Neuron Classification
Neurons are classified based on the number of processes extending from the cell body. 1. Multipolar – most common, several dendrites, 1 axon 2. Bipolar – 1 main dendrite & 1 axon 3. Unipolar – axon & dendrites fuse into 1 process that exits the cell body
Nerves & Tracts
A nerve is composed of one to several thousands of axons plus associated connective tissue and blood vessels within the PNS. They contain afferent and/or efferent fibres; a nerve may be sensory, motor or mixed. Each nerve follows a specific path to a specific region of the body. A nerve can also carry both somatic &/or autonomic information. Connective tissue components are arranged in a nerve similarly to the arrangement seen in skeletal muscle. Fibroblasts and collagen fibres surrounding individual axons constitute the endoneurium. Nerve fascicles are bound by the perineurium. Several fascicles of the nerve are bound together by the epineurium which is continuous with the surrounding connective tissue. Nerves are classified as either cranial or spinal. The 12 pairs cranial nerves are numbered based on what order they exit the brain. The 42 pairs of spinal nerves are classified according to location of where they exit along the vertebral column. A tract is a bundle of axons located in the CNS. A tract is classified as either grey matter which is made up of neuronal cell bodies, dendrites, unmyelinated axons, axon terminals & neuroglia located within the spinal cord and brain. White matter is made up of myelinated axons that surrounds grey matter in the spinal cord and brain.
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