Sphincters autonomic control

Neurobiological components of colorectal and anal sphincter mechanisms and pathophysiology are similar to the above-mentioned vesical components. In both systems, central, peripheral, and autonomic nervous system reflexes, partly involuntary and partly voluntary, interweave critically for appropriate function. Function and control are mediated through the lower spinal cord, as well as via cortical centers requiring coordinated voluntary (and reflex) relaxation of external sphincters, (reflex) relaxation of internal sphincters, and simultaneous coordinated contraction of detrusor... 

In the peripheral nervous system, norepinephrine is an important neurotransmitter in the sympathetic branch of the autonomic system. Sympathetic nerve transmission operates below the level of consciousness in controlling physiological function of many organs and tissues of the body. The sympathetic system plays a particularly important role in regulating cardiovascular function in response to postural, exertional, thermal, and mental stress. With sympathetic activation, the heart rate is increased, peripheral arterioles are constricted, skeletal arterioles are dilated, and the blood pressure is elevated. In addition, sympathetic nerve stimulation dilates pupils inhibits smooth muscles of the intestines, bronchi, and bladder and closes the sphincters. Sympathetic signals work in balance with the parasympathetic portion of the autonomic nervous system to maintain a stable internal environment. 

Certain chronic diseases of the CNS (eg, cerebral palsy, multiple sclerosis, stroke) are associated with abnormally high reflex activity in the neuronal pathways that control skeletal muscle the result is painful spasm. Bladder and anal sphincter control are also affected in most cases and may require autonomic drugs for management. In other circumstances, acute injury or inflammation of muscle leads to spasm and pain. Such temporaiy spasm can sometimes be reduced with appropriate drug therapy. 

Lower urinary-tract function is under the control of the somatic and autonomic nervous system. The latter is comprised of the sympathetic and parasympathetic nervous systems. Sympathetic nerves originate in the thoracolumbar region of the spinal cord at TIO to LI. Parasympathetic nerves arise from the sacral area of the spinal cord at the level of S2 to S4. Somatic nerves from the sacral cord course through the pelvic plexus and the pudendal nerve to the external sphincter region. 

A number of CWAs exert their effects by modulating neuronal control over ocular function (Table 38.2). Autonomic neurons provide input to the intrinsic ocular muscles (the sphincter pupillae, the dilator pupillae, and the ciliary muscle) and e lacrimal glands. Neuronal afferents in the eye include sensory neurons from the conjunctiva and cornea, reflexive contributions to the iris, ciliary muscle, and eyelids, and the densely innervated retina. Finally, the extraocular muscles and eyelids are controlled by cholinergic motor neuron inputs. 

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