CHAPTER 1 STIMULI AND RESPONSES

CHAPTER 1
STIMULI AND
RESPONSES

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1.1 HUMAN NERVOUS SYSTEM

FUNCTION :
• Detect stimuli
• Sends information in the

form of impulses
• Interprets impulses
• Produces appropriate

responses

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CENTRAL Spinal Cranial nerve Peripheral
NERVOUS cord Sensory nervous
SYSTEM receptor system

Spinal nerve

Diagram showing the
organization of the human

nervous system

Organisation of Nervous System

Human nervous system

Central nervous system Peripheral nervous system

Brain Spinal cord Spinal nerves Cranial nerves

ACTION IN HUMAN

VOLUNTARY INVOLUNTARY

Are conscious actions that are carried Takes place spontaneously and unconsciously
out voluntarily Or without prior thought

Controlled by the brain Controlled by the Reflex actions involve the
Examples : walking, running, MEDULLA OBLONGATA SPINAL CORD
Examples: heartbeat, Examples: removing the
eating and drinking breathing, peristalsis hand when it touches a hot
kettle or withdrawing the leg
when one steps on a nail

IMPORTANCE OF THE HUMAN NERVOUS SYSTEM IN LIFE

To control and coordinate organs and parts of the body
Protect our body from danger, for example the muscles will react if our body gets

in touch with heat or sharp objects
Injuries to central nervous parts, medulla oblongata will affect actions such as

heartbeat and breathing
A damaged nervous system would cause a temporary or permanent paralysis in a

person
In more serious cases, the person would most probably depend on machines for

breathing

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1.2 STIMULI AND RESPONSES IN HUMANS

HUMAN SENSORY
ORGANS

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STRUCTURE OF THE HUMAN EYE AND ITS FUNCTIONS

Name: CILIARY MUSCLES Name: CHOROID Name: SCLERA
F: Muscle tha changes the thickness C : Black layer C : Strong layer
F: Prevents reflection inside the eye F : Protect and maintain the shape of the
of the lens
Supplies oxygen and nutrients to eyeball
Name: CORNEA the eye
C : transparent layer Name: RETINA
F : refracts and focuses light on the retina C: It contains many photoreceptors known as cones

Name: EYE LENS and rods
C : transparent and elastic convex F: Detects light and produces nerve impulses
F: Focuses light on the retina
Name: YELLOW SPOT
Name: PUPIL C : part of the retina, there are a lot of
C : Opening in the centre of the iris
F: Controls the amount of light entering the eye photoreceptor
F: very sensitive to light

Name: IRIS Name: BLIND SPOT Name: OPTICAL NERVE
C : The coloured part of the eye C: A point on the retina where the optic C : Nerve fibre
F: Controls the size of the pupil and thus the F : carries nerve impulses from the retina
nerve leaves the eye. There are no
amount of light entering the eye photoreceptors here to the brain
F: Images that fall on this spot cannot be
Name: AQUEOUS HUMOUR Name: SUSPENSORY Name : VITREOUS HUMOUR
C : Tranparent fluid LIGAMENT detected C : transparent jelly like substances
F: Maintains the shape of the F : Maintains the shape of eyeball and
C : Strong fibre
eyeball and focuses light focuses light on the retina
inwards F: hold the lens of the eye

Name : CONJUNCTIVA
C : Transparent membrane
F : Protects the front part of the

sclera

The retina has two types of photoreceptors, rods and cones:
• Rod cells – sensitive towards different intensity of light including dim light

- this cell is not sensitive to colours
• Cone cell – sensitive towards colours in a bright environment

- there are three types of cone cells that are sensitive to red, green and blue lights

Rod cell

Cone cell

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STRUCTURE OF THE HUMAN EAR AND ITS FUNCTIONS

Name : OSSICLES Name : OVAL WINDOW
F : strengthens the vibrations and F : transfers the sound vibrations

transfers them to the oval window from the ossicles to the cochlea

Name : EARLOBE Name : SEMICIRCULAR CANAL
F : collect sound waves and F : Controls the body balance

directs them into the Name : AUDITORY NERVE
ear canal F : sends nerve impulses from

the cochlea to the brain to
be interpreted

Name : EARCANAL Name : EARDRUM Name : COCHLEA
F : direct the sound waves F : vibrates at the same frequency F : Detects and converts the

to the eardrum as the sound waves and sound waves into nerve
transfers the vibration to the impulses
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Name : EUSTACHIAN TUBE
F : Balances the air pressure on

both sides of the eardrum

STRUCTURE OF THE HUMAN NOSE

NASAL CAVITY NERVE TO THE
BRAIN
NOSE
NOSTRILS TONGUE Sensory cell (covered
by a layer of mucous)

