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OCR A-Level Biology Nervous Transmission Summary
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Handwritten Notes from an Oxford Medical Student detailing all the necessary A* content for Nervous Transmission in OCR A-Level Biology
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Potentian differenceResting Potential :
across a membrane at rest -70 mu
:
The sodium potassium pump transports Nations out of the axon and Zkt ions in
.
2
Low sodium concentration inside the axon causes some Nat to diffuse back in
.
3
Low potassium concentration outside the axon causes lots of kt to diffuse out
4
Most of the
gated sodium channels are closed whilst many potassium channels are open
.
↳The outside of the axon is more positive so a potential difference of -70mv is present
Action Potential :
Occurs when protein Channels
change shape
:Sodium
voltage-gated closed at
resting potential
ion channels are
C .
Energy of a stimulus triggers some voltage-gated ion channels to open
↳ Sodium ions diffuse into the axon,
reducing the potential difference
.
3 Positive feedback occurs - more voltage-gated sodium ion channels open -> Depolarisation
4 At +40mv the sodium channels close and the
voltage gated potassium ion channels open
.
S .
Potassium ions will diffuse out of the axon
6 As more potassium ions diffuse out rapidly the axon is
hyperpolarised until the
.
voltage gated potassium ion channels close and the sodium-potassium purp returns the
axon to
resting potential
s
Repolarisation
~Action potential is propogated down the axon by triggering further depolarisation
and the transfer of electrical charge
Period Prevents
Refractory : backwards transmission
by dosing the voltage-gated sodium ion
channels and
preventing the movement of sodium ions
Saltatory Conduction Myelinated :
axons transfer electrical impulses very quickly
↳ Depolarisation at the nodes of ranvier action
potential jumps between
->
can
only occur
conduction localised circuit
nodes
by saitatory in a
Factors
Affecting impulse speed Large :
axon diameter and
high temperature -> fast imprises
All or
Nothing principle always triggered once a threshold
A response is amount is reached
:
↳ same sized action
potential is always triggered
↳The larger the stimulus the more action potentials are triggered
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