Synapses

Question 1

What does synaptic bulb contain a lot and why?

Answer 1

1- SER - makes and secretes lipids - forms memb around vesicles.
2- RER - makes and secretes proteins - to make NT.
3- mitochondria - aerobic resp - ATP - energy to move vesicles to pre-synaptic memb and repackage NT after use.

Question 2

Why does receptors on post synaptic neurone have a specific 3D shape?

Answer 2

• complimentary to shape of ACh molecule -> ACh can bind -> trigger a response.

Question 3

Transmission of N.I across cholinergic synapse.

Answer 3

1- A.P arrives at synaptic bulb.
2- voltage gated Ca2+ channels open.
3- Ca2+ diffuse into synaptic bulb.
4- Cause vesicles to move and fuse with pre-synaptic memb.
5- ACh released into cleft by exocytosis and diffuse across it.
6- ACh molecules bind to receptors on Na+ channels on post SM.
7- Na+ channels open, Na+ diffuses across post SM into post SN.
8- Generator potential is created.
9- If the G.P exceeds the T.P a new A.P is triggered at post SN.

Question 4

What happens if there is too much ACh remaining in cleft?

Answer 4

Na+ channels continue to open in post synaptic memb = continuous A.P = constant stimulation.

Question 5

Breakdown of ACh.

Answer 5

Acetylcholine -> choline and ethanoic acid.
Enzyme : acetylcholine esterase.

Question 6

What does excitory NTs do and what is an example of one?

Answer 6

• cause Na+ channels to open -> depolarisation of post SM.
• A.P more likely to happen in next neurone.
  E.g. ACh.

Question 7

What does inhibitory NTs do and what is an example of one?

Answer 7

• Cause Cl- channels to open in post SM, NOT Na+ channels.
• A.P less likely to happen in next neurone.
• makes inside of post SM even more negative compared to outside.
• bigger stimulus needed to cause enough Na+ to enter to reach +40mv for A.P

Question 8

Spatial summation at synapse.

Answer 8

• more than 1 pre-synaptic neurone connects to 1 post
• 1 neurone alone doesn’t release enough NT to trigger A.P at post
• together, when A.P passes along them enough NT is released to reach T.P for A.P to be triggered/

Question 9

Temporal summation at synapses.

Answer 9

• Single pre SN releases NTs several times in quick succession, due to several A.P in short time.
• A.P needs to be close enough to trigger A.P in post SN.
• If time between each A.P is too long, not enough NT is released to trigger A.P.

Question 10

Main roles of synapses.

Answer 10

1- ensure A.P are unidirectional, as NT is only released from pre SN and receptors are only on post SN.
2- Filter out low level stimuli -> not enough NT released -> no response at post SN -> NI stops.
3- Neurones from diff parts of the body meet at 1 synaptic junction -> for responses needed for diff stimuli at once.
4- Habituation -> neurone repeatedly stimulated -> NT runs out -> neurone can’t respond again until NT remade and repackaged.
5- amplify NI -> lots of A.P at 1 post SN = T.P reached.
6- Help more links between stored and new info.