Nervous coordination-synaptic transmission

Question 1

why does the pre-synaptic neurone have many mitochondria and smooth endoplasmic reticulum?

Answer 1

1. energy needed to manufacture neurotransmitters at the golgi apparatus
2. smooth ER packages them in vesicles

Question 2

describe how acetylcholine is used in the synaptic transmission of a nerve impulse

Answer 2

1. incoming impulse cuases depolarisation in the pre-synaptic knob
   - this causes voltage gated Ca2+ channel to open
   - Ca2+ diffuses into the pre-SN
2. the influx of Ca2+ causes synaptic vesicles to fuse with the pre-synaptic membrane
   - exocytosis of neurotransmitters into the synaptic cleft
   - the Ca2+ ions are pumped back out of the pre-synaptic knob via active transport
3. Ach released into the synaptic cleft
   - diffuse across the cleft from a higher to lower concentration, down the concenteration gradient
   - Ach fits into specific cholingeric receptors on the surface of ligan-gated-Na+ channels on the post-synaptic membrane
4. This open the Na+ channels
   - Na+ diffuses into the post- SN and cause depolarisation
   - once the threshold (+40) is met a new AP is generated
5. Ach is then hydrolysed by Achesterase into acetate and choline
   - products then diffuse back into the pre-SN
   - this allows the NT to be recycled
   - the Na+ chan
   - Na+ channels close once the NT is released
6. the break down of the NT prevents APs from being constantly generated
   - ATP released by the mitchondria is then used to reassemble the Ach
   - stored in vesicles for future use

Question 3

explain why nerve impulses can only be transmitted in one direction

Answer 3

1. Neurotransmitter can only be produced in the pre-synaptic neurone
2. the synaptic vesicles can only be found on the the pre-S membrane
3. receptors only found on the post-S membrane

Question 4

what is meant by spatial summation at a synapse

Answer 4

1. Impulses from different pre-SN that synapse on the same post-SN added together
2. easier to reach the threshold needed to generate an action potential if there are insufficent neurotransmitters

Question 5

what is meant by temporal summation at a synapse?

Answer 5

1. if 2 (or more) impulses are sent in quick succession of each other from the SAME pre-SN

Question 6

what is the difference between excitatory and inhibitory neurotransmitters?

Answer 6

1. excitatory
   - depolarise the post-SN
   - making it fire an action potential if the threshold is reached
2. inhibitory
   - hyperpolarises the post-SN preventing an AP from firing

Question 7

how do excitatory NTs work?

Answer 7

1. NT fit into its complementory receptors on the post-S membrane
2. opens Na+ channels
3. Na+ diffuses into the post- SN
4. depolarisation occurs, AP is generated

Question 8

how do inhibitory NTs work?

hint: 2 ways

Answer 8

1. NT fit into its complementory receptors on the post- S membrane
2. opens the K+ channels
3. K+ diffuse out of the post-SN
4. inside is more negative than the outside, hyperpolarised
5. threshold potential cannot be reached so no AP is generated
6. NT fit into complementory receptors on the poat-S membrane
7. opens the Cl- channels
8. CL- enters the post-SN
9. hyperpolarisation

Question 9

what are the effects of stimulant drugs on synaptic transmission?

Answer 9

1. stimulates the release of more NTs
2. stops the breakdown of NTs at their receptor

so APs are constantly being fired

Question 10

describe the effects of an inhibitory drug on synaptic transmission

Answer 10

1. Stops the release of NTs
2. Blocks the receptors on the Na+/K+ channels so influx of Na+ is prevented, depolarisation cannot occur so AP cannot be generated
3. Blocks transporter proteins so the NT cannot be recycled once hydrolysed, so more APs cannot be generated