2.6 Lundy Ch. 2 (3) Flashcards
How is the meaning of an action potential determined?
by the neural pathway in which it is conducted, not the signal itself
all-or-none
- minimally sufficient stimuli trigger
- stronger stimuli don’t change signal
trigger zone/axon hillock
region in neurons with a high concentration of Na+ channels
AP generation involves a sudden influx of this into the cell
Na+
through Na+ channels in axon hillock
How do local potentials produce an action potential?
- summated membrane depolarization beyond threshold
- causes Na+ channels to open
What is the threshold membrane potential to develop an AP?
-55 mV
depolarization and repolarization in action potential
1: -55 mV » Na+ channels open
2: Na+ flows in and depolarizes
3: K+ channels open and get rapid repolarization
Why is there hyperpolarization?
K+ flowing out
refractory period
- membrane is hyperpolarized
- difficult to regenerate action potential
absolute refractory period
membrane unresponsive to stimuli
relative refractory period
- stimulus may activate
- must be stronger than normal to activate an AP
purpose of refractory period
- promotes forward propagation
- prevents backflow
What restores the membrane to normal RMP from hyperpolarization?
Na/K pump
contributing factors to faster AP propagation
- increased diameter of axon
- myelination
benefit of insulation through myelination
prevents current flow across axonal membrane
Without insulation, the amplitude of the potential would
dissipate down the axon
nodes of Ranvier allow
ion flow across the membrane
nodes have high densities of
Na+ and K+ channels
What causes regeneration of the AP?
depolarization at the nodes of Ranvier
saltatory conduction
AP seems to jump from node to node
AP maintains this due to saltatory conduction
- size
- shape
