These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute. !Announcements*!!!"Readings:!Ch.21!Outline*of*Today’s*Lecture**I. Visceral!Motor!System*Today’s*Lecture*Visceral*Motor*System*Slide*1*!**Somatic vs Visceral Nervous Systems!Somatic (voluntary) !• motor neurons are in the CNS !• motor neurons have very precise connections with their targets!Visceral or autonomic (involuntary)!• motor (or effector) neurons are in the PNS!• effector neurons have diffuse connections!Two main subdivisions that work in opposition to each other!! Sympathetic!! Parasympathetic!! (These are integrated with a 3rd subdivision, the enteric nervous system, that we'll get to later on)!!BISC*421*Hirsch,*Judith*2012*Fall*Week*6*Lecture*19*October*12*! !Slide*3*!• Don't!need!to!memorize!every!ganglion!and!its!target!*********!"#$%&&'()*+&,-&'.()*+&& /0-01"#$%&231+&045&6()31+&Ganglia (clumps of cells, in this case nerve cells. These lie outside of the PNS) Preganglionic Lies within the CNS Output goes to the ganglia Postganglionic Lies in the PNS Output from ganglia that goes to effectors (muscles, glands, organs etc.) Transmitters Preganglionic connections, cholinergic, via nicotinic receptors (iontropic) Postganglionic Sympathetic, noradrenergic Parasympathetic, cholinergic via muscarinic receptors –metabotropic, mediated by G proteins No, I do not expect you to memorize every single ganglion and its target. Terminology etc. Subdivisions of the PNS! !Slide*4*!• Sympathetic!nervous!system"!Incre a s e s!h e a r t!ra t e ,!makes!p u pils!dilate ,!in h ib it s!d ig e s tio n ,!inhibits!n a sa l!se c ret io ns ,!in h ibit s!p ro d u c tio n !o f!sa liva!• Parasympathetic!NS"!slows!hea r t!ra t e !makes!p u pils!cont ra c t,!s timulate s!d ig e st io n ,!c a u se s !n a sal!secretions,!stimulates!the!bladder,!liver!and!kidneys!*******Sympathetic 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 stellate ganglia). Remaining 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. (No, you do not have to memorize the names of individual ganglia) ! Sympathetic!*para = next to! !Slide*5*!***********Preganglionic 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 onto many 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.!Sympathetic!! !Slide*6*!• Don't!need!to!memorize!Slide*7*!**Fig. 1. The anatomical dissection of the rami communicantes of the thoracic sympathetic ganglia. BP, brachial plexus; SG, stellate ganglion; T2, the second sympathetic ganglion; 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). Purely for illustration – do not memorize the legends, please. 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 they innervate (unlike the sympathetic ganglia) Parasympathetic!! !Slide*8*!**********Preganglionic cells in the brainstem project along the cranial nerves Edinger-Westphal nucleus: pupil size and lens accommodation Salivitory nucleus: drooling etc. Dorsal motor nucleus of vagus: slows heart rate, reduces lung volume and promotes digestion. 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 neurons Sacral Cord: controls bladder, gut and genitals. Parasympathetic !You do not need to memorize the names of all brainstem nuclei! !Slide*9*!***********Enteric Motor System Input from parasympathetic is via the vagus nerve (and intermediate 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 cord! !Slide*10*!• Will!not!be!asked!to!name!specific!brain!loci"!brainstem!will!do !Slide*11*via input to dorsal root ganglia relayed through neurons in the spinal cord Periphery: A) To provide feedback to ensure that all organs are working properly and on the same team. 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 fibers in the visceral motor system than 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.)