The autonomic nervous system - RR Miselis, gross anatomy lec #4. This might not make sense right away - probably have to go over and over it to make it make sense. In general, the ANS helps to maintain homeostasis. Homeostasis is th physiological process of maintaining physological parameters w/in certain limits compatible w/life. Eg, core temperature, blood glucose, pO2, etc etc. Homeostasis is accomplished using 3 major effectors, including the ANS, the endocrine system, and behavior. (behavior - ectotherms, basking in sun or moving to shade, etc. Eating and drinking...) Our focus is the ANS. It's like studying a highway map. [slide- primitive chordate. tadpole looking thing, w/notochord instead of spinal column] So, there is a somatic nervous system, which goes to muscles and skin, and the "visceral" autonomic nervous system, which goes to the viscera. [slide- bizarre street names] Vertebrates are made of a series of body segments, developing from paired somites that can be viewed in the develping embryo. Each somite is fairly similar. Forelimbs and hindlimbs represent specialized somites developements. So, the body is metameric, and the body segments are innervated in a similar way, with individual spinal cord segements and associated spinal nerves innervating various body segments. A pair of spinal nerves emerges alongside each vertebra, and innervates the lateral and ventral structures. The segmental innervation is maintained even in the more specialized fore and hind limbs. DERMATOME = skin area innervated by all the sensory neurons of an individual dorsal root ganglion. You use this information when doing a neuro exam; pinpricks should elicit a particular response in a particular area.... not in handout, but know: in the peripheral NS, the autonomic NS innervates the viscera, and the somatic innervates the muscle and skin. When you get up to the brain, there are also visceral and somatic areas of the nervous system. Autonomic - takes at least 2 motor neurons to get from CNS to organ of innervation. (general visceral efferent flow) Preganglionic fiber = 1st motor neuron. Postganglionic fiber = 2nd motor neuron. Somatic NS -only takes one motor neuron to get to skeletal muscle from CNS. (general skeletal efferent flow) [slide- ANS of dog, mapped out] ANS takes origin at different areas of CNS, and utilizes different kinds of ganglia in the periphery. ANS has sympathetic, parasympathetic, and enteric divisions. Sympathetic and parasympathetic are separate...sympathetic is more widely divergent; "fight or flight"; catabolic responses; activates organs and tissues to support action. Parasympathetic generally more active during rest, more anabolic, builds up body reserves rather than uses them up. So, some organs have dual innervations w/psns and sns. The sympathetic NS is the only division of the ANS that innervates the muscles which make hair stand on end, the erector pili. There is no parasympathetic innervation of the erector pili. The vascular smooth muscles are important in maintenace of blood pressure by maintaining tone...sympathetic innervation is involved in the volume shifting of blood via changes in muscle tone of small vessels. No parasympathetic innervation of the smooth muscle of vascular beds. Sweat glands only get sympathetic innervation, too. The alimentary canal has parasympathetic "activating" innervation (promotes peristalsis, digestion) and sympathetic, which closes things, reduces secretions, reduces motility, etc. See p.4 of handout. p2 handout shows alpha motor neuron innervating skeletal muscle - refer to diagram. If you look at dorsolateral areas of abd and thorax, you can see the sympathetic trunk, which is th major location of peripheral ganglia, where pre and post ganglionic fibers meet. It's just lateral to vertebral column, buried in the muscle. SNS takes its origin from the thoracolumbar spinal cord - T1 to L4 or so. Most of the second motor neurons are in the sympathetic trunk, esp if nerve is going to innervate any of the skin or vascular smooth muscle, it will come from paravertebral ganglia. Also if going to heart/thorax. Abdominal and pelvic viscera 2nd motor neurons will be in prevertebral ganglia, not paravertebral ganglia. These are located near major arteries in the abdominal cavity. parasympathetic "craniosacral" division - 1st motor neurons (preganglionics) mostly located up in brain, some in sacral spinal cord segments. sacral preganglionics go to terminal ganglia, which have very short postganglionic fibers - ending in the wall of the organ being innervated, seen in GI/Pelvic viscera. All visceral organs of abd/thorax are innervated by vagus nerve and sympathetic trunk (seen in thorax dissection as one thing in carotid sheath.) Head ganglia are ganglia for parasympathetic for structures of head. don't fit rule of terminal ganglia, don't terminate on wall of organ it innervates. So, head ganglia are somewhat remote from the organ of innervation. -that covers sympathetic and parasympathetic. [slide- p3 handout-sympathetic NS usually considered to have shorter preganglionic fibers, and longer postganglionic fibers. Parasympathetic have longer preganglionic fibers, and short postganglionic fibers.] [slide- p6 of handout, fig 4- sympathetic shown in thoracolumbar cord, sympathetic trunk, spinal nerves used. splanchnic nerves are heading to celiac and caudal ganglia and plexi.] [slide p 8 of handout, fig 5. 3,7,9,10 spinal nerves used for preganglionic fibers. pelvic nerve carries innervation to pelvic viscera. vagus nerve is major parasympathetic nerve to lung, heart, stomach, pancreas, small intestine.] 4 cranial nerves carry autonomic fibers, will cover in a later lecture. if impulse is originating in spinal cord, and a lateral horn is seen then it must be sypathetic system. sympathetic fibers to the trunk and extremities follow the spinal nerves, whereas fibers to the visceral organs form separate nerves and follow the main vessels to the organ. ventral root - white connecting ramus - effector (sweat gland, erector pili) ventral root - paravertebral ganglion - named nerve Sensory signals are processed in the enteric NS, prevertebral ganglia, spinal ord, and brain stem. There are sensory neurons for the visceral/autonomic system Dealing w/autonomic innervation of gut, could have a sensory fiber coming from gut, cell body of which would bein dorsal root ganglion, fiber of which would travel same path as rest of fibers out to gut. enteric nervous system ENS - visceral fiber with origin in gut passing into brain or spinal cord, carrying sensory information into CNS. when you deal w/enteric NS, many sensory fibers exist in gut, but don't go back to CNS, but rather only carry messages to the terminal ganglia in the gut. There are many ganglia in the gut, with motor neurons between them. And the sensory fibers carry info to the postganglionic fibers of the terminal ganglia. So, the gut can operate disconnected from the brain. This was postulated back in the 1920s, but was only recently accepted. check out diagram p 12 "gut sensory receptors relay info to both ens and cns"