L4: Action Potentials Flashcards Preview

Physiology I - EXAM 1 > L4: Action Potentials > Flashcards

Flashcards in L4: Action Potentials Deck (7):
1

What are the three characteristics of an action potential?

All-or-none: it either happens or it doesn't

Self propagating: each region of depolarization serves to generate action potentials on either side

Non-decremental: doesn't decrease in strength

2

What are the types of ion channels with regard to what they respond to?

Open :
-Slow leak channels - always open
Gated:
-Ligand gated: require attachment of neurotransmitter or hormone to receptor
-Voltage gated: require a change in membrane potential

3

Describe and Compare sodium ion channels and potassium ion channels.

Sodium channels
-have two gates: activation and inactivation
-Has four domains - which have 6 hydrophobic transmembrane segments

Potassium channels
-Have a single gate

4

What are the voltages associated with the opening and closing of the channel gates during the propagation of an action potential?

Sodium channels
-Both opened between -90 and +35
-Activation gate opens around -70 to -50 (top)
-Inactivation closed between +35 and -90 (bottom)

Potassium channels
-Closed at -90mV
-Slow activation opens the gate from +35 to -90

Resting stage: -90mv

Depolarization: becomes permeable to sodium

Repolarization: sodium channels close and potassium channels open more than normal

Hyperpolarization:

5

Explain two ways that axons might increase the speed of conduction of an action potential.

Myelination - increases membrane resistance

Larger fiber diameter - offers large cross sectional area to internal flow of current

6

What is absolute refractory period?

A second action potential can not be elicited no matter how strong the stimulus is

Most fast sodium ion channels are open or in the inact state

7

What is relative refractory period?

Stronger than normal stimulus can cause action potential

Mechanism is the elevated potassium conductance