Fiber, nerve

Nerol oxide Nerve agents Nerve degeneration Nerve fibers Nerve gas... 

Neuropeptide Y. Neuropeptide Y [82785 5-3] (NPY) (255) is a 36-amiao acid peptide that is a member of a peptide family including peptide YY (PYY) [81858-94-8, 106338-42-5] (256) and pancreatic polypeptide (PPY) [59763-91-6] (257). In the periphery, NPY is present in most sympathetic nerve fibers, particulady around blood vessels and also in noradrenergic perivascular and selected parasympathetic nerves (66). Neurons containing NPY-like immunoreactivity ate abundant in the central nervous system, particulady in limbic stmctures. Coexistence with somatostatin and NADPH-diaphorase, an enzyme associated with NO synthesis, is common in the cortex and striatum. 

Local anesthetics produce anesthesia by blocking nerve impulse conduction in sensory, as well as motor nerve, fibers. Nerve impulses are initiated by membrane depolarization, effected by the opening of a sodium ion channel and an influx of sodium ions. Local anesthetics act by inhibiting the channel s opening they bind to a receptor located in the channel s interior. The degree of blockage on an isolated nerve depends not only on the amount of dmg, but also on the rate of nerve stimulation (153—156). 

In one biosensor design, the chem preceptive nerve fibers of the anteimules of the blue crab Callinectes sapidus are coimected to a micropipet electrode. This assembly has been termed a receptrode (2). The receptrode created from Callinectes sapidus responds to the presence of amino acids (1) (qv) in concentrations as low as 10 M. 

Nerven-, nerve, neuro-. -entzundung,/. neuri. tis. -faser,/. nerve fiber, -gewebe, n. nerve tissue, -kitt, m. (Anat.) neuroglia, -kunde, -lehre, /. neurology, -masse, /. = Nerven-stoff, -reiz, m. nervous stimulus, -stoff, m. nerve substance, neural substance, -system, -werk, n. nervous system, -zelle, /. nerve cell. 

Tree like networks of nerve fiber called dendrites protrude outward from the neuron s cell body, or soma. Extending outward from the soma is also a long fiber called the axon that itself eventually branches out into a set of strands and sub strands. At the ends of these strands are the transmitting ends of communication junctions between nerve fibers called synapses. The receiving ends of these junctions exist both on dendrites and on the somas themselves. Each neuron is typically connected to several thousand other neurons. 

Sphingomyelins are the second major group of phospholipids. These compounds have sphingosine or a related dihydroxyamine as their backbone and are particularly abundant in brain and nerve tissue, where they are a major constituent of the coating around nerve fibers. 

Multiple scelerosis is an autoimmune disease mediated by T and B lymphocytes and macrophages. This is characterized by extensive inflammation and demyelination of the myelin sheath that surrounds the nerve fiber. The death of the nerve fiber results in a variety of symptoms that can lead to impairment of movement, paralysis, and death. 

N euro transmitters are chemical substances called neurohormones. These are released at Hie nerve ending that facilitate the transmission of nerve impulses. The two neurohormones (neurotransmitters) of the sympathetic nervous system are epinephrine and norepinephrine Epinephrine is secreted by the adrenal medulla Norepinephrine is secreted mainly at nerve ending of sympathetic (also called adrenergic) nerve fibers (Pig. 22-2). 

Antiadrenergic drugs—drug that block adrenergic nerve fibers. These dm i block the adrenergic nerve fibers within the central nervous system (CNS) or within the peripheral nervous system. 

Electron microscopic study reveals an incalculably small space between nerve endings and the effector organ (eg, tlie muscle, cell, or gland) diat is innervated (or controlled) by a nerve fiber. Fbr a nerve impulse to be transmitted from die nerve ending (motor end plate) across die space to die effector organ, a neurohormone is needed. 

Myasthenia gravis is a disease tiiat involves rapid fatigue of skeletal muscles because of die lack of ACh released at die nerve endings of parasympathetic nerve fibers. Drugs used to treat this disorder include ambeno-nium (Mytelase) and pyridostigmine (Mestinon). 

Cholinergic blocking dragp inhibit die activity of acetylcholine in parasympadietic nerve fibers (see Chap. 24 for a description of die role of acetylcholine in the transmission of nerve impulses across parasympadietic nerve fibers). When die activity of acetylcholine is inhibited, nerve impulses traveling along parasympadietic nerve fibers cannot pass from die nerve fiber to die effector organ or structure ... 

The cardiotonics affect the transmission of electrical impulses along the pathway of the conduction system of tiie heart. The conduction system of die heart is a group of specialized nerve fibers consisting of die SA node, die AV node, the bundle of His, and die branches of Purkinje (Fig. 39-2). Each heartbeat (or contraction of tiie ventricles) is tiie result of an electrical impulse tiiat normally starts in tiie SA node, is tiien received by die AV node, and travels down die bundle of His and through tiie Purkinje fibers (see Fig. 39-2). The heartbeat can be felt as a pulse at the wrist and otiier areas of die body where an artery is close to the surface or lies near a bone When the electrical impulse reaches the... 

