How it works Human body

DID YOU KNOW? Mitochondrial disease occurs when mitochondria malfunction – there is a huge variety of symptoms

What powers your cells?

Discover how mitochondria produce all the energy your body needs

Mitochondria are known as the batteries maintain life - by controlling Krebs Cycle which They are deeply linked with evolution of all
of cells because they use food to make is the set of reactions that produce ATP. life. It is believed mitochondria formed over a
energy. Muscle fibres need energy for billion years ago from two different cells, where
us to move and brain cells need power to Mitochondria are found in nearly every cell the larger cell enveloped the other. The outer
communicate with the rest of the body. They in your body. They are found in most eukaryotic cell became dependent on the inner one for
generate energy, called adenosine triphosphate cells, which have nucleus and other organelles energy, while the inner cell was reliant on the
(ATP), by combining oxygen with food molecules bound by a cell membrane. This means cells outer one for protection.
like glucose. without these features, such as red blood cells,
don’t contain mitochondria. Their numbers This inner cell evolved to become a
However, mitochondria are true biological also vary based on the individual cell types, mitochondrion, and the outer cells evolved to
multi-taskers, as they are also involved with with high-energy cells, like heart cells, form building blocks for larger cell structures.
signalling between cells, cell growth and the containing many thousands. Mitochondria are This process is known as the endosymbiotic
cell cycle. Theyperform all of these functions by vital for most life – human beings, animals and theory, which is Ancient Greek for ‘living
regulating metabolism - the processes that plants all have them, although bacteria don’t. together within.’

Inside the mitochondria Phospholipid
bilayer
Take a tour of the cell’s energy factory
Every mitochondria has
ATP synthesis a double-layered

ATP is the basic energy unit of the cell surface composed of
and is produced by ATP synthase phosphates and lipids.
enzymes on the inner membrane at its
interaction with the matrix. Outer membrane

Mitochondrial DNA The outer membrane contains
large gateway proteins, which
Mitochondria have their control passage of substances
own DNA and can divide to
produce copies. through the cell wall.

Inner membrane Mitochondria produce © SPL
fuel for everyday activities
This layer contains the
key proteins that such as exercise
regulate energy
How many are
production inside the in a cell?
mitochondria, including
The number of mitochondria in a
ATP synthase. cell depends on how active that
particular cell is and how much
Inter-membrane energy it requires to function. As a
space general rule, they can either be low
energy without a single
This contains proteins mitochondrion, or high energy with
and ions that control thousands per cell. Examples of
high-energy cells are heart muscles
what is able to pass in or the busy liver cells, which are
and out of the organelle active even when you’re asleep,
and are packed with mitochondria
via concentration to keep functioning. If you train
gradients and ion pumps. your muscles at the gym, those
cells will develop more
Cristae mitochondria as an adaptive
mechanism to help provide energy.
The many folds of the
inner membrane 151

increase the surface
area, allowing greater
energy production for

high-activity cells.

Matrix

The mitochondrial matrix
contains the enzymes, ribosomes

and DNA, which are essential to
allowing the complex energy-
producing reactions to occur.

CURIOUS QUESTIONS

Is it possible This CT scan of the brain has fused
PET images over it, showing activity
of different regions when the patient
is exposed to a range of stimuli

to see our
thoughts?

The brain is perhaps the most vital of
the body’s vital organs, yet in many
ways it’s also the least understood

At its most simple level, the brain is a This DTI view of the© SPL
series of interconnecting neurons that brain uses the high
relay electrical signals between one © SPL
another. They are ‘all or none’ transmitters water content in
as, like a computer, they either transmit a neurons to show fine
signal (like a binary ‘1’) or do not (‘0’). Different structure and activity
neurons are receptive to different stimuli,
such as light, touch and pain. The complex brain. It has also led to benefits for imaging
activity of these neurons is then interpreted other diseases in other parts of the body,
by various parts of the brain into useful including several forms of cancer.
information. For example, light images from
the eye are relayed via the optic nerve to the These advanced imaging techniques
occipital cortex located in the back of the include scans to produce images of the
skull, for interpretation of the scene in front anatomical structure of the brain, and
of you. interpretation of energy patterns to
determine activity or abnormalities.
The generation and interpretation of Scientists have started to ascertain which
thoughts is a more complex and less well parts of the brain function as we form
understood process. In fact, it is a science of its different thoughts and experience different
own, where there are many definitions of emotions. This means we are very much on
what a ‘thought’ is, and of what defines the brink of seeing our own thoughts.
consciousness. In an effort to better define
these, doctors, scientists and psychologists
have turned to novel imaging techniques to
better understand the function of our minds.
Research into understanding brain activity
and function has led to some of the most
advanced imaging techniques available. This
has helped to treat conditions such as
Alzheimer’s dementia, epilepsy and stroke,
as well as mental illnesses where there is not
necessarily a physical problem within the

How can we view the brain?

Computed © Oliver Stollmann Magnetic resonance Functional MRI (fMRI)
tomography (CT) imaging (MRI)
This form of MRI uses blood-
This combines multiple X-rays MRI uses strong magnetic oxygen-level-dependent
to see the bones of the skull fields to align the protons in (BOLD) contrast, followed by a
and soft tissue of the brain. It’s water molecules in various strong magnetic field, to detect
the most common scan used body parts. When used in tiny changes in oxygen-rich
after trauma, to detect injuries the brain, it allows intricate and oxygen-poor blood. By
to blood vessels and swelling. anatomical detail to be showing pictures to invoke
However, it can only give a visualised. It has formed the certain emotions, fMRI can
snapshot of the structure so basis of novel techniques to reveal which areas are active
can’t capture our thoughts. visualise thought processes. during particular thoughts.

152 | How It Works

DID YOU KNOW? CT scanning of the brain was invented in the early-Seventies

Picking apart the brain

The frontal lobes The sensory and
motor cortexes
The frontal lobes of the folded
cerebral cortex take care of The pre- and post-central gyri
thought, reasoning, decisions and receive the sensory information
memories. This area is believed to from the body and then dispatch
be largely responsible for our orders to the muscles, in the form of
individual personalities. signals through motor neurons.

The occipital cortex

In the posterior fossa of the skull,
this cortex receives impulses from

the optic nerves to form images.
These images are in

fact seen upside down, but this
area enables them to be

interpreted the right way up.

The brainstem © Alamy The cerebellum

Formed from the midbrain, The cerebellum is responsible
pons and medulla oblongata, for fine movements and
the brainstem maintains the
vital functions without us co-ordination. Without it, we
having to think about them. couldn’t write, type, play
These include respiration and musical instruments or
heart function; any damage
to it leads to rapid death. perform any task that requires
precise actions.

© SPL

The pituitary gland Positron emission Imaging
tomography (PET) Alzheimer’s
This tiny gland is responsible
for hormone production This bleeding-edge technology Alzheimer’s disease is a potentially
throughout the body, which detects gamma rays emitted debilitating condition, which can lead
can thus indirectly affect our from biologically active tissues to severe dementia. The ability to
emotions and behaviours. based on glucose. It can pick diagnose it accurately and early on has
up unusual biological activity, driven the need for modern imaging
Diffusion tensor such as that from cancer. There techniques. The above image shows a
imaging (DTI) have been recent advances to PET scan. The right-hand side of the
combine PET with CT or MRI to image (as you look at it) shows a normal
This MRI variant relies on the obtain lots of data quickly. brain, with a good volume and activity
direction of water diffusion range. On the left-hand side is a patient
within tissue. When a magnetic affected by Alzheimer’s. The brain is
gradient is applied, the water shrunken with fewer folds, and a lower
aligns and, when the field is range of activity – biologically speaking,
removed, the water diffuses there are far fewer neurons firing.
according to a tissue’s internal
structure. This allows a 3D How It Works | 153
image of activity to be built up.

