28 Hypothalamus & Limbic Centers

28 Hypothalamus & Limbic Centers - PSL302: Lecture...

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: PSL302: Lecture 28, by Prof. MacKay! Monday, Nov. 22, 2010 Hypothalamus & Limbic System: Controller & Programmer of Autonomic Fxns - Higher order homeostatic fxns of ANS, principally involving hypothalamus Micturition: urination; voiding the bladder - Partly under reflex control (involving parasympathetic system) + programmed control - At spinal cord: sacral reflex driven by bladder stretch receptors - Drives parasympathetic efferents (in intermediolateral section of sacral cord ! ! -> bladder muscles contract = urination - All there is in newborn infant/sp.c. Injuries = incontinence = no suppression - Control of reflex occurs at brainstem - At brainstem: Pontine centers organize reflex: oppose one another for control 1) Sequence of relaxation of external sphincter muscle + pelvic floor muscles - Time to pee: turn off (inhibit) Onuf's nucleus - Turn ON Barrington's nucleus (in Pons) = disinhibit & activate sacral reflex ! ! ! = promote urination 2) Continence: lateral Pons -> project into bladder motor nucleus - Also activate voluntary motor centers - I.e. Onuf's nucleus: innervates ext. sphincters -> closes urethra - Default: normally active -> tonically contracting ext. sphincters ! ! ! = suppress urination - At midbrain: PAG zone selects continence/micturition (autonomic programming area) - Controls which centers in pons are active - Relies on input from hypothalamus (medial preoptic n.), amygdala & limbic frontal lobe - Tells PAG when appropriate to urinate and when it's not mus & Limbic System November 22, 2010 Limbic System control: Pontine programing: micturition & continence centers Spinal R fl S i l Reflex: parasympathetic 1 of 7 PSL302: Lecture 28, by Prof. MacKay! Monday, Nov. 22, 2010 Homeostasis: definition - Maintenance of a stable, internal body envmt (`milieu interieur') - Product of many physiological control circuits (negative feedback loops) - Hypothalamus is major coordinator of homeostatic control - Hypothalamus is major regulator of core parameters - I.e. plasma glucose, osmolality;Systemtemperature Hypothalamus & Limbic body - Sensors w/i hypothalamus to detect changes in these parameters - Corrective mechs (programmed) initiated: autonomic endocrine + somatomotor Hypothalamus - Ideal location: interface w/ - Endocrine system (via pituitary) - Autonomic circuitry (in PAG) - Somatomotor systems (via reticular formation's postural centers) - Interacts w/ brainstem motor + autonomic centers (PAG) via axonal projections - Brainstem: modulatory centers - I.e. Raphe->serotonergic, locus ceruleus->noradrenergic = fxnally part of sympathetic system - Reticular formation: postural programming - Interacts w/ endocrine system via pituitary - On bottom -> hormone secretion Hypothalamus & Limbic System - Can coordinate complete physiological response to challenges to internal envmt Pituitary Body - Provides an interface btwn CNS and endocrine system - 2 modes of commc w/ hypothalamus: 1) Direct axonal projections: hormone release from terminals - Neuron produces ADH -> excitation = release at posterior pituitary provides an interface between CNS and - E.g. ADH, anti-diuretic hormone 2) `releasing hormone' intermediary: carried to endocrine system pituitary in portal system of - Secreted from median eminence (base 2 modes to communicate with hypothal.: hypothalamus) -> carried via portal system to anterior 1) axonal projections: release of hormone pituitary from terminals (e.g. ADH) ( g ) - E.g. CRH, corticotropin releasing hormone 2)`releasing hormone' intermediary; carried Ex 1. ADH neurons in supraoptic n. -> axonal projection to posterior hypothalamus -> release ADH into bloodstream to pituitary in portal system (e.g. CRH) Ex 2. Paraventricular neurons -> axonal projection to median eminance of hypothalamus -> release CRH into bloodstream via portal system -> carry signal to anterior pituitary -> release adrenocortocotropin hormone (ACTH) = affect adrenal glands Novembe No Pituitary Body Temperature regulation Thermoreceptors at base of hypothalamus 2 of 7 too cold skin vasoconstriction, piloerecki t i ti il e e tion, brown fat thermogenesis, decreased cardiac output, shift of fluid out of plasma, PSL302: Lecture 28, by Prof. MacKay! Monday, Nov. 22, 2010 Temperature regulation - Thermoreceptors at base of hypothalamus (although skin thermoreceptors project here: advance warning of temp, vs. core body temp) - Too cold: heat loss, generate heat in body - Skin vasoconstriction: heat loss from skin (sympathetic) - Piloerection: flow of air across skin = heat loss from skin (sympathetic) - Brown fat thermogenesis: generate heat thru fat breakdown - Hypothalamus -> Raphi nuclei -> serotonergic - cardiac output: circulation to skin (parasympathetic) - Shift of fluid out of