Action Potentials 1 Flashcards
What changes potential in a neruon
Membrane permeability or ion concentration changing
What happens when potential becomes more negative
Hyperpolarisation - potential inside moves closer to Ek
What happens when potential becomes less negative
Depolarisation - potential inside cell moves away toward Ena
What’s a action potential
Fluctuation caused by short opening of vgic that spreads along a axon.
Occur after membrane potential reaches certain voltage called threshold 55mV
Significance of action potentials
Frequency encodes information (language which neurons communicate)
Stimulus examples
Physical - electric current or mechanical stretch
Chemical - drug or synaptic excitation
3 stages of AP
- Membrane potential reaches threshold followed by fast depolarisation
- Repolarisation
- After hyperpolarisation
What happens when membrane potential MP reaches threshold
Sudden activation of voltage gated Na+ channels (Pna increases) MP shifts toward Ena
What happens after channels inactivate quickly
A transient opening of voltage gated K+ channels leading to repolarisation
What happens after hyperpolarisation
Membrane potential shifts toward Ek+
What happens when voltage threshold is reached
Sodium channels open and Na+ ions move into cell along both concentration and electrical gradients
Influx of Na+ slows and stops when:
Inside potential becomes positive (moves toward Ena) and attracts Na+ less
Na+ channels inactivate
Is amplitude affected by stimulus
No. Each AP is all or nothing and usually constant amplitude of 100mV
How can action potentials be evoked externally
Under experimental situations. You can provide electrical stimulation via a battery
How can action potentials be evoked internally
Under physiological situations, post synaptic potentials build up
