Action potential

Question 1

what are the only two excitable cells

Answer 1

nerve and muscle cells

- generate electrical signals when stimulated

Question 2

Define time constant

Answer 2

how fast you charge the membrane.

Question 3

Define the length constant

Answer 3

how fast signal decays over distance.

- longer the length, the slower the decay

Question 4

Define hypercalcemia

Answer 4

increased extracellular calcium conc
- causes decreased AP firing due to larger amount of depolarization needed to meet threshold (raises threshold)
Caused by Hyperparathyroidism

Question 5

Define Hypocalcemia

Answer 5

decreased extracellular calcium conc
- cuases AP to fire more readily due to lowering the threshold.
Caused by Hypoparathyroidism

Question 6

Does calcium affect resting potential

Answer 6

No

Question 7

Describe the membrane at rest

Answer 7

Channels are all closed. Permeability to potassium&raquo_space; than permeability to sodium

Question 8

describe the depolarization phase

Answer 8

sodium channels open and sodium rushes into the cell making the membrane LESS NEGATIVE
- increase in permeability of sodium.

Question 9

Peak of action potential

Answer 9

sodium channels become inactivated.

- Pna&raquo_space; Pk

Question 10

Repolarization phase

Answer 10

Sodium channels remain inactive and potassium channels open (potassium flows out of cell)
- Pk incrases

Question 11

Hyperpolarization phase

Answer 11

occurs when potassium channesl remain open long enough

- 2nd action potential can occur but at a high cost.

Question 12

Describe how local anesthetics work

Answer 12

they block sodium channels –> inhibits AP generation –> reduces pain

Question 13

Define absolute refractory period

Answer 13

Sodium channels can NOT depolarize membrane due to too many sodium channels inactivated (not enough channels available to cause enough of a spike to reach threshold.

Question 14

Define relative refractory period

Answer 14

Stronger than normal stimulus to elicit a new actio npotential
- delayed potassium channel opening and closing causes the membrane to be hyperpolarized and some channels remain open that oppose the depolarization.

Question 15

Describe factors influencing speed of action potential propagation

Answer 15

• LARGER the axon diameter, the FASTER the conduction velocity
• MORE MYELIN the Less membrane resistance and capacitance causing a FASTER velocity

Question 16

Describe Saltatory conduction

Answer 16

Action potentials only generated in nodes of ranvier (where Na channels are located)
-More efficient since less membrane generates AP’s (less work for Na/K pump)

Question 17

Define Multiple sclerosis

Answer 17

central nervous system autoimmune disease

• causes demyelination and sometimes destruction of CNS axons
• damage to oligodenderocytes (responsible for myelination of CNS)

Question 18

Define Guillain- Barre syndrome

Answer 18

• symtomes caused by damage to peripheral myeling

- recoverable due to effective remyelination in the PNS