3.5.3 Responses in the Human
Nervous System
Objectives – What you will need to
know from this section
 Outline the nervous system components: central
nervous system (CNS) and the peripheral nervous
system (PNS)
 Receptor messages are carried through these systems
by nerve cells or neurons.
 Outline the structure & function of the neuron including:
cell body, dendrites, axon, myelin sheath, schwann cell,
and neurotransmitter vesicles & synaptic cleft
 Outline impulse movement & synapse.
 Explain activation & inactivation of neurotransmitter.
1
 The structure and function of a neuron: variation in size
and shape.
 Neuron -- Three part structure:
> dendrite(s) receive information and carry it towards the
cell body,
> the axon conducts nerve impulses away from the cell
body,
> the cell body contains the nucleus and other organelles
and
produces neurotransmitter chemicals.
 Explain the role & position of 3 types of neuron -sensory/motor/inter
 Movement of nerve impulse.
(Detailed knowledge of electrochemistry not required.)
 Knowledge that the conduction of nerve impulses along a
2
3
 Outline the senses with the brain as an interpreting centre.
 Outline the CNS, brain & spinal cord.
State location & function of cerebrum / hypothalamus /
pituitary gland / cerebellum / medulla oblongata
Label &/or draw diagrams of spinal cord (cross section)
indicating : white matter, grey matter, central canal, 3 layer
protective tissue-meninges.
 Spinal nerves containing dorsal and ventral roots that
project from the spinal cord
4
 Outline disorders from NS disorders: paralysis/Parkinson's
including: Cause/Prevention/Treatment
 Outline PNS including the location nerve fibres & cell
bodies.
 State the role, structure & mechanism of the Reflex
arc/action.
 The sense organs contain receptors, with the brain as an
interpreting centre for received information.
 Knowledge of the five senses and related organs.
 Study the eye and the ear – recognition and fuction of the
main parts.
• Corrective measures for long and short sight or for a
hearing defect.
The Nervous System
 Organisms must be aware of what is happening around them,
as this affects their survival chances.
 Co-ordination of an organism’s activities is
carried out by the nervous system and the
endocrine system.
 A nervous system allows an organism to
detect and respond to stimuli in its internal
or external environment.
 A stimulus is any change in your
environment
e.g. a flash of light, a noise, a fly
landing on your nose.
 The nervous system relies on
electrical signals, carried by
specialised cells [neurons], and
is involved in fast responses.
 The central nervous system (CNS)
is your brain and spinal cord.
 The brain keeps a check on
internal organs and activities,
such as the level of carbon
dioxide or water in the blood.
 The peripheral nervous system
(PNS) is the nerves branching
from the CNS to all parts of the
body.
Comparison of the endocrine and nervous systems - 1
Endocrine
Cells involved
Gland
Message
Chemical
(Hormone)
Carried by
Blood
Message sent to
Cells throughout
the body
Received by
Target organ
Comparison of the endocrine and nervous systems - 1
Endocrine
Nervous
Cells involved
Gland
Sense receptor
Message
Chemical
(Hormone)
Electrical(Impulse)
Carried by
Blood
Nerve cell
Message sent to
Cells throughout
the body
A specific cell or
tissue
Received by
Target organ
Effector (muscle or
gland)
Comparison of the endocrine and nervous systems -- 2
Endocrine
Speed of
transmission
Usually slow
Effects
Can be widespread
Duration
long-lasting
(hours)
Comparison of the endocrine and nervous systems -- 2
Endocrine
Nervous
Speed of
transmission
Usually slow
Rapid
Effects
Can be widespread Localised usually
Duration
long-lasting
(hours)
Usually brief
(seconds)
LEARNING CHECK
• Co-ordination of an organism’s activities is
carried out by what 2 body systems?
• Distinguish between the CNS and PNS.
• What is a neuron?
• What is an impulse?
• List the main differences between the
endocrine and nervous systems.
NS ----- Co-ordination & Response
 A stimulus is any change in your environment
 A receptor is a nerve cell that detects the stimulus
 A neuron is a specialised cell that carries electrical messages
(impulses) around the body.