CURIOUS QUESTIONS

How anaesthesia works

By interfering with nerve transmission these special drugs stop pain signals
from reaching the brain during operations

Anaesthetics are a form of drug widely The body under general anaesthetic Memory
used to prevent pain associated with
surgery. They fall into two main categories: What happens to various parts of General anaesthetic affects
local and general. Local anaesthetics can be either the body when we’re put under? the ability to form memories;
applied directly to the skin or injected. They are used the patient doesn’t remember
to numb small areas without affecting Brain activity the operation and often won’t
consciousness, so the patient will remain awake
throughout a procedure. Electroencephalograms (EEGs) recall coming to either.
show that the electrical
Local anaesthetics provide a short-term blockade activity in the brain drops to a Airway
of nerve transmission, preventing sensory neurons state deeper than sleep,
from sending pain signals to the brain. Information mimicking a coma. Loss of consciousness and
is transmitted along nerves by the movement of muscle relaxation suppress
sodium ions down a carefully maintained Nil by mouth
electrochemical gradient. Local anaesthetics cut breathing and prevent
off sodium channels, preventing the ions from General anaesthetics suppress coughing, so a tube and
travelling through the membrane and stopping the gag reflex and can cause
electrical signals travelling along the nerve. vomiting, so to prevent ventilator are used to
choking patients must not eat maintain the airway.
Local anaesthesia isn’t specific to pain nerves, so it before an operation.
will also stop information passing from the brain to Nausea
the muscles, causing temporary paralysis. Heart rate
Many anaesthetics
General anaesthetics, meanwhile, are inhaled The circulatory system is cause nausea. Often
and injected medications that act on the central slowed by anaesthetic, so antiemetic drugs that
nervous system (brain and spinal cord) to induce a heart rate, blood pressure prevent vomiting are
temporary coma, causing unconsciousness, muscle and blood oxygen are all given after surgery.
relaxation, pain relief and amnesia. continuously monitored.
© Getty
It’s not known for sure how general anaesthetics Pain neurons
‘shut down’ the brain, but there are several proposed
mechanisms. Many general anaesthetics dissolve in Unlike with local
fats and are thought to interfere with the lipid anaesthetic, pain
membrane that surrounds nerve cells in the brain. neurons still fire under
They also disrupt neurotransmitter receptors, general anaesthesia,
altering transmission of the chemical signals that let but the brain does
nerve cells communicate with one another. not process the
signals properly.
Comfortably numb
Muscle relaxation
If large areas need to be anaesthetised while the
patient is still awake, local anaesthetics can be A muscle relaxant is often
injected around bundles of nerves. By preventing administered with the
transmission through a section of a large nerve, anaesthetic; this causes
the signals from all of the smaller nerves that paralysis and enables lower
feed into it can’t reach the brain. For example, doses of anaesthetic to be used.
injecting anaesthetic around the maxillary nerve
will not only generate numbness in the roof of
the mouth and all of the teeth on that side, but
will stop nerve transmission from the nose and
sinuses too. Local anaesthetics can also be
injected into the epidural space in the spinal
canal. This prevents nerve transmission through
the spinal roots, blocking the transmission of
information to the brain. The epidural procedure
is often used to mollify pain during childbirth.

154

DID YOU KNOW? The scientists who revealed bacteria caused gastric ulcers had to drink their own experiment to prove it!

What causes stomach ulcers?

Originally thought to be the result of stress, we now know that bacteria are the culprits…

Normally a thick layer of An ulcer in the making Gastrin
alkaline mucus effectively
protects the cells lining Once bacteria breach the stomach lining, it can no The inflammatory
the stomach from the low pH of longer protect itself from its acidic contents… response increases
stomach acid. If this mucus production of the
becomes disrupted, however, acid Neutralising Helicobacter pylori hormone gastrin. This in
comes into contact with the organ’s stomach turn stimulates the
lining, damaging the cells and acid Bacteria burrow through the formation of more
resulting in an ulcer. mucus in the stomach to escape stomach acid.
H pylori break down damage by acid. They stick to the
Around 60 per cent of stomach Damage
ulcers are caused by inflammation urea to make cells of the interior lining.
due to chronic infection by the As the cells become
bacterium Helicobacter pylori. ammonia. This is damaged a wound opens
Bacterial by-products damage up in the stomach wall. If this
the cells lining the stomach, used to produce becomes deep enough it can
causing a breakdown of the top perforate blood vessels
layers of tissue. bicarbonate to causing bleeding.

Non-steroidal anti- neutralise
inflammatory drugs (NSAIDs),
like ibuprofen and aspirin, also dangerous
cause stomach ulcers in large
doses. They disrupt the enzymes stomach acid.
responsible for mucus production,
diminishing the protective barrier.

Enzymes Ammonia

H pylori produce proteases The ammonia made by
and phospholipases – the bacteria as a defence
enzymes that damage the against acid damages the
proteins and cell cells lining the stomach,
membranes of the causing inflammation.
stomach cells.

Why do we sometimes
get mouth ulcers?

Ulcers are small lesions usually In other cases, recurrent ulcers may
triggered by physical damage to the be symptomatic of conditions
inside of the mouth, for example including B12 or iron deficiencies,
biting your cheek accidentally, gastrointestinal diseases or
eating sharp food or brushing your immunosuppressant diseases such
teeth. They are very rarely as HIV. Ulcers are sometimes
contagious and usually heal within triggered by sensitivity to certain
ten days. Recurrent ulcers have a foods including strawberries,
variety of causes, the most common almonds, tomatoes, cheese,
being stress and hormonal changes. chocolate and coffee.

© Alamy “They are rarely contagious
and usually heal in ten days”

155

CURIOUS QUESTIONS

Why do we feel love?

The hormones and chemicals that cause us to fall head over heels

7. Nucleus 8. Deactivate prefrontal cortex 3. Prefrontal cortex
accumbens
The nucleus accumbens then pushes the prefrontal Messages are then sent to the
The secretion of cortex for action, but it deactivates, suspending prefrontal cortex, the brain’s
feelings of criticism and doubt. decision-making centre, where it
dopamine stimulates the judges if the potential romantic
partner is a good match.
nucleus accumbens, an

area of the brain that plays

a vital role in addiction.

6. Hormone levels 1. Amygdala 4. Hypothalamus

As dopamine levels increase, When you see If the attraction is there,
levels of serotonin, the someone you like, the the prefrontal cortex
hormone responsible for mood amygdala, the area of stimulates the
and appetite, decrease, the brain responsible hypothalamus, which
causing feelings of obsession. for emotions, releases the
recognises it as a neurotransmitter
2. Hippocampus positive experience. dopamine, causing feeling
of ecstasy.
The hippocampus, the
memory forming area of
the brain, records this
pleasant experience
making you want to seek it
out again.

5. Norepinephrine

Norepinephrine, another
neurotransmitter similar to
adrenalin, is also released,
which gets your heart racing
and causes you to sweat.

9. Deactivate
amygdala

The amygdala also deactivates,
reducing the ability to feel fear
and stress and creating a more
happy, carefree attitude.

How do enzymes keep you alive?

