Axons and dendrites are extensions of cell bodies and form the white matter of the nervous system. Axons are found deep in the brain and in groups,called tracts,at the periphery of the spinal cord. They are referred to as nerves or nerve fibres outside the brain and spinal cord.
AXONS.
Each nerve cell has only one axon,which begins at a tapered area of the cell body,the axon hillock. They carry impulses away from the cell body and are usually longer then the dendrites.
Structure of an axon. The membrane of the axon is called the axolemma and it encloses the cytoplasmic extension of the cell body.
Myelinated neurones. Large axons and those of peripheral nerves are surrounded by a myelin sheath. This consists of a series of schwann cells arranged along a length of the axon. Each one is wrapped around the axon so that is covered by a number of concentric layers of schwann cell plasma membrane. Between the layers of plasma membrane there is a small amount of fatty substance called myelin. The outermost layer of the schwann cell plasma membrane is the neurilemma.
DENDRITES.
These are the many short processes that receive and carry incoming impulses towards cell bodies. They have the same structure as axons but are usually shorter and branching. In motor neurones dendrites form part of synapse and in sensory neurones they form the sensory receptors that respond the specific stimuli.
