Action potential Flashcards
(18 cards)
what are the only two excitable cells
nerve and muscle cells
- generate electrical signals when stimulated
Define time constant
how fast you charge the membrane.
Define the length constant
how fast signal decays over distance.
- longer the length, the slower the decay
Define hypercalcemia
increased extracellular calcium conc
- causes decreased AP firing due to larger amount of depolarization needed to meet threshold (raises threshold)
Caused by Hyperparathyroidism
Define Hypocalcemia
decreased extracellular calcium conc
- cuases AP to fire more readily due to lowering the threshold.
Caused by Hypoparathyroidism
Does calcium affect resting potential
No
Describe the membrane at rest
Channels are all closed. Permeability to potassium»_space; than permeability to sodium
describe the depolarization phase
sodium channels open and sodium rushes into the cell making the membrane LESS NEGATIVE
- increase in permeability of sodium.
Peak of action potential
sodium channels become inactivated.
- Pna»_space; Pk
Repolarization phase
Sodium channels remain inactive and potassium channels open (potassium flows out of cell)
- Pk incrases
Hyperpolarization phase
occurs when potassium channesl remain open long enough
- 2nd action potential can occur but at a high cost.
Describe how local anesthetics work
they block sodium channels –> inhibits AP generation –> reduces pain
Define absolute refractory period
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.
Define relative refractory period
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.
Describe factors influencing speed of action potential propagation
- LARGER the axon diameter, the FASTER the conduction velocity
- MORE MYELIN the Less membrane resistance and capacitance causing a FASTER velocity
Describe Saltatory conduction
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)
Define Multiple sclerosis
central nervous system autoimmune disease
- causes demyelination and sometimes destruction of CNS axons
- damage to oligodenderocytes (responsible for myelination of CNS)
Define Guillain- Barre syndrome
- symtomes caused by damage to peripheral myeling
- recoverable due to effective remyelination in the PNS
