Action potentials

Question 1

Describe synaptic transmission.

Answer 1

1. Action potential arrives at axon terminal
2. Opening of voltage-gated calcium channels leads to calcium influx
3. Synaptic vesicles containing neurotransmitter fuse with pre-synaptic membrane and neurotransmitters are released via exocytosis
4. Transmitters cross the synaptic cleft by diffusion and bind to specific receptors
5. This opens Sodium channels on post-synaptic membrane, causing action potential to continue.
6. Negative feedback

Question 2

What is a neurotransmitter?

Answer 2

A chemical released from a nerve cell which transmits a nerve impulse from a nerve cell to another nerve, muscle, organ or tissue

Question 3

What are the 3 types of neurotransmitter? And give examples of all these.

Answer 3

Amino acids

• glutamate
• GABA

Amines

• acetylcholine
• dopamine

Peptides
-endorphins

Question 4

Which is the most prevalent excitatory neurotransmitter in the brain and spinal cord?

Answer 4

Glutamate

Question 5

Which is the most common inhibitory neurotransmitter?

Answer 5

GABA

Question 6

Which neurotransmitter do all motor neurons in the PNS use?

Answer 6

Acetylcholine

Question 7

Which neurotransmitter is opioid like and significant in the control of pain perception.

Answer 7

Endorphins

Question 8

What is the resting potential?

Answer 8

Inside of cell is negative compared to outside.

-70mV

Question 9

Describe an action potential.

Answer 9

1. The membrane is at resting potential
2. An action potential begins with a depolarizing stimulus- for example, a neurotransmitter bringing to a specific ion channel and allowing Na+ to enter the cell
3. The initial depolarisation stimulates the opening of further Na+ channels and further entry of Na+ through those channels adds to the local membrane depolarisation.
4. When the membrane reaches threshold potential depolarisation becomes a positive feedback loop- more open Na channels leading to more Na influx and so on.
5. This overshoots and membrane becomes positive on the inside and negative on the outside!
6. Na permeability suddenly drops as inactivation gates block Na channels.

Meanwhile, the sluggish K+ channels finally allow K+ to leave the cell, repolarizing the membrane.

7. Low voltage causes both channels to go back to their ‘closed’ states
8. After hyperpolarization- because K+ closes quite slowly, K+ permeability following an AP is shortly a bit higher than it should be. But this eventually stops.

Question 10

What is the difference between absolute refractory period and relative refractory period?

Answer 10

Absolute: Na+ is already open or inactivated, so a 2nd stimulus will not cause another AP

Relative: After hyperpolarisation - the stimulus has to be very strong to work

Question 11

What is a excitatory synapse?

Answer 11

One in which an action potential in a presynaptic neuron increases the probability of an action potential occurring in a postsynaptic cell.

Question 12

What is an inhibitory synapse?

Answer 12

One which makes a postsynaptic neuron less likely to generate an action potential.