action potential

describe sodium and potassium channels in nerve cells

they are voltage gated which means they can open and close based on the voltage across the membrane

what happens when a signal is sent to a sensory receptor or dendrite

sodium channels open and sodium enters the neuron

what does an influx of sodium cause

causes the membrane potential to become positive (depolarization)

what happens if there is a sufficient change in membrane potential

• adjacent voltage gated sodium channels open which generates a wave of depolarization (action potential) that spreads down the axon

• it also activates the voltage gated potassium channels which causes potassium to exit the neuron passively

what does an efflux of potassium cause in the membrane

the membrane potential to become negative again (repolarization)

what does the changes in membrane potential end up causing

• the charge is back to normal but:

• before the neuron can fire again, the original distribution of ions, must be re established by the sodium and potassium pump

• this causes an inability for another action potential during this time, this ensures nerve impulses only travel in one direction

Impulse generation con’t

• the depolarization of one point in a neuron starts a chain reaction down the length of the neuron and the sodium gates in the next area open

• we get a wave motion or chain reaction which moves down the nerve fibre