3.6.2 Neurone co ordination

-When outside axon is more positive than inside making inside have a -ve potential (around -65mV)
-Not sending nerve impulse and axon said to be polarised

1)There are sodium potassium pumps(co-transport) which 3 Na+ ions move out and 2 K+ ions move in
2)Na+ ions and K+ ions diffuse naturally in and out
3)But more potassium gates are opened compared to sodium gates so more K+ ions diffuse out while less Na+ ions can go in
This maintains the electro gradient making the inside be more negative than outside

when a stimulus of sufficient size is detected and its energy causes the reversal of resting potential

1)Energy of a stimulus causes Na voltage gate channels to open
2)Due to the electrochemical gradient Na ions diffuse in triggering a reversal in potential difference
3)As Na ions diffuse in more Na channels open
4)Once AP of +40mV is established Na+ voltage gates close and some voltage K+ channels open
5)K + ions now diffusing out cause more channels to open
6)The outward diffusion of K+ ions cause a temporary overshoot making the inside more negative than usual
7)Closable K+ ion gates close and Na/K pump causes RP to re-establish

If stimulus doesnt reach a certain threshhold, AP is not form
All successful stimuli produce the same AP strength
The larger the stimulus, the higher the AP frequency

Whem membrane can't be stimulated and produce a AP at that moment

1) Ensures AP only travels in forward direction. As going both directions would prevent response
2)Ensures AP's are discrete/separate - allows us to detect/calculate strength of stimuli
3)Limits the number of AP's passing at once

1)Myelin sheath - forces AP to jump from "node" to "node"
2)Axon diameter - larger means AP is quicker since ions tend to leak less and potential difference is more easily maintained
3)Temparature - molecules move faster and increases efficiency of enzymes involved in respiration (ATP needed for Na/K pump)

Connection between neurones or a muscle

Synaptic knob

1)AP at end of presynaptic neuorone cause Ca channels to open causing Ca to diffuse in
2)Excess calcium cause synpatic vesicles to fuse with membrane, releasing acetylcholine into cleft
3)Acetylcholine diffuse across and bind to receptors on Na channels. This opens the Na channels
4)Influx of Na+ ions move in generating new AP in post synaptic neurone

1)Acetylcholinesterase hydrolyses it into choline and ethanoic acid
2)These then diffuse back in presynaptic neurone(recycle) which prevents continuous formation of AP
3)ATP from mitochondria recombine them into acetylcholine and stored in vesicles while Na+ channels now close in post synaptic neurone

When low frequency AP can trigger new AP in postsynaptic neurone through rapid build up of neurotransmitter

Spatial summation: Multiple presynaptic neurones together release enough neurotransmitter to form new AP
Temporal summaion: Single presynaptic neurone repeatedly release neurotransmitter in a short period of time to form new AP

hyperpolarises post synaptic neurone preventing formation of AP

1)Pre synaptic neurone releases GABA neurotransmitter
2)Binds to Cl - protein channels on post synaptic neurone and opens them
3)Cl- ion move in post synaptic neureone by FD.
4)Gaba also causes K+ channel to open so K+ move out of axon
5)Combined effect causes a hyperpolarisation (even more negative than usual one like -80mV) making it hard to form AP

Excitatory neurotransmitter = depolarises post synaptic neurone forming AP
Inhibitory neurotransmitter = hyperpolarises post synaptic neurone preventing formation of AP

Synapse between a motor neurone and a muscle very similar to a normal one

cholinergic is neurone