Synaptic Transmission

Question 1

What is a synapse?

Answer 1

Junction between 2 nerve cells
Junction between

Junction between neuron + skeletal muscle fibre = neuromuscular junction

Question 2

Does a neuron have multiple synapses?
if yes then why?

Answer 2

Yes- cell body has multiple inputs from other nerves terminal boutons

Question 3

Describe the structure of a synapse at rest

Answer 3

• without neurotransmitter being released

Question 4

Describe what happens when an action potential is triggered at a synapse

Answer 4

1. Action potential depolarises pre-synaptic membrane
2. VG calcium channels open = influx of Ca2+
3. Vesicles containing neurotransmitter fuse with pre-synaptic membrane
4. Neurotransmitter released via exocytosis into synaptic cleft
5. Binds to receptors on post-synaptic membrane = triggers response
6. Enzyme breaks down neurotransmitter released
7. Reuptake molecules take up neurotransmitter ready for next release

Question 5

What is summation?
+ what can it cause?

Answer 5

= Non-propagated response that has no refractory period so multiple post-synaptic potentials can add together
= changes post-synaptic excitability making it more/less likely to fire

-IPSP and EPSP can summate and cancel each other out

Question 6

What are the 2 types of local non-propagated responses and what is the difference between them? + their location

Answer 6

• Excitatory postsynaptic potential (EPSP)- cells more likely to fire AP- mainly on dendrites
• Inhibitory postsynaptic potential (IPSP)- cells less likely to fire AP- mainly on cell body

Question 7

Describe how an EPSP works at a neuromuscular junction

Answer 7

1. Neuromuscular junction- 2 ACh bind to nicotinic receptor which activates them on post-synaptic membrane of skeletal muscle
2. = Opens Na+ channels = influx of sodium = depolarisation

= small graded response so no refractory period
= EPSP can summate and reach threshold and trigger an AP = muscle contraction

Question 8

Describe how an IPSP works

Answer 8

1. Inhibitory neurotransmitter binds to receptors on post-synaptic membrane
2. = opens negative ion channels = influx of negative ions into cell = membrane becomes more negative = hyperpolarisation

= AP threshold further from membrane potential

Question 9

What are the 2 types of summation and whats the difference?

Answer 9

Spatial = EPSP close together can combine potentials to reach AP threshold

Temporal = EPSP occuring close in time can summate to pass AP threshold

Question 10

Describe the event of presynaptic inhibition

Answer 10

Presynaptic inhibition:

= adjacent neuron releases neurotransmitter and inhibits VG Ca2+ channels on presynaptic neuron = less neurotransmitter released

Question 11

What are the different classes of neurotransmitter? + examples

Answer 11

Amino acids- glycine
Classical neurotransmitters- ACh, noradrenaline
Peptides- TRH
Others- ATP

Question 12

Name a specialised synapse

Answer 12

neuromuscular junction

Question 13

What neurotransmitter is involved at a neuromuscular junction and where is it produced and synthesised?

Answer 13

Acetylcholine
Synthesis = via acetyl CoA
Produced = krebs cycle

Question 14

Describe how an AP is triggered at a neuromuscular junction and what happens after?

Answer 14

1. 2 ACh required to activate cholinergic receptors
2. = influx of Na+ generates EPSP in postsynaptic membrane
3. Millions of EPSPs summate to bring membrane potential to AP threshold
4. Skeletal muscle contracts
5. AChE = enzyme that removes ACh and breaks it down into choline + acetate from postsynaptic membrane and returns it to presynaptic cell