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27 Autonomic Nervous System

27 Autonomic Nervous System - PSL302 Lecture 27 by Prof...

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Unformatted text preview: PSL302: Lecture 27, by Prof. MacKay! Friday, Nov. 19, 2010 Autonomic Nervous System - Part of CNS controlling internal organs, endocrine fxn, blood flow, etc. - Maintains le milieu interieur - 2 efferent subsystems: 1) Sympathetic: stress-related, `fight or flight` -> "husband" = warrior 2) Parasympathetic: restorative, nutritive -> "wife" = housekeeper Autonomic Nervous System Sympathetic efferents - Pre-ganglionic efferents from intermediolateral horn of thoracic cord - Synapse in chain of ganglia parallel to cord - Post-ganglionic efferents project to target tissue - Transmitter is noradrenaline (NA) Muscle Sympathetic Effects - Exception: ACh is transmitter at skin sweat glands November 19, 2010 Muscle sympathetic effects - Major influence is noradrenergic vasoconstriction - Tonically active to maintain blood pressure (w/ every - Or else blood would pool in your muscles - Extremely important for regulation of BP - Part of baroreflex - Stimulus: Metabolite accumulation during muscle contraction causes vasodilation Diagram: Cross-section of thoracic spinal cord - Intermediolateral horn: bump at intermediate lvl (not in lumbar/cervical cord) - Where sympathetic efferents' cell bodies located - Axons exit sp.c. from ventral horns (likeNervous System Autonomic motor neurons) - Don't go synapse w/ muscles but to sympathetic ganglion outside of sp.c. - Post-ganglionic neuron go out to target organs Diagram: Sympathetic chain - Ganglia organize outputs (gather inputs -> send to target organs) - Network of intercxns btwn ganglia - Collected together based on fxnal relevance (for particular target organs) - Lots of commc amongst ganglia on both sides - Some outside backbone: in PNS - Some not part of sympathetic chain: - Closer to target organs: organize efferents for parts of gastrointestinal tracts - Topmost: superior cervical ganglion -> organize sympathetic efferents to head - I.e. smooth muscle contractions of iris, tear & salivary glands - Sympathetic signals to pineal body (controlling melatonin release) from here Major influence is noradrenergic vaso vasoconstriction; tonically active to maintain blood pressure extremely important for regulation of blood beat pressure; part of baroreflex of your heart!) Metabolite accumulation during muscle contraction causes vasodilation November 19, 2010 2 1 of 7 PSL302: Lecture 27, by Prof. MacKay! Friday, Nov. 19, 2010 Autonomic Nervous System No Parasympathetic efferents Originate in several cranial motor nuclei (III, VII, IX and X-vagus), and intermediolateral part of sacral cord project to ganglia embedded in target organ, e.g. S-A node of heart, enteric nervous system of gut Parasympathetic efferents - Originate in intermediolateral part of sacral cord (at bottom) ACh is transmitter; exception is NO (e.g. - No chain of ganglia: efferents go directly to target organ penile erection) - Projection from ganglia embedded in target organ - Other origins of parasympathetic system in brainstem - Several cranial motor nuclei (III, VII, IX + X-vagus): autonomic components - IIIrd: ocular mvt -> efferents: ciliary ganglia = regulate iris+lens thickness - VIIth & IXth: regulate tear & salivary glands - Xth cranial nucleus = vagus nerve: exclusively autonomic fxns - Originates in brainstem's medulla - Wanders throughout trunk: innervate all kinds of organs - Major parasympathetic nerve: promote relaxation - Diagram: target organs of vagus nerve - Parasympathetic target organs: - I.e. S-A node of heart (pacemaker: heart rate) - I.e. Enteric nervous system of gut (promote digestion) - At these terminations, ACh (asphocholine) is transmitter - Exception: NO -> vasodilator (e.g. gut, penile erection) 11-5 2 of 7 PSL302: Lecture 27, by Prof. MacKay! Friday, Nov. 19, 2010 Diagram: cross-sectionEnteric Nervous System of gut - Enteric nervous system: parasympathetic ganglion of gut (target of vagus nerve), - Networks of neurons embedded w/i gut wall System muscle layers -> two parts Autonomic Nervous btwn - Myenteric plexus: btwn circular muscles + longitudinal muscles - Submucosal plexus: under