 An impulse is an electrical message that is carried along a
neuron.
Neuron structure
 The cell body contains the nucleus and other organelles and
produces neurotransmitter chemicals.
 A dendron is a short fibre that receives information and carries
it towards the cell body.
 The axon is a very long fibre that conducts impulses away
from the cell body.
 A dendron is a short
fibre that receives
information and
carry it towards the
cell body.
 Dendrites are
small branches of
a dendron.
 Many Schwann cells wrap their fatty cell membranes
around an axon, forming a myelin sheath.
 The myelin sheath insulates the neuron from electrical
impulses flowing in other neurons.
There are three types of Neuron :
 Sensory neuron –carries
messages from the sense
organ to the central nervous
system (CNS).
 Interneuron –connects
sensory and motor neurons
and so carries messages
within the CNS.
 Motor neuron –carries
impulses from the CNS to
muscles and glands.
 Synapse—region where two neurons come into close contact.
 Synaptic cleft—the gap between two
neurons, bridged by chemicals
(neurotransmitters).
 Neurotransmitter
—chemical
released across a
synaptic cleft to
carry a signal
from one neuron
to another.
 The chemical is
then destroyed or
removed
SYNAPSE
LEARNING CHECK
• What is a stimulus?
• What is a receptor?
• Name the main parts of a neuron and give
one function of each.
• Distinguish between a sensory and motor
neuron.
• Distinguish between synapse and synaptic
cleft.
• What are neurotransmitters?
The Brain
 The brain is composed of over 100 billion neurons, each
receiving messages simultaneously from thousands of other
neurons.
 The brain is
protected by the skull
bones, meninges
(three membranes)
and cerebrospinal
fluid.
 The cerebrum is our
conscious brain, with
different parts having
different jobs to do.
hypothalamus
 The hypothalmus is
the centre for the
regulation of the
internal organs.
cerebrum
pituitary
 The pituitary ‘[master] gland secretes hormones that stimulate
other glands to release their hormones.
Conscious actions
A conscious action is one where the brain makes a considered response.
Here’s what happens:
4) The brain
3) Here another sensory neuron
decides to move
carries the signal to the brain
away the hand
5) This impulse is
sent by MOTOR
NEURONS to the
hand muscles (the
effectors) via the
spinal chord…
2) The impulse is carried
by SENSORY NEURONS
to the spinal chord
1) Receptors in
your skin detect
a stimulus
Stimulus
6) Which then
moves the hand
away
Receptor
Motor Neuron
Sensory Neuron
Effector
Coordinator
Response
 The cerebellum co-ordinates processes that we have
learned to do automatically, such as speaking.
Medulla
oblongata
cerebellum
 The medulla oblongata co-ordinates involuntary,
automatic processes — such as breathing, heartbeat.
LEARNING CHECK
• Name the 3 main parts of the brain and one
function of each.
• How is the brain protected?
• What is meant by “conscious action”?
• What does the term “involuntary” mean?
• Distinguish between the cerebrum and the
cerebellum.
 The spinal cord is well
protected by the
vertebrae, meninges
(three membranes) and
cerebrospinal fluid.
 It transmits impulses to
and from the brain and
controls many reflex
actions.
A cross-section through the spinal cord shows a small central
canal, filled with cerebrospinal fluid, surrounded by an area of
grey matter, shaped somewhat like the letter H.
Grey matter contains cell bodies and dendrites (regions of a
neuron that have no white myelin covering).
Outside the grey matter, the spinal cord consists of white
matter (containing axons only).
In humans, 31 pairs of
spinal nerves branch off
from the spinal cord.
Each spinal nerve has a
dorsal root and a ventral
root.
The dorsal root consists of
nerve fibres carrying
information into the spinal
cord from the senses.
The dorsal root ganglion is
a swelling that consists of
the cell bodies of the
sensory neurons.
The ventral root consists of
nerve fibres carrying
information out from the
spinal cord, to the muscles
and glands.