The proteins that speed up your body’s chemical reactions Enzymes such as
trypsin work to help

break down
proteins

Enzymes increase the speed of reactions undergoes a reaction such as dividing or © Thinkstock
that take place inside cells by lowering the merging with another molecule without having
energy-activation requirement for to expel energy in a collision with another
molecular reactions. Molecules need to react molecule. The enzyme releases it and floats on
with each other to reproduce, but our bodies within the cell’s cytoplasm. The molecule and
provide neither the heat nor the pressure active site need to match up perfectly in order
required for these reactions. for the sped-up reaction to take place. For
example, a lactose molecule would fit into a
Each cell contains thousands of enzymes, lactase enzyme’s active site, but not that of a
which are amino acid strings rolled up into a ball maltase enzyme.
called a globular protein. Each enzyme contains
a gap called an active site into which a molecule Interestingly enough, enzymes don’t get used
can fit. Once inside the crack, the molecule – up in the process, so they can theoretically
which becomes known as a substrate – continue to speed up reactions indefinitely.

156

DID YOU KNOW? Despite what TV dramas have you believe, CPR using a defibrillator is rarely successful in real life

Correcting heart
rhythms Howcanalittleelectricitybeusedto

fix a heart that’s beating off-kilter?

6. Natural pacemaker 8. Low energy 3. Timing the shock

The heart has its own internal Resetting an abnormal The heart is vulnerable when it
pacemaker known as the sinoatrial heart beat uses fairly is between beats, so to prevent
node. Delivering a small electric low-energy shocks of just
shock to this resynchronises the 50-200 joules. a cardiac arrest, the shock is
organ’s natural electrical activity. timed to coincide with the
4. Arrhythmia pumping of the ventricles.
5. Electric shocks
If the heart beats too fast, or BEFORE CARDIOVERSION
Low-energy electric shocks at an irregular pace, it
are delivered to the heart becomes unable to Atrial fibrillation
through the electrodes. effectively pump blood
around the body.

1. Paddles

Two metallic plates are
placed on the patient’s
chest across the heart.

2. Conductive gel 7. Cardioversion AFTER CARDIOVERSION
machine
A saltwater-based gel is Normal ECG
used so the current can The machine records the
travel from the electrodes electrical activity of the
and through the skin. heart and calculates the
electric shocks required
to restore the organ to
its normal rhythm.

Why’s salt Do women have
bad for Adam’s apples?
the heart?
You may not realise, but actually everyone has an Adam’s
Simply put, too much salt is bad apple, but men’s are usually easier to see in their throat.
for you as it increases the It’s a bump on the neck that moves when you swallow,
demand on your heart to pump named after the biblical Adam. Supposedly, it’s a chunk of the
blood around the body. This is Garden of Eden’s forbidden fruit stuck in his descendants’
because when you eat salt it causes throats, but it’s actually a bump on the thyroid cartilage
retention of increased quantities of surrounding the voice box. Thyroid cartilage is shield-shaped
water, which increases your blood and the Adam’s apple is the bit at the front.
pressure, and this places more strain
on your heart. Most doctors Why do men’s Adam’s apples stick out more? This is partly
recommend moderating salt intake. because they have bonier necks, but it is also because their
larynxes grow differently from women’s during puberty to
accommodate their longer, thicker vocal cords, which give them
deeper voices.

How It Works | 157

CURIOUS QUESTIONS

What causes Oesophagus
a rumbling
stomach? This muscular pipe
connects the throat
Discover how the small to the stomach.
intestine is really to blame…
Stomach Liver Lungs
Waves of involuntary muscle contractions Rectum
called peristalsis churn the food we eat Food is churned and
to soften it and transport it through the mixed with gastric
digestive system. The contractions are caused by juices to help it to
strong muscles in the oesophagus wall, which take break down.
just ten seconds to push food down to the stomach.
Muscles in the stomach churn food and gastric Small intestine
juices to break it down further.
Here, liquid food
Then, after four hours, the semi-digested combined with trapped
liquefied food moves on to the small intestine gases can make for some
where yet more powerful muscle contractions embarrassing noises.
force the food down through the intestine’s bends
and folds. This is where the rumbling occurs. Air
from gaseous foods or that swallowed when we eat
– often due to talking or inhaling through the nose
while chewing food – also ends up in the small
intestine, and it’s this combination of liquid and
gas in a small space that causes the gurgling noise.

Rumbling is louder the less food present in the
small intestine, which is partly why people
associate rumbling tummies with hunger. The
other reason is that although the stomach may be
clear, the brain still triggers peristalsis at regular
intervals to rid the intestines of any remaining
food. This creates a hollow feeling that causes you
to feel hungry.

“After four Large intestine
hours, the semi-
digested liquefied Food passes from the
food moves to the small intestine to the
small intestine” large intestine where
it is turned into faeces.

Are seasickness and altitude
sickness the same thing?

No, they’re not – altitude sickness is a collection signals’ about a moving environment – for © Thinkstock
of symptoms brought on when you’re suddenly instance, when your eyes tell you that your
exposed to a high-altitude environment with immediate surroundings (such as a ship’s
lower air pressure so less oxygen enters our body. cabin) are still as a rock, while your sense of
The symptoms can include a headache, fatigue, balance (and your stomach!) tells you something
dizziness and nausea. quite different.

Seasickness, on the other hand, is a more This is the reason why closing your eyes or
general feeling of nausea that’s thought to be taking a turn out on deck will often help, as it
caused when your brain and senses get ‘mixed reconciles the two opposing sensations.

158

DID YOU KNOW? Common pregnancy cravings are pickles, chocolate and ice cream

How do cravings work?

Is a child destined to develop a taste for all things sweet?

Hunger and cravings are two very different Our mothers’ diet can influence our preferences This endless conversation can cause our appetite
things. While one is about survival, the for certain foods. Scientists have found that flavours and cravings to change. The gut bacteria are also
other satisfies the nagging need for are transmitted from mother to baby via the heavily involved; when they break down large
something sugary. It’s believed we all develop a taste amniotic fluid surrounding the foetus in the womb. quantities of fibre, they produce a specific compound
for sweetness in infancy. This stems from the Once born, the probability of the child disliking the that is sent to the brain, triggering it to feel full and
predominant sweet taste of our mother’s milk; when flavours they have already experienced is reduced. satisfied from the recently ingested meal.
we taste it, the brain’s reward centres light up,
causing us to derive pleasure from this experience. Our gut also plays a large role in cravings. The gut So should we consider cravings as a sign of food
As we continue to consume our mother’s milk this contains an almost separate autonomous system addiction? Although high-sugar and high-fat foods
pleasure is reinforced, which could explain how our that governs the digestion lining. This vast network exhibit some of the hallmarks of addiction, the
sugar cravings originate. of 100 million neurones constantly samples the consensus is that it’s actually the behaviour around
ingested food, relaying this information to the brain. eating these foods that we are addicted to.

People commonly Tricking our
crave the sweet senses
taste and
Does a spoon’s colour change the way yoghurt
melt-in-the-mouth tastes? In reality it doesn’t, but the colour of
texture of chocolate cutlery can alter how you think something
tastes. A recent study fed a group of volunteers
the same yoghurt using a white and a black
spoon. The results showed that the yoghurt was
perceived to taste sweeter on the white spoon.
Altering the spoon’s weight was then tested.
The lighter spoons caused the participants to
feel the yoghurt was denser and more
luxurious. Scientists are unsure what
mechanism causes these bizarre results, and
want to carry out further research into why we
make these associations.

Can the latest technology stop cravings?

One of the most recent inventions is a microchip Ghrelin is the body’s hunger-inducing © Science Museum; Thinkstoc
that aims to control cravings, developed by Kings hormone. By using a ghrelin antagonist, scientists
College London’s Centre for Bio-Inspired aim to suppress this hormone’s activity, stopping
Technology. Once implanted in the body, the chip cravings from ever materialising. This research
will use electrodes to monitor the signals that are has implications for cravings of other substances
consistently passing between the gut and the too. Scientists have hypothesised that due to the
brain. By ‘listening’ to the communication similarities between this system and that
between the two organs, the microchip will be responsible for craving nicotine and alcohol, it
able to recognise signals for cravings and alter may be possible to switch off these cravings as
these before they reach the brain. well as those related to food.

