AXON

also called Nerve Fibre, portion of a nerve cell (neuron, q.v.) that carries nerve impulses away from the cell body. A neuron typically has one axon, which is rarely branched. Axons connect neurons with other neurons or with muscle or gland cells. The axon of a motor neuron may be quite long, reaching, for example, from the spinal cord down to a toe. Most axons of vertebrate animals are enclosed in a myelin sheath (or fatty membrane), which increases the speed of impulse transmission. A large, sheathed axon may transmit impulses at 90 m (300 feet) per second, while small, unsheathed fibres conduct impulses at only millimetres per second.