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The Nerve Impulse - Coggle Diagram
The Nerve Impulse
The Resting Potential
-
- outside membrane +ve relative to inside
- of about 70mV
maintained as when neurone NOT conducting an impulse
- cell surface membrane = IMPERMEABLE (to flow of Na+)
if permeable, Na+ diffuse IN,
down conc gradient
The Action Potential
- when neurone is stimulated
- membrane PERMEABLE to ions
- due to positive ions outside relative to inside
- ions DIFFUSE INTO NEURONE
- down conc gradient
- potential difference decreases to
- THRESHOLD POTENTIAL
- inside -55mV relative to outside
- ∴ gated ion channels open
- opening of gated ion channels
- rapidly INCREASES rate of diffusion
- of ions INTO neurone
5.causes DEPOLARISATION
- inside positive to outside
- of +40mV
reversal of potential difference
- peak of AP (inside +40mv to outside)
- RECOVERY PHASE (refractory period) starts
- +ve ions diffuse/pumped OUT of neurone
- REPOLARISATION
- resting potential restored
- +ve ions move OUT of neurone
repolarisation must occur before a further AP can develop
why?
- gated ion channels are closed
- resting potential not fully restored
-
- HYPERPOLARISATION
- slight overshoot
- inside more NEGATIVE than normal resting potential
- (more -ve than -70mV)
- resting potential restored
- now axon can conduct another nerve impulse
Why occurs?
Neurones...
-
are polarised
or
- have potential difference
- have electrochemical gradient
- across cell surface membrane
-
Important
Features
REFRACTORY
PERIOD
during repolarisation
- membrane not depolarised again
- until resting potential restored
-
THRESHOLD
STIMULUS
-
only at a critical point will an AP occur
- small degree of depolarisation can occur
- without resulting in AP
-
-
ALL OR
NOTHING LAW
D: once threshold stimulus
reached, AP occurs
-
AP all have
- SAME INTENSITY
- regardless of INTENSITY of STIMULUS
-