5.3.5 synpases 1

Question 1

cholinergic synapse

Answer 1

synapse which uses acetylcholine as its neurotransmitter

Question 2

neurotransmitter

Answer 2

chemical used as signalling molecule between 2 neurones in synapse

Question 3

synapse

Answer 3

junction between 2 neurones where 1 neurone can communicate with/signal to another neurone

Question 4

gap between 2 neurones

Answer 4

synaptic cleft

Question 5

what does the pre-synaptic knob end in

Answer 5

swelling called ‘pre-synaptic bulb’

Question 6

specialised features within pre-synaptic bulb

Answer 6

• many mitochondria = ATP
• large amount of smooth endoplasmic reticulum = packages neurotransmitter into vesicles
• large number of vesicles = contain molecules of acetylcholine (diffuse across synaptic cleft)
• number of voltage-gated calcium ion channels on plasma membrane

Question 7

features of post-synaptic membrane

Answer 7

• ## specialised sodium-ion channels which respond to neurotransmitter

Question 8

features of specialised sodium-ion channels on post-synaptic membrane

Answer 8

• channels consist of 5 polypeptide molecules
• 2 of polypeptides have special receptor site specific to acetylcholine
• receptor sites have complementary shape to acetylcholine

Question 9

what happens when acetylcholine present in synaptic cleft

Answer 9

• binds to 2 receptor sites on post-synaptic membrane
• causes sodium channels to open

Question 10

12 sequence of events in transmission of signal across synaptic cleft (transmission across synapse)

Answer 10

1. action potential arrives at synaptic bulb
2. voltage-gated sodium ion channels open
3. calcium ions diffuse into synaptic bulb
4. calcium ions cause synaptic vesicles to move to/fuse with pre-synaptic membrane
5. acetylcholine released by exocytosis
6. acetylcholine diffuses across cleft
7. acetylcholine molecules bind to receptor sites on sodium channels in post-synaptic membrane
8. sodium ion channels open
9. sodium ions diffuse across post-synaptic membrane into post-synaptic neurone
10. generator potential/excitatory post-synaptic potential generated
11. if sufficient generator potentials combine = potential across post-synaptic membrane reaches threshold potential
12. new action potential created in post-synaptic neurone

Question 11

describe role of acetylcholinesterase

Answer 11

• enzyme found in synaptic cleft
• hydrolyses acetylcholine to ethanoic acid (acetic acid) & choline
• stops transmission of signals = synapse doesn’t continue to produce action potentials in post-synaptic neurone

Question 12

what happens to the ethanoic acid & choline from hydrolysing acetylcholine

Answer 12

• recycled & re-enter synaptic bulb by diffusion
• recombined to acetylcholine using ATP from respiration in mitochondria

Question 13

what happens to the recycled acetylcholine

Answer 13

stored in synaptic vesicles for future use