synaptic transmission

Question 1

Describe the structure of a synapse

Answer 1

Question 2

What are cholinergic synapses?

Answer 2

Synapses that use the neurotransmitter acetylcholine (ACh)

Question 3

Describe transmission across a cholinergic synapse

Answer 3

Question 4

Explain what happens to acetylcholine after synaptic transmission

Answer 4

• It is hydrolysed by acetylcholinesterase
  ● Products are reabsorbed by the presynaptic neurone
  ● To stop overstimulation - if not removed it would keep binding to receptors, causing depolarisation

Question 5

Explain how synapses result in unidirectional nerve impulses

Answer 5

● Neurotransmitter only made in / released from pre-synaptic neurone
● Receptors only on post-synaptic membrane

Question 6

Explain summation by synapses

Answer 6

● Addition of a number of impulses converging on a single post-synaptic neurone
● Causing rapid buildup of neurotransmitter (NT)
● So threshold more likely to be reached to generate an action potential

Question 7

Describe spatial summation

Answer 7

● Many pre-synaptic neurones share one synaptic cleft / post-synaptic neurone
● Collectively release sufficient neurotransmitter to reach threshold to trigger an action potential

Question 8

Describe temporal summation

Answer 8

● One pre-synaptic neurone releases neurotransmitter many times over a short time
● Sufficient neurotransmitter to reach threshold to trigger an action potential

Question 9

Describe inhibition by inhibitory synapses

Answer 9

● Inhibitory neurotransmitters hyperpolarise postsynaptic membrane as:
○ Cl- channels open → Cl- diffuse in
○ K+ channels open → K+ diffuse out

● This means inside of axon has a more negative charge relative to outside / below resting potential
● So more Na+required to enter for depolarisation
● Reduces likelihood of threshold being met / action potential formation at post-synaptic membranes

Question 10

Describe the structure of a neuromuscular junction

Answer 10

Very similar to a synapse except:
● Receptors are on muscle fibre sarcolemma instead of postsynaptic membrane and there are more
● Muscle fibre forms clefts to store enzyme eg. acetylcholinesterase to break down neurotransmitter

Question 11

Compare transmission across cholinergic synapses and neuromuscular
junctions

Answer 11

Question 12

Use examples to explain the effect of drugs on a synapse

Answer 12

● Some drugs stimulate the nervous system, leading to more action potentials, eg.:
○ Similar shape to neurotransmitter
○ Stimulate release of more neurotransmitter
○ Inhibit enzyme that breaks down neurotransmitter → Na + continues to enter
● Some drugs inhibit the nervous system, leading to fewer action potentials, eg.:
○ Inhibit release of neurotransmitter eg. prevent opening of calcium ion channels
○ Block receptors by mimicking shape of neurotransmitter