As you can see in the following figure, a biological neuron is composed of the following:

• A cell body or soma
• One or more dendrites, whose responsibility is to receive signals from other neurons
• An axon, which in turn conveys the signals generated by the same neuron to the other connected neurons

This is what a biological neuron model looks like:

The neuron activity is in the alternation of sending the signal (active state) and rest/reception of signals from other neurons (inactive state).

The transition from one phase to another is caused by the external stimuli represented by signals that are picked up by the dendrites. Each signal has an excitatory or inhibitory effect, conceptually represented by a weight associated with the stimulus. The neuron in an idle state accumulates all the signals received until they have reached a certain activation threshold.