Only one impulse can pass along a nerve fiber at any given time. After the passage of an impulse, tiiere is a brief pause, or interval, before the next impulse can pass along the nerve fiber. This pause is called the refractory period, which is the period between the transmission of nerve impulses along a nerve fiber. By... 

Lidocaine (Xylocaine), die representative class I-B drug, raises the threshold of the ventricular myocardium. Threshold is a term applied to any stimulus of the lowest intensity that will give rise to a response in a nerve fiber. A stimulus must be of a specific intensity (strength, amplitude) to pass along a given nerve fiber (Fig. 40-2). 

To further illustrate the threshold phenomenon using plain figures instead of precise electrical values, a certain nerve fiber has a threshold of 10. If a stimulus rated as 9 reaches the fiber, it will not pass along the fiber because its intensity is lower than die fiber s threshold of 10. If another stimulus reaches the fiber and is rated 14, it will pass along the fiber because its intensity is greater than the fiber s threshold of 10. If the threshold of a fiber is raised from 10 to 15, only the stimuli greater dian 15 can pass along the nerve fiber. 

After the stimulus has passed along the nerve fiber, the ions move back to their original place until another stimulus occurs. 

A stimulus must reach the threshold to cause a response in a nerve fiber. Note that stimuli a, b, and d do not reach the threshold therefore, they do not cause a response in a nerve fiber. Stimuli c, e, f, and g do reach and surpass the threshold, resulting in stimulation of nerve fiber. 

After receiving lidocaine hydrochloride (Xylocaine HCI), the threshold is raised to a higher level, allowing fewer stimuli to reach the threshold. This results in decreased stimulation of the nerve fiber and prevents conduction of the nerve impulses causing the arrthvthmia. 

Vitamin B12 is essential to growth, cell reproduction, the manufacture of myelin (which surrounds some nerve fibers), and blood cell manufacture. The intrinsic factor, which is produced by cells in the stomach, is necessary for the absorption of vitamin B12 in the intestine A deficiency of the intrinsic factor results in abnormal formation of erythrocytes because of the body s failure to absorb vitamin B12, a necessary component for blood cell formation. The resulting anemia is a type of megaloblastic anemia called pernicious anemia. 

Topical anesthetics temporarily inhibit the conduction of impulses from sensory nerve fibers. These drug s may be used to relieve itching and pain due to skin conditions, such as minor bums, fungus infections, insect bites, rashes, sunburn, and plant poisoning, such as poison ivy. Some are applied to mucous membranes as local anesthetics. Examples of local anesthetics include benzocaine (Lanacane), dibucadne (Nupereainal), and lidocaine (Xylocadne). 

The smooth muscle cell does not respond in an all-or-none manner, but instead its contractile state is a variable compromise between diverse regulatory influences. While a vertebrate skeletal muscle fiber is at complete rest unless activated by a motor nerve, regulation of the contractile activity of a smooth muscle cell is more complex. First, the smooth muscle cell typically receives input from many different kinds of nerve fibers. The various cell membrane receptors in turn activate different intracellular signal-transduction pathways which may affect (a) membrane channels, and hence, electrical activity (b) calcium storage or release or (c) the proteins of the contractile machinery. While each have their own biochemically specific ways, the actual mechanisms are for the most part known only in outline. 

In a nerve process or skeletal muscle fiber, the spread of activity is essentially only in one dimension, along the fiber. However, in smooth muscle the situation is rather more complex geometrically, and all three dimensions are involved. Action potentials conduct electrotonically just as they do in nerve fibers but they do so in three dimensions. In situ, regions supporting action potentials are not pointlike but tend to be large and the spread from them is more like a surface, approximating a plane. 

Animal cell cultures that are initiated from cells removed directly from the animal are called primary cultures (Figure 2). Primary cultures include both explant cultures (i.e., cultures initiated from small pieces of intact tissue), as well as cultures initiated from preparations of individual or dispersed cells (obtained from intact tissue by mechanical or proteolytic dismption). Nerve fiber explant cultures in blood plasma were among the earliest types of tissue cultures (Harrison, 1907). Cells grow out from such tissue explants and form a single layer of cells completely filling the tissue culture vessel surface. Such cell cultures are called confluent monolayers. Confluent monolayers can then be treated with trypsin, so as to remove the individual cells from the culture vessel surface. The resulting cell suspension is then transferred into other culture containers, so that more viable monolayer... 

Harrison, R.G. (1907). Observations on the living developing nerve fiber. Proc. Soc. Exptl. Biol. Med. 4, 140-143. 

Laine P. Naukkarinen A. Heikkila L, Pentilla A. Kovanen PT Adventitial mast cells cormect with sensory nerve fibers in atherosclerotic coronary arteries. Circulation 2000 101 1665. 

Figure 41-1. Ratio of protein to lipid in different membranes. Proteins equal or exceed the quantity of lipid in nearly all membranes. The outstanding exception is myelin, an electrical insulator found on many nerve fibers.

When large areas of the membrane are depolarized in this manner, the electrochemical disturbance propagates in wave-like form down the membrane, generating a nerve impulse. Myelin sheets, formed by Schwann cells, wrap around nerve fibers and provide an electrical insulator that surrounds most of the nerve and greatly speeds up the propagation of the wave (signal) by allowing ions to flow in and out of the membrane... 

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