5.1.3 synapses

Question 1

key features of a synapse structure

Answer 1

synaptic cleft
presynaptic neurone
postsynaptic neurone
synaptic knob
synaptic vesicles
neurotransmitter receptors

Question 2

what is the synaptic cleft?

Answer 2

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

Question 3

what is the presynaptic neurone?

Answer 3

neurone along which the impulse has arrived

Question 4

what is the postsynaptic neurone?

Answer 4

neurone that receives the neurotransmitter

Question 5

what is the synaptic knob?

Answer 5

the swollen end of the presynaptic neurone

Question 6

what does the synaptic knob contain?

Answer 6

many mitochondria and large amounts of endoplasmic reticulum to enable it to manufacture neurotransmitters

Question 7

what is the synaptic vesicles?

Answer 7

vesicles containing neurotransmitters

Question 8

what are neurotransmitter receptors?

Answer 8

receptor molecules which the neurotransmitter binds to in the postsynaptic membrane

Question 9

what are the two categories of neurotransmitters?

Answer 9

excitatory
inhibitory

Question 10

what is an excitatory neurotransmitter?

Answer 10

result in the depolarisation of the postsynaptic neurone
if the threshold is reached in the postsynaptic membrane, an action potential is triggered

Question 11

what is an inhibitory neurotransmitter?

Answer 11

result in the hyperpolarisation of the postsynaptic membrane
prevents an action potential from being triggered

Question 12

how does synaptic transmission occur?

Answer 12

action potential reaches the end of the presynaptic neurone
depolarisation of the presynaptic membrane causes calcium ion channels to open
calcium ions diffuse into the presynaptic knob
causes synaptic vesicles containing neurotransmitters to fuse with the presynaptic membrane
released by exocytosis
neurotransmitter diffuses across the synaptic cleft and binds with receptor
causes sodium ion channels to open
sodium ions diffuse into postsynaptic neurone

Question 13

what happens once an action potential has been triggered in the postsynaptic neurone?

Answer 13

it is removed
acetycholine is broken down by enzymes which releases them from the receptors
products are taken back into the presynaptic knob

Question 14

what are the roles of a synapse?

Answer 14

ensure impulses are unidirectional as receptors are only on postsynaptic neurone
allow an impulse from one neurone to be transmitted to a number of neurones at multiple synapses
a number of neurones may feed in to the same synapse with one postsynaptic neurone

Question 15

what is summation?

Answer 15

the amount of neurotransmitters builds up sufficiently to reach the threshold then this triggers an action potential

Question 16

what is spatial summation?

Answer 16

occurs when a 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 17

what is temporal summation?

Answer 17

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