synaptic transmission

Question 1

what is a synapse

Answer 1

the junction between a neurone and another neurone OR a neurone and an effector cell

Question 2

what is the tiny gap between the cells at a synapse called

Answer 2

synaptic cleft

Question 3

what is the presynaptic neurone and what does it have which contains what

Answer 3

the presynaptic neurone is the one before the synapse, it has a swelling called a synaptic knob which contains synaptic vesicles filled with chemicals called neurotransmitters

Question 4

what happens when an action potential reaches the end of the presynaptic neurone

Answer 4

it causes neurones to be released into the synaptic cleft that diffuse across to the postsynaptic membrane and bind to specific receptors

Question 5

what is the postsynaptic neurone

Answer 5

the postsynaptic membrane is the one after the synaptic cleft

Question 6

when neurotransmitters bind to neurones what may they trigger

Answer 6

an action potential in a neurone to cause an muscular contraction or a gland to secrete a hormone

Question 7

why are impulses unidirectional

Answer 7

because the receptors are only on the postsynaptic membrane so they can only travel in one direction

Question 8

why are neurotransmitters removed from the cleft, how are they removed

Answer 8

so that the response doesn’t keep happening. they’re taken back into the presynaptic neurone or broken down by enzymes and the products are taken back into the neurone

Question 9

what are synapses that use acetylcholine called

Answer 9

cholinergic synapse

Question 10

in stages what happens when an action potential reaches the presynaptic neurone (5 steps)

Answer 10

1) the action potential stimulates a voltage gated calcium ion channel to open which means calcium ions diffuse into the synaptic knob
2) the influx of calcium ions causes the synaptic vesicles to move into the presynaptic membrane and release the acetylcholine into the synaptic cleft - this is exocytosis
3) acetylcholine diffuses across the synaptic cleft and binds to the specific cholinergic receptors on the postsynaptic membrane
4) this causes sodium ion channels in the postsynaptic neurone to open and the influx of sodium ions into the postsynaptic membrane causes depolarization and if the threshold is reached an action potential is reached
5) acetylcholine is removed from the synaptic cleft by an enzyme called acetylcholinesterase and the products are re-absorbed by the presynaptic neurone.

Question 11

what do excitatory transmitters do

Answer 11

when neurotransmitters depolarise the postsynaptic membrane making it fire an action potential if the threshold is reached

Question 12

what do inhibitory transmitters do

Answer 12

inhibitory transmitters hyperpolarise the postsynaptic membrane which prevents it from firing an action potential

Question 13

what is summation

Answer 13

when the effect of neurotransmitters released from many neurones or one neurone that’s stimulated many times in a short period of time is added together

Question 14

what is spatial summation

Answer 14

when many neurones connect to one neurone and the small amount of neurotransmitters released from each is added together to trigger an action potential, but sometimes some of the neurones may release an inhibitory neurotransmitter which could mean no action potential

Question 15

what is temporal summation and why does it mean there’s more of a chance of an action potential being fired

Answer 15

when two or more action potentials arrive in a short period of time from the same presynaptic neurone. this makes it more likely to fire an action potential because more neurotransmitter is released into the synaptic cleft

Question 16

what is a neuromuscular junction

Answer 16

a synapse between a motor neurone and a muscle cell

Question 17

what neurotransmitter do neuromuscular junctions use and what does it bind to on the postsynaptic membrane

Answer 17

uses acetylcholine which binds to cholinergic receptors called nicotinic cholinergic receptors

Question 18

what are the 3 differences between neuromuscular junctions and cholinergic synapse

Answer 18

1) the postsynaptic membrane has lots of folds that form clefts that contain the enzyme that breaks down acetylcholine called acetylcholinesterase
2) the postsynaptic membrane has more receptors than other synapses
3) acetylcholine is always excitatory at a neuromuscular junction so when a motor neurone fires an action potential it normally triggers a response in a muscle cell

Question 19

what are agonists and how do they work, give an example

Answer 19

some drugs have the same shape as neurotransmitters so they mimic their action at receptors which means more receptors are activate, an example in nicotine

Question 20

what are antagonists and how do they work, give an example

Answer 20

some drugs block receptors so they cant be activated be neurotransmitters so fewer receptors are activated, an example is curare, this can lead to the muscle being paralysed

Question 21

some drugs inhibit the enzyme that break down neurotransmitters, what does this mean and give an example

Answer 21

some drugs inhibit the enzyme that breaks down neurotransmitters which means there’s more neurotransmitters in the synaptic cleft to receptors and they’re there for longer, an example is nerve gases which can lead to loss of muscle control

Question 22

what are the final 2 types of drugs that can stimulate and inhibit, give example

Answer 22

1) some drugs can stimulate the release of neurotransmitters so more receptors are activated, an example is amphetamines
2) some drugs inhibit the release of neurotransmitters from the presynaptic neurone so fewer receptors are activated, an example is alcohol