Somatic systems

Anatomically, the nervous system is divided into the central nervous system (CNS) consisting of the brain and the spinal cord and the peripheral nervous system comprised of neural cells forming a network throughout the body. The peripheral system is itself subdivided into two sections the somatic system, where control of skeletal muscles allows movement and breathing, and the autonomic system which controls the actions of smooth muscle, cardiac muscle and glandular tissues. Further subdivision of the autonomic system based on anatomical and biochemical factors creates the sympathetic and parasympathetic nervous systems. 

The penis is mainly supplied by the internal pudendal artery, and three major sets of veins, superficial, intermediate, and deep veins, drain it. Drug-induced changes in neurotransmitter action can affect local blood flow. Vascular supply, intrinsic smooth muscles of the penis, and adjacent striated muscles are controlled by nerves arising from the thoracolumbar sympathetic, the lumbosacral parasympathetic, and the lumbosacral somatic systems. The pudendal nerve is the major somatic pathway innervating the male genitalia. 

Although the nervous system is often discussed in terms of peripheral and central components, it should be regarded as a highly integrated whole in which the central nervous system (brain and spinal cord) plays a critical information gathering and processing role. The peripheral nervous system is often divided into the autonomic and somatic components. The somatic system controls the voluntary functions of the body, like those of the skeletal muscles. The... 

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... 

Studies of neuromuscular junctions of the autonomic nervous system as early as 1904 led to the suggestion that adrenaline might be released at the nerve endings. Later it was shown that, while adrenaline does serve as a transmitter at neuromuscular junctions in amphibians, it is primarily a hormone in mammals. Nevertheless, it was through this proposal that the concept of chemical communication in synapses was formulated. By 1921, it was shown that acetylcholine is released at nerve endings of the parasympathetic system, and it later became clear the motor nerve endings of the somatic system also release acetylcholine. 

The preganglionic fibers terminating in the adrenal medulla, the autonomic ganglia (both parasympathetic and sympathetic), and the postganglionic fibers of the parasympathetic division use acetylcholine as a neurotransmitter (Figure 4.2). Cholinergic neurons innervate voluntary muscles of the somatic system and are also found in the CNS. 

Within the skeletal muscle. These neurons - the a-motoneurons - are not part of the autonomic but of the somatic system. 

Visceral manipulations use manual techniques (the physician s contact with the somatic system) to balance forces that create stresses on the visceral organs. 

Defecation starts with stimulation of the sensory nerve fibers of the rectum, leading to an involuntary spinal reflex that causes contraction of the rectum and the opening of the internal and external sphincters. The voluntary, somatic system completes the evacuation, after which the brain sends signals to the external sphincter to close and inhibit further elimination. Any damage to the CNS, such as a cerebrovascular accident, brain tumor, multiple sclerosis, or motor neuron diseases, can impair the bowel s volrmtary and involuntary responses. These CNS changes may result in inaccurate, involrmtaiy responses of the bowel, such as flaccidity of the rectum, expulsion of contents, or sphincter and rectal hyperactivity (3). 

Toxic trauma can be defined broadly as the dismption of somatic systems and their function by exposure to a toxic chemical. Ingested poisoning in its conventional form is only one example of toxic trauma. As we shall see in later chapters, toxic exposure can also arise from inhalation of gases or exposure of the skin to liquids or solids. Like physical trauma, toxic trauma can produce early or late effects with potential fatality at aU stages. 

The wide range of CW agents and toxic industrial chemicals produces patterns of toxic trauma which can be analysed according to actions on somatic systems. In the case of agents which act upon the central and peripheral nervous systems, there is a good understanding of the pathophysiological mechanisms which has led to a... 

While medical countermeasures are effective against the neurotoxins, they are not so against DNA toxins where multiple somatic systems are involved and there is general organ failure. 

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