علم الأعصاب

Descriptions of the nervous system can sound contradictory.

Neurons are often said to carry electrical signals. But we also hear constantly about neurotransmitters like dopamine, serotonin, glutamate, and GABA: chemicals that neurons use to communicate with one another.

So which is it?

The useful answer is: both.

A typical neural signal repeatedly changes form. Within a neuron, information can travel as an electrical change in the cell membrane. At most synapses, the junctions between neurons, that electrical signal is converted into a chemical one. The receiving neuron then converts the chemical message back into an electrical change of its own.

The nervous system is therefore not purely electrical or purely chemical. It is an enormous network built around translating between the two.

Within a Neuron and Between Neurons

A useful first approximation is:

Within a neuron, signaling is electrical. Between neurons, signaling is usually chemical.

That is not a perfect rule. Some neurons communicate through electrical synapses, and the electrical activity inside a neuron is itself inseparable from chemistry. But as a mental model, it gets surprisingly far.

Imagine one neuron receiving signals from many others. Neurotransmitter molecules bind to receptors on its surface and alter what electrically charged particles, called ions, can move through the neuron's membrane.

Those changes affect the electrical voltage across the membrane.