The Neuron and Action Potentials

Anatomy and Resting State

The neuron is the basic signalling cell of the nervous system, driven by three core structures. Dendrites receive incoming signals, the soma integrates them, and the axon carries outgoing signals away.

Axons are often wrapped in a myelin sheath, speeding up signals across its gaps. At rest, the neuron maintains a resting potential of $-70$ mV, meaning the inside is negatively charged relative to the outside.

When signals push the membrane to its threshold, positive ions rush in. This electrical spike is the action potential, which sweeps down the axon.

Firing Rules and Limits

The all-or-none principle dictates that an action potential either fires completely or not at all. A stronger stimulus never creates a bigger spike; it increases the frequency of firing instead.

Pitfall: Do not confuse stimulus strength with spike size. After firing, a refractory period must pass before the neuron can fire again.