159

CURIOUS QUESTIONS

What causes Why do
the knee-jerk feet smell?
reaction?
Producing up to a pint of
Why does your leg kick out when the doctor taps sweat each day, no wonder
just below your knee? your feet get a bit whiffy

Doctors often test the knee-jerk, or patellar reflex, to look for potential neurological Sweat actually keeps the skin of our feet moist
problems. Lightly tapping your patellar tendon just below the kneecap stretches the and flexible to cope with the constantly
femoral nerve located in your thigh, which in turn causes your thigh muscle (quadriceps) changing pressure when we walk. Without this
to contract and the lower leg to extend. When struck, impulses travel along a pathway in the moisture the skin would dry and crack, and walking
dorsal root ganglion, a bundle of nerves in the L4 level of the spinal cord. Reflex actions are would become extremely painful. Despite the huge
performed independently of the brain. This allows them to happen almost instantaneously – number of glands (250,000 per foot) and amount of
within about 50 milliseconds in the case of the knee-jerk reflex. This reflex helps you to maintain sweat that comes from our feet, remember it’s still just
balance and posture when you walk, without having to think about every step you take. salt and water. The odour comes from the bacteria that
live on human skin which, while unsettling, are
The knee-jerk step-by-step 3. Interneuron perfectly natural.

1. Quadriceps and hamstring muscles The interneuron provides a Our socks are a dark, moist-infested feast for
connection between the them, as they eat sweat and dead skin. It is the waste
The knee-jerk reflex means that the quadriceps muscles products they excrete from this consumption that are
contract at the same time the hamstring muscle relaxes. sensory and motor neurons. what smells bad. The more the bacteria eat the worse
our feet smell. To keep the smell down, make sure
you change your socks and let your shoes air for 24
hours if you can. Also, wash your feet and spray them
with antiperspirant!

Sensory neuron 2. Sensory neuron 4. Motor neuron
Motor neuron
Interneuron The sensory, or afferent The motor, or efferent
neuron, receives an impulse neuron, carries the nerve
from the femoral nerve.
impulse to the muscles.

5. Spinal cord

The spinal cord has both grey
matter, which contains nerve cell
bodies, and white matter, which

contains the nerve fibres.

“Reflex actions are performed The wonderful smell of
independently of the brain” freshly cut grass, daisies

160 and feet…

DID YOU KNOW? Writers’ cramp occurs in the hands and lower arms but is actually a form of dystonia, a neurological condition

Blisters shouldn’t be Cramp
burst as they are the explained
body’s way of protecting

deeper skin layers

What are blisters? Why do our muscles tense up?

Why do burns cause bubbles to develop Cramp is an involuntary contraction of a muscle, often in a limb such
below the surface of the skin? as the leg, that can cause pain and discomfort for seconds, minutes or,
in extreme cases, for several hours. They are most common after or
Though our skin is an amazing and fills the spaces between the layers during exercise, coinciding with low blood sugar levels, dehydration
protector against the elements, it can of skin to cushion the underlying skin and a high loss of salt from sweating. Although the full range of
become damaged by such factors as and protect it from further damage. As causes is something of a mystery due to limited research in the area,
heat, cold, friction, chemicals, light, more and more serum pours into the cramp is believed to be the result of muscle fatigue. If a muscle has
electricity and radiation, all of which space, the skin begins to inflate under been shortened through prolonged use, but is repeatedly stimulated,
‘burn’ the skin. A blister is the resulting the pressure, forming a small balloon it isn’t able to properly relax. A reflex arc from the central nervous
injury that develops in the upper layers full of the serous liquid. Given time to system to the muscle informs it to continue contracting when it is not
of the skin as a result of such burns. heal, the skin will reabsorb the plasma necessary, leading to a painful spasm known as cramp as the muscle
after about 24 hours. continually attempts to contract. This is why athletes pushed beyond
The most common example of a their limits, such as football players who have to play extra time in a
blister, which we’ve no doubt all Similarly, a blood blister is a variation match, will often experience this condition.
experienced at some time, is due to the of the same injury where the skin has
repeated friction caused by the material been forcefully pinched or crushed but Rest
of a pair of shoes rubbing against, and not pierced, causing small blood vessels
irritating, the skin. The resulting water to rupture, leaking blood into the skin. At rest the calf
blister is a kind of plasma-filled bubble All blisters can be tender but should muscle is in its
that appears just below the top layers of never be popped to drain the fluid as relaxed position.
your skin. The plasma, or serum – which this leaves the underlying skin
is a component of your blood – is unprotected and invites infection into Stretch
released by the damaged tissue cells the open wound.
When the leg is
bent or stretched

the calf muscle
will contract, and
then relax when

it is not.

Blister caused by Plasma
second-degree burns
Serum is released by the damaged
© SPL tissues into the upper skin layers to
prevent further damage below in the

epidermal layer. It also aids the
healing process, which is why you
should avoid popping your blisters.

Skin Duration Cramp

When any type of burn is Any generated Prolonged
experienced, the overlying skin cramp usually lasts stretching of the
expands as it receives the for a few seconds, leg prevents the
protective plasma/serum. however some calf muscle from
severe cases can relaxing, which can
Damage last hours.
lead to cramp.
This particular example of a blister burn Fluid reabsorbed
has caused damage to the keratinocytes 161
in the skin. Second-degree burns are After a day or so the serum will be
most often caused when the skin comes absorbed back into the body and the
into contact with a hot surface, such as raised skin layers will dry out and flake
an iron or boiling water, or even after
exposure to excessive sunlight. off in their own time.

CURIOUS QUESTIONS

Do we control our brains or
do our brains control us?

An experiment at the Max Planck Institute, Berlin, in 2008
showed that when you decide to move your hand, the
decision can be seen in your brain, with an MRI scanner,
before you are aware you have made a decision. The delay is
around six seconds. During that time, your mind is made up but
your consciousness doesn’t acknowledge the decision until your
hand moves. One interpretation of this is that your consciousness
– the thing you think of as ‘you’ – is just a passenger inside a
deterministic automaton. Your unconscious brain and your body
get on with running your life, and only report back to your
conscious mind to preserve a sense of free will. But it’s just as valid
to say that when you make a decision, there’s always background
processing going on, which the conscious mind ignores for
convenience. In the same way, your eye projects an upside-down
image onto your retina, but your unconscious brain turns it the
right way around.

Gelotology is the study What happens
of laughter and its when we laugh?
effects on the
human body

Which muscles react when we find
something funny and why is
laughter so hard to fake?

Laughing can sometimes be on top of this, the zygomaticus major
completely involuntary and also pulls the upper lip upward
involves a complex series of and outward.
muscles, which is why it’s so difficult
to fake and also why an active effort The sound of our laugh is
is required to suppress laughter in produced by the same mechanisms
moments of sudden hilarity at which are used for coughing and
inopportune moments. speaking: namely, the lungs and the
larynx. When we’re breathing
In the face, the zygomaticus major normally, air from the lungs passes
and minor anchor at the cheekbones freely through the completely open
and stretch down towards the jaw to vocal cords in the larynx. When they
pull the facial expression upward; close, air cannot pass, however

© Alamy when they’re partially open, they
generate some form of sound.
Laughter is the result when we
exhale while the vocal cords close,
with the respiratory muscles
periodically activating to produce
the characteristic rhythmic sound
of laughing.

