Autonomic Nervous System PDF

Introduction ○ The autonomic nervous system is comprised of the SNS, PNS, and ENS. ○ The autonomic nervous system is sometimes called the involuntary nervous system because it carries out its functions without requiring a conscious effort. It influences a wide array of physiological processes via it...

Introduction ○ The autonomic nervous system is comprised of the SNS, PNS, and ENS. ○ The autonomic nervous system is sometimes called the involuntary nervous system because it carries out its functions without requiring a conscious effort. It influences a wide array of physiological processes via its innervation of smooth muscle, cardiac muscle, and pacemaker cells, exocrine and endocrine glands, adipose tissue, liver cells, and lymphatic tissue. ○ In fact, skeletal muscle is the only innervated part of the body that is not under the control of the autonomic nervous system. The ultimate responsibility of the autonomic nervous system is to maintain homeostasis despite perturbations exerted by the external and internal environments. Although survival may be possible without the autonomic nervous system, the ability to adapt to environmental stressors and other challenges is severely compromised. The autonomic nervous system also plays a role in the body's response to an emotional experience. The importance of understanding the functions of the autonomic nervous system is underscored by the fact that so many prescription and over-the-counter drugs exert their actions on the elements of the autonomic nervous system or its effector targets. change is an autonomic activity contribute to many diseases (eg, hypertension, heart failure) ○ Also, many neurologic disorders are associated with autonomic dysfunction Sympathetic division of the ANS ○ In contrast to alpha motor neurons, Which are located at all spinal segments, sympathetic preganglionic neurons are located in the IML of only the first thoracic to the third or fourth lumbar segments. Thus, the sympathetic nervous system is called the thoracolumbar division of the autonomic nervous system. ○ But axons of the sympathetic preganglionic neurons leave the spinal cord at the level at which their cell bodies are located and exit via the ventral group along with axons of alpha and y motor neurons. They then separate from the ventral root via the white rami communicans and project to the adjacent sympathetic paravertebral ganglion, where some of them end on the cell bodies of the postganglionic neurons. ○ Paravertebral ganglia are located adjacent to each thoracic and upper lumbar spinal segment; in addition there are a few ganglia adjacent to the cervical and sacral spinal segments. ○ The ganglia are connected to each other via the axons of preganglionic neurons that travel rostrally and caudally, to terminate on postganglionic neurons located at some distance. ○ Together these ganglia and axons form the sympathetic chain bilaterally ○ note that, despite the fact that there are no cervical or sacral sympathetic preganglionic neurons, the sympathetic chain includes cervical ganglia that provide innervation to structures in the head (eg, eye and salivary glands) and sacral ganglia that provide innovation of pelvic organs Parasympathetic division of the ANS ○ The parasympathetic nervous system is called the craniosacral division of the autonomic nervous system because of the location of its preganglionic neurons within several cranial nerves nuclei (3,7,9, and 10), And IML of the sacral spinal cord ○ the cell bodies in the Edinger Westphal nucleus Of the oculomotor nerve project to the ciliary ganglia to innervate the sphincter constrictor muscle of the iris and the ciliary muscle ○ neurons in the superior salivatory nucleus of the facial nerve project to this sphenopalatine ganglion to innervate the lacrimal glands and nasal and Palatine mucous membranes and to the submandibular ganglia to innovate the submandibular and sublingual glands, The cell bodies in the inferior salivatory nucleus of the glossopharyngeal nerve project to the otic Ganglion to innervate the parotid salivary gland. Vagal preganglionic Fibers synapse in ganglia cells clustered within the walls of visceral organs; but, these parasympathetic postganglionic fibers are very short ○ neurons in the nucleus ambiguus innervate the sinoatrial and atrioventricular nodes in the heart; and neurons in the dorsal motor vagal nucleus innervate the esophagus, trachea, lungs, and gastrointestinal tract. ○ the parasympathetic sacral outflow pelvic nerve supplies the pelvic viscera via branches of the second to Fourth sacral spinal nerves Horner syndrome ○ Horner syndrome is a rare disorder resulting from interruption of preganglionic or postganglionic sympathetic innervation to the face. ○ The problem can result from injury to the nerves, injury to the carotid artery, a stroke or lesion in the brainstem, or a tumor in the lung. ○ In most cases the problem is unilateral, with symptoms occurring only on the side of the damage. ○ The hallmark of horner syndrome is the triad of anhidrosis (reduced sweating), ptosis (drooping eyelid), and miosis (constricted pupil). ○ Symptoms also include enophthalmos (sunken eyeball) and vasodilation Autonomic dysfunction ○ Drugs, neurodegenerative diseases, trauma, inflammatory processes, and neoplasia are a few examples of factors that can lead to dysfunction of the ANS. ○ The types of dysfunction can range from complete autonomic failure to autonomic hyperactivity ○ Among disorders associated with autonomic failure are orthostatic hypotension, neurogenic syncope (vasovagal response), erectile dysfunction, neurogenic bladder, GI dysmotility, sudomotor failure, and horner syndrome ○ Autonomic hyperactivity can be the basis for neurogenic hypertension, cardiac arrhythmias, neurogenic pulmonary edema, myocardial injury, hyperhidrosis, hyperthermia, and hypothermia