Synaptic Transmission

Question 1

Describe process of synaptic transmission

Answer 1

1 - action potential arrives at pre synaptic neurone, stimulates voltage gated calcium ion channels to open
2 - Ca2+ ions diffuse into synaptic knob —> are pumped back out after transmission via active transport
3 - influx of calcium ions causes synaptic vesicles to fuse w pre synaptic membrane (exocytosis)
4 - vesicles release neurotransmitters into synaptic cleft
5 - Neurotransmitter diffuses across the synaptic cleft and binds to post synaptic neurone —> causes Na-ion channels in post-synaptic neurone to open
6 - Action potential generated due to influx of Na ions
7 - Neurotransmitters removed and broken down by enzyme, reabsorbed by presynaptic neurone

Question 2

Name an example of a neurotransmitter and the enzyme breaking it down

Answer 2

Acetylcholine —> broken down by acetylcholineesterase

Question 3

How do inhibitory neurotransmitters affect transmitters?

Answer 3

Hyperpolarise presynaptic membrane by causing entry of chloride ions (make potential diff negative), preventing action potential firing

Question 4

How do excitatory neurotransmitters affect transmitters?

Answer 4

Depolarise post-synaptic membrane, making it fire its own action potential if threshold is reached

Question 5

What type of neurotransmitter is acetylcholine?

Answer 5

Both inhibitory and excitatory —> e.g inhibitory in the heart

Question 6

Name the features of synaptic transmission

Answer 6

Unidirectional, summation and inhibition

Question 7

Define unidirectional in referal to synaptic transmission

Answer 7

Action potential only travels in one direction (from presynaptic neurone to postsynaptic neurone)

Question 8

Define summation

Answer 8

Effect of neurotransmitters released from many neurones being added together; increases likelihood of firing action potential

Question 9

Describe difference between the two types of summation

Answer 9

spatial summation = when 2+ presynaptic neurones release their neurotransmitters at the same time into same post synaptic neurone —> sum of all neurotransmitters (whether excitatory or inhibitory) determines whether action potential is generated
temporal summation = when 2+ nerve impulses arrive in quick succession from the same presynaptic neurone —> increases chance of action potential as more neurotransmitter is released