The risorius muscle is used to
smile, but affects a smaller portion
of the face and is easier to control
than the zygomatic muscles. As a
result, the risorius is more often
used to feign amusement, hence
why fake laughter is easy to detect
by other humans.

“Laughter is produced by the same mechanisms
used for coughing and speaking”

162

DID YOU KNOW? It is highly likely that pirates wore eye patches to condition their eye to see better in the dark

What is the maximum What is dandruff?
distance the human
eye can see? Dandruff is when dead skin cells fall off the scalp. This is
normal, as our skin is always being renewed. About half
Dust, water vapour and pollution in the air will rarely let you see more than 20 the population of the world suffers from an excessive
kilometres, even on a clear day. Often, the curvature of the Earth gets in the way amount of this shedding, which can be triggered by things like
first – eg at sea level, the horizon is only 4.8km away. On the top of Mt Everest, temperature or the increased activity of a microorganism that
you could theoretically see for 339km, but in practice cloud gets in the way. For a truly normally lives in everyone’s skin, known as malassezia globosa.
unobstructed view, look up. On a clear night, you can see the Andromeda galaxy with Dandruff is not contagious and there are many treatments
the naked eye, which is 2.25 million light years away. available, the most common is specialised shampoo.

Our line of sight can be impeded by © Horoporo
many things, from pollution to the

curvature of the Earth

Why do eyes
take a while to
adjust to dark?

At the back of the eye on the retina, there are
two types of photoreceptors (cells which
detect light). Cones deal with colour and fine
detail and act in bright light, while rods deal with
vision in low-light situations. In the first few
minutes of moving into a dark room, cones are
responsible for vision but provide a poor picture.
Once the rods become more active, they take over
and create a much better picture in poor light. Once
you move back into light, the rods are reset and so
dark-adaption will take a few moments again.
Soldiers are trained to close or cover one eye at
night when moving in and out of a bright room, or
when using a torch, to protect their night vision.
Once back in the dark, they reopen the closed eye
with the rods still working and, as a result,
maintain good vision. This allows them to keep
operating in a potentially hostile environment at
peak operational efficiency. Give it a try next time
you get up in the middle of the night, it may help
you avoid tripping over in the dark.

163

CURIOUS QUESTIONS

© Thinkstock Why do some people
have allergies and
some don’t?

Allergies can be caused by two things: host and environmental
factors. Host is if you inherit an allergy or are likely to get it due
to your age, sex or racial group.Environmental factors can
include things such as pollution, epidemic diseases and diet.

People who are likely to develop allergies have a condition known as
‘atopy’. Atopy is not an illness but an inherited feature, which makes
individuals more likely to develop an allergic disorder. Atopy tends to
run in families.

The reason why atopic people have a tendency to develop
allergic disorders is because they have the ability to produce the
allergy antibody called ‘Immunoglobulin E’ or ‘IgE’ when they
come into contact with a particular substance. However, not
everyone who has inherited the tendency to be atopic will develop an
allergic disorder.

“People who are likely
to develop allergies
have a condition known
as ‘atopy’”

Eczema explained The histamine increase
can cause itching,
leading to open sores

What causes the skin to react to otherwise harmless material?

Eczema is a broad term for a range of Under the skin Allergen © Alamy; J Kadavoor; Thinkstock
skin conditions, but the most entry route
common form is atopic dermatitis. What happens inside the body when eczema flares up?
People with this condition have very The cells of the skin are
reactive skin, which mounts an Ceramides normally tightly bound
inflammatory response when in contact together to prevent
with irritants and allergens. Mast cells The membranes of skin cells contain waxy lipids contaminants from
release histamine, which can lead to to prevent moisture evaporation, but these are entering the body, but in
itching and scratching, forming sores often deficient in eczema. eczema there are gaps.
open to infection.
Allergen Inflammatory
There is thought to be a genetic response
element to the disease and a gene Eczema is commonly triggered
involved in retaining water in the skin by the same things as many The immune system
has been identified as a potential allergies – anything from pet produces a response to
contributor, but there are many factors. hair to certain types of food. allergens beneath the skin,
leading to redness, itching
Eczema can be treated with steroids, Water loss and also inflammation.
which suppress immune system
activity, dampening the inflammation The skin is less able
so skin can heal. In serious cases, to retain water,
immunosuppressant drugs – used to leading to dryness
prevent transplant rejection – can and irritation.
actually be used to weaken the immune
system so it no longer causes
inflammation in the skin.

164

DID YOU KNOW? Pollen is the most common type of allergy, which we refer to as Hayfever

It turns out that growing
pains don’t have much to do
with growth after all

What are
growing
pains?

The medical name for growing
pains is ‘recurrent nocturnal
limb pain in children’, and it
describes the sensation of aching,
crampy pain most often felt at night in
the lower half of the legs.

Children and preteens are often told
that they experience these aches and pains
because they are growing, but this is
untrue. If the pain really were caused by
growth itself, doctors would expect to be
visited by children that were going through
a growth spurt, but there does not seem to
be any link between periods of rapid bone
growth and experience of ‘growing pains’.

The pain is not in the bones or joints but
is actually in the muscles and soft tissues,
and one of the best explanations is that the
pain is the result of strain or overuse of the
muscles and joints during the day.

Squinting can help to Why can we see
focus the light if it is clearer when
not quite in line we squint?

It doesn’t work for everyone, but for some people
things come into focus when they half close their
eyes. This is because of the way that the eye
focuses light.

A flexible lens bends the light as it passes into the eye,
focusing it on a highly sensitive spot on the retina, called
the fovea. The lens changes shape depending on the
distance to the object, ensuring that the light is always
concentrated on this spot.

As we get older, the lens becomes less flexible and
cannot focus the light as well. By half closing our
eyelids, we can put a little pressure on our eyeballs,
changing their shape manually and helping to bring the
light into focus.

165

CURIOUS QUESTIONS

Monozygotic twins
are a rarity

What
are twins?

Twins are becoming more prevalent due to medical
developments, but how and why do they occur?

The number of twins, or multiples, being potentially impact the chances of conceiving Strange, but
born is actually on the rise due to the dizygotic twins. Also, if the mother is going true…
increase in use of fertility treatments through fertility treatments, she is much more
such as IVF as people wait longer to have likely to become pregnant with multiples. There are many stories of identical twins being
children. The number of twins surviving early separated at birth and then growing up to lead
births is also increasing due to improved It will become apparent quite early on that a very similar lives. One example described in the
medical knowledge. mother is carrying twins as this is often picked 1980 January edition of Reader’s Digest tells of
up during early ultrasound scans. There can be two twins separated at birth, both named James,
However, twins are still a relatively rare other indications such as increased weight gain who both pursued law-enforcement training and
occurrence making up only around two per or extreme fatigue. Although twins are often had a talent for carpentry. One named his son
cent of the living world’s population. Within born entirely healthy and go on to develop James Alan, and the other named his James Allan
this, monozygotic twins (from one ovum) make without problems later in life due to medical and both named their dogs Toy. There were also
up around eight per cent with dizygotic (from advances, twins can be premature and smaller the Mowforth twins, two identical brothers who
two ovum) seen to be far more common. than single births due to space constrictions lived 80 miles apart in the UK, dying of exactly the
within the womb during development. same symptoms on the same night within hours of
While there is no known reason for each other.
the occurrence of the split of the ovum that “It is believed twins
causes monozygotic twins, the chances of ‘run in the family’,
having twins is thought to be affected by often seeming to
several different factors. It is believed twins skip generations”
‘run in the family’, often seeming to skip
generations, while the age, weight, height, race
and even diet of the mother are thought to

166

DID YOU KNOW? Female monozygotic twins are more common due to the increased likelihood of male mortality in the womb

