The Visceral System

The peripheral nervous system is organized into two divisions. These are the somatic nervous system (SNS) and the autonomic nervous system (ANS). The somatic nervous system acts on skeletal muscles to produce voluntaiy movement. The autonomic nervous system, known as the visceral system, is responsible for involuntary movement and controls the heart, respiratory system, gastrointestinal system, and the endocrine system (glands). 

The autonomic nervous system—also known as the visceral system— involuntarily regulates smooth muscles and glands including the heart, respiratory system, GI tract, peristalsis (digestion), bladder, and eyes. 

Physiological Classifications of Contaminants. The physiological classification of air contaminants is difficult, because the type of action of many gases and vapors depends on concentrations (55). For example, a vapor at one concentration may exert its principal effect as an anesthetic but, at a lower concentration, the same vapor may iujure the nervous system, the hematopoietic (blood-forming) system, or some visceral organ (see Toxicology). 

Leishmaniasis affects some 12 million humans aimuaHy ia an area where 350 million are at risk. It is a complex of at least two protozoan diseases, consisting primarily of cutaneous and visceral forms. A mucocutaneous form is considered by some to be another distinct variety. Clinical manifestations of the disease range from an asymptomatic infection to an infection ia which there is considerable destmction of cutaneous tissue and mucous membranes. Leishmaniasis can often be fatal, especially ia the visceral form. The seriousness of the disease depends on the state of the immunological system of the... 

Because of its motor, i.e., activating effect on vascular smooth muscle and its inhibitory effect on intestinal smooth muscle, the sympathetic nervous system has been cast into the role of the component of the nervous system that executes control of visceral function in times of physical emergency for the organism. The phrase fight or flight has been often used to describe the circumstances in which the adrenergic transmitters of the sympathetic system are dominant over the cholinergic parasympathetic system. This concept is perhaps oversimplified but it has the utility of a first approximation of how the two components of the ANS interact in the periphery. Sensory inputs which lead to increased blood pressure, for example, activate the sympathetic pathways. 

The autonomic nervous system (ANS), also known as the visceral or involuntary nervous system, functions below the level of consciousness. Because it innervates cardiac muscle, smooth muscle, and various endocrine and exocrine glands, this nervous system influences the activity of most of the organ systems in the body. Therefore, it is evident that the ANS makes an important contribution to the maintenance of homeostasis. Regulation of blood pressure gastrointestinal responses to food contraction of the urinary bladder focusing of the eyes and thermoregulation are just a few of the many... 

The autonomic nervous system is by definition that part of the nervous system that innervates smooth muscle, cardiac muscle and glands. It is thus a motor system. Perception arising from the viscera involves pathways similar to those arising from the body surface and skeletal muscle. Thus there are visceral afferent fibres that pass from the viscera to the central nervous system. Such impulses then ascend the spinal cord to the thalamus and are thence relayed to the post-central gyrus of the brain (or sensory cortex). Visceral reflex arcs use visceral afferent fibres to convey impulses to the cord, but the efferent limb of such a visceral reflex is the autonomic nervous system. Although visceral reflexes are under higher central control, it is usually impossible to bring them under the control of the will. 

The autonomic nervous systems modulates the visceral functions of the organism. A pharmacological interference with the autonomic nervous system offers the possibility to influence this modulation in case of dysfunction. The autonomic nervous system... 

Anatomical differences between the peripheral somatic and autonomic nervous systems have led to their classification as separate divisions of the nervous system. These differences are shown in Figure 9.1. The axon of a somatic motor neuron leaves the CNS and travels without interruption to the innervated effector cell. In contrast, two neurons are required to connect the CNS and a visceral effector cell of the autonomic nervous system. The first neuron in this sequence is called the preganglionic neuron. The second neuron, whose cell body is within the ganglion, travels to the visceral effector cell it is called the postganglionic neuron. 

Many visceral organs are innervated by both divisions of the autonomic nervous system. In most instances, when an organ receives dual innervation, the two systems work in opposition to one another. In some tissues and organs, the two innervations exert an opposing influence on the same effector cells (e.g., the sinoatrial node in the heart), while in other tissues opposing actions come about because different effector cells are activated (e.g., the circular and radial muscles in the iris). 