intestinal mucosa November 19, 2010 ENS Enteric Nervous System Nitric Oxide (NO) - Gaseous transmitter: produced on demand - Potent vasodilator (relaxation of smooth muscle in blood5vessels) - No vesicle: volatile gas diffuses right thru membranes - Produced by NO synthase upon activation by Ca++ influx (cf. exocytosis) - Result: binds to receptor guanylyl cyclase and activates it (metabotropic: [cGMP]) - Viagra acts not by increasing pdc of NO, but blocks enzymes breaking down cGMP - Trigger sticks around at higher lvls than normal -> vasodilation everywhere! Functional effects of ANS - Sympathetic: stress response -> `fight or flight' - Cardiac output = "heart pounds" - Breathing rapid & shallow = "panting" - Skin vasoconstriction (blood diverted: gut+skin -> muscle) = "white face" ENS - Sweating (but cold!) = "clammy palms" - Piloerection (make you look fiercer but doesn't work for humans) = "hair raised" - Parasympathetic: restorative, nutritive -> "housekeeping" - Cardiac output - Slow breathing - Digestion promoted - Promotes urination + defecation - The 2 systems are complementary rather than antagonistic - Operate under diff conditions, so don't fight each other - Parasympathetic active all the time, vs. sympathetic active momentarily - Reflexes can operate in ANS, for example... 5 3 of 7 PSL302: Lecture 27, by Prof. MacKay! Friday, Nov. 19, 2010 Pupillary Light Reflex: adjusts amt of light entering eyeball according to light conditions - Uses ON and OFF afferents to luminance and darkness detectors, respectively - Too bright -> parasympathetic reflex via IIIrd Pupillary Light Reflex cranial nerve - Ciliary ganglion -> activate circular iris muscles = pupils narrow rapidly - Too dark -> sympathetic reflex via thoracic cord (at bottom, then back up...) Parasympathetic: short - Sympathetic chain -> activate radial pathway; fast muscles = pupils dilate slowly - Reflex organized in pretectal nuclei of midbrain - In front of superior colliculus - Receive retinal input (ON/OFF responses) - Olivary pretectal n.: luminance detectors Sympathetic: long pathway via S h h i - -> IIIrd n. -> ciliary gang. i l thoracic cord; slow - -> circular muscles = pupils narrow rapidly - Posterior pretectal n.: darkness detectors - -> thoracic cord (down) -> sup. cerv. gang. (up) - -> radial muscles = pupils dilate slowly Sensory receptor w/i retina: rare - Not rods & cones but photosensitive retinal ganglion cells - Contain light-absorbing pigment melanopsin (similar absorbance spectrum to rhodopsin in rods -> peak in blue-green range & not sensitive to L wavelengths) - Same receptors also important for other autonomic fxns - Not for interpreting visual info = distinguish background illumination - I.e. synchronizing circadian rhythms w/ day/night cycle, pupillary light reflex Sensory Receptor Brainstem autonomic centers - Specialized in regulating specific organs - I.e. Cardiovascular center: oversee cardiovascular system - I.e. Respiratory pattern generator in lateral medulla/pons: "inhale-exhale" - Sympathetic modulatory tracts: adjust overall lvls of activity in entire NS - From Raphe nuclei (serotonin) + locus ceruleus (NA) - PAG (periaquectal gray): midbrain `premotor' center for autonomic behavioural programs - I.e. Fight, fear, feeding, vocalization, sex, etc. Retinal ganglion cells that contain a lightabsorbing pigment, melanopsin same receptors also important for other autonomic functions, such as synchronizing Reticular activating systems: core systems w/i brainstem circadian rhythms with day/night = essential! - Everything depends on support from these systems: if dysfxnal -> coma cycle - Modulatory: cause a global shift in CNS activity, mainly metabotropic mechs - Cholinergic, serotonergic, & adrenergic - Work together but have slightly diff fxns - Responsible for global shifts btwn various lvls of consciousness (i.e. sleep-wake) Melanopsin-containing ganglion cells 4 of 7 Autonomic Nervous System November 19 Autonomic Nervous System November 19 PSL302: Lecture 27, by Prof. MacKay! Friday, Nov. 19, 2010 - Cholinergic: - Determines lvl of attention, and sleep-wake cycle - Originate from medal septal n. + basal n. of Meynert, in pons+medulla, overlap into midbrain - Mainly ascending - Projects into cortex, basal ganglia, thalamus, rest of brainstem - Turns ON activity of NS in brain - Doesn't bother w/ cerebellum or spinal cord ! = no direct motor control - Serotonergic: - For stressful situations: influences mood, sleepwake cycle - Originate from Raphe nuclei at midline (throughout pons & medulla) - Project throughout NS + cerebellum + spinal cord - Serotonin depolarizes motor networks: background facilitation Autonomic Nervous System November 19, 201 - Noradrenergic: - For stressful situations, vigilance - Originates at locus ceruleus: specific jxn in midbrain + pons - Project down into spinal cord + cerebellum + NS - Responses to stressful situations: activate motor networks -> mvt starts - Background support for pattern generators w/i brainstem + spinal cord Autonomic Nervous System - Also dopaminergic system: localized activation Histamine activating system - Originates in posterior hypothalamus (diencephalon): tuberomamillary nucleus - "Master" activating system: regulates others - Transmitter: histamine Histamine Activating System - Projects thru-out forebrain + activating systems in brainstem - Important in sleep-wake control (supports waking state) Originates in the posterior hypothalamus: - Anti-histamines can make you drowsy: turn off tuberomamillary nucleus histamine system (maintain waking state) projects throughout forebrain and to other activating systems in brainstem important in sleep/wake control ( pp p p (supports waking state) November 19, 2010 5 of 7 Cardiovascular Center PSL302: Lecture 27, by Prof. MacKay! Autonomic Nervous System Friday, Nov. 19, 2010 November Cardiovascular center - Centrally located in ventrolateral medulla (VLM), beside respiratory center - Longitudinal column of neurons running anterior -> posterior - Divide into rostral + caudal halves - Rostral half excites sympathetic efferents -> raises BP + heart rate - Caudal half inhibits rostral half -> drops BP Cardiovascular Control Areas Autonomic Nervous System November 19, 2010 Baroreflex: baroreceptors -> n. Solitary tract -> VLM -> sympathetic output - Baroreceptors in cardiovascular system - Sensory nucleus = n. Solitary tract (also processes taste) - Entire cardiovascular system cuts swathe Cardiovascular across medulla Control Areas - From n. Solitary tract to ventrolateral cell column - Includes n. Ambiguus (part of vagus n.) - Vagus n. split in half: part is Xth nerve - Other in ventral location -> influence CV system (beside VLM) - Rostral half excite sympathetic efferents, vs. caudal half inhibit rostral half - If BP baroreceptors discharge - input into n. Solitary tract -> signals caudal half - sympathetic drive to heart = vasoconstriction Autonomic Nervous System - -ve feedback - If BP baroreceptors discharge (afferent input) - input into n. Solitary tract -> activate rostral half - sympathetic drive to heart = vasoconstriction - Respiratory CPG close to VLM - Beside + overlapping cardiovascular center! - Blood in CV system distributes O2 from respiratory system to body tissues - The two have to work together - If heart rate (HR) respiratory rate (RR) - Raphe nuclei at midline: reticulospinal neurons - Postural centers, CPG - Work closely w/ ANS (CV + R systems) - When generating posture+locomotion, must change HR & RR - So lots of commc w/i brainstem nuclei November 13 Periaqueductal Gray (PAG) Organized into longitudinal columns, columns according to behavioral pattern 6 of 7 e.g. fight (rage) column projects to cardiovascular center in medulla, and raph which releases serotonin in spinal cord PSL302: Lecture 27, by Prof. MacKay! Friday, Nov. 19, 2010 @ midbrain: Periaqueductal gray (PAG) - Grey matter around aqueduct of Sylvius (links IVth ventricle, under cerebellum + IIIrd ventricle, in midline btwn hypothalamus&thalamus on each side) - Organized into longitudinal columns: programs ANS behavioural patterns - Communicates w/ brainstem centers + modulatory tracts (activating systems) - Heavy interaction w/ hypothalamus: interface w/ endocrine system (hormone release)! Nervous System November 19, 2010 - Strategic location of PAG - E.g. "Fight/rage" column - Projects to CV center (in medulla) + Raphe nuclei (releases serotonin in spinal cord) ! = depolarizes all motoneurons + inhibits pain transmission in dorsal horn 7 of 7 ...
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