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MECHANISME
OF SENSE OF

SMELL

Air that contains The dissolve chemicals The nerve impulses are
chemical substances stimulate the sensory then send to the brain

dissolve in mucus cell to produce to be interpreted
impulses

STRUCTURE OF THE HUMAN TONGUE

Taste buds
Taste buds have many

sense cells

Papilla
Spotted surface that has

taste buds

Chemical substances These chemical would then seep The nerve impulses
in the food dissolve in into the taste buds and stimulate are then sent to the
saliva when it is being the receptor and then produce brain to be interpreted

chewed nerve impulses

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Pain receptor Cold receptor

Heat receptor Hair

Epidermis Touch receptor
Erector Muscle
Dermis Pressure receptor
Sweat Gland
STRUCTURE OF
Fat layer THE HUMAN SKIN

MECHANISME OF HEARING IN HUMAN

1. Ear lobe 7. Brain
receives and interprets the
gather sound sound waves

6. Auditory
nerves carry
the impulses
to the brain

2. Ear canal 3. Eardrum 4. The sound vibrations are 5. Cochlea
channels the vibrates then send to the cochlea converts the
sound to the through oval window vibrations into
eardrum impulses

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MECHANISME OF SIGHT IN HUMAN

Vitreous humour

Cornea Retina

Aqueous humour Nerve to
the brain
Lens
The brain interpretes the
Light rays from the object enter the eye through the nerve impulses. Image
cornea, aqueous humour, lens and straight to formed is smaller and
upright
vitreous humour and the light ray is focused on the
retina Photoreceptors are stimulated by the light ray to
produce nerve impulses which are sent to the brain
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by the optic nerve

SKIN SENSITIVITY TOWARDS STIMULI AT DIFFERENT PARTS OF
THE BODY

Sensitivity of skin towards stimuli depends on :
1. Number of receptors – the higher the number of receptors, the higher

the sensitivity of the skin
2. Thickness of epidermis – the thinner the epidermis, the higher the

sensitivity of the skin

The doctor injects The blind use the tips
the patient on the of their fingers to
arm or the buttocks
because the skin read Braille because
the fingertips are
there is less highly sensitive
sensitive

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SENSITIVITY OF TONGUE TOWARDS DIFFERENT TASTE STIMULI

All areas on the tongue are sensitive to five tastes which are sweet, salty,
sour, bitter and umami tastes

Umami Umami is a savoury food
taste for example the
taste of boiled meat
water, butter and

monosodium glutamate
(MSG)

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COMBINATION OF SENSE OF TASTE AND SMELL

• When a person has a cold, he cannot taste the food properly
because the chemical substances in the food do not reach the
sense cells in the nose as a result of excessive mucus

• The same thing happens when we close our nose, food becomes
less appetizing when there is no assistance from the smell sense

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LIMITATION OF SIGHT

• Is the ability of the eyes to see objects.
• Human eyes cannot see objects that are very tiny or objects that are too far away

• Examples : Optical illusion and blind spots
• Optical illusion occurs when the object that is being viewed is different from the actual

situation

The blind spot happens when the image
that falls on the blind spot cannot be
seen. In some situations, blind spots
cause danger especially when driving

Optical illusion XO

• Close your left eye. Look at the cross with your right
eye and slowly move towards your eye

• At a certain distance from the eye, the cross would
disappear from your view

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DEVICES TO
OVERCOME THE
LIMITATION OF THE
SENSE OF SIGHT

MICROSCOPE X-RAY MACHINE

ULTRASOUND MACHINE
TELESCOPE

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DEFECT OF SIGHT AND WAYS TO CORRECT THEM

SHORT-SIGHTEDNESS

F : An individual who suffers from short-sightedness
cannot see objects that are far away clearly
Image is focused in front of the retina

Cause: - The lens is too thick
- Eyeball is too long

Correction : By using concave lens

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DEFECT OF SIGHT AND WAYS TO CORRECT THEM

LONG-SIGHTEDNESS

F : An individual who suffers from long-sightedness
cannot see objects that are near to him / her
clearly

Image is focused behind of the retina

Cause: - The lens is too thin
- Eyeball is too short

Correction : By using convex lens

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DEFECT OF SIGHT AND WAYS TO CORRECT THEM

