synapses

Question 1

what is neuromuscular junction

Answer 1

specialised cholerginic synapse between a motor neurone and muscle cell

Question 2

neuromuscular junctions work as a cholerginic synapse except:

Answer 2

-receptors on post-synaptic membrane are nicotinic cholerginic receptors
-there are clefts in post synaptic membrane which store AchE
-more receptors on post synaptic membrane
-Ach is always excitatory so an action potential in a motor neurone usually results in a response

Question 3

why are impulses unidirectional

Answer 3

vesicles with neurotransmitters are only released from the presynaptic membrane

receptors for neurotransmitters are only found on the post synaptic membrane

Question 4

transmission of impulse

Answer 4

-action potential arrives at synaptic knob of presynaptic neurone
-Ca2+ channels open and Ca2+ enter the pre synaptic neurone by diffusion.
-vesicles fuse with pre synaptic membrane releasing acetyl choline NT into synaptic cleft
-Ach diffuses across synaptic cleft and binds to cholinergic receptors with a complementary shape on the post synaptic membrane
-Na+ channels in post synaptic membrane open and Na+ move in, depolarising the neurone
-if threshold is reached, action potential generated

Question 5

what is summation

Answer 5

-excitatory neurotransmitters depolarise post synaptic membrane = action potential if threshold reached

-inhibitory NTs hyperpolarise post synaptic membrane = prevent action potential

Question 6

what is spacial summation?

Answer 6

2 or more presynaptic neurones release nt at same time
-if both nt are excitatory, the effects add together inc chance of threshold being reached in post synaptic neurone= action potential

-if excitatory and inhibitory its are released they cancel each other out, decreasing chance of threshold reached=no action potential

Question 7

what is temporal summation

Answer 7

2 or more impulses arrive from same presynaptic neurone in quick succession

-chance of threshold being reached= action potential is increased as there is more nt in synaptic cleft

Question 8

drugs could:

(4)

Answer 8

-be same shape as nt therefore bind to receptors preventing the nt from binding= no action potential eg nicotine

-inhibit AChE so ACh remains in synaptic cleft = more action potential losing control eg nerve gas

-stimulate release of more nt eg amphetamines

-block Ca2+ channels in presynaptic membrane= neurotransmitter not released from cleft