12.4 Flashcards
Membrane potential
Voltage difference across a cell membrane which fluctuates based on ion movement
Resting potential
-70mV
Depolarization
Becomes more positive less negative
More Na+
Hyperpolorization
Membrane potential becomes more negative less positive
Local potential
-Changes in potential membrane at site of stimulation
-Graded
-Decremental = decrease in strength as they spread away from point of stimulation
- reversible
Action potential
-Rapid all or none electrical signals
-initiated at axon when threshold is reached -55
-nondecremental
Sequence steps:
1. Depolarization
2. Repolarization
3. Hyperpolarization
Depolarization in an action potential
Voltage gated Na+ channels open allowing Na+ in
Causes rapid rise in membrane potential
Repolarization in action potential
-Na+ channels inactive stopping Na+ from entering
-K+ channels open allowing K+ to exit restoring negative charge
Hyperpolariztion in action potential
Membrane temporarily becomes more negative than empty due to K+ channels opening and inactivation of. A+ channels
Continuous conduction in unmyelinated axons
-process is slower due to lack of insulation
-in unmyelinated axons action potentials occur along the entire length of axon
-Na+ diffuses to adjacent segments triggering new action potentials in a wave like matter
Salvatore conduction in myelinated axons
-action potentials jump from node to node increasing conduction speed
-action potentials can only be generated at the nodes where voltage gated ion channels are concentrated
Refractory period
-time following an action potential
-neuron is less responsive to stimuli
Absolute refractory period
No stimulus can trigger another action potential due to inactive Na+ channels
Relative refractory period
A stronger than normal stimulus is required to trigger a new action potential occurring during hyperpolarization
Electrical current
Flow of charged particles
Why does K+ have the greatest influence on RMP
-K+ is 40x more concentrated in ICF than ECF
-K+ leak channels always open
Graded
Vary in magnitude with stimulus strength
Reversible
If stimulus ceases membrane voltage quickly returns to normal resting potential
All or none law
-if threshold is reached neuron fires up to maximum voltage
-if threshold is not reached it does not fire
