Neuron

A neuron is a nerve cell — the fundamental signalling unit of the brain and nervous system. Each neuron integrates incoming information and, when conditions are met, passes a signal on to other neurons, muscles, or glands. The adult human brain contains roughly 86 billion of them, interconnected by trillions of synaptic contacts.

A typical neuron has three functional regions. Dendrites — branching extensions from the cell body — receive incoming signals from hundreds or thousands of other neurons. The cell body (or soma) integrates those inputs. The axon then carries an outgoing electrical pulse toward the next cell. This division of labour makes neurons effective long-range messengers.

How it works · its role

Neurons communicate in two steps. First, an electrical signal — the action potential — travels along the axon. It is all-or-nothing: either the incoming signals reach a threshold and the neuron fires, or they do not. This binary quality gives the nervous system a degree of precision.

At the end of the axon, the action potential triggers the release of chemical messengers called neurotransmitters into the narrow gap between cells, known as the synapse. Those molecules drift across, bind to receptors on the neighbouring neuron, and shift its likelihood of firing in turn.

Excitatory neurotransmitters (such as glutamate) push the next neuron toward firing; inhibitory ones (such as GABA) hold it back. The signal ends when the neurotransmitter is taken back into the releasing cell, broken down by enzymes, or diffuses away.

Relevance to substances & effects

Virtually every psychoactive substance works by intervening somewhere in the neuron's signalling cycle — altering the release of neurotransmitters, how long they linger in the synapse, or the sensitivity of receptors on the receiving neuron.

Stimulants such as amphetamines increase signalling by forcing dopamine and norepinephrine release and blocking their reuptake, raising the likelihood that neurons in reward and attention circuits will fire. Depressants including alcohol and benzodiazepines enhance the inhibitory effect of GABA, broadly slowing neuronal activity and producing sedation.

Classic psychedelics such as psilocin and LSD do not simply flood synapses — they bind directly to specific serotonin receptors on neurons in sensory and associative cortex, distorting how those cells respond to incoming signals.

Opioids act on receptors in pain-processing neurons, suppressing their output and producing pain suppression and euphoria. Cannabis compounds act on endocannabinoid receptors distributed across many circuit types, modulating both excitatory and inhibitory neurons simultaneously.

Because neurons are the shared target, effects from different substance classes can stack or cancel in ways that depend on exactly which receptors and which circuits are involved.