| nervous system, sympathetic | A part of the nervous system that accelerates the heart rate, constricts blood vessels, and raises blood pressure. The sympathetic nervous system together with the parasympathetic nervous system (that slows the heart rate, increases intestinal and gland activity, and relaxes sphincter muscles) constitute the autonomic nervous system. (12 Dec 1998) |
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| nervous tissue | A highly differentiated tissue composed of nerve cells, nerve fibres, dendrites, and a supporting tissue (neuroglia). (05 Mar 2000) |
| nervous tunic of eyeball | Light sensitive layer of the eye. In vertebrates, looking from outside, there are four major cell layers: (i) the outer neural retina, which contains neurons (ganglion cells, amacrine cells, bipolar cells) as well as blood vessels, (ii) the photoreceptor layer, a single layer of rods and cones, (iii) the pigmented retinal epithelium (PRE or RPE), (iv) the choroid, composed of connective tissue, fibroblasts and including a well vascularised layer, the chorio capillaris, underlying the basal lamina of the PRE. Behind the choroid is the sclera, a thick organ capsule. In molluscs (especially cephalopods such as the squid) the retina has the light sensitive cells as the outer layer with the neural and supporting tissues below. See: retinal rods, retinal cones, rhodopsin. (18 Nov 1997) |
| nervousness | Excessive excitability and irritability, with mental and physical unrest. (18 Nov 1997) |
| metameric nervous system | That part of the nervous system which innervates body structures developed in ontogeny from the segmentally arranged somites or, in the head region, branchial arches. The term implies reference to the neural mechanisms intrinsic to the spinal cord and brainstem (represented by the sensory nuclei, motoneuronal cell groups, and their associated interneurons in the reticular formation); by strict definition it should exclude the autonomic nervous system. (05 Mar 2000) |
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| coeliac (nervous) plexus | The most substantial, superior portion of the abdominal aortic plexus lying anterior to the aorta at the level of origin of the coeliac trunk (vertebral level T-12); the coeliac ganglia lie within the plexus; it is formed by contributions from the greater splanchnic and vagus (especially the posterior or right vagus) nerves and communicating branches to and from the superior mesenteric and renal plexuses and ganglia; most sympathetic, parasympathetic and visceral afferent fibres serving the abdominal viscera pass through this plexus. Synonym: plexus coeliacus, solar plexus. (05 Mar 2000) |
| Henle's nervous layer | The layers of the retina from the outer plexiform to the nerve fibre layer inclusive. Synonym: Henle's nervous layer. (05 Mar 2000) |
| high pressure nervous syndrome | <syndrome> A syndrome of tremors, nausea, dizziness, and decreased motor and mental performance which develops in those who dive deeply (c. 1000 ft) usually breathing a mixture of oxygen and helium. Nitrogen is not a factor as it is in inert gas narcosis. (12 Dec 1998) |
| pulmonary branch of autonomic nervous system | Pulmonary branches of cardiac plexuses and cardiaopulmonary splanchnic nerves. Synonym: rami pulmonales systematis autonomici. (05 Mar 2000) |
| sympathetic nervous system | <anatomy, physiology> One of the two divisions of the vertebrate autonomic nervous system (the other being the parasympathetic nervous system). The sympathetic preganglionic neurons have their cell bodies in the thoracic and lumbar regions of the spinal cord and connect to the paravertebral chain of sympathetic ganglia. Innervate heart and blood vessels, sweat glands, viscera and the adrenal medulla. most sympathetic neurons, but not all, use noradrenaline as a post ganglionic neurotransmitter. (19 Jan 1998) |
| syndrome, nervous colon | See Syndrome, irritable bowel. (12 Dec 1998) |
| system, parasympathetic nervous | : A part of nervous system that slows the heart rate, increases intestinal and gland activity, and relaxes sphincter muscles. The parasympathetic nervous system together with the sympathetic nervous system (that accelerates the heart rate, constricts blood vessels, and raises blood pressure) constitute the autonomic nervous system. (12 Dec 1998) |
| system, sympathetic nervous | A part of nervous system that accelerates the heart rate, constricts blood vessels, and raises blood pressure. The sympathetic nervous system together with the parasympathetic nervous system (that slows the heart rate, increases intestinal and gland activity, and relaxes sphincter muscles) constitute the autonomic nervous system. (12 Dec 1998) |
| internal carotid (nervous) plexus | An autonomic plexus surrounding the internal carotid artery in the carotid canal and cavernous sinus, and sending branches to the tympanic plexus, sphenopalatine ganglion, abducens and oculomotor nerves, the cerebral vessels, and the ciliary ganglion. Synonym: internal carotid venous plexus. (05 Mar 2000) |
| involuntary nervous system | <anatomy> Neurons that are not under conscious control, comprising two antagonistic components, the sympathetic and parasympathetic nervous systems. The autonomic nervous system regulates key functions including the activity of the cardiac (heart) muscle, smooth muscles (e.g., of the gut), and glands. The autonomic nervous system has two divisions: 1. The sympathetic nervous system that accelerates the heart rate, constricts blood vessels, and raises blood pressure. 2. The parasympathetic nervous system slows the heart rate, increases intestinal and gland activity, and relaxes sphincter muscles. (03 Jul 1999) |
| enteric nervous system | Two ganglionated neural plexuses in the gut wall which form one of the three major divisions of the autonomic nervous system. The enteric nervous system innervates the gastrointestinal tract, the pancreas, and the gallbladder. It contains sensory neurons, interneurons, and motor neurons. Thus the circuitry can autonomously sense the tension and the chemical environment in the gut and regulate blood vessel tone, motility, secretions, and fluid transport. The system is itself governed by the central nervous system and receives both parasympathetic and sympathetic innervation. (12 Dec 1998) |