Multiple pregnancies, Formation of
multiple problems? identical and
fraternal twins
There are many difficulties with twin It is also suspected that as many as one in
pregnancies – mainly due to the limited size eight pregnancies may have started out as a Monozygotic (MZ), or identical, twins are formed by the
of the mother’s womb. Multiple pregnancies potential multiple birth, but one or more of the egg splitting soon after fertilisation, and from those
rarely reach full term due to these limits, foetuses does not progress through identical split groups of cells, two separate foetuses will
twins averaging at around 37 weeks. Also, development to full term. start to grow. Monozygotic twins are therefore genetically
because of the lack of space and eggs splitting identical and will be the same sex, except when mutations
in the womb, further complications such as “Conjoined twins or very rare syndromes occur during gestation. No reason
conjoined twins can occur. Conjoined twins can be a problem is known for the occurrence of the split of the ovum, and
can be a problem dependant on where dependant on where the father has no influence over whether identical twins
they’re joined. If it is by a vital organ or bone they’re joined” are produced.
structure, one or both may die following birth
as they grow – or during an operation to Twins inside Dizygotic (DZ) twins, however, are produced when the
separate them. the womb female’s ovaries release two ovum and both are fertilised
and implanted in the womb wall. They can be known as
Placenta fraternal twins as genetically they are likely to only be as
similar as siblings. They will also have separate placentas,
Provides a metabolic where MZ twins will share one, as they are entirely
interchange between separate to each other – they are just sharing the womb
the twins and mother. during gestation. This kind of twin is far more common.

Uterine wall

The protective wall
of the uterus.

Amniotic sac Monozygotic 1. Sperm
fertilises egg
A thin-walled sac that 2. Fertilised
surrounds the fetus egg splits In MZ twins, only one
during pregnancy. egg and one sperm
At some point very are involved.
early on, the fertilised
egg will split and two
separate foetuses will
start to form. These
will be genetically
identical.

Umbilical cord

A rope-like cord
connecting the fetus
to the placenta.

Genetically Cervix Dizygotic 3. Sperm
identical, but why fertilise
do twins differ? The lower part of the 4. Separate
uterus that projects eggs separate
continue eggs
into the vagina. to develop
In DZ twins, two
From studying identical, monozygotic twins, different parents. Often we see a similar IQ In DZ twins, both separate eggs are
we can attempt to decipher the level of impact and personality displayed, whether or not foetuses will
environment has on an individual and the they grow up together, but even these and continue to develop fertilised by
influence genes have. As the genetics of the other lifestyle choices can vary dependant independently to different sperm.
individuals would be identical, we can say on environment. each other. These will implant
that differences displayed between two independently in
MZ twins are likely to be down to Ultimately, it is hard to draw firm
environmental influences. conclusions from twin studies as they will be the mother’s
an unrepresentatively small sample within a womb wall,
Some of the most interesting studies look at much larger population and we often find that commonly on
twins that have been separated at birth, often both environment and genetics interact to opposite sides.
when individuals have been adopted by influence an individual’s development.
167

CURIOUS QUESTIONS

How do alveoli
help you breathe?

The lungs are filled with tiny balloon-like
sacs that keep you alive

Gas exchange occurs in the lungs, where toxic the final point of the respiratory tract, as the venous system on the other side of the
gases (carbon dioxide) are exchanged for bronchi break down into smaller and smaller epithelial layer.
fresh air with its unused oxygen content. Of tubes, leading to the alveoli, which are grouped
all the processes in the body that keep us together and look like microscopic bunches of The alveoli of the lungs have evolved to
functioning and alive, this is the most important. grapes. Around the alveoli is the epithelial become specialised structures, maximising
Without it, we would quickly become unconscious layer – which is amazingly only a single cell their efficiency. Their walls are extremely thin
through accumulation of carbon dioxide within the thick – and this is surrounded by extremely and yet very sturdy. Pulmonary surfactant is a
bloodstream, which would poison the brain. small blood vessels called capillaries. It is thin liquid layer made from lipids and proteins
here that vital gas exchange takes place that coats of all the alveoli, reduces their
The two lungs (left and right) are made up of between the fresh air in the lungs and the surface tension and prevents them crumpling
several lobes, and the fundamental building deoxygenated blood within the capillary when we breathe out. Without them, the lungs
blocks of each are the tiny alveolus. They are would collapse.

Alveoli anatomy Type I pneumocytes Breathe in,
breathe out
How alveoli enable gas exchange These large, flattened cells form
95 per cent of the surface area of The alveoli function to allow gas
an alveolus, and are the very thin exchange, but since they’re so
diffusion barriers for gases. small, they can’t move new air
inside and out from the body
Type II without help. That’s what your
pneumocytes respiratory muscles and ribs do,
hence why your chest moves as
These thicker cells form you breathe. The diaphragm,
the remaining surface area which sits below your heart and
of the alveoli. They secrete lungs but above your abdominal
surfactant, which prevents organs, is the main muscle of
the thin alveoli collapsing. respiration. When it contracts, the
normally dome-shaped diaphragm
Oxygenated blood flattens and the space within the
chest cavity expands. This
The freshly oxygenated reduces the pressure compared to
blood is taken away by the outside atmosphere, so air
capillaries and enters the rushes in. When the diaphragm
relaxes, it returns to its dome
left side of the heart, to shape, the pressure within the
be pumped through chest increases and the old air –
the body. now full of expired carbon dioxide
– is forced out again. The muscles
between the ribs (called
intercostal muscles) are used
when forceful respiration is
required, such as during exercise
Try taking a deep breath and
observe how both your chest
expands to reduce the pressure!

One cell thick Deoxygenated Macrophages © DK Images; Thinkstock
blood arrives
The alveolus wall is just These are defence
one cell thick, separated The capillary veins bring cells that digest
from the blood capillaries
by an equally thin deoxygenated blood from the bacteria and particles
basement membrane. present in air, or that
right side of the heart, which have escaped from the
168
has been used by the body blood capillaries.

and now contains toxic CO .
2

DID YOU KNOW? More than 90 per cent of migraine sufferers cannot function during an attack

How do dilating
eye drops work?

Discover how they are used to diagnose
and treat eye conditions

Sight is one our most important senses, so Before and after
maintaining good eye health is
absolutely essential. However, eyesight A better look inside the eye Dilated pupil
problems can be difficult to detect or treat on
the surface, so specialist eye doctors will Contracted pupil Dilating eye drops will
often use dilating eye drops in order to get a temporarily paralyse the
better look inside the eye at the lens, retina and A contracted pupil will appear much muscle that constricts
optic nerve. smaller and let less light into the the pupil, which means
eye, which makes it difficult to see the pupil will remain
The drops contain the active ingredient the retina and optic nerve inside. dilated for much longer.
atropine, which works by temporarily relaxing
the muscle that constricts the pupil, enabling it Optic nerve Retina Our eyes need good
to remain enlarged for a longer period of time care to stay healthy
so a thorough examination can be performed. The optic nerve carries This light-sensitive tissue
Some dilating eye drops also relax the muscle electrical impulses from converts incoming light Ray of light
that focuses the lens inside the eye, which the retina to the brain, into electrical impulses.
allows an eye doctor or optometrist to measure which then interprets them These impulses are then The size of the pupil will determine
a prescription for young children who can’t as visual images. sent to the optic nerve. how much light enters the eye.
perform traditional reading tests.
Dilated pupils let in more light, which
Dilating eye drops are not only used to help means you can see a larger portion
perform procedures, they may also be of the retina and optic nerve.
administered after treatment, as they can
prevent scar tissue from forming. They are also The lens
occasionally prescribed to children with
lazy-eye conditions, as they will temporarily It is positioned behind the pupil
blur vision in the strong eye, causing the brain and helps focus light onto the
to use and strengthen the weaker eye. retina. Some dilating eye drops
relax the muscle around it to
prevent the lens from focusing.

