BISC 421 1st Edition Lecture 17 Outline of Current LectureI. Visceral Motor SystemCurrent LectureVisceral Motor SystemSomatic vs Visceral Nervous SystemsSomatic (voluntary)• motor neurons are in the CNS • motor neurons have very precise connections with their targetsVisceral or autonomic (involuntary)• motor (or effector) neurons are in the PNS• effector neurons have diffuse connectionsTwo main subdivisions that work in opposition to each other:SympatheticParasympathetic(These are integrated with a 3rd subdivision, the enteric nervous system, that we'll get to later on)Subdivisions of the PNSTerminology etc.Ganglia (clumps of cells, in this case nerve cells. These lie outside of the PNSPreganglionic Lies within the CNS Output goes to the gangliaPostganglionic Lies in the PNS Output from ganglia that goes to effectors (muscles, glands, organs etc.)Parasympathetic, cholinergic via muscarinic receptors –metabotropic, mediated by G proteinsSympatheticSympathetic system:Preganglionic cells live in the lateral horn in the thoracic and lumbar levels of the spinal cord.Most sympathetic ganglia lie in the*paravertebral, sympathetic trunk (or chain). Some of these ganglia have special names, like the superior cervical and stellateRemaining sympathetic ganglia (the prevertebral ganglia) are tucked elsewhere-- between the cord and effector organs. These ganglia are the celiac and the superior and inferior mesenteric.•Sympathetic nervous system-‐ Increases heart rate, makes pupils dilate, inhibits digestion, inhibits nasal secretions, inhibits production of saliva•Parasympathetic NS-‐ slows heart rate makes pupils contract, stimulates digestion, causes nasal secretions, stimulates the bladder, liver and kidneysSympatheticPreganglionic neurons live in the lateral horn of the spinal cord and exit through the ventral root. They are tonically active. Their axons are myelinated, run through the spinal nerve and reach the sympathetic chain ganglia via the white communicating rami. Some axon collaterals travel outside of the home ganglion to link to neighboring ganglia and others exit through the spinal nerves to reach the prevertebral ganglia.1 preganglionic sympathetic axon will synapse ontomany postganganglionic sympathetic neurons.Postganglionic neurons (in either the symapthetic (paravertebral) chain ganglia or prevertebral ganglia have unmyelinated axons.Postganglionic cells in the sympathetic chain ganglia send axons via the gray communicating rami or through other branches to reach the effectors.Fig. 1. The anatomical dissection of the rami communicantes of the thoracicsympathetic ganglia. BP, brachial plexus; SG, stellate ganglion; T2, the second sympatheticganglion; T3, the third sympathetic ganglion; T4, the fourth sympathetic ganglion; N1,the first intercostal nerve; N2, the second intercostal nerve; N3, the third intercostal nerve;N4, the fourth intercostal nerve. Arrowheads indicate the rami communicantes.Fig 2. For the sympathetic system, synaptic contact between pre- and post- ganglionic neurons frequently takes place within the para-vertebral ganglia located in pairs on either side of the spinal cord segments, forming neural chains that run up and down both sides of the spinal cord (sympathetic trunks, or sympathetic chains).Parasympathic system: preganglionic components lie in the brainstem and sacral vertebrae (S1-5)Note that the postganglionic nuclei are located near, or even within, the organs theyinnervate (unlike the sympathetic gangliaParasympatheticPreganglionic cells in the brainstem project along the cranial nervesEdinger-Westphal nucleus: pupil size and lens accommodationSalivitory nucleus: drooling etc. Dorsal motor nucleus of vagus: slows heart rate, reduces lung volume and promotesdigestion.Preganglionic cells in the sacral cord project from the lateral horn via the ventral root, and splanchnic nerve to the postganglionic cells etc.1 preganglionic parasympathetic axons will synapse onto few postganganglionic neuronsSacral Cord: controls bladder, gut and genitals.Input from parasympathetic is via the vagus nerve (andintermediate gray zone in the sacral cord-not illustrated) directly to neurons in the wall of the gut (in essence, these are the postganglionic cells).Input from the sympathetic system comes in via the prevertebral ganglia.The neuronal plexes in the gut:A) Myenteric (Auerbach’s) plexus–controls smooth muscle.B) Submucosal (Meissner’s)plexus-controls secretions etc.Together, these plexes house as many neurons as the spinal cordSignals that modulate the visceral system come from Periphery and the BrainPeriphery:A) To provide feedback to ensure that all organs are working properly and on the sameteam.B) To let the brain know what’s going on below.These sensory signals are relayed through the dorsal root ganglia and nuclei associated with the glossopharyngeal and vagus nerves. (Note that there are many fewer such sensory fibersin the visceral motor systemthan in sensory systems)Pressure (e.g. baroreceptors in heart, bladder, gut) Chemical milieu (e.g. chemosensory cells sensitive to partial pressure of oxygen, carbon dioxide in the carotid bodies etc.)PainResponses are mediated byA) Reflex loops in the spinal cord or analogous loci such as B) Nuclei in the brain (nucleus of the solitary tract, medullary reticular formation etc."The night before Easter Sunday of that year [1920] I awoke, turned on the light, and jotted down a few notes on a tiny slip of thin paper. Then I fell asleep again. Itoccurred to me at six o'clock in the morning that during the night I had written down something most important, but I was unable to decipher the scrawl." He would pause at thispoint and tell me how he had tried all day, unsuccessfully, to remember his dream and to interpret the scribbled note. He said that he went to bed early Sunday night and read for a while before turning out the light. Then, Onkel Otto continued, in an animated tone, he woke up at two or three in the morning, most unusual for him, and, yes, he knew what his dreamhad been about the previous night. He got up immediately and went to the laboratory.“The hearts of two frogs were isolated, the first with its nerves, the