Action Potentials

Question 1

What is an action potential?

Answer 1

A rapid change in electrical potential across the plasma membrane of a cell

Question 2

Give three examples of cells which can generate action potentials

Answer 2

Nerve cells
Muscle cells
Endocrine cells

Question 3

Describe what happens when an electrical potential arrives at the soma, to cause the all or nothing response

Answer 3

1. Signals (excitatory or inhibitory) arrive from neighbouring pre-synaptic neurones, by entering the dendrites
2. Now called Electrotonic potentials, they spread passively (graded response, or decremental spread) from the dendrites to the soma. By graded, it is proportional to the level of excitation and how it affects the level of potential
3. Negative and positive electrotonic potentials are integrated (summed) within the soma. If there are more excitatory > inhibitory responses, the net response is excitatory
4. Sum of electrotonic potentials reaches axon hillock
   If the net electric potential > the threshold at the axon hillock, an action potential is fired. This is the all or nothing response

Question 4

The “all or nothing” response is not graded, what is another phrase for this?

Answer 4

Non-decremental spread

Question 5

The summative integration of excitatory / inhibitory potentials at the soma is graded. What is another phrase for this?

Answer 5

Decremental spread

Question 6

What is the resting potential in a neurone?

Answer 6

• 70 mV

Question 7

At rest, what is the configuration of the Na+ and K+ channels?

Answer 7

Closed

Question 8

What is the threshold potential?

Answer 8

• 55 mV

Question 9

At depolarisation, what happens?

Answer 9

Voltage gated Na+ ion channels open and Na+ moves inside, raising the potential

Question 10

Give an example of a channel which moves ions by Active Transport

Answer 10

Na+ / K+ pump

Question 11

The Na+ / K+ pump moves how many ions across?

Answer 11

3 Na+ out of the cell
2 K+ into the cell

via ATP

Question 12

What is the highest the potential can raise to during an action potential firing?

Answer 12

+ 40 mV

Question 13

From + 40 mV, how does the cell reduce the potential back to normal?

Answer 13

The Na+ ion channels close, and the K+ channels open. K+ moves out, lowering the potential down and overshooting a little

Question 14

Axon conductive velocity depends on two things. What are they?

Answer 14

Axon diameter

Myelination

Question 15

What is Carbamazespine used for and how does it work?

Answer 15

Treats epilepsy and nerve pain

Voltaged gated Na+ blocker, preventing the firing of an action potential

Question 16

What is the mechanism of action for Tetrodotoxin (TTX)?

Answer 16

Voltaged gated Na+ blocker, preventing the firing of an action potential

Question 17

Give two examples of ester-based local anaesthetics

Answer 17

Cocaine

Procaine

Question 18

Give three examples of amide-based local anaesthetics

Answer 18

Lidocaine
Bupivocaine
Ropivacaine