Nerve cell

The posterior lobe of the pituitary, ie, the neurohypophysis, is under direct nervous control (1), unlike most other endocrine organs. The hormones stored in this gland are formed in hypothalamic nerve cells but pass through nerve stalks into the posterior pituitary. As early as 1895 it was found that pituitrin [50-57-7] an extract of the posterior lobe, raises blood pressure when injected (2), and that Pitocin [50-56-6] (Parke-Davis) causes contractions of smooth muscle, especially in the utems (3). Isolation of the active materials involved in these extracts is the result of work from several laboratories. Several highly active posterior pituitary extracts have been discovered (4), and it has been deterrnined that their biological activities result from peptide hormones, ie, low molecular weight substances not covalendy linked to proteins (qv) (5). 

Contraction of muscle follows an increase of Ca " in the muscle cell as a result of nerve stimulation. This initiates processes which cause the proteins myosin and actin to be drawn together making the cell shorter and thicker. The return of the Ca " to its storage site, the sarcoplasmic reticulum, by an active pump mechanism allows the contracted muscle to relax (27). Calcium ion, also a factor in the release of acetylcholine on stimulation of nerve cells, influences the permeabiUty of cell membranes activates enzymes, such as adenosine triphosphatase (ATPase), Hpase, and some proteolytic enzymes and facihtates intestinal absorption of vitamin B 2 [68-19-9] (28). 

The concept of discrete neurotransmitter recognition sites or receptors on nerve cells was based on work on systems physiology and dmg action (1). It was not until 1921 however, that it was shown that information could be transferred between neurons via a chemical, in this instance acetylcholine [51-84-3] (ACh), C H gN02 (1). 

Histamine AND histamine antagonists). It is formed from histidine by the enzyme L-histidine decarboxylase. In the periphery, histamine is stored ia mast cells, basophils, cells of the gastric mucosa, and epidermal cells. In the CNS, histamine is released from nerve cells and acts as a neurotransmitter. The actions of histamine ate terrninated by methylation and subsequent oxidation via the enzymes histamine-/V-methyltransferase and monoamine oxidase. 

The human body has more than 600 muscles. The body s movement is performed by muscle contractions, which are stimulated by the nervous system. This system links muscle tissue to the spinal cord and brain. The network of nerve cells which carries the brain s signals directs the flow of muscular energy. Most muscular activity occurs beyond the range of the conscious mind. The body, working through the neuromuscular network, manages... 

Choline functions in fat metaboHsm and transmethylation reactions. Acetylcholine functions as a neurotransmitter in certain portions of the nervous system. Acetylcholine is released by a stimulated nerve cell into the synapse and binds to the receptor site on the next nerve cell, causing propagation of the nerve impulse. 

Hydrogen cyanide From metal plating, blast furnaces, dyestuff works Metal fabricating, primary metals, textiles Capable of affecting nerve cells... 

FIGURE 17.8 (a) Rapid axonal transport along microtnbnles permits the exchange of material between the synaptic terminal and the body of the nerve cell, (b) Vesicles, mnltivesicn-lar bodies, and mitochondria are carried throngh the axon by this mechanism. 

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. 

It is tempting to view ANNS as simplified versions of biological nervous systems. Yet even the most complex neurocomputers, with several million neurons, are unable to mimic the behavior of a fly, which has approximately one million nerve cells. This is because the nerve system of the fly has far more interconnections than are possible with current-day neurocomputers, and their neurons are highly specialized to perform necessary tasks. The human brain, with about 10 billion nerve cells, is still several orders of magnitude more complex. 

The adrenergic system is an essential regulator that increases cardiovascular and metabolic capacity during situations ofstress, exercise, and disease. Nerve cells in the central and peripheral nervous system synthesize and secrete the neurotransmitters noradrenaline and adrenaline. In the peripheral nervous system, noradrenaline and adrenaline are released from two different sites noradrenaline is the principal neurotransmitter of sympathetic neurons that innervate many organs and tissues. In contrast, adrenaline, and to a lesser degree noradrenaline, is produced and secreted from the adrenal gland into the circulation (Fig. 1). Thus, the actions of noradrenaline are mostly restricted to the sites of release from sympathetic nerves, whereas adrenaline acts as a hormone to stimulate many different cells via the blood stream. 

Long nerve-cell process transmitting the action potential and ending as the synapse. 

