Transmission Across a Cholinergic Synapse

Question 1

What happens when an action potential arrives at the presynaptic neurone?

(volt - g. Ca+ - Ca+ - synap. knob - f.d.)

Answer 1

Voltage - gated calcium channels open, allowing calcium ions to enter the synaptic knob by facilitated diffusion

Question 2

What does the influx of calcium ions cause?

(SV. - down syn. knob - fuse w/ pres. mem. - rlse. AC - syn. cleft)

Answer 2

Causes synaptic vesicles to move down synaptic knob and fuse with the presynaptic membrane, releasing acetylcholine into the synaptic cleft

Question 3

What happens when acetylcholine binds to the receptor sites of the sodium channels on the postsynaptic membrane?

(Na+ chnls. open - Na+ diff. in - trig. depo.)

Answer 3

Sodium ion channels open, allowing sodium ions to diffuse in, triggering depolarisation

Question 4

How is acetylcholine removed from the receptor site?

(AC - brkn. dwn. - ACesterase. - chol. + ace. acid)

Answer 4

It is broken down by acetylcholinesterase into choline and ethanoic acid (acetic acid)

Question 5

How does acetylcholine cross the synaptic cleft?

(A crs. synptc. clft. - rpd. diff. - shrt. diff. pathway. - bind - R/S - Na+ chnls. - P/S mem.)

Answer 5

Acetylcholine cross the synaptic cleft by rapid diffuses due to the short diffusion pathway, it then binds to receptor sites on the Na+ channels on the postsynaptic membrane

Question 6

How is a new action potential generated in the postsynaptic neurone?

(inflx. - Na+ - depo. mem. - rch. - thshld. value - trig. AP.)

Answer 6

The influx of sodium ions depolarises the membrane, reaching the threshold value and triggering an action potential

Question 7

What happens to sodium ion channels when acetylcholine is removed?

(clse. - no Na+ inflx. - RP. of post. neur. rest.)

Answer 7

They close, stopping sodium ions influx and resting potential of the postsynaptic neurone is restored

Question 8

Why is acetylcholine broken down after transmission?

(prev. - cont. stim. - presynp. neur. - ens. dis. nrv. imp.)

Answer 8

To prevent continuous stimulation of the presynaptic neurones, ensuring discrete nerve impulses

Question 9

How does the synaptic cleft affect the action of acetylcholine

(synaptic cleft = nrrw. - AC - SDD - pre to post. - inc diff. rate - rate of rctin.)

Answer 9

The synaptic cleft is very narrow, so acetylcholine has a short diffusion distance from the presynaptic to the postsynaptic neurone, increasing the rate of diffusion and therefore the rate of reaction.

Question 10

Outline the process of transmission cholinergic synapse (8 steps)

1. AP - pre. neur. - depo. - pre. mem.
2. VG - Ca+ chan. - Ca+ in - syn. kn. - faci.diff. - synp. ves. - down syn. kn.
3. Synp. ves. - AC - pre. mem. - AC - syn. clft.
4. AC diff. - bind - rec. sit. - Na+ chan. - opn
5. Na+ diff. - post. neur. - AP in post. neur.
6. ACesterase hydro. AC - chol. + acid type
7. Chol. + acid type - bck pre. neur. - recomb. - AC
8. ATP - new AC - syn. vesic.

Answer 10

1. Action potential arrives at the presynaptic neurone and depolarises the presynaptic membrane
2. Voltage - gated calcium channels open. Ca+ ions diffuse into the synaptic knob by facilitated diffusion. This causes synaptic vesicles to move down the synaptic knob
3. Synaptic vesicles containing acetylcholine fuse with the presynaptic membrane, allowing the neurotransmitter to be released into the synaptic cleft
4. Acetylcholine diffuses across the synaptic cleft, where it binds to receptor sites on sodium channels, causing them to open
5. Sodium is diffuse into the postsynaptic neurone, which leads to an action potential inside the postsynaptic neurone
6. Acetylcholinesterase hydrolyses acetylcholine into choline and acetic acid
7. Choline and ethanoic acid are taken back into the presynaptic neurone, where they recombine to form acetylcholine
8. Energy from ATP is used to transport the recombined acetylcholine back into the synaptic vesicles

Question 11

What happens to acetylcholine (ACh) after it has performed its function?

(hydro. - E. - acetylcholinesterase - products?)

Answer 11

Acetylcholine is hydrolysed by the enzyme acetylcholinesterase into ethanoic acid (acetyl) and choline

Question 12

What happens to the ethanoic acid (acetyl) and choline after acetylcholine is broken down?

(diff. - synp. cleft. - presyn. neur.)

Answer 12

They diffuse back across the synaptic cleft into the pre - synaptic neurone

Question 13

What role does ATP play in the recycling of acetylcholine?

(prov. E. - trans. - AC synap. ves.)

Answer 13

ATP provides energy to transport acetylcholine back into the synaptic vesicles

Question 14

Where is the newly synthesised acetylcholine stored?

Answer 14

In synaptic vesicles in the pre - synaptic membrane

Question 15

What happens to sodium ion channels when acetylcholine is no longer present in the synaptic cleft?

Answer 15

The sodium ion channels close in the absence of acetylcholine