1.4 Neural Firing

Resting potential and the action potential

A neuron at rest has a resting potential of about -70mV, with more negative ions inside the cell than outside. When stimulated past a threshold, an action potential fires: positive ions (sodium) rush in, briefly reversing the charge, following an all-or-none principle — the neuron either fires completely or not at all.

Refractory period and neural firing rate

After firing, the neuron enters a brief refractory period where it resets its ions and cannot fire again immediately. Stronger stimuli don't produce a bigger action potential — they increase the rate/frequency of firing, not the intensity of each individual firing event.

Synaptic transmission

When an action potential reaches the axon terminal, it triggers release of neurotransmitters into the synaptic gap (synapse). These chemicals bind to receptor sites on the next neuron's dendrites. Leftover neurotransmitter is cleared via reuptake, ending the signal and allowing the sending neuron to reabsorb it.

Key terms

Resting potential

The stable negative electrical charge (~-70mV) of a neuron at rest, with more negative ions inside than outside.

Action potential

A brief electrical charge that travels down the axon when the neuron fires, caused by ion movement across the membrane.

All-or-none principle

A neuron either fires completely at full strength or does not fire at all; there's no partial firing.

Refractory period

A brief resting phase after a neuron fires, during which it resets ions and cannot fire again immediately.

Reuptake

The process by which a sending neuron reabsorbs excess neurotransmitters from the synapse, stopping the signal.

Try an AP-style question

The all-or-none principle means…

1. a neuron fires fully or not at all
2. neurons never rest
3. every neuron fires at once
4. neurons fire at varying strengths