Synapses

Question 1

what are synapses?

Answer 1

the gaps between the end of the axon of one neurone and the dentrite of another ,where an action potential is transmitted

Question 2

explain the function of synapses (6)

Answer 2

-an action potential arrives at the synaptic knob. depolarisation of this leads to the opening of Ca2+ channels and Ca2+ diffuses in.
-vesicles containing the neurotransmitter move towards and fuse with the presynaptic membrane. the neurotransmitter is released to the synaptic cleft
-neurotransmitter diffuses down the conc gradient across the synaptic cleft to the postsynaptic membrane. complementary receptors here so that the neurotransmitter binds.
-Na+ channels on the postsynaptic membrane open and Na+ ions diffuse in. if enough neurotransmitter, then enough Na+ diffuses above the threshold, and the postsynaptic neurone is depolarised.
-the neurotransmitter is released from the receptor, Na+ channels close and the postsynaptic membrane can re-establish a resting potential. neurotransmitters are then transported back to the presynaptic membrane and recycled.

Question 3

why do neurotransmitters only move in one direction?

Answer 3

-vesicles are only on one side of the neurone
-the postsynaptic membrane is in one direction only

Question 4

what are the neurotransmitters involved in the cholinergic synapse?

Answer 4

acetylcholine

Question 5

what are the enzymes breaking down neurotransmitters in the cholinergic synapse called and what do they form?

Answer 5

acetyl CoA

choline and acetyl

Question 6

what is summation?

Answer 6

the rapid buildup of neurotransmitters in a synapse to generate an action potential, either by spatial or temporal summation

Question 7

describe spatial summation

Answer 7

when many different neurones collectively trigger a new action potential by combining the neurotransmitters released to exceed the threshold

Question 8

describe temporal summation

Answer 8

when one neurone releases neurotransmitters repeatedly over a short period to add up to the threshold value

Question 9

what does the inhibitory synapse cause?

Answer 9

Cl- ions to move into the postsynaptic neurone and K+ ions to move out

this combined effect of negative ions moving in and and positive ions moving out makes the membrane potential increase to -80mV, so an action potential is unlikely

Question 10

what is hyperpolarisation?

Answer 10

the membrane potential increasing to -80mV

Question 11

what is the neuromuscular junction?

Answer 11

a synapse occuring between a motor neurone and a muscle (end of reflex arc)

Question 12

compare the neuromuscular junction and the cholinergic synapse (5 points)

Answer 12

-excitatory vs excitatory or inhibitory
-connects motor neurone to muscle vs connects 2 neurones
-end point for action potential vs a new action potential is generated
-unidirectional (due to neurotransmitters) vs receptors only on postsynaptic membrane
-acetylcholine binds to muscle fibre receptors vs post synaptic membrane receptors