The cell bodies of the
motor neurons are
positioned within the grey
matter of the cord.
 The spinal cord
transmits impulses to
and from the brain and
controls many reflex
actions.
REFLEX ACTION --- The Reflex Arc
 A reflex action is a quick, automatic response to a
particular stimulus.
Interneuron
REFLEX ACTION --- The Reflex Arc
Suppose you touch a hot flame.
Interneuron
Almost instantly you pull your hand away.
In this brief instant, a message has been carried by a sensory
neuron from pain receptors in the skin to the spinal cord.
In the spinal cord, the message is passed on to an interneuron
and then to a motor neuron, and so into muscles that respond by
contracting and pulling your hand from the flame.
Interneuron
This response
saves the body
from injury.
Interneuron
The response is called a reflex action, as it does not
involve conscious control, and is predictable and
automatic.
Many of the activities of the body, such as breathing and
keeping our balance, are regulated by reflex actions.
LEARNING CHECK
•
•
•
•
•
•
•
How is the spinal cord protected?
Distinguish between grey and white matter.
Distinguish between dorsal and ventral root
What is meant by reflex action?
Give some examples of reflex action>
What is an interneuron?
Distinguish between cell bodies and
ganglions.
Nervous System Disorder
Parkinson’s disease is a nervous system disorder, normally
seen in older people, in which muscles become rigid and
movement is slow and difficult, with persistent tremors [shaking].
It is caused by the brain reducing the normal amount of
dopamine that it makes.
There is at present no means of preventing it, but giving L-dopa
(which the body changes into dopamine) can relieve the
symptoms in many patients.
SENSE ORGANS
 Animals have specialised senses to provide them with
information about their environment.
 The five senses are sight, hearing, touch, taste and
smell.
 A receptor is a cell that can detect a stimulus
 A stimulus is any change in your environment, e.g. light,
sound.
Sense
Organ
Sight
Eye
Hearing
Ear
Touch
Skin
Taste
Tongue
Smell
Nose
Stimulus detected
light [by rods and cones in the
retina]
sound [receptors in cochlea]
touch, pressure, temperature and
pain [receptors spread throughout
body]
chemicals [taste buds detect
sweet, sour, salt and bitter].
chemicals [receptors in the nasal
cavity detect vapours]
The EYE
 Eyelids
can
cover
and
protect
the
eyes.
Eyelid
Conjunctiva
Cornea
 Conjunctiva
— thin
transparent
lining
protecting
the cornea.
 Cornea—front transparent part of the sclera. It focuses light
rays on the retina.
Sclera
Choroid
Retina
 Sclera—tough
fibrous outer
layer – the
‘white’ of the
eye;
it maintains the
shape of the
eyeball.
 Choroid—contains blood vessels supplying food and
oxygen to the cells of the eye.
 Retina—the innermost layer that contains the receptor
cells [rods and cones].
 The fovea is
where our
best vision is
[mainly
cones]
 The front
region of the
choroid is
specialised
into the iris
Fovea
Iris
 Iris—contains blood vessels and melanin [giving us
our eye colour], and controls the amount of light
entering the eye [through the pupil].
Pupil
 In bright light, pupil
constricts.
 In dim light, the
pupil dilates.
 Ciliary body [muscle] — thickened edge of the choroid
that controls the shape of the lens
Ciliary muscle
 Suspensory
ligaments —
hold the lens
in place.
Suspensory ligaments
Lens
 Lens—like a magnifying glass, it focuses the light
rays on the retina.
 Lens—focuses the light rays on the retina.
 Accommodation is the ability of the lens to change its shape
(focal length) to form a clear image.
LEARNING CHECK
• Name the 5 senses and the organs involved.
• Name the 3 main layers of the eye and the
function of each.
• What is the function of the
[a] iris, [b] lens, [c] cornea, [d] fovea
• What is accommodation?
Close Vision
 For close vision, the ciliary muscle contracts, the
suspensory ligaments relax, the lens becomes thicker.
Distant Vision
 When the eye is at rest, the lens is thin, has a long focal
length and is adapted for seeing distant objects.