plasma: overall blood volume - Shivering (somatomotor system: dorsal hypothalamus -> raphe) - Too hot - Skin vasodilation: heat loss (sympathetic) - Sweating: evaporation heat loss (sympathetic) - ACh transmitter (not NA) to turn on sweat glands - Hypothalamus & Limbic System If NA, leak over = vasoconstriction! - cardiac output - Shift of fluid into plasma from ECF - ADH release = water retention - Coordinated at preoptic hypothalamus Diagram: At hypothalamus... - Preoptic area - Cooling (ADH release) - Dorsal posterior hypothalamus warming - Heat generation in body - Dorsomedial nucleus - Brown fat thermogenesis - Posterior nucleus cooling - Shivering * Both act thru Raphe nuclei - Suprachiasmatic nucleus - Retinal input=circadian rhythms - Paraventricular nucleus - CRH release -> ACTH release - -> adrenal glands - Supraoptic nucleus - Regulate plasma osmolality (ADH release) - Arcuate nucleus - Regulation of feeding ([glucose]plasma) Regulation of Feeding - Arcuate nucleus control: 2 opposing systems of neurons - NPY, neuropeptide-Y = drives feeding -> HUNGER (via paraventricular n., PVN) - Melanocortin = suppress feeding -> SATIETY - Neurons in ventromedial & arcuate nucleus act as glucoreceptors in hypothalamus Arcuate [glucose] firing of - Discharge in relation to ambient glucose lvls: nucleus control: 1 setrateneurons (NPY) drives feeding via paraventricular n.; other - Inhibit NPY cells = inhibit drive to feed neurons (melanocortin) suppress feeding - Leptin, secreted by adipose tissue = long-term suppression of feeding Neurons - Inhibit NPY cells + promote melanocortin in ventromedial (& arcuate) nucleus act as glucoreceptors; discharge in relation to ambient glucose levels, inhibit drive to eat 3 of Leptin, secreted by adipose tissue, provides long- 7 term suppression of feeding November 22 Regulation of Feeding PSL302: Lecture 28, by Prof. MacKay! Hypothalamus & Limbic System Monday, Nov. 22, 2010 November 22, 2 Diagram: Schematic cross-sec of hypothalamus - Arcuate nucleus: arcs around IIIrd ventricle (in midline -> extends up to thalamus) - Two opposing systems: mutually inhibitory - NPY neurons = HUNGER - Project into PVN - Melanocortin neurons = SATIETY - Inhibitory cxns w/ NPY cells - SATIETY HUNGER - [Glucose] -> bind to glucoreceptors in VM+arcuate n. = inhibit NPY cells - Leptin + insulin -> arcuate n. = promote melanocortin cells - PPY (released from gut) -> arcuate n. = inhibit NPY cells (-ve feedback) - Other gut hormones (i.e. CCK, OEA, GLP-1) influence localized vagal Hypothalamus & Limbic System afferents November 22, 2010 - HUNGER SATIETY - Ghrelin (released by empty stomach) -> arcuate n. = activate NPY cells Hormonal and vagal feedback to control feeding Feedback from GI Tract Feedback from GI tract -Several hormones secreted by the gut feedback to hypothalamus and/or brainstem: Several hormones secreted by the gut feedback to -Ghrelin (empty stomach) = feeding hypothalamus and/or brainstem: -PYY (intestine) + insulin (pancreas) promotes feeding Ghrelin from empty stomach = feeding Hypothalamus & Limbic System -CCK, OEA, GLP-1 secreted by duodenum pancreas PYY from intestine and insulin from activate vagal afferents feeding inhibit -Via NTS =inhibit OEA, GLP-1 secreted by duodenum CCK, feeding CCK OEA GLP 1 t db d d activate vagal afferents; via NTS inhibit feeding Membrane tension sensitive ion channel November 22, 20 membrane is stressed by Plasma Osmolality swelling of cell - Osmoreceptors in supraoptic nucleus (osmoreceptor), the cation channel closes. - Secretory cell membrane has stretch-inactivated Plasma cation channels Osmolality - LOOSE -> channels OPEN Osmoreceptors in supraoptic nucleus; - STRETCHED -> channels pulled CLOSED secretory cell membrane has stretch- Regulates ADH release fro posterior pituitary inactivated cation channels - Setset pointis 295 mOsmol/l point is 295 mOsmol/l - cell shrinks cation channels ope >295:>295: Hypotonic, dehydration = [water] 95: ce s s c o c e s open - Cell shrinks: spikes increased ADH release membrane loose -> cation channels OPEN - Supraoptic n. firing <295: cell swells cation channels close -> ADH release = water retention few-spikes decreased ADH release <295: Hypertonic = [water] - Cell swells: membrane stretched -> cation channels CLOSE - Supraoptic n. firing -> ADH release ADH Model of stretch-inactivated membrane channel. When 8 Anti Diuretic Hormone, also known as Anti-Diuretic Hormone `vasopressin' 4 of 7 Hormone: increases water permeability of collecting ducts in kidney water retention Neurotransmitter in brainstem: facilitates Adrenal cortex PSL302: Lecture 28, by Prof. MacKay! Monday, Nov. activated in stressful situations by reticular 22, 2010 activating systems, etc. ADH - Anti-Diuretic Hormone: also known as vasopressin paraventricular n. CRH release into p ve cu . C e e se o - Hormone action: water permeability of collecting ducts in