Synaptic Transmission

Question 1

Outline the first step in Synaptic Transmission:

Answer 1

An action potential reaches the axon terminal causing vesicles to fuse with cell membrane and release neurotransmitters

Question 2

Outline the second step in Synaptic Transmission:

Answer 2

Neurotransmitters diffuse across the synaptic gap before binding to receptors in post-synaptic neuron

Question 3

Outline the third step in Synaptic Transmission:

Answer 3

Neurotransmitters can either lead to excitation or inhibition. Excitatory (e.g dopamine) makes post-synaptic neuron more likely to fire. Inhibitory (e.g serotonin) makes post-synaptic neuron less likely to fire.

Question 4

Outline the fourth step in Synaptic Transmission:

Answer 4

Summation occurs, all excitatory and inhibitory neurotransmitters that have bind to the receptors are added up. If there are more excitatory neurotransmitters, it will fire an action potential. If there are more inhibitory neurotransmitters, it won’t fire an action potential.

Question 5

Outline the fifth step in Synaptic Transmission:

Answer 5

After neurotransmitters have exerted their excitatory or inhibitory effects when binding to receptors, they un-bind (dissociate) and return to pre-synaptic neuron’s axon terminal through re-uptake transporters and are essentially recycled. Any remaining in synaptic gap are broken down by enzymes.

Question 6

Why can neurons only transmit information in one direction at a synapse?

Answer 6

• Diffusion only occurs when going from a high concentration to a low concentration (So can only go from axon terminal in pre-synaptic neuron to dendrites in post-synaptic neuron)
• Synaptic vesicles are only found in pre-synaptic neuron (where neurotransmitters are)
• Receptors are only found in post-synaptic neuron (where the neurotransmitters bind to)

Question 7

How can drugs increase Synaptic Transmission?

Answer 7

• By blocking re-uptake transporters
• Leading to a build up of neurotransmitters in the synapse, so they continue binding to receptors in post-synaptic neuron and exert their excitatory or inhibitory effects
• Example would be antidepressants increasing serotonin levels (for depression)

Question 8

How can drugs decrease Synaptic Transmission?

Answer 8

• By occupying post-synaptic receptors but not exerting any effect
• Blocks neurotransmitters from binding to those receptors, so they cannot exert their excitatory or inhibitory effects
• Example would be antipsychotics decreasing dopamine levels (for schizophrenia)