Neurons, and neurons in immense numbers, are the mainstay of the mind. But what does a typical neuron look like? And what gives it the ability to pass on activation, to form connections that are useful and versatile? Below is a look at a typical cortical neuron, piece by piece, to provide a sense of how its structure facilitates overall neural structure. The neuron is a pyramidal neuron, the name deriving from its shape, which is widest on the top where the dendrites spread, grows thinner at the cell body, and then thinner along the axon. Pyramidal neurons, like this one, account for 70% of the neurons in the cortex of the brain.

DENDRITES		Dendrites are extensions of the main cell body. Each neuron in the cortex (cortical neuron) tends to have a large number of branches from its apical dendrite, the dendrite at the apex or top (as seen to the left of this current text). Basal dendrites extend directly off the base of the cell body in this diagram. Several terminal buttons of other neurons, shown here in yellow and green, attach to the dendrites. In the diagram, the yellow buttons are inhibitory and the green ones are excitatory. Terminal buttons connect with dendrites or the cell body, making dendrites a primary place from which neurons get their input.
CELL BODY		The cell body of a neuron is its metabolic center. Neurons are maintained and directed by their cell bodies. At the center of the cell body is the nucleus, seen here as a purple sphere. The nucleus is the structure that contains the DNA for the cell. Cell bodies branch off into dendrites, which receive neural impulses, and axons, which are used for transmission. In this diagram, the terminal buttons of other neurons are seen in yellow and green. If enough activation were to spread from other neurons across the synapses and to the neuron pictured, this one would continue to pass the activation down its axon to further neurons.
AXON		The axon extends from the cell body of the neuron at a junction called the axon hillock. From there, the axon continues on like a cable, connecting the neuron to further neurons that may be at a long distance away. To spread activation along its axon, an electrical signal called an action potential is used. Originating from the axon hillock, an action potential is all-or-none and typically lasts 1 millisecond. Usually, neurons send multiple action potentials when they are activated. The speed of action potentials is greatly facilitated by a system of thick insulation (the myelin sheath) and the gaps in this insulation (called the nodes of Ranvier), as the underlying chemistry of the impulses causes them to "jump" from one node to the next. This myelin covering does not begin immediately from the cell body -- the axon is first without covering in the grey matter areas of the brain, and further along the axon the myelin sheath begins, giving the white matter its characteristic color.
TERMINAL BUTTONS		At the end of the axon of a neuron are its terminal buttons. These serve as the connections to other neurons. The points at which terminal buttons meet the dendrites or cell bodies of other neurons are called synapses, with the two sides separated by a synaptic cleft. To bridge this divide, the signalling neuron sends neurotransmitters across the synaptic cleft to the receiving neuron. The signal is passed in this way, allowing each further neuron to continue the activation on to other neurons.

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© 2000 Rice University. This document, or any portion hereof, may be used for non-commercial informational purposes only. Any copy of this document, or portion hereof, must include the copyright notice (http://www.rice.edu/about/cr-notice.html) in its entirety. All neuron images on this page are the original work of Dan DeHanas, © 2001.