kidney = water retention - Neurotransmitter action in brainstem: facilitates learning + memory processes portal hypophysial vessels triggers ACTH release from anterior pituitary into HPA-Axis (endocrine parallel w/ sympathetic system) - Hypothalamus -> anterior Pituitary -> Adrenal cortex general circulation adrenal cortex - Hypothalamus: CRH release into portal hypophysical vessels - Ant. Pituitary: triggers ACTH release into general circulation - Adrenal cortex: triggers glucocorticoid release - Paraventricular n. activated in stressful situations by reticular activating systems,etc. - Net excitatory effect from amygdala (basal ganglion for limbic system) - Net inhibitory effect from hippocampus - Negative feedback: - [Glucocorticoids]plasma to certain lvl -> PVN = CRH release - Slow + fast feedback: - Fast: use endocannabinoids - Slow: block gene transcription of CRH + ACTH Glucocorticoid Regulation HPA-axis regulates release of adrenal glucocorticoids Negative feedback of cortisol: blocks action of CRH on pituitary, release of CRH, and transcription of ACTH gene 5 of 7 PSL302: Lecture 28, by Prof. MacKay! Endocannabinoids (eCB) Monday, Nov. 22, 2010 Endocannabinoids (eCB) - Neurotransmitter released from CRH neurons = suppress HPA axis - Mimics active ingredient in marijuana (relaxant) - Cortisol feedback triggers eCB release - Diffuses thru near vicinity: binds to receptors on excitatory boutons along CRH neurons from amygdala (releasing glutamate) - eCB pre-synaptically inhibits CRH neurons = excitatory input - Retrograde transmission across synapse: signal in opposite direction Cortisol feedback triggers eCB release from CRH neurons; eCB then prepre synaptically inhibits excitatory input to CRH neurons Hypothalamus & Limbic System J.Neurosci. 30(45): 14980-14986 (2010) November 22 - Hypothalamus (PAG) controlled from limbic parts of NS (up in cerebrum) - Amygdala is part of limbic center Amygdala - Part of basal ganglia controlling autonomic behaviours - Location: deep inside temporal lobe, at end of tail of caudate nucleus (of thalamus) - Input from limbic cortex + autonomic brainstem - Output generally inhibitory on PAG-hypothalamus - Recall: pallidum is exclusively inhibitory - Amygdala is not -> excites HPA axis! - Lesions can result in uncontrolled autonomic behaviours (e.g. `sham rage', hypersexuality) - Cats: complete rage response but no rage - Primates: hypersexuality - Responses to lesions are species-specific Amygdala Part of basal ganglia controlling autonomic behaviors input from `limbic' cortex, autonomic brainstem output generally inhibitory on PAGp g y y G hypothalamus Emotion-related memory lesions can result in uncontrolled autonomic - Memories related to emotional experiences, esp fearful behaviors strengthen cxns btwn ones, rely on amygdala for consolidation (potentiate synapses -> (e.g. `sham rage', hypersexuality) neurons = lay down memory) - Again, the amygdala is not the site of memory storage - That is distributed in association and limbic cortex: signal other parts of limbic system to store the memory = coordinate memory storage Emotion-related memory Memories related to emotional experiences, experiences Limbic cortex especially fearful ones, rely on the - Location: Border regions of cerebral cortex at edge of hemisphere amygdala for consolidation - Phylogenetically old part of cortex - Subserves emotional experience, motivation + memory consolidation is not the site of again, the amygdala - Principle parts around edges: memory storage; that is distributed in - Cingulate gyrus: medial edge btwn frontal + parietal lobesand limbic cortex association - Hippocampal region: lateral edge of temporal lobe - Insula: bottom of lateral fissure - Projects strongly to rest of limbic system -> hypothalamus, PAG, amygdala 6 of 7 PSL302: Lecture 28, by Prof. MacKay! Monday, Nov. 22, 2010 Diagram: Cross-sec of L cerebral hemisphere -Midline to right, edges of cerebral cortex to left -Medial edge of temporal lobe: hippocampus (curled up) -Adjacent parahippocampal gyrus -Medial edge of frontal + parietal lobes: cingulate gyrus -Bottom of lateral fissure: insula -In primitive cerebral cortex: zones would be continuous -Make up entire cortical sheet, i.e. nsula: sensory region -As neocortex developed, bulged out + pushed original portions apart > edge regions retained for cingulate System + hippocampus...ut insula gyrus Hypothalamus & Limbic isolated in middle + pushed down November 22, 2010 Diagram: Medial view of limbic cortex from midline (view of hemisphere) - Cingulate gyrus swings around in circle 13 - Meets up w/ parahippocampal gyrus - Hippocampus curlicue at bottom - Add in insula (on other side at bottom of lateral fissure) 14 7 of 7 ...
View Full Document

This note was uploaded on 03/27/2012 for the course PSL PSL300 taught by Professor Mackayfrench during the Fall '11 term at University of Toronto- