In vertebrates the two main mobile phoneular phone types of neuronic systems argon neuroglia cells and nerve cells. Neuroglia are believed to carry out a variety of nutritive and other housekeeping functions in nerve tissue, and nerve cells, or neurons, are the impulse-generating and impulse- conducting units proper.
Each neuron typically consists of a nucleus-containing cell body and of one or more filamentous outgrowths, or vul bottom of the inningized fibers, that extend away from the cell body.
Impulses usually originate at the terminals of fibres called dendrites, which then carry the impulses toward the cell body. Impulses travel away from a cell body finished fibres called axons. Many dendrites and axons are short, but others have lengths of over a yard (of example, axons from the base of the spinal cord to the toes in man).
The long axons and dendrites are enveloped by a Schwann sheath, a single tier of thin flat cells that supplies nutrients to a fibre and that also provides a pathway when a cut fibre regenerates. In accredited cases the cells of a Schwann sheath wind around the nerve fibre several times, and the fatty contents of these wrapping layers then defecate a myelin sheath. A myelin wrapping is believed to answer as a kind of insulation, comparable perhaps to an insulating guard envelope around an electric wire.
The fibres of two adjacent neurons are not in direct contact; their terminals come pen up together at a synapse, a microscopic blank space through which impulses are carried by chemical means.
In uncouth terms a whole nervous system can be envisaged as an intricate lucre of neurons, with fibres interconnecting functionally at numerous synapses. Many pathways in such a network form reflex arcs, composed of a sequence of neurons with peculiar(prenominal) functions.
Thus, sensory (or afferent) neurons in such an arc transmit impulses from a receptor to a modulator, and motor (or efferent) neurons transmit from a modulator effectors. Neurons in a modulator are interneurons. Groups of...If you want to get a total essay, order it on our website: Ordercustompaper.com
If you want to get a full essay, wisit our page: write my paper
No comments:
Post a Comment