Sympathetic nerve fiber

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. 

Because catecholamines travel in the blood, organs and tissues throughout the body are exposed to them. Therefore, they are capable of stimulating tissues that are not directly innervated by sympathetic nerve fibers, hepato-cytes, and adipose tissue, in particular. As a result, the catecholamines have a much wider breadth of activity compared to norepinephrine released from sympathetic nerves. 

Figure 14.1 Effect of autonomic nervous system stimulation on action potentials of the sinoatrial (SA) node. A normal action potential generated by the SA node under resting conditions is represented by the solid line the positive chronotropic effect (increased heart rate) of norepinephrine released from sympathetic nerve fibers is illustrated by the short dashed line and the negative chronotropic effect (decreased heart rate) of acetylcholine released from parasympathetic nerve fibers is illustrated by the long dashed line.

Angiotensin II causes vasoconstriction by direct stimulation of ATj receptors on the vascular smooth muscle. It also enhances release of the neurotransmitter norepinephrine from the sympathetic nerve fibers present in the blood vessels. The vasopressor effects of Ag II may be inhibited pharmacologically in order to decrease TPR and treat hypertension. An important class of orally active drugs is the ACE inhibitors, including captopril and enalopril, which prevent formation of Ag II. More recently, angiotensin receptor antagonists have been developed that act at the vascular smooth muscle. These drugs, which include losartin and valsartan, are also orally active. 

The activation of the stress systems affects all tissues of the organism, and the peripheral immune system is no exception. These effects are mediated through at least tw o pathways via the HPA axis and by virtue of the innervation of lymphatic tissues by autonomic nerve fibers, especially from the sympathetic nervous system. All lymphoid tissues, primary (bone marrow and thymus) as well as secondary (spleen, lymph nodes, and gut-associated lymphoid tissue) are innervated by sympathetic nerve fibers. As discussed above, most lymphoid cells express catecholamine receptors, including B-lymphocytes, CD4- and CD 8-positive T cells, dendritic cells, monocytes, and macrophages. 

Catecholamines are endogenous compounds and are synthesized in the brain, the adrenal medulla, and by some sympathetic nerve fibers. The biosynthesis of catecholamines begins with the hydroxylation of tyrosine by tyrosine hydroxylase to form L-dopa, which is decarboxylated by aromatic amino acid decarboxylase to form dopamine. Norepinephrine... 

Bjorklund H, Hoffer B, Olson L, et al. 1981. Differential morphological changes in sympathetic nerve fibers elicited by lead, cadmium and mercury. Environ Res 26 69-80. 

Afferent arteriole Sympathetic nerve fibers Granular cells... 

Menesini-Chen, M. G., Chen, J. S., and Levi-Montalcini, R., Sympathetic nerve fibers ingrowth in the central nervous system of neonatal rodent upon intracerebral NGF injections, Arch. Ital. Biol., 116, 53, 1978. 

The sympathetic nervous system is a subdivision of the autonomic nervous system (or visceral motor system), which provides automatic, involuntary regulation of smooth muscle, cardiac muscle, and glandular activity or secretions. Sympathetic nerve fibers reach the nasal mucosa, and when stimulated, sympathetic nerve terminals release norepineph-... 

Human beings react with increased sympathoadrenal activity when they are confronted with challenging events or situations demanding active involvement The secretion in the peripheral blood of the catecholamines adrenaline and noradrenaline are important parts of this reaction. Sympathetic innervation via the splanchtuc nerve stimulates the adrenal medulla. This gland secretes adrenaline and a small fraction of the circulating noradrenaline in the blood. The latter hormone is secreted mainly at the ptesynaptic endplates of the (postganglionic) sympathetic nerve fibers. It has been shown that the ex-... 

GFR is also regulated by sympathetic nerve fibers which innervate arterioles of the glomerulus and by several hormones (angiotensin II, atrial natriuretic peptide (ANP), nitric oxide, endothelin, prostaglandins). 

From the superior pharyngeal branch, the carotid branch arises to the carotid canal. This carotid branch ascends through the foramen lacerum and accompanies the internal carotid artery up to the cavernous sinus, where it anastomoses with the inferolateral trunk and with the recurrent artery of the foramen lacerum, arising from the C5 portion of the carotid siphon, which supplies the internal carotid artery wall and sympathetic nerve fibers. 

Sympathetic ganglia (Cammermeyer 1956) may be slightly fibrotic with rare lymphocytic nodules. There were conspicuous reactive changes and loss of ganglion cells in one of this author s case (T. A.). Sympathetic nerve fibers traversing the ganglia were not involved. 

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