6B Synaptic Transmission

Question 1

Define a synapse

Answer 1

the junction between one neurone and another or between a neurone and an effector

Question 2

Define synaptic cleft

Answer 2

a tiny gap between the cells at a synapse

Question 3

Define synaptic knob

Answer 3

a swelling at the presynaptic knob

Question 4

What does the synaptic knob contain

Answer 4

synaptic vesicles which contain neurotransmitters

Question 5

What happens when an action potential reaches the end of a neurone

Answer 5

this causes neurotransmitters to be released into the synaptic cleft

Question 6

What is the presynaptic neurone

Answer 6

the one before the synapse

Question 7

What is the postsynaptic neurone

Answer 7

the one after the synapse

Question 8

Where do neurotransmitters diffuse to

Answer 8

to the post synaptic neurone where they bind to specific receptors

Question 9

What happens when neurotransmitters bind to receptors

Answer 9

this may cause an action potential, muscle contraction or cause a hormone to be secreted

Question 10

What direction are nerve impulses

Answer 10

unidirectional

Question 11

Why are neurotransmitters removed from the cleft

Answer 11

so that the response doesn’t keep happening

Question 12

What are neurotransmitters broken down by

Answer 12

Enzymes

Question 13

Step 1 of Ach transmitting the nerve impulse across a cholinergic synapse

Answer 13

An action potential arrives at the presynaptic knob of the presynaptic neurone

This stimulates voltage gated calcium ion channels in the presynaptic neurone to open

Calcium ions diffuse into the synaptic knob

Question 14

Step 2 of Ach transmitting the nerve impulse across a cholinergic synapse

Answer 14

The influx of calcium ions into the synaptic knob causes synaptic vesicles to move to and fuse to the presynaptic membrane

The vesicles release ACh into the synaptic cleft by exocytosis

Question 15

Step 3 of Ach transmitting the nerve impulse across a cholinergic synapse

Answer 15

ACh diffuses across the synaptic cleft and binds to specific cholinergic receptors on the post synaptic membrane

This causes sodium ion channels on the postsynaptic neurone to open

The influx of sodium ions into the postsynaptic membrane causes depolarisation an action potential on the post synaptic membrane is generated if threshold is reached

ACh is removed from the synaptic cleft so the response doesn’t keep happening it’s broken down by an enzyme acetylcholinesterase and then the products are re-absorbed by the presynaptic neurone

Question 16

Define excitatory neurotransmitters

Answer 16

neurotransmitters that depolarise the membrane making it fire an action potential eg acetylcholine at cholinergic receptors

Question 17

Define inhibitory neurotransmitters

Answer 17

neurotransmitters that hyperpolarise the postsynaptic membrane preventing it from firing an action potential eg cholineric synapses in the heart

Question 18

Define spatial summation

Answer 18

sometimes many neurones connect to one neurone

The small amount of neurotransmitter released from each neurones can be enough altogether to reach threshold in the postsynaptic membrane to reach threshold for an action potential to be generated

If some neurones release an inhibitory neurotransmitter then the total effect may be no action potential

Question 19

Define temporal summation

Answer 19

when two or more nerve impulses arrive in quick succession from the same presynaptic neurone, this makes an action potential more likely because more neurotransmitter is released into the synaptic cleft

Question 20

Define neuromuscular junctions

Answer 20

a synapse between a motor neurone and a muscle cell

Question 21

What neurotransmitter do neuromuscular junctions use

Answer 21

acetylcholine which binds to receptors called nicotinic cholinergic receptors

Question 22

Differences between neuromuscular junctions and cholinergic synapses

Answer 22

Postsynaptic membrane has lots of folds that form clefts that store acetylcholinesterase

Postsynaptic membrane has more receptors

ACh is always excitatory at a neuromuscular junction

Question 23

How do agonists affect the action of neurotransmitters at synapses

Answer 23

Agonists are the same as neurotransmitters so they mimic their action at receptors

Question 24

How do antagonists affect the action of neurotransmitters at synapses

Answer 24

Antagonists block receptors so they can’t activated by neurotransmitters this means fewer if any receptors are activated

Question 25

How do nerve gases that inhibit acetylcholinesterase affect the action of neurotransmitters at synapses

Answer 25

There are more neurotransmitters in the synaptic cleft to bind to receptors and they are there for longer. This may lead to loss of muscle control

Question 26

How do amphetamines affect the action of neurotransmitters at synapses

Answer 26

They stimulate the release of neurotransmitter from the presynaptic neurone so more receptors are activated

Question 27

How does alcohol affect the action of neurotransmitters at synapses

Answer 27

This inhibits the release of neurotransmitters from the presynaptic neurone so fewer receptors are activated