The action of administered acetylcholine on effector systems innervated by parasympathetic postganglionic neurons (smooth muscle cells, cardiac muscle cells, and exocrine gland cells) resembled the actions produced by the naturally occurring plant alkaloid muscarine. The actions of both acetylcholine and muscarine on the visceral effectors are similar to those produced by parasympathetic nerve stimulation. Furthermore, the effects of acetylcholine, muscarine, and parasympathetic nerve stimulation on visceral effectors are antagonized by atropine, another plant alkaloid. 

A. Liposomal amphotericin B was approved by the US. Food and Drug Administration to treat visceral leishmaniasis. Pentavalent antimony compounds, pentamidine, amphotericin B, and aminosi-dine (paromomycin) have all been demonstrated efficacious here. The liposomal amphotericin appears to be better taken up by the reticuloendothelial system, where the parasite resides, and partitions less in the kidney, where amphotericin B traditionally manifests its toxicity. In addition to being better tolerated by patients, it has proved to be very effective in India, where resistance to antimony drugs is widespread. This patient appears to have acquired his infection there, where many infected patients develop darkening of the skin, hence the name kala-azar, or black sickness. Albendazole, an anthelmintic, has no role here. Atovaquone, a naphthoquinone, is used to treat malaria, babesiosis, and pneumocystosis. Pyrimethamine-sulfadoxine is used to treat malaria and toxoplasmosis. Proguanil inhibits the dihydrofolate reductase of malaria parasites and is used in combination with atovaquone. 

Building the correlation table, 13 compounds were initially found to give a false negative result in FETAX. Five of these, which gave inconclusive results in FETAX, were reclassified after taking into account the presence of major, specific and rare malformations (e.g., of the heart and/or eyes). Interestingly, the positive mammalian result for these five compounds was based on a few visceral malformations (mainly of the cardiovascular system) in a single species (two in rats and three in rabbits). 

The nervous system is conventionally divided into the central nervous system (CNS the brain and spinal cord) and the peripheral nervous system (PNS neuronal tissues outside the CNS). The motor (efferent) portion of the nervous system can be divided into two major subdivisions autonomic and somatic. The autonomic nervous system (ANS) is largely independent (autonomous) in that its activities are not under direct conscious control. It is concerned primarily with visceral functions such as cardiac output, blood flow to various organs, and digestion, which are necessary for life. The somatic subdivision is largely concerned with consciously controlled functions such as movement, respiration, and posture. Both systems have important afferent (sensory) inputs that provide information regarding the internal and external environments and modify motor output through reflex arcs of varying size and complexity. 

Large doses of glucocorticoids have been associated with the development of peptic ulcer, possibly by suppressing the local immune response against Helicobacter pylori. They also promote fat redistribution in the body, with increase of visceral, facial, nuchal, and supraclavicular fat, and they appear to antagonize the effect of vitamin D on calcium absorption. The glucocorticoids also have important effects on the hematopoietic system. In addition to their effects on leukocytes, they increase the number of platelets and red blood cells. 

MacLean Paul D. 1955. "The Limbic System ( Visceral Brain ) and Emotional Behavior." Archives of Neurology and Psychiatry 73 130-34. 

The PNS is further divided into functional sections known as the autonomic and somatic systems. The autonomic nervous system is also called the involuntary system. It regulates, without conscious effort, the visceral motor and sensory organs and muscles, as well as other smooth muscle and glands. The somatic is the voluntary nervous system which... 

The efferent portion of the peripheral nervous system can be further divided into two major functional subdivisions, the somatic and autonomic systems (see Figure 3.1). The somatic efferents are involved in voluntarily controlled functions such as contraction of the skeletal muscles in locomotion. The autonomic system functions involuntarily to regulate the everyday needs and requirements of the body without the conscious participation of the mind. It is composed primarily of visceral motor (efferent) neurons that innervate smooth muscle of the viscera, cardiac muscle, vasculature and the exocrine glands. 

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