Module 3: synaptic transmission

Question 1

where does a synapse occur?

Answer 1

At the end of the axon - presynaptic neuron/axon terminal - and post synaptic neuron (attached to other neuron area)

Question 2

What are the steps of synaptic transmission?

Answer 2

1. action potential reaches the axon terminal of the presynaptic neuron
2. Ca2+ enters synaptic knob
3. neurotransmitter is released by exocytosis into synaptic cleft
4. neurotransmitter binds to receptors that are an integral part of chemically gated channels on the subsynaptic membrane of the postsynaptic neuron
5. binding of neurotransmitter to receptor opens the specific channel

Question 3

how is synaptic transmission terminated?

Answer 3

1. breakdown by enzymes
2. diffusion away from the synapses and broken down elsewhere
3. reuptake into the presynaptic terminal, or nearby astrocytes

Question 4

what is a postsynaptic response called?

Answer 4

postsynaptic potential

Question 5

what are ligand-gated ion channels?

Answer 5

1. essential in synaptic transmission
2. receptor that opens in response to the binding of a specific neurotransmitter
3. mediate local/graded potentials, fast signals

Question 6

What is a chemically gated ion channel?

Answer 6

1. open in response to binding of the appropriate neurotransmitter
2. responsible for triggering graded/local potentials at a synapse

Question 7

what is a voltage-gated ion channel?

Answer 7

1. open in response to changes in membrane potential
2. responsible for triggering action potential in an axon

Question 8

What is an excitatory synapse?

Answer 8

1. generate excitatory postsynaptic potentials
2. depolarise the postsynaptic membrane, closer to action potential initiation threshold

Question 9

What is an inhibitory synapse?

Answer 9

1. generate inhibitory postsynaptic potentials
2. hyperpolarise the postsynaptic membrane, further from the action potential initiation threshold

Question 10

do graded/local potentials decrease in size as they spread?

Answer 10

Yes

Question 11

what is temporal summation?

Answer 11

when 2 EPSPs from the same presynaptic neuron occur close in time to depolarise the membrane to threshold

Question 12

what is spatial summation?

Answer 12

2 EPSP from different presynaptic neurons occur close in time to depolarise the membrane threshold

Question 13

why don’t local/graded potentials create action potentials on their own?

Answer 13

1. they don’t have a strong enough voltage to cause one
2. There are not enough voltage-gated Na+ channels in the areas to create a positive feedback loop.

Question 14

how do local/graded potentials create an action potential?

Answer 14

1. temporal summation
2. spatial summation:

Question 15

what are the effects that synaptic transmission is dependent on?

Answer 15

1. the type of cell it’s terminating on
2. the type of neurotransmitter the neuron releases
3. the types of neurotransmitter receptors on the postsynaptic membrane