ASTIGMATISM
F : Sight defect causes a person to see

one part of an object clearer than the
other parts.
Cause: - irregular curve on the surface of

the cornea
Correction : By using cylindrical lens

Cylindrical lens

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LIMITATION OF HEARING

• Is the limitation on the ability of our ears to hear
• Human can hear sounds in the frequency range of 29 Hz to 20000Hz

• Hearing defect happen when a person is unable to hear sounds.
• Caused of hearing defect :
i. Infection
ii. Injury

iii. exposure to prolonged loud sound
iv. aging factor

• Damage to the outer ear or middle ear can be corrected through medication
or surgery

• Damage to the inner part of ear is more difficult to correct.
• Cochlea implants can be used to correct a damaged cochlea
• Damage to the auditory nerve cannot be corrected neither through

medication nor surgery

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HEARING AID DEVICES

Stethoscope used to
hear the heartbeat

An amplifier is used to A hearing aid
amplify the sound

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Be THANKFUL FOR THE GIFT OF SENSORY ORGAN

• God has blessed us with a complete set of sensory organs
• We should be grateful for this blessing and maintain a healthy lifestyle and

keep away from activities that would affect our sensory organs
• An individual who is exposed to high risk professions such as the firemen, have

to wear safety gear / personal protective equipment (PPE)
• Workers who exposed to loud noises such as at the airport have use earmuffs

or earplugs

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1.3 STIMULI AND RESPONSES IN PLANTS

• Plants can detect stimuli such as light, water, gravity and touch
Responses of plants

Tropism Nastic movement

• Is the directed responses of • Are responses towards stimuli such as touch which
the plant towards stimuli comes from various directions
from a particular directions
• Nastic movement happen faster than tropism
• Grows toward stimuli is • Nastic movements function as a defence for the
known as positive tropisms
plant against danger
• Grows away from the • Examples : Photonasty – movement towards light
stimuli is known as • Thermonasty – response towards temperature
negative tropism
stimuli
• Seismonasty – response toward touch stimuli

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TROPISMS

PHOTOTROPISMS HYDROTROPISMS GEOTROPISMS THIGMOTROPISMS

• Response toward light • Response towards water • Response of plants • Is the plant’s
• Positive phototropism • The root show positive towards gravity responses toward
ensures that the tips and touch
hydrotropism as they • Positive geotropism
leaves grow towards grow towards the enables the plant’s • The plants have
light so that the plants direction of water roots to grow deeper tendrils or twinning
get enough sunlight to into the soil with a stems that creep on
carry out photosynthesis • This response enables the any objects or other
plants to get sufficient strong grip and obtain plants that touch it
water and dissolved water and minerals
minerals • The shoots of the • This response helps
plants show negative the plant to get

geotropism sunlight and support

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1.4 THE IMPORTANCE OF RESPONSES TOWARDS STIMULI IN OTHER ANIMALS

STEREOSCOPIC VISION MONOCULAR VISION

A pair of eyes in front of their head Eyes located on the sides of their head

Vision field is narrow A wide vision field

The vision fields overlap giving a three-dimensional view The vision fields do not overlap or only a slight overlap

Distance, size and depth of object can be estimated more accurately as Cannot estimate distance, size and objects accurately because two

a result of one’s ability to view an image three-dimensionally dimensional images form in this vision filed

Advantage : Advantage :
Helps animals in hunting because of the ability to estimate distance A wide vision filed helps the animals to detect their enemies which
accurately come from any direction

Human and most predators like the tiger and the lion Most preys like the rabbit, mouse and deer

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STEREOPHONIC HEARING HEARING FREQUENCY OF ANIMALS

• Is hearing using both ears ANIMAL HEARING FREQUENCY
• Advantages : RANGE
i. Enables humans to determine the location Bat
Dog 2000 – 110000 Hz
of their prey accurately Dolphin 67 – 45000 Hz
ii. Enables the prey to escape from the Rat 40 – 10000 Hz
Sea lion 200 – 80000 Hz
predator the moment it knowns the Cat 450 – 50000 Hz
location of the predator Elephant 45 – 64000 Hz
16 – 12000 Hz

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Sensory Organs Ensure The Survival Of Animals On Earth

• Eel – responds by producing electricity to defend itself besides hunting for its prey

• Female beetle (Melolontha) - secretes a strong pheromone which is detected by the male beetle’s antennae for
breeding

• A small type of spider (Lyssomanes viridis) – has complex eyes, more than a pair of eyes which enable it to see
very clearly

• Fish – has the lateral line, the sensory organ of which is sensitive towards vibration, pressure and sounds

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