Inside the neuron

Grouping of the Neural Tissues:

A neural fibre is a general term for any process projecting from the cell body, in other words, a dendrite or an axon. Most commonly though, it refers to an axon and its sheath.
The term white matter refers to groups of myelinated axons from many neurons. Myelin has a whitish colour that gives white matter its name. A nerve consists of a group of myelinated nerve fibres in the PNS. An example of a nerve is the sciatic nerve in the thigh. Most nerves contain both sensory and motor fibres. The term tract is used to indicate a bundle of fibres located in the CNS. Tracts may run long distances up or down the spinal cord or connect parts of the brain with each other and with the spinal cord. Spinal tracts that conduct impulses up the cord and carry sensory impulses are called ascending tracts. Spinal tracts that carry impulses down the cord carry motor impulses and are called descending tracts.

The gray matter of the nervous system contains neuron cell bodies and dendrites or bundles of unmyelinated axons. The absence of myelin in these neuron parts accounts for the gray colour. Groups of neuron cell bodies located in the PNS are known as ganglia (singular = ganglion). However, clusters of neuron cell bodies and dendrites in the CNS are known as nuclei.

In the brain, gray matter is found covering its outer surface and the nuclei lie in deeper regions. In the spinal cord, gray matter is located internally in regions called horns, which are surrounded by groups of white matter tracts called columns.

On to the functions of neurons...

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