L4: Action Potentials Flashcards Preview

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

Flashcards in L4: Action Potentials Deck (7):

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


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

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


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


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



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


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


What is relative refractory period?

Stronger than normal stimulus can cause action potential

Mechanism is the elevated potassium conductance