 Accommodation is the ability of the lens to change its shape
(focal length) to form a clear image.
Seeing things at different distances
For distant objects,
the ciliary muscle
relaxes and so the
suspensory ligaments
pull tight, pulling the
lens thinner – the light
doesn’t bend as much.
For close objects the
ciliary muscle contracts,
allowing the lens to go
fat, thus bending the
light more.
 Aqueous humour—watery liquid that supplies the lens and
cornea with nutrients and helps keep the shape of the
cornea and lens.
Aqueous humour Vitreous humour
 Vitreous humour—gel that helps maintain the shape of the
eye.
 When light rays focus on the retina, receptor cells are
stimulated and impulses are carried along the optic nerve to
the brain.
Optic nerve
Blind
Spot
 Blind spot—where the optic nerve fibres pass through the
retina and there is no room for receptors.
Eye Defects
 Long-sighted :
You are long-sighted if you can clearly see objects a long
way off, but you cannot see things close by.
 Reading glasses [convex lenses] can correct the problem.
Eye Defects
 Short-sighted
You are short-sighted if you can clearly see objects close
to you, but you cannot see things in the distance.
 Glasses with concave lenses can correct the problem.
LEARNING CHECK
• Explain how the ciliary body and
suspensory ligaments alter the lens.
• What is the function of the
[a] humours, [b] optic nerve?
• If you are longsighted, what does it mean?
• What could be a possible cause?
• What type of lens can rectify it?
The EAR
 Pinna—outer visible
ear, funnels sound
into the ear canal.
 Ear canal —tube leading
to the ear drum. It has
hairs and wax glands to
trap dirt and germs.
 Eardrum—membrane of
skin that vibrates when
sound waves hit it.
Eardrum
Pinna
Ear
Canal
 Middle ear—air-filled cavity
containing three small bones
[ossicles] and the Eustachian
tube
Middle
Ear
Ossicles
 Ossicles— 3 small bones
[hammer, anvil and stirrup], that
amplify the sound.
 Eustachian tube—keeps air
pressure equal on each side of
the eardrum.
 It opens when we swallow,
cough, etc.
Eustachian
tube
 Inner ear—contains a
coiled, fluid-filled tube
called the cochlea and the
semi-circular canals.
Inner Ear
Semi-circular canals
 Cochlea—contains
nerves that convert
sound vibrations into
electrical impulses.
 Semi-circular canals—help
us keep our balance and
posture.
Cochlea
 The pinna (ear lobe) channels the sound (vibrations in
the air) towards the eardrum, which then vibrates.
 In turn, this vibrates the hammer, anvil and stirrup
bones, which amplify the sound.
 The stirrup pushes on the oval window of the cochlea,
moving the liquid inside.
 Special hairs on 30,000 receptor cells detect the
movement and send signals to the brain along the
auditory nerve.
 The brain interprets these as sounds, and we ‘hear’.
 Semi-circular canals—help us keep our balance and posture.
 The three semicircular canals are curved tubes, each about
15mm long and filled with fluid.
 Head movements are detected by nerves inside the canals.
 The brain responds
by sending
messages through
the cerebellum,
which trigger reflex
actions in our
muscles.
 This helps us keep our whole body balanced as we move.
Ear Defects
Deafness
Deafness can be caused by long exposure to a high level of
noise, drugs, or ear infections.
Damage to the eardrum, ossicles [bones], and cochlea,
which can be caused by loud sounds, produces incurable
deafness.
Workers exposed to
prolonged sounds of over 90
decibels [dB] are obliged by
law to wear ear protection.
Any exposure to 140 dB
causes immediate damage
to hearing.
The SKIN as a Sense Organ
LEARNING CHECK
• What is the function of the
[a] pinna, [b] 3 ossicles, [c] cochlea, [d]
semi-circular canals, [e] eustachian tube?
• Outline how vibrations in the air are
eventually “heard” by our brain.
• Name a common ear defect.
• Give some possible causes & treatments.
• How might you reduce your risks of this
defect?