Lecture 5: Action Potential Flashcards
Can action potentials happen during the refractory and relative refractory phases?
refractory - no
relative refractory - requires greater stimulation
What happens to action potentials with lowered external Na+?
smaller, slower action potentials
What three voltage-sensitive mechanisms generate action potentials?
- activation of Na+ conductance
- delayed activation of K+ conductance
- inactivation of Na+ conductance
The undershoot of the membrane potential is due to open _____, which gradually close, and the _____ is restored
- voltage gated K+ channels
- resting membrane potential
What does activation of Na+ conductance lead to? How does this happen?
- depolarization of membrane potential
- voltage-dependent Na+ channels open; ions rush down conc gradient INTO the cell; + charge accumulates inside cell and across membrane
What does delayed activation of K+ conductance lead to? How does this happen?
- hyperpolarization of membrane potential
- K+ ions rush OUT of cell down conc gradient; reduction of + charge inside cell membrane
What does inactivation of Na+ conductance lead to? How does this happen?
- refractory period
- voltage-dependent Na+ channels transition into non-conductive state as voltage-gated K+ channels begin to close; cell is refractory = doesn’t fire action potentials in response to stimulation; inactivation gates open, Na+ gates close
What does a stimulus do?
depolarizes membrane potential above threshold
Getting an action potential during relative refractory period depends on _____
K+ channel (K+ conductance)
To measure changes in Na+ and K+ conductances, the ______ approach was used.
voltage-clamp
The amount of current which must be injected by the voltage clamp is a measure of the ______
current flowing across the membrane
What two types of voltage-dependent ionic currents did the voltage clamp technique reveal?
- early inward Na+
2. late outward K+
Which ion channel is blocked by tetrodotoxin (TTX)?
Na+
Which ion channel is blocked by tetraethylammonium bromide (TEA)?
K+
-also blocks Ach receptor
What phase occurs from Na+ channel inactivation?
absolute refractory period
Which part of action potential propagation involves active flow?
gating of voltage-gated channels and associated Na+ influx
Which part of action potential propagation involves passive flow?
depolarization
APs first reverse the sign of the mem pot at their peak (1_____; gNa increases) and then 2______ the mem pot (undershoot; gK increases), yielding a 3____ period during which it is impossible, then hard (4____) for the axon to produce another AP. Undershoot then 5____ (gK decreases) and mem pot returns to normal
- overshoot
- hyperpolarizes
- refractory
- relative refractory
- dissipates
The length constant is a measure of ______. It is related to the resistance of the _______ and resistance to _______.
- efficiency of electrical conduction
- membrane
- axial conduction
The time it takes for depolarization to spread is determined by both the ____ and the _____ per unit length of axon
- axial resistance
- membrane capacitance
How is conduction velocity increased?
- increase axon diameter
- decrease capacitance
How does myelination affect capacitance?
decreases capacitance
what is myelination?
wrapping on glial cells around axon
What cells form myelin in the CNS/PNS?
CNS - oligodendrites
PNS - Schwann cells
Where are action potentials generated in myelinated axons?
nodes of ranvier
What does saltatory conduction mean?
APs jump between nodes of Ranvier
