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Related to Axons: central nervous system, peripheral nervous system, myelin sheath


see nervous systemnervous system,
network of specialized tissue that controls actions and reactions of the body and its adjustment to the environment. Virtually all members of the animal kingdom have at least a rudimentary nervous system.
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; synapsesynapse
, junction between various signal-transmitter cells, either between two neurons or between a neuron and a muscle or gland. A nerve impulse reaches the synapse through the axon, or transmitting end, of a nerve cell, or neuron.
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a neurite, or axis cylinder; the process of a nerve cell along which neural impulses proceed from the cell body to innervated organs and other nerve cells.

Only one axon branches off each neuron, or nerve cell. The nutrition and growth of the axon depends on the neuron body; upon transection of the axon, its peripheral portion dies, but the central portion preserves its viability. Large animals possess axons—for example, those proceeding from the spinal cord to the extremities—that may reach a length of one meter or more when their diameter is several millimicrons (mμ). In some animals—for example, squid and fish—huge axons are found which measure hundreds of mμ in thickness. In axoplasm—that is, the protoplasm of axons—there are extremely thin fibrils, known as neurofibrils, as well as mitochondria and the endoplasmic network. Depending on whether axons are covered with a myelic (fatty) membrane or not, they are known as medullated or nonmedullated nerve fibers. The structure of the membranes and the diameters of the axons that constitute the nerve fiber are the factors that determine the rate of stimulus transmission along the nerve. The terminal sections of the axon, or terminals, branch off and make contact with other nerve, muscle, and gland cells. Stimuli are transmitted through these contact points, which are known as synapses. A nerve is a collection of axons.


The process or nerve fiber of a neuron that carries the unidirectional nerve impulse away from the cell body. Also known as neuraxon; neurite.
References in periodicals archive ?
This research success arises from Bittner's discovery that nerve axons of invertebrates which have been severed from their cell body do not degenerate within days, as happens with mammals, but can survive for months, or even years.
We discovered that VEGF is able to attract nervous system axons.
The mechanism by which acetylcholine receptors on axons lower neurons' firing thresholds remains uncertain, Metherate says.
Content providers will use Axon to power their Web sites, software and hardware applications.
As the growth cone moves through the environment, receptors on its filopodial structure allow maximum contact with the specific guidance signals, located within the extracellular matrix or the surface of nearby axons (Goldberg & Burmeister, 1989).
The pale areas of fibrosis that were observed on light microscopy corresponded to regions of active demyelination, as indicated by accumulations of myelin debris and the presence of large-diameter axons that were devoid of myelin sheaths (figure 3).
Our hope is to develop drugs that will block the pathway, and protect the axons by keeping the calcium out," he said.
In MS, the myelin becomes damaged and the axon cannot effectively transmit electrical impulses.
They also found that damaging skin cells anywhere in the body promoted the regeneration of nearby sensory axons, demonstrating that injured skin cells are the source of the signal.
While experimenting on optic nerves in rats, Larry Benowitz of Children's Hospital in Boston and his colleagues discovered by accident that scratching or poking the lens in an animal's eye could prompt damaged neurons to regrow axons farther toward the brain than researchers had ever seen.
Others suggest blocking some of the sodium channels, which are tiny pores on the axons, to enhance nerve conduction and protect the axons.
Axons from the ambiguous nucleus have a larger circumference than the retrofacial axons.