synaptic transmission

Question 1

define a synapse

Answer 1

a junction between neurones responsible for unidirectional chemical transmission by neurotransmitters

Question 2

explain how synapses are uni-directional

Answer 2

• there are neurotransmitter receptors only on the post-synaptic membrane
• neurotransmitters are released from the pre-synaptic knob
• diffuse from high to low concentration across the synaptic cleft

Question 3

describe synaptic divergence

Answer 3

• when one neurone joins many neurones
• spreading the action potential across the body

Question 4

describe synaptic convergence

Answer 4

• many neurones join a single neurone
• amplifies the signal

Question 5

describe spatial summation

Answer 5

• a weak stimulus may only create a few action potentials which doesn’t trigger an action potential in the post-synaptic neurone
• when a neurotransmitter from multiple neurones combine to trigger an action potential in the post-synaptic neurone

Question 6

describe temporal summation

Answer 6

• a single action potential doesn’t always trigger an action potential in the post-synaptic membrane
• a strong stimulus will cause more frequent action potentials
• releasing more neurotransmitters in the pre-synaptic cleft, they add up to trigger an action potential in the post-synaptic membrane

Question 7

outline transmission across a cholinergic synapse

Answer 7

1. an action potential arrives at the pre-synaptic knob
2. causes voltage-gated calcium ion channels to open, calcium ions diffuse in
3. vesicles full of acetylcholine fuse with the pre-synaptic membrane
4. acetylcholine diffuses across the synaptic cleft
5. acetylcholine binds to receptors with a complementary tertiary structure on the postsynaptic membrane
6. some sodium ion channels open allowing sodium to diffuse through the post-synaptic membrane
7. if threshold is reached the voltage-gated sodium ion channels open
8. an action potential is triggered in the post-synaptic membrane
9. enzyme acetylcholinesterase breaks down acetylcholine and stops the response
10. products are re-absorbed into the pre-synaptic knob and recycled

Question 8

what does sacro stand for

Answer 8

muscle

Question 9

what is a neuromuscular junction

Answer 9

a synapse between a motor neurone and a muscular fibre

Question 10

compare transmission in the neuromuscular junction vs cholinergic synapse

Answer 10

1. neuromuscular junction has more receptors on post-synaptic membrane than cholinergic synapse
2. in neuromuscular junction the postsynaptic membrane has clefts (nicotinic cholinergic receptors) which store acetylcholinesterase which breaks down acetylcholine, unlike
3. in neuromuscular junctions acetylcholine is always excitatory, so when a motor neurone fires an action potential it triggers a response in a muscle cell, this isn’t the case for a synapse between 2 neurones

Question 11

describe the different ways drugs act as synapse inhibitors

Answer 11

1. mimic a neurotransmitter - nicotine mimics acetylcholine and binds to cholinergic receptors in the brain so more receptors are activated
2. stimulate a release of a neurotransmitter - amphetamines force dopamine out of presynaptic neurone into synaptic cleft increasing the number of receptors activated