Why do we get migraines?

Discover how these mega-headaches strike

Those who suffer from migraines pain sometimes subsiding after the
know they are a constant sufferer has been sick.
concern as they are liable to
strike at any time. Essentially, a It is thought that migraines occur
migraine is an intense pain at the front when levels of serotonin in the brain
or on one side of the head. This usually drop rapidly. This causes blood
takes the form of a heavy throbbing vessels in the cortex to narrow,
sensation and can last as little as an which is caused by the brain
hour or two and up to a few days. Other spasming. The blood vessels widen
symptoms of a migraine include again in response, causing the
increased sensitivity to light, sound and intense headache. Emotional
smell, so isolation in a dark and quiet upheaval is often cited as a cause for
room often brings relief. Nausea and the drop in serotonin in the brain, as
vomiting is also often reported, with is a diet in which blood-sugar levels
rise and fall dramatically.

CURIOUS QUESTIONS

What are Pins and
‘pins and needles is the
needles’? result of nerves
that have been
prevented from
sending signals
firing all at once

The numb sensation of your leg ‘going to sleep’ isn’t © Thinkstock
caused by cutting off the blood circulation. It’s the
pressure on the nerves that is responsible. This
squeezes the insulating sheath around the nerve and
‘shorts it out’, blocking nerve transmission. When
pressure is released, the nerves downstream from the
pinch point suddenly all begin firing at once. This
jumble of unco-ordinated signals is a mixture of pain
and touch, hot and cold all mixed together, which is why
it’s excruciating.

“This squeezes the
insulating sheath
around the nerve and
‘shorts it out’”

© Thinkstock Why do Are there other ‘funny
paper
cuts hurt bones’ in the body?
so much?
The term ‘funny bone’ is misleading because it
Paper can cut your skin as it is refers to the painful sensation you experience
incredibly thin and, if you when you trap your ulnar nerve between the
were to look at it under a skin and the bones of the elbow joint. This happens in
high-powered microscope, it has the so-called cubital tunnel, which directs the nerve
serrated edges. Critically though, a over the elbow but has little padding to protect against
sheet of loose paper is far too soft external impacts. The ulnar nerve takes its name from
and flexible to exert enough the ulna bone, which is one of two bones that runs
pressure to pierce the skin, hence from the wrist to the elbow; the other is the radial bone,
why they are not a more frequent or radius.
occurrence. However, if the paper
is fixed in place – maybe by being No other joint in the human skeleton combines these
sandwiched within a pack of conditions and duplicates the this erroneously named
paper – a sheet can become stiff reaction so we only have one ‘funny bone’.
enough to attain skin-cutting
pressure. Paper cuts are so painful
once inflicted as they stimulate a
large number of pain receptors –
nociceptors send nerve signals to
the spinal cord and brain – in a
very small area due to the
razor-type incision. Because paper
cuts tend not to be deep, bleeding
is limited, leaving pain receptors
open to the environment.

170

DID YOU KNOW? The Funnybones books were first published in 1980 and the TV series aired in 1992

Why do our muscles
ache? Learn what causes stiffness and pain in our muscles

for days after exercise

N ormally, when our muscles contract they Weight lifting and the body Bending
shorten and bulge, much like a
bodybuilder’s biceps. However, if the What happens to your biceps when you pump iron? Normally when the biceps
muscle happens to be stretched as it contracts it Pain muscle group contracts it
can cause microscopic damage. shortens, pulling the forearm
The soreness associated
The quadriceps muscle group located on the with exercise is the result of towards the shoulder.
front of the thigh is involved in extending the repetitive stretching of
knee joint, and usually contracts and shortens to contracted muscles. Stretching
straighten the leg. However, when walking
down a steep slope, say, the quadriceps contract Straightening As the muscle tries to contract,
to support your body weight as you step the weight pulls in the opposite
forward, but as the knee bends, the muscles are As the arm straightens out, the direction, causing microscopic
pulled in the opposite direction. This tension biceps are stretched, but the
results in tiny tears in the muscle and this is the weight is still pulling down on the tears within the muscle cells.
reason that downhill running causes so much hand, so the muscles remain partly
delayed-onset pain. contracted to support it.

At the microscopic level, a muscle is made up
of billions of stacked sarcomeres, containing
molecular ratchets that pull against one another
to generate mechanical force. If the muscle is
taut as it tries to contract, the sarcomeres get
pulled out of line, causing microscopic damage.
The muscle becomes inflamed and fills with
fluid, causing stiffness and activating pain
receptors – hence that achy feeling you get after
unfamiliar exercise.

The leptin (LEP) The fat hormone
gene was originally
discovered when a Discover how the body manages to
random mutation keep track of its energy reserves
occurred in mice,
making them put In order to know how much food to eat, the human body needs a way of
on weight assessing how much energy it currently has in storage. Leptin – more
commonly known as the ‘fat hormone’ – essentially acts as our internal
fuel gauge. It is made by fat cells and tells the brain how much fat the body © Alamy
contains, and whether the supplies are increasing or being used up.

Food intake is regulated by a small region of the brain called the
hypothalamus. When fat stores run low and leptin levels drop, the
hypothalamus stimulates appetite in an attempt to increase food intake and
regain lost energy. When leptin levels are high, appetite is suppressed,
reducing food intake and encouraging the body to burn up fuel.

It was originally thought that leptin could be used as a treatment for
obesity. However, although it is an important regulator of food intake, our
appetite is affected by many other factors, from how full the stomach is to an
individual’s emotional state or their food preferences. For this reason, it’s
possible to override the leptin message and gain weight even when fat stores
are sufficient.

CURIOUS QUESTIONS

Why do the Why shouldn’t
upper arm we eat raw
and upper meat?
leg have
only one Meat can harbour many different bacteria, viruses and
bone? even parasites. Cooking meat properly destroys
them, making meat much safer for consumption.
The makeup of the human skeleton is a fantastic Bacteria and viruses can make you ill, while parasites can
display of evolution that has left us with the grow inside your gut and even migrate to your brain. Food
ability to perform incredibly complex tasks poisoning is a very serious business and by not cooking meat
without even thinking about them. There are several thoroughly, you are greatly increasing your chances of getting
different types of joint between bones in your body, something nasty. People quite often eat raw meat such as
which reflect their function; some are strong and steak tartare, but it requires extra care in the preparation.
allow little movement, others are weak but allow free Besides safety, cooking meat also makes it taste better. By
movement. The forearm and lower leg have two cooking meat and other foods, humans can get much more
bones, which form plane joints at the wrist and ankle. energy than from chewing raw food alone.
This type of joint allows for a range of fine movements,
including gliding and rotation. The hinge joints at © Thinkstock
your elbows and knees allow for less lateral
movement, but they are strong. Shoulders and hips,
though, are ball-and-socket joints, which allow for a
wide range of motion.

“Laughter is
produced by the
same coughing”

How do © Mark Wolfe
inoculations
work?

The terms ‘inoculation’ and ‘vaccination’ are used
interchangeably. They involve introducing a foreign
substance (antigens) into the body, causing
antibody production. These can either be dead, made less
harmful, or just contain certain bits that cause disease.

White blood cells called B lymphocytes recognise these
antigens, and produce antibodies to neutralise them.
After the initial encounter, a group of B lymphocytes are
made called ‘memory cells’, which produce antibodies
faster if exposed to the same antigen again.

