Sympathetic nervous system innervations

Figure 15.5 Effects of sympathetic and parasympathetic nervous activity on mean arterial pressure. The parasympathetic nervous system innervates the heart and therefore influences heart rate and cardiac output. The sympathetic nervous system innervates the heart and veins and thus influences cardiac output. This system also innervates the arterioles and therefore influences total peripheral resistance. The resulting changes in cardiac output and total peripheral resistance regulate mean arterial pressure.

The sympathetic nervous system innervates the major lymphoid organs such as the spleen with nerve fibers reaching both the vasculature and the parenchyma where lymphocytes, primarily T cells (T helper type 1-2, T l, T j2), reside (Friedman and Irwin, 1997). T cells possess receptors for both norepinephrine and neuropeptide Y that are released in response to sympathetic nerve stimulation. The adrenergic receptors are primarily the subtype, which is consistent with data demonstrating that (32 agonists can markedly influence the immune system (Kohm and Sanders, 2001). For example, stimulation of T cell receptors results in increased cyclic AMP formation, which can modulate cytokine expression, i.e., decreasing... 

Adrenaline is the main hormone released from the adrenal medulla. The glandular cells in this structure correspond to the second, postganglionic neuron of the sympathetic nervous system. Furthermore, adrenaline can be found in chromaffin cells in various tissues. For the better understanding of the function of noradrenaline it is important to realize that this substance, as a neuronal transmitter, affects only the innervated target structure, that is it acts mainly locally. Among these effects are the activation of the musculus dilatator to widen the pupillae in response to a reduced light intensity, an increase in heart rate as a response to a blood pressure drop due to a reduction of the peripheral resistance or constriction... 

The preganglionic neurons of the sympathetic nervous system have their cell bodies in the thoracic and lumbar regions of the spinal cord, termed the thoracolumbar division. The preganglionic neurons of the parasympathetic division have their cell bodies in the brainstem and in the sacral region of the spinal cord, termed the craniosacral division. The cranial part of the parasympathetic nervous system innervates structures in the head, neck, thorax, and abdomen (e.g., the stomach, part of the intestines, and pancreas). The cranial parasympathetic fibers leave the CNS in the oculomotor, facial, glos-... 

B. Smooth muscle relaxation is primarily under the influence of the sympathetic nervous system. This control is primarily through P2-receptors. Pi-Receptors are found chiefly in the heart and adipose tissue. tti-Receptors are at postjuctional sites on tissues innervated by adrenergic neurons. 2-Receptors are usually presynaptic, while Ps-adreno-ceptors appear to be primarily in adipose tissue. 

Both the parasympathetic and sympathetic nervous systems provide extrinsic gastrointestinal innervation. Parasympathetic stimulation increases muscle contraction of the gut, while sympathetic stimulation inhibits contractions. Stimulation of either a- or 13-adrenoceptors will result in inhibition of contractions. The intramural nervous system consists of a myenteric (Auerbach s) plexus between the circular and longitudinal muscle areas and a submucosal (Meissner s) plexus between the muscularis mucosa and the circular muscle layers. These two plexuses contain stimulatory cholinergic neurons. 

The chemical transmitters may be small molecules— notably acetylcholine, norepinephrine, epinephrine, serotonin, dopamine, or histamine. Acetylcholine and norpeinephrine are the dominant neurotransmitters in the parasympathetic and sympathetic nervous systems, respectively. Dopamine and serotonin are employed primarily in the central nervous system. Neurotransmitters may also be more complex peptides (small proteins) such as substance P, vasopressin, endorphins, and enkephalins. The latter agents are of particular importance to our considerations of opium since they represent the endogenous opiates—agents that exist within the body whose actions are mimicked by exogenous, or outside, agents such as morphine, heroin, codeine, and so on. These neurotransmitters serve to convey information between neurons across the synaptic cleft (the junction where two neurons meet) or at the neuroeffector junction (the site between neuron and an innervated organ such as muscle or secretory gland). 

Lowenfeld12 identified the components of the fight reflex that were controlled by parasympathetic and sympathetic innervation of the smooth muscles controlling pupil diameter. They concluded that the parasympathetic nervous system must be intact to observe the light reflex the sympathetic nervous system influences the shape of the reflex. For example, in the absence of sympathetic innervation, the constriction velocity is increased and the dilation velocity is decreased. Conversely, in situations of increased sympathetic tone, the constriction is sluggish and incomplete, and the pupil slowly returns to its baseline size. The effects of abused drugs on these and other components of the light reflex were studied in the experiment described below. 

