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Summary SNAB A level Biology Topic 8 Specification Notes
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Specification summary notes for Topic 8
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🧠TOPIC 8 : GREY MATTER
8.1 :Know the structure and function of sensory, relay and motor neurones including
the role of Schwann cells and myelination.
Sensory Neurone:
Has receptors on one end and synaptic endings on the other end
the cell body is in the middle of the neurone
axon carries the impulses away from the cell body
Transmit nerve impulses from a receptor to a relay neurone in the CNS
Relay Neurone
Cell body in the middle
Synaptic endings on both ends of the neurone
Transmit nerve impulses between neurones
Motor Neurone
Transmit nerve impulses from relay to sensory to an effector
Long axon
Many short dendrites around the cell body
axon terminals on muscle fibres
What is the role of Schwann cell
makeup the myelin sheath wrapped around axon
What is the role of myelin sheath
provide electrical insulation
TOPIC 8 : GREY MATTER 1
, speeds up nerve transmission
Acts as phagocytes to remove cell debris
8.2 : i) Understand how the nervous systems of organisms can cause effectors to
respond to a stimulus.
How do pupils dilate
In low light condition photoreceptors detect changes and send impulses via
the sympathetic nervous system for radial muscles to contract and circular
muscles to relax
How do pupils constrict
In high light conditions photoreceptors detect and via the parasympathetic
nervous system cause radial muscles to relax and circular muscles to
contract
8.3 Understand how a nerve impulse (action potential) is conducted along an axon
including changes in membrane permeability to sodium and potassium ions and
the role of the myelination in saltatory conduction.
Action Potential
Stimulus = some sodium channels open allowing sodium ions to diffuse into
the neurone =depolarisation
Once threshold value of -55mV reached more sodium channels open so
there is an influx of sodium ions
Change p.d to +40mV start of repolarisation
Sodium channels close and potassium ions channel open
Potassium diffuses out of neurone down the conc gradient and eventually
restore the resting potential
Slight delay in the K channels cause hyperpolarisation
Return to normal resting potential -70mV
What happens after resting potential restored
TOPIC 8 : GREY MATTER 2
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