“They involve introducing
antigens into the body”

172

DID YOU KNOW? Light affects the sleeping pattern of blind people, as ganglion cells are different from those that allow us to see

What causes
insomnia?

Why checking your phone before bed could
be spoiling your sleep

Most of us experience insomnia at some Light sensitivity Pineal gland
point in our lives, finding it difficult to
drift off and stay asleep, despite How light affects your ability to sleep The suprachiasmatic
having plenty of opportunity to. Typical The ganglion layer nucleus sends
causes of insomnia include stress and anxiety,
but did you know that your gadgets could be to The retina of the eye contains a information from the
blame, too? layer of photosensitive ganglion photosensitive
cells, which contain a ganglion cells to
Our sleepiness and wakefulness photopigment melanopsin, called the pineal gland,
throughout the day and night is regulated by the ganglion layer. located in the
our circadian rhythm. This is essentially our epithalamus
body clock, creating physical, mental and Light section of
behavioural changes that occur in our bodies sensitivity the brain.
over a roughly 24-hour cycle. Circadian
rhythms are found in most living things, Unlike the other Melatonin
including animals, plants and many tiny photoreceptors in the
microbes, and they are created by natural eye, photosensitive When the photosensitive ganglion
factors in the body. However, they also ganglion cells cells detect darkness, a message
respond to signals from the environment, contribute little to
such as light, so that we remain in sync with vision, but they are is sent to the pineal gland to
the Earth’s rotation. sensitive to light. produce melatonin, a hormone

All forms of light, both natural and artificial, that can cause drowsiness.
affect our body clock, as when the
photosensitive retinal ganglion cells in our Filter out blue
eyes detect light, they send this information to light with a pair
the suprachiasmatic nucleus (SCN) – the group of amber-tinted
of nerves in the brain that control circadian
rhythms. When light is detected, the SCN will glasses
delay the production of melatonin, a hormone
that sends us to sleep. However, the retinal 173
ganglion cells have been found to be
particularly sensitive to the blue light with a
short wavelength of 480 nanometres emitted
by most computer, smartphone and tablet
screens. Exposure to a lot of this type of light
in the hours before we go to bed has been
proven to suppress melatonin levels, making
it difficult for us to get to sleep.

“Laughter is Suprachiasmatic nucleus Optic nerve
produced by the
same coughing” The suprachiasmatic nucleus is a tiny The photosensitive ganglion cells
area of neurons, located in the have long fibres that connect to
hypothalamus area of the brain, which the optic nerve and eventually
controls circadian rhythms. reach the suprachiasmatic nucleus.

Blocking blue light ©Art Agency

The best way to reduce your or phone before bed, there are ways glasses and goggles in a range of
exposure to blue light is to avoid that you can do so and still get a good styles. Alternatively, you could use
staring at a screen within two hours night’s sleep. Wearing special computer software such as f.lux
prior to going to bed. Instead, glasses with amber-coloured lenses (justgetflux.com) and smartphone
illuminate the room with the will filter out blue, low-wavelength apps such as Twilight (play.google.
warmer, longer-wavelength light light, allowing you to stare at your com) that automatically adjusts your
from regular incandescent bulbs or screen for as long as you like. screen to filter out blue light between
even candles. However, if you just Companies such as Uvex (uvex- sunset and sunrise, replacing it with
can’t resist staring at your computer safety.co.uk) make blue-blocking a softer red light.

CURIOUS QUESTIONS

Why does
blonde hair
look darker
when it’s wet?

Dry blonde hair has a rough, tiled surface – something like fish
scales. When light rays hit these scales, they bounce off in all
directions. Some of the light reaches your eyes and makes
the hair look brighter; it’s like shining a torch on the hair.

When you wash your hair, a thin film of water forms around each
fibre. Light rays pass into the film of water, bounce around inside, and
there’s a chance they’ll get absorbed by the hair. Since the light gets
trapped inside the water, less of it reaches your eyes, so the hair
actually appears a lot darker.

“A thin film of water forms
around each fibre”

© Thinkstock

How quickly
does human
hair grow?

Human hair grows on average 1.25 centimetres (0.5
inches) per month, which is equivalent to about 15
centimetres (six inches) per year. There are several
variables that can affect hair’s growth rate such as age, health
and genetics. Each hair grows in three stages, the first being
the anagen phase where most growth occurs. The longer your
hair remains in this stage dictates how long and quickly it
develops; this can last between two and eight years and is
followed by the catagen (transitional) and telogen (resting)
phases. Hair growth rates vary across different areas of the
head, with that on the crown growing the fastest.

“Each hair grows in three
stages, the first being the
anagen phase”

174

DID YOU KNOW? You can donate your hair to charities such as the Little Princess Trust to make sick children wigs

Why do we get angry?

How does this primal emotion override our normal thought processes?

As far as we know, anger is one of the being treated unfairly. As soon as someone the prefrontal cortex is less than two seconds.
oldest and most primitive forms of shouts at you or gives you an angry look, the This would explain the popularity of the
emotion. It is believed to have been amygdala in your brain sounds the alarm, age-old advice of counting to ten if you feel your
hard-wired in our brains many thousands of prompting the release of two key hormones – blood boiling.
years ago, to help us survive tougher times. adrenaline and testosterone – which prime the
Back then, resources like food, potential mates body for physical aggression. It’s widely accepted that men and women feel
and shelter were relatively scarce. Anger was anger differently. Women are more likely to feel
therefore a vital emotion, giving our ancestors As well as the amygdala, the prefrontal cortex anger slowly build up, which takes time to
the necessary drive and power to survive when is also activated by the anger trigger. This part diffuse, whereas men are more likely to
their safety, or chance to mate, was threatened. of the brain is responsible for decision-making describe the feeling as a fire raging within them
and reasoning, making sure you don’t react that quickly eases. This is thought to be due to
Although our lives are less frequently in irrationally to the situation. According to men having a larger amygdala than women,
danger than our ancestors’, our brains still studies, the time between initially getting and is why a man is statistically more likely to
react to certain anger triggers, one of which is angry and the more measured response from be aggressive than a woman.

Can getting Inside your brain Amygdala
angry be good
for you? Find out how the brain processes anger and The amygdala alerts your
what happens to your body as a result body, preparing it for
Many people view anger as a
negative emotion that wastes Prefrontal cortex potential action. It sends
energy and has no benefits. Yet as signals telling your
with all human emotions, anger The decision-making area of adrenal glands to
has evolved to serve an the brain is also activated, produce adrenaline.
evolutionary purpose. Having said and acts to balance out the
this, getting angry will only have a potentially rash reaction that
positive effect if it is used in the the amygdala promotes.
correct way. If we sit down and
discuss why someone or Trigger
something has made us angry,
then anger is working in the right Seeing or hearing a
way; if we can’t regulate our anger trigger event can
response, it’s unlikely to improve a spark an anger
situation in the long run. Studies response from the
have shown that releasing anger in amygdala in just a
a rational way is actually good for quarter of a second.
you. On the other hand, storing
anger up is known to negatively Flushing red
affect certain people, potentially
leading to depression. Constant, The rise in adrenaline
chronic anger can lead to high causes blood vessels
blood pressure and even heart to dilate to improve
disease in the long term. blood flow. The
dilation of the veins
in your face can
make your face flush.

Explaining why something has Teeth grinding ©; Thinkstock
made you angry is much more
likely to resolve an issue than People have different
exploding with rage physical responses to
anger, but common
reactions include grinding
teeth, clenching fists and
tensing muscles.

trialSpofefcieral HUMAN ANATOMY THE BODY AT WORK CURIOUS QUESTIONS
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HUMAN ANATOMY THE BODY AT WORK CURIOUS QUESTIONS

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