FIGURE 14.5 The autonomic nervous system innervates smooth muscle, cardiac muscles, and gland. ACh = acetylcholine N = nicotinic cholinergic receptors M = muscarinic cholinergic receptors S = sympathetic chain P = parasympathetic chain E = epinephrine D = dopamine NE = norepinephrine Sup. = superior Inf. = inferior. 

Cholinesterase inhibitors have less marked effects on vascular smooth muscle and on blood pressure than direct-acting muscarinic agonists. This is because indirect-acting drugs can modify the tone of only those vessels that are innervated by cholinergic nerves and because the net effects on vascular tone may reflect activation of both the parasympathetic and sympathetic nervous systems. The cholinomimetic effect at the smooth muscle effector tissue is minimal since few vascular beds receive cholinergic innervation. Activation of sympathetic ganglia may increase vascular resistance. 

The brain and the immune system are accepted as the two major body s adaptive systems (Elenkov et al., 2000). The brain can modulate immune functions and the immune system also sends messages to the brain. The communication between these two systems is done mainly by the hypothalamic-pituitary-adrenal axis and the autonomic nervous system (ANS). The sympathetic nervous system (SNS), which is part of the ANS, innervates the lymphoid organs (Elenkov et al., 2000) (Flierl et al., 2007). Catecholamines, like dopamine, serotonin, epinephrine and norepinephrine, are the end products of the SNS. 

A low level of tonic activity of the sympathetic nerves to vascular smooth muscle adrenergic receptors exists so that withdrawal of sympathetic vasomotor tone results in vasodilatation and reduced pressure. Conversely, enhancement of sympathetic vasomotor tone augments the level of vasoconstriction leading to elevated pressure. While the parasympathetic branch of the autonomic nervous system innervates some blood vessels, it does not generally play a role in regulating peripheral resistance. 

Q4 The ganglionic transmitter of both divisions of the autonomic nervous system is acetylcholine. The major postganglionic neurotransmitter of the sympathetic nervous system is norepinephrine (noradrenaline), but a small number of structures are innervated by sympathetic, cholinergic fibres. These fibres release acetylcholine and the structures innervated include the sweat glands and blood vessels supplying skeletal muscle. In the parasympathetic system the postganglionic neurotransmitter is acetylcholine. 

Lesions of the retina, optic nerve, chiasm, and optic tract do not cause anisocoria. A lesion in the midbrain produces a subtle and transient anisocoria. However, most neurologic causes of anisocoria involve lesions in the efferent pupillary pathway. These defects arise due to asymmetric disruptions of the parasympathetic or sympathetic nervous systems that innervate the iris.The presence of anisocoria may help to limit a lesion to this pathway but does not localize the lesion s location within that pathway. 

Most lymphoid tissues are innervated by the sympathetic nervous system, both directly and indirectly. These same tissues express receptors for a variety of hormones, including classical... 

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. 

BZ is a competitive inhibitor of muscarinic receptors associated with the parasympathetic nervous system that innervate the eyes, heart, respiratory system, skin, gastrointestinal tract, and bladder. The sweat glands, innervated by the sympathetic nervous system, are also modulated by muscarinic receptors. By any route of exposure, the onset of action is approximately 1 h, with peak effects occurring 8h postexposure. Signs and symptoms gradually subside over 2-4 days. Most of the absorbed BZ is excreted via the kidney. 

The heart responds constantly to hormonal and nervous system signals. Sympathetic nervous system terminals releasing norepinephrine are found in cardiac cells of the atria and ventricles. This allows for reflex regulation of heart muscle contractility. Sympathetic innervation is also present to the SA node and AV junction, where norepinephrine release acts to increase heart rate (enhanced phase 4 depolarization) and also to increase conduction velocity by reducing the AV junction impedance to conduction. Parasympathetic innervation is provided by cranial nerve 10, the vagus nerve, to the SA node and the AV junction. These fibers release acetylcholine, which slows SA node activity (decreasing the rate of phase 4 depolarization) and decreases conduction throughout the AV junction. 

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