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The human internal environment is regulated in large measure by the integrated activity of the autonomic nervous system and endocrine glands Their visceral and homeostatic functions, essential to life and survival, are involuntary Why nature has divorced them from volition is an interesting question One would like to think that the mind, being preoccupied with discriminative, moral, and esthetic matters, should not have to be troubled with such mundane functions as breathing, regulation of heart rate, lactation, swallowing, and sleeping Claude Bernard expressed this idea in more sardonic terms when he wrote, nature thought it prudent to remove these important phenomena from the caprice of an ignorant will While relatively few neurologic diseases exert their effects primarily or exclusively on the autonomic-neuroendocrine axis, there are numerous medical diseases that implicate this system in some way hypertension, asthma, and certain dramatic disorders of cardiac conduction, such as ventricular tachycardia, to name some of the important ones And many more general neurologic diseases involve the autonomic nervous system to a varying extent, giving rise to symptoms such as syncope, sphincteric dysfunction, pupillary abnormalities, diaphoresis, and disorders of thermoregulation Also, a wide variety of commonly used pharmacologic agents in uence autonomic functions, making them the concern of every physician Finally, in addition to their central role in visceral innervation, autonomic parts of the neuraxis and parts of the endocrine system are utilized in all emotional experience and its display as discussed in Chap 25 Breathing is unique among autonomic nervous system functions While continuous throughout life, it is not altogether automatic being partly under volitional control Current views of the central and peripheral control of breathing, and the ways in which it is altered by certain diseases are of considerable interest to neurologists, if for no other reason than the frequency of respiratory failure resulting from numerous neurologic conditions such as coma, cervical spinal cord injury, and neuromuscular diseases the main ones being Guillain-Barre syndrome, myasthenia gravis, amyotrophic lateral sclerosis, and poliomyelitis Treatment of the resultant respiratory failure constitutes a most important part of the specialty of neurologic intensive care Many of these same comments pertain to the function of swallowing, which is largely automatic and continues at regular intervals even in sleep, but can also be initiated voluntarily Furthermore, swallowing fails in similar ways to breathing as a consequence of certain neurologic diseases The autonomic and endocrine systems, though closely related, give rise to disparate clinical syndromes, so that each is accorded a separate chapter This chapter deals with the autonomic nervous system and the next with the hypothalamus and neuroendocrine disorders The following discussion of anatomy and physiology serves as an introduction to both chapters 452.

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The most remarkable feature of the autonomic nervous system (also called the visceral, vegetative, or involuntary nervous system) is that a major part of it is located outside the cerebrospinal system, in proximity to the visceral structures that it innervates This position alone seems to symbolize its relative independence from the cerebrospinal system Also, in distinction to the somatic neuromuscular system, where a single motor neuron bridges the gap between the central nervous system (CNS) and the effector organ, in the autonomic nervous system there are always two efferent neurons serving this function one (preganglionic) arising from its nucleus in the brainstem or spinal cord and the other (postganglionic) arising from specialized nerve cells in peripheral ganglia This fundamental anatomic feature is illustrated in Fig 26-1 From a strictly anatomic point of view, the autonomic nervous system is divided into two parts: the craniosacral, or parasympathetic, and the thoracolumbar, or sympathetic (Figs 26-2, 26-3, and 26-4) Functionally, the two parts are complementary in maintaining a balance in the tonic activities of many visceral structures and organs This rigid separation into sympathetic and parasympathetic parts, while useful for purposes of exposition, is not altogether absolute physiologically For example, Blessing points out that the scheme does not provide a thorough explanation for each of the homeostatic functions that are under control of complex systems of central and peripheral neurons And from a neurologist s perspective, the two components are often affected together Nonetheless, the notion of a balanced autonomic system has stood the test of time and remains a valid neuroanatomic and neurophysiologic concept The Parasympathetic Nervous System (Fig 26-2) There are two divisions of the parasympathetic nervous system cranial and sacral The cranial division originates in the visceral nuclei of the midbrain, pons, and medulla These nuclei lie in close proximity to the somatic afferent nuclei and include the Edinger-Westphal pupillary nucleus, superior and inferior salivatory nuclei, dorsal motor nucleus of the vagus, and adjacent reticular nuclei Axons (preganglionic bers) of the visceral cranial nuclei course through the oculomotor, facial, glossopharyngeal, and vagus nerves The preganglionic bers from the Edinger-Westphal nucleus traverse the oculomotor nerve and synapse in the ciliary ganglion in the orbit; axons of the ciliary ganglion cells innervate the ciliary muscle and pupillary sphincter (see Fig 14-7) The preganglionic bers of the superior salivatory nucleus enter the facial nerve and, at a point near the geniculate ganglion, form the greater super cial petrosal nerve, through which they reach the sphenopalatine ganglion; postganglionic bers from the cells of this ganglion innervate the lacrimal gland (see also Fig 47-3) Other bers.

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Gray rami (post-ganglionic)

White rami (preganglionic)

Figure 26-1 Sympathetic out ow from the spinal cord and the course and distribution of sympathetic bers The preganglionic bers are in heavy lines; postganglionic bers are in thin lines (Reproduced by permission from Pick)