| UN | ulnar nerve; undernourished; unilateral neglect; urea nitrogen; urinary nitrogen |
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| UNCV | ulnar nerve conduction velocity |
| nerve, efferent | A nerve that carries impulses away from the central nervous system. The word efferent comes from the latin ex', away or out + ferre , to bear = to bear out or carry away. (12 Dec 1998) |
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| nerve ending | <physiology> A connection between excitable cells, by which an excitation is conveyed from one to the other. 1. Chemical synapse: one in which an action potential causes the exocytosis of neurotransmitter from the presynaptic cell, which diffuses across the synaptic cleft and binds to ligand gated ion channels on the post synaptic cell. These ion channels then affect the resting potential of the post synaptic cell. 2. Electrical synapse: one in which electrical connection is made directly through the cytoplasm, via gap junctions. 3. Rectifying synapse: one in which action potentials can only pass across the synapse in one direction (all chemical and some electrical synapses). 4. Excitatory synapse: one in which the firing of the presynaptic cell increases the probability of firing of the postsynaptic cell. 5. Inhibitory synapse: one in which the firing of the presynaptic cell reduces the probability of firing of the postsynaptic cell. (10 Jan 1998) |
| nerve endings | Specialised terminations of peripheral neurons. Nerve endings include neuroeffector junction(s) by which neurons activate target organs and sensory receptors (see receptors, sensory) which transduce information from the various sensory modalities and send it centrally in the nervous system. Presynaptic nerve endings are presynaptic terminals. (12 Dec 1998) |
| nerve fascicle | A bundle of nerve fibres surrounded by perineurium. (05 Mar 2000) |
| nerve fibre | The axon of a nerve cell, ensheathed by oligodendroglia cells in brain and spinal cord, and by Schwann cells in peripheral nerves. (05 Mar 2000) |
| nerve fibres | Slender processes of neurons, especially the prolonged axons that conduct nerve impulses. (12 Dec 1998) |
| nerve fibres, myelinated | Grayish white nerve fibres whose axons are encased in a myelin sheath which may in turn be enclosed by a neurilemma (a thin membrane spirally enwrapping the myelin layers). (12 Dec 1998) |
| nerve field | The regional distribution of nerve terminals. (05 Mar 2000) |
| nerve force | An obsolete terms denoting the property of nerve tissue to conduct stimuli. (05 Mar 2000) |
| nerve graft | A nerve, or part of a nerve, used as a graft. (05 Mar 2000) |
| nerve growth cone | <cell biology> A specialised region at the tip of a growing neurite that is responsible for sensing the local environment and moving toward the neuron's target cell. Growth cones are hand shaped, with several long filopodia that differentially adhere to surfaces in the embryo. Growth cones can be sensitive to several guidance cues, for example: surface adhesiveness, growth factors, neurotransmitters and electric fields (galvanotropism). (18 Nov 1997) |
| nerve growth factor | <growth factor> A peptide (13.26 kD) of 118 amino acids (usually dimeric) with both chemotropic and chemotrophic properties for sympathetic and sensory neurons. Found in a variety of peripheral tissues, nerve growth factor attracts neurites to the tissues by chemotropism, where they form synapses. The successful neurons are then protected from neuronal death by continuing supplies of nerve growth factor. It is also found at exceptionally high levels in snake venom and male mouse submaxillary salivary glands, from which it is commercially extracted. Nerve growth factor was the first of a family of nerve tropic factors to be discovered. Amino acids 1-81 show homology with proinsulin. Besides its peripheral actions, nerve growth factor selectively enhances the growth of cholinergic neurons that project to the forebrain and that degenerate in Alzheimer's disease. Acronym: NGF (18 Nov 1997) |
| nerve growth factor antiserum | An antiserum containing antibodies against nerve growth factor; when injected into newborn animals the majority of sympathetic ganglion cells are permanently destroyed, resulting in hypoinnervation of peripheral tissues. Synonym: NGF antiserum. (05 Mar 2000) |
| nerve growth factors | Factors which enhance the growth potentialities of sensory and sympathetic nerve cells. (12 Dec 1998) |
| nerve implantation | Planting one nerve into the sheath of another nerve. (05 Mar 2000) |