Component of the myelin sheath surrounding the axons of nerve cells. Additional compounds of the myelin sheath are phospholipids, cholesterol, cerebrosides, and specific keratins. The myelin sheath constitutes an isolating barrier during electrophysiological axonal signaling. 

Transport supplies nerve cells with neurotransmitter, which is used to replenish secretory vesicles, thus uptake occurs on the cell surface and on the secretory vesicle. 

While these functions can be a carried out by a single transporter isoform (e.g., the serotonin transporter, SERT) they may be split into separate processes carried out by distinct transporter subtypes, or in the case of acetylcholine, by a degrading enzyme. Termination of cholinergic neurotransmission is due to acetylcholinesterase which hydrolyses the ester bond to release choline and acetic acid. Reuptake of choline into the nerve cell is afforded by a high affinity transporter (CHT of the SLC5 gene family). 

The transporters for 5HT, noradrenaline and dopamine, biogenic monoamines, are genetically related, exist as single isoforms and are expressed on the surface of nerve cells, which use monoamines as (or convert them into) their cognate neurotransmitter. The single-isoform monoamine transporters fulfil all three fundamental functions (reuptake, limiting synaptic transmission, and control of the extracellular neurotransmitter concentration). Inactivation of DAT, NET, or SERT results in an increased extracellular lifetime and level of monoamine neurotransmitter, but decreased intracellular storage and evoked release (Fig. 3). 

Tliere are examples that cells have an intracellular reserve of functional transporter moieties EAAC1, GAT1, CHT are predominantly - while NET only in some nerve cells - localized in the cell interior where transporters are stored membrane-bound in vesicles. Regulation occuts by transporter redistribution. Increased surface density leads to increased transport capacity while transporter internalization suppresses uptake. 

Neurotransmitters are molecules that convey a signal from one nerve cell to the other. Neurotransmitters can be biogenic amines (e.g. norepinephrine, serotonin),... 

The raphe nuclei are a cluster of nuclei found in the brainstem, where they are located in the medial portion of the formatio reticularis, the raphe. (The raphe is the junction of the left and right brainstem hemisphere, hence the name raphe=seam). Serotonergic nerve cells in the CNS originate from the raphe nuclei, i.e., their rostral portion, and because of their wide-ranging projections appear to supply serotonin (5HT) to the rest of the brain. 

Reuptake transporters are structures within the cell membranes of the presynaptic nerve terminal that serve to transport biogenic amines released from vesicles back into the nerve cell. These structures are targets for antidepressants, which block the transporter, thus increasing the bioavailability of neurotransmitters at postsynaptic receptors. 

Varizella zoster vitus (VZV) is a highly contagious herpesvirus causing chickenpox upon primary infection. After recovery, the vims stays dormant in nerve roots. Weakening of the immune system, e.g. in people over the age of 60 or under immunosuppressive therapy, can lead to reactivation of VZV. This recurrence causes shingles (herpes zoster), a painful rash that develops in a well-defined band corresponding to the area enervated by the affected nerve cells. 

Herpes zoster (shingles) is caused by the varicella (chickenpox) virus. It is highly contagious. The virus causes chickenpox in the child and is easily spread via the respiratory system. Recovery from childhood chickenpox results in the infection lying dormant in the nerve cells. The virus may become reactivated later in life as the older adult s immune system... 

Cholinergic transmission, but nerve cell chain originates in the thoracolumbar part of the spinal cord and is therefore sympathetic, alpha, a beta, 3. 

Generally, anticonvulsants reduce the excitability of the neurons (nerve cells) of the brain. When neuron excitability is decreased, seizures are theoretically reduced in intensity and frequency of occurrence or, in some instances, are virtually eliminated. For some patients, only partial control of the seizure disorder may be obtained with anticonvulsant drug therapy. 

Levodopa is a chemical formulation found in plants and animals that is converted into dopamine by nerve cells in the brain. Levodopa does cross die blood-brain barrier, and a small amount is dien converted to dopamine. This allows the drug to have a pharmacologic effect in patients witii Parkinson s disease (Pig. 29-1). Combining levodopa witii another drug (carbidopa) causes more levodopa to reach die brain. When more levodopa is available, the dosage of levodopa may be reduced. Carbidopa has no effect when given alone. Sinemet is a combination of carbidopa and levodopa and is available in several combinations (eg, Sinemet 10/100 has 10 mg of carbidopa and 100 mg of levodopa Sinemet CR is a time-released version of die combined drugs). 

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