Download structure-function-of

KA 3: The cells of the nervous system
and neurotransmitters at synapses
(a) Structure
and function
of neurones
NS cells and
neurotransmitters
at synapses
(b)
Neurotransmitters
at synapses
(e) Mode of action
of recreational
drugs
(d)
Neurotransmitters,
mood and behaviour
(c) Function of converging,
diverging and reverberating
pathways
By the end of this section you will
be able to …..
• Be able to identify the following structures in a diagram:
– Dendrites
– Cell body
– Axons
– Myelin sheath
• State the function of the above structures
• State what is what meant by myelination
• State the difference in impulse conduction between 2 year
olds and adolescents and adults
• Describe the effects of destroyed myelin sheaths
• State 4 functions of glial cells
Neurones
• The CNS is complex
network of:
– Nerve cells called
NEURONES
• They receive and
transmit electrical
signals
– Glial cells
• Support and maintain
the neurones
Neurones
• The human body
contain billions of
neurones, which must
all be coordinated to
provide the body with
rapid means of
communication and
control.
• There are 3 types of
neurones which are
structurally adapted
to suit their
function:
– Sensory neurones
– Inter neurones
– Motor neurones
Structure of a Neurone
Cell
body
Axon
Direction of impulse
Dendrites
Myelin Sheath
Node (gap
lacking myelin)
• Axon – a single nerve fibre that carries impulse away from cell
body to the next neurone (or in the case of motor neurone, to
the muscle or gland)
• Cell body – control centre of cell’s metabolism, contains a
nucleus and clusters of ribosomes
• Dendrites – (several) receive nerve impulses and pass them onto
the cell body
• Myelin Sheath - fatty material which surrounds the axon which:
– Insulates the axon and
– Increases speed of conduction from node to node
Remember the pathway!
DENDRITES
CELL BODY
AXON
Myelination
• Myelination is the development of
myelin around axon fibres
• It is a long process – myelination is not
complete at birth, so continues from
birth to adolescence.
• As a result, responses to stimuli in the
first two years of life are not as rapid
or coordinated as those of an older
child or adult
Myelination
Destruction of myelin sheaths
• In some diseases (such as polio, multiple
sclerosis and Tay-Sachs disease) the
myelin sheath around the axons
becomes destroyed or damaged.
• This can cause a loss in coordination
and therefore affects physical
movement
Name of
Disease
Polio
Multiple
Sclerosis
Tay-Sachs
disease
Causes
Symptoms Treatment
Polio
• Caused by virus
• Virus spreads along nerve
pathways destroying motor
neurones
• Fever, neck and back muscle
pain, asymmetrical weakness
of certain muscles,
paralysis of 1 or more limbs
• No cure
• Only pain treatment
• Polio vaccine for prevention
Multiple
Sclerosis
• Unknown cause
• Some studies suggest autoimmune destruction of myelin sheaths
• The demyelinated nerve fibres are unable to transmit nerve impulses
efficiently
• Numbness, walking difficulties, impaired vision, progressive loss of
coordination, can be persistent or sudden attacks
• No cure
• Helping to regain functions after attacks
• Other treatments to reduce attacks available, but they have adverse
side effects
Tay-Sachs
Disease
• Caused by a genetic disorder
where by the sufferer will inherit
a defective recessive allele from
both parents
• Sufferer cannot make an enzyme
which breaks down a fatty
material, so this fatty substance
builds up around the neurones –
they become swollen (distended)
and incapable of functioning
• Region of retina shows up as a red
spot
• Infantile TSD = continuous
deterioration of physical and
mental abilities from 6 months,
deaf, blind, paralysis, death at 4
years
• No cure. Care can be given to ease
symptoms
Glial Cells
• Several types of
glial cells
• Physically support
neurons and produce
the myelin sheath.
• They also maintain
a homeostatic
environment around
the neurones and
remove debris by
phagocytosis.
Task: use page 248 to label your
diagram
Summary
• https://www.youtube.com/watch?v=cUG
uWh2UeMk