Synapse

Question 1

what is a synapse -cholinergic synapse- and what is the gap called

Answer 1

-a junction between two or more neurones
-gap between neurones is called the synaptic

Question 2

what is the role of a presynaptic neurone

Answer 2

carries the action potential and causes the release of a neurotransmitter

Question 3

what is a neurotransmitter and what does it cause

Answer 3

chemical called acetyl choline which diffuses across the gap, generates new action potential in the postsnyaptic neurone

Question 4

describe the features and their function of the synaptic knob on the presynaptic neurone

Answer 4

-myelin sheath
-axon of presynaptic neuron
-membrane of presynaptic neurone
-Smooth endoplasmic reticulum= for manufacturing neurotransmitters and vesicles containing ACh
-voltage gated calcium ion channels= allow diffusion of Ca+2 into the synaptic knob
-mitochondria= to release ATP for active processes

Question 5

describe the features of the post-synaptic neurone and where does ACh bind

Answer 5

-membrane of postsynaptic neurone
-sodium ion channels
-Acetyle choline binds to complimentary receptor sites on sodium ion channels on post synaptic membrane

Question 6

what is acetylcholinesterase

Answer 6

an enzyme found in the cleft that hydrolyses ACH and products re-enter the bulb and are recycled

Question 7

explain the steps of transmission across a cholinergic syapse

Answer 7

1. action potential arrives at the end of the presynaptic neurone
2. calcium ion channels in synptic knob open
   3.calcium ions enter knob
   4.synaptic vesibles containing neurotransmitter fuse with presynaptic membrane
   5.acetylcholine is released into the synaptic cleft
   6.acetylcholine fuses with receptor sites on the sodium ion channel
3. there is an influx of sodium ions into the postsynaptic neurone down a conc grad triggering a new action potential
   8.acetylcholinesterase hydrolyses acetylcholine into choline and ethanoic acid (acetyl) which diffuses back into the presynaptic neurone
4. ATP released by mitochondria recombine choline and ethanoic acid into acetlycholine which is stored in synaptic vesicles for future use
5. sodium ion channels close

Question 8

what are the features of a synapse and what do they mean

Answer 8

-unidirectional= only presynaptic bulbs contain the neurotransmitter so ACh on only released into cleft to diffuse to post-synaptic membrane

-temporal summation= quick succession action potential from one neurone, sum of those action potentials are enough to reach threshold value

-spatial summation= multiple pre-synaptic neurones to one post synaptic neurone to reach threshold

-inhibition= some pre-synaptic neurones can produce inhibitory post synaptic potentials (IPSP)= prevent an action potential in post synaptic neurone or reduce effect of summation

-Habituation= synapse fatique, no neurotransmitter available after repeated stimulation so neurone can no longer respond to a stimulus e.g getting used to a smell or background noise

Question 9

what is an excitatory post-synaptic potential (EPSP)

Answer 9

one action potential arriving at synapse will cause few vesicles containing ACh to fuse with presynaptic membrane, producing a small depolarisation= EPSP
= not enough to cause an action potential

several EPSPs may be needed to reach the threshold and trigger an action potential =summation