Neuronal Electrophysiology

Question 1

What is the difference between the action potentials of cardiac muscle compared to that of skeletal and smooth muscle?

Answer 1

Cardiac action potentials are much longer due to the delayed relaying of the AV node.

Question 2

What does higher membrane resistance result in?

Answer 2

Higher membrane resistance will keep ions within the cell more and allow them to travel further down the neuron cell. It will increase the Space Constant.

Question 3

What does higher internal resistance result in?

Answer 3

High internal resistance will prevent the spread of the action potential within the cell and it will reduce the Space Constant as a result.

Question 4

What is the space constant?

Answer 4

Space constant is the distance where the signal decays to 37% of the original and it determines the speed of conduction.

Question 5

What inactivates Na channels in the action potentials of neurons?

Answer 5

Na channels are deactivated by depolarization.

Question 6

What Na channel gates are open at resting potential?

Answer 6

m activation gate is closed

h inactivation gate is open

Question 7

What Na channel gates are open at activation?

Answer 7

m activation gate is open

h inactivation gate is open

Question 8

What Na channel gates are open at inactivation?

Answer 8

m activation gate is open

h inactivation gate is closed

Question 9

As the resting membrane potential increases what happens to Na channel availability?

Answer 9

Less Na channels are available as the RMP increases as it becomes more and more depolarized.

Question 10

What is the absolute refractory period?

Answer 10

The time where stimulus is unable to generate another action potential

Question 11

What is the relative refractory period?

Answer 11

The time where the neuron has not fully recovered but it can generate an action potential. The stimulus must be stronger than normal though.

Question 12

How does myelination affect conduction? And the space constant?

Answer 12

Myelination rapidly increase the rate of conduction by increasing the membrane resistance, which in turn, increases the space constant.

Question 13

How does extracellular hypercalcemia affect membrane excitability?

Answer 13

Decreases membrane excitability by raising the threshold for Na channel activation.

Question 14

How does extracellular hypocalcemia affect membrane excitability?

Answer 14

Increases membrane excitability by lowering the threshold for Na channel activation.

Question 15

How does hyperventilation affect membrane excitability?

Answer 15

Blows off CO2 which increases the pH and lowers the amount of Ca in the plasma -> increases membrane excitability

Question 16

How does hypoventilation affect membrane excitability?

Answer 16

Retains excess COS which decreases the pH and increases the amount of Ca in the plasma -> decreases the membrane excitability

Question 17

What is the effect of elevated K on membrane excitability?

Answer 17

Increased extracellular K will increase the resting membrane potential which will deactivate Na channels leading to slower conduction.

Increasing the RMP will make it easier to reach threshold for action potentials though.

Question 18

What is the purpose of the long cardiac action potential?

Answer 18

It protects the heart from aberrant electrical activity.

Question 19

How does Ca2+ modulate Na+ channel activity?

Answer 19

The proteins on the extracellular membrane are negative and calcium binds to them. This causes the h inactivation gate to close as it thinks the membrane is depolarized due to the +2 charge of Ca.

Question 20

Where are the Na channels found on the axons?

Answer 20

Only on the nodes of Ranvier

Question 21

How does myelination increase membrane resistance?

Answer 21

The myelin covers up the K+ channels to reduce leakage and thus the membrane resistance increases as a result.