synapses

Question 1

stages in the pre-synaptic nob
1.
2.
3.

Answer 1

1. an action potential arrives at the pre-synaptic nob, cauing the membrane to depolarise
2. this causes the voltage gated Ca²ᐩ channels to open. Calcium ions diffuse in
3. vesicles containing acetlycholine (ACh) (neurotransmitter) fuse with the presynaptic membrane and release ACh to the synaptic cleft

Question 2

stages in the synaptic cleft
4. 
5. 
6.
7.

Answer 2

4. Acetylcholine (ACh) diffuses across the synaptic cleft
5. ACh binds to receptors on the post-synaptic membrane
6. this causes some Naᐩ channels to open so Naᐩ diffuses in
7. if threshold is reached all voltage gated Naᐩ channels open

Question 3

stages in the post-synaptic membrane/nob
8.
9.
10.

Answer 3

8. an action potential is triggered in the post synaptic membrane (bc sodium moves IN)
9. acetylcholinesterase breaks down ACh so the response/action potential stops
10. the breakdown products are reabsorbed into the presynaptic nob

Question 4

what does summation do generally?

Answer 4

• increases the amount of neurotransmitter in the synaptic cleft in 2 ways

Question 5

temporal summation

Answer 5

• increases the frequency of action potentials in 1 NEURON!
• so more NT released
• so more Naᐩ channels open on the post synaptic membrane

Question 6

spatial summation

Answer 6

• MULTIPLE NEURONS release NT

- so enough Naᐩ channels on the post-synaptic membrane are open to trigger the opening of v-gated Naᐩ channels

Question 7

inhibitory neurotransmitters

Answer 7

• neurotransmitter released which causes Cl- channels and Kᐩ channels on post-synaptic neurone to open
• Cl- ions move into the post synaptic membrane and kᐩ move out causing the charge to DROP even more negative
• this = HYPERPOLARISATION so therefore it is far more difficult to reach threshold so a bigger stimulus is needed to trigger an action potential