synaptic transmission

Question 1

synapse

Answer 1

the junction between 2 neurones (or a neurone and an effector)

Question 2

synaptic cleft

Answer 2

• gap which separates the axon of one neurone from dendrite of next neurone

Question 3

presynaptic neurone

Answer 3

neurone along which the impulse has arrived

Question 4

postsynaptic neurone

Answer 4

neurone that receives the neurotransmitter

Question 5

synaptic knob

Answer 5

• swollen end of the presynaptic neurone
• contains many mitochondria and large amounts of endoplasmic reticulum to enable it to manufacture neurotransmitters

Question 6

synaptic vesicles

Answer 6

• vesicles containing neurotransmitters
• vesicles fuse with presynaptic membrane and release contents into synaptic cleft

Question 7

neurotransmitter receptors

Answer 7

receptor molecules which the neurotransmitter binds to in the post synaptic membrane

Question 8

excitatory neurotransmitter

Answer 8

• result in depolarisation of postsynaptic neurone
• if threshold is reached in post synaptic membrane, an action potential is triggered
• e.g. acetylcholine

Question 9

inhibitory neurotransmiter

Answer 9

• result in hyperpolarisation of post synaptic membrane
• prevents action potential being triggered
• e.g. GABA

Question 10

process of synaptic transmission

Answer 10

• action potential reaches end of presynaptic neurone
• depolarisation of pre synaptic membrane causes calcium ion channels to open
• calcium ions diffuse into presynaptic knob
• causes synaptic vesicles to fuse with pre-synaptic membrane
• neurotransmitters released into synaptic cleft by exocytosis
• neurotransmitter diffuses across synaptic cleft and binds to specific receptor molecule on postsynaptic membrane
• causes sodium ion channels to open
• sodium ions diffuse into postsynaptic neurone
• triggers action potential and impulse is propagated along postsynaptic neurone

Question 11

why does the neurotransmitter have to be removed from the synapse

Answer 11

• so the stimulus isnt maintained
• so another stimulus can arrive at the synapse and affect it
• prevents response from happening again
• allows neurotransmitter to be recycled

Question 12

how is acetylcholine retaken up

Answer 12

• hydrolysed by enzyme acetylcholinesterase
• which is released from receptors on presynaptic membrane
• hydrolysed to give choline and ethanoic acid (acetyl)
• products are taken back into presynaptic knob to reform acetylcholine with ATP released from mitochondria

Question 13

cholinergic synapses

Answer 13

use neurotransmitter acetylcholine

Question 14

where are cholinergic synapses common

Answer 14

• in CNS of vertebrates
• at neuromuscular junctions where neurotransmitter reaches receptors of muscle cell, causing it to contract

Question 15

roles of synapses

Answer 15

• ensure impulses are unidirectional as receptors are only present on postsynaptic membrane
• allow 1 impulse from 1 neurone to be transmitted to a number of neurones at multiple synapses, resulting in a single stimulus creating a number of simultaneous responses
• a number of neurones may feed into the same synapse with a single postsynaptic neurone, resulting in stimuli from different receptors interacting to produce a single result

Question 16

summation

Answer 16

when neurotransmitter amounts build up sufficiently to reach the threshold so an action potential is triggered

Question 17

spatial summation

Answer 17

• occurs when number of presynaptic neurones connect to one postsynaptic neurone
• each releases neurotransmitter which builds up to a high enough level in the synapse to trigger an action potential in the single postsynaptic neurone

Question 18

temporal summation

Answer 18

• occurs when single presynaptic neurone releases neurotransmitter as a result of an action potential several times over a short period
• builds up in the synapse until the quantity is sufficient to trigger an action potential

Question 19

size of synaptic cleft

Answer 19

20-30nm