic information differently, and develop narrow, specific
to learn language, and individuals tend to dislike this means everyday situations interests. These can be a source
some never become verbal. socializing, finding its complex can be overwhelming. Self- of comfort and enjoyment,
Those who do speak may rules confusing and frightening. soothing, routine behaviors are possibly because the structure
have trouble using words Nevertheless, this is not to say common, and can help people and order of familiar topics
to communicate with those with autism never form with autism calm themselves provides respite from the
others as an adult. strong social bonds. when anxious. confusing social world.

Autism spectrum Rare prodigious qualities Increased connections
Occasionally, those with When any brain grows,
Autism spectrum disorders (including autism show incredible nonessential nerve cell
Asperger’s syndrome) are probably caused skills in areas such as math, connections are pruned.
by unusual patterns of connectivity in music, or art. This may be It is thought that in autism,
the brain. Genes are known to play due to a characteristic pattern this process is inhibited,
a role because autism runs in the of brain processing that resulting in too
family, although why they affect some focuses on details. many connections.
people only mildly while others
need care throughout their lives
isn’t known.

246 247MIND MATTERS

Extraordinary minds

SENSORY SHORT-CIRCUITS Hallucinations

Some people have crossovers between their senses. Hallucinations are surprisingly common;
many recently bereaved people report seeing
Some see letters or numbers as colored while others their spouse, and almost everyone has seen
something nonexistent out of the corner of an
might taste coffee when hearing a C-sharp. Their eye. These are a normal by-product of our brains’
attempts to make sense of the world.
condition is called synesthesia and it happens because

they do not undergo the same nerve-cell pruning

process that other people do during their childhood

brain development. The result is extra connections

between the brain’s sensory

areas. Synethesia is thought 1
to be genetic because it

tends to run in families.

However, since some 2
identical twins have

synesthesia while the other

twin does not, genetics 3
cannot be the entire story.

NUMBERS SEEN EXPERIENCING Types of
AS COLORS HALLUCINATIONS hallucinations
You may think
BY THE AGE OF 5, THOSE WITH somebody called
SUPERIOR AUTOBIOGRAPHICAL your name, but
MEMORIES START TO nothing was said,
REMEMBER EVERYTHING or you may see a
shadow out of the
corner of your
eye. These are all
common types of
hallucinations.

Memory champions 3 1
8
Some people have amazing memories, but they mostly
use techniques such as placing the items that need to be Number 9 is
remembered along a familiar route. A handful of people pictured dangling
with a condition called superior autobiographical memory like fruit from a
automatically remember every insignificant event that has
happened to them for their entire lives. One individual with 9 favorite tree
this condition had an enlarged temporal lobe and caudate
nucleus—both areas of the brain that are linked to memory.

NEW NEURAL CONN Memory pathway 1
If you need to remember a sequence of 4
ECTIONS numbers, one way to do so is to associate
each number with a place or object you see
on your journey to work. Fitting a “3”
in the window of a car or building,
for instance, helps retain that
number in place in the sequence.

Index amylase 142, 144, 145 auditory cortex 95 immune cells 174
anaerobic respiration 131 autism 107, 246 nutrient transport 145
A anaphylaxis 186 axons 62, 66, 78 oxygen/carbon dioxide
angina 128 transport 114–17, 120–21
acceleration sense 93 anosmia 96 B production 120
acetic acid 149 antibiotics 48, 148, 173, 176 red blood cells 13, 16, 116–17,
Achilles tendon 37, 54, 55, 71 antibodies 169, 171, 172–73, B cells
acne 47, 223 antibody production 175, 179, 120, 139
actin 56–57, 131 175, 178–79, 180 180 supplies/waste transport 121
adenine 16, 17 anticodons 20, 21 migration to lymph nodes volume 120
adenosine 234, 235 antidepressants 243 171 water balance 152–53
adenovirus 176 antifungal medications self test 170, 171 blood clots 46, 49, 126–27
ADH (antidiuretic hormone) stimulation by T cells 178, blood groups 171
177 180 blood pressure 124–25, 197
152, 153 antigens 170, 171, 178–79, types 178 blood vessels
adipose cells 13 action/relaxation 68–69
adrenal glands 191, 193, 238, 180–81 babies at birth 217
anus 147 birth 216–17 blockages 127
240, 241 anxiety 196 birth weight and length 38 blood flow 127, 128
aerobic respiration 130–31 aorta 128 bone growth 38 blood pressure 124–25, 197
afterimages 83 apoptosis 15, 27 breastfeeding 219 in bones 36
aging appendix 147 cognitive development 218–19 coronary 128
armpits 172 microbes 173 damage and repair 126–127
age spots 225 arms senses 219 fight or flight response 241
bones 38–39, 48 healing 175
cell death 225 bones 49, 54–55 baby teeth 42 immune response 174–75
DNA damage 26 fetal development 212 back pain 70 pregnancy effects 214
free radicals 224 microbes 172 bacteria, friendly 146, 147, water balance 152, 153
hair loss 225 muscles 54–55, 58–59 see also arteries; capillary
hearing loss 95, 225 nerve problems 70 148–49, 164, 165, 172–73 networks; veins
immune response 175 nonverbal communication bacterial infections 43, 168, body language 108–109
memory loss 233 body odor 245
nerve deterioration 225 108 174–75, 176, 178–79; see also body ownership sense 101
osteoarthritis 51 arrhythmias 129 infections body position sense 100–101
osteoporosis 48, 50, 51 arteries bone marrow 24, 36, 120, 170,
skin 32, 225 balance 92–93 178
teeth 42 action/relaxation 68 baldness 225 bones
telomere length 224 blockages 127, 128 belly button 172 aging 48, 50
vertebrae 71 blood pressure 124, 125 bicarbonate 147 blood vessels 36
vision changes 86, 87, 225 carrying oxygen-poor blood biceps 54, 55, 58, 59 calcium release 194
wound repair 175 bile 141, 144, 145, 154, 155, 157 calcium storage 195
airways 68, 112–13, 114, 118–19, 114 binocular vision 84 exercise benefits 50
186; see also breathing carrying oxygen-rich blood bipolar disorder 243 fractures 38, 48–49
alcohol 61, 92, 152, 157, 196 birth 216–217 function 36
aldosterone 199 124 bite impression 42 growth 38–39, 223
alleles 17 coronary 128 bladder 69, 150, 151, 153, 215 healing 49
allergies 186, 187 exercise benefits 134 blindspots 82 joints see joints
altitude effects 115 hepatic 154–55 blisters 47 osteoporosis 48, 50–51
alveoli 113, 114–15 menstrual cramps 206 bloating 149, 164, 165 skeletal arrangement 37
amino acids 14, 20–21, 138, 139, penile erection 204 blood strength 36
144, 145, 157 renal 150 structure 36–37, 50
amygdala 96, 97, 237, 239, 240 structure 124 circulation through body 125
arthritis 51, 186 circulation through heart
aspergillus fungus 177
asthma 187 122–23
astigmatism 86 components 120
atherosclerosis 128 filtration 150–51, 154–55
atrial fibrillation 129