neurologic disorders
Overview of the Autonomic Nervous System
Anatomy of the Autonomic Nervous System
The autonomic nervous system receives input from parts of the central nervous system (CNS) that process and integrate stimuli from the body and external environment. These parts include the hypothalamus, nucleus of the solitary tract, reticular formation, amygdala, hippocampus, and olfactory cortex. The sympathetic and parasympathetic systems each consist of 2 sets of nerve bodies: Preganglionic: This set is located in the CNS, with connections to another set in ganglia outside the CNS. Postganglionic: This set has efferent fibers that go from the ganglia to effector organs (see figure The autonomic nervous system ). The preganglionic cell bodies of the sympathetic system are located in the intermediolateral horn of the spinal cord between T1 and L2 or L3. The sympathetic ganglia are adjacent to the spine and consist of the vertebral (sympathetic chain) and prevertebral ganglia, including the superior cervical, celiac, superior mesenteric, inferior mesenteric, and aorticorenal ganglia. Long fibers run from these ganglia to effector organs, including the following: Smooth muscle of blood vessels, viscera, lungs, scalp (piloerector muscles), and pupils Heart Glands (sweat, salivary, and digestive) The preganglionic cell bodies of the parasympathetic system are located in the brain stem and sacral portion of the spinal cord. Preganglionic fibers exit the brain stem with the 3rd, 7th, 9th, and 10th (vagus) cranial nerves and exit the spinal cord at S2 and S3; the vagus nerve contains about 75% of all parasympathetic fibers. Parasympathetic ganglia (eg, ciliary, sphenopalatine, otic, pelvic, and vagal ganglia) are located within the effector organs, and postganglionic fibers are only 1 or 2 mm long. Thus, the parasympathetic system can produce specific, localized responses in effector organs, such as the following: Blood vessels of the head, neck, and thoracoabdominal viscera Lacrimal and salivary glands Smooth muscle of glands and viscera (eg, liver, spleen, colon, kidneys, bladder, genitals) Muscles of the pupil 