Anatomy of a neuron

Neurons come in many shapes and sizes.

The most recent published estimate puts the number of neurons in the human brain at 86 billion. How many different types of neuron are there? That depends on how we choose to classify them. Historically they were divided up by form and function, that is, their shape and what they are thought to do. This is useful for characterising cells in a part of the nervous system with a clearly defined anatomy and function, for example those that make up the retina at the back of the eye.

They can be grouped based on the chemicals that they use to communicate: dopamine, glutamate and serotonin are examples of small molecules released by neurons to transmit signals to others in their networks.

Most recently, advances in genetic technology mean that we can profile the genes characteristically expressed by neurons in certain areas or pathways of the brain.

Shape, role, chemicals and genes; these four ways to attempt to categorise neurons all have their uses and limitations and there are entire fields of neuroscience – neuromorphometry, neurophysiology, neuropharmacology and neurogenetics – devoted to each. The details of these are beyond the current scope of this website, nevertheless there are general features of a neuron that it is useful to be familiar with.

See also: