Download ACTION POTENTIALS

ACTION POTENTIALS
-A neuron is negatively charged when at rest (this is polarization)
- negative 70 millevolts
-This is due to three important ions:

Chloride (-)(they are all inside the neuron and cannot move)

Potassium (+) (they can move freely inside and outside the neuron)

Sodium (+) (they exit and enter the neuron through doors and pumps)
When a neuron is at rest, it is negatively charged because of the large chloride ions inside of
it. Sodium ions want to enter the neuron from outside (due to polarity differences) but
cannot, due to the semipermeable neural membrane.
When the sodium channels open, sodium rushes into the neuron, causing the neuron to
become very positively charged (up to +40 millevolts). This is depolarization. Potassium
leaves the neruon at this point, due to the repelling polarity of positive sodium ions. After this
the channels close, and the sodium pumps remove sodium ions from the membrane this
repolarizes the membrane to a more negative charge than before the action potential. As
potassium returns back into the neuron (due to polarity), the neuron returns to its resting
voltage (-70 millevolts)
Individual action potentials are all 'ALL or NOTHING'. There is no variation in them.
Stronger stimulus simply cause a higher frequency of action potentials to fire through the
stimulated neurons.
-55 millevolts is the threshold level. Any stimulus which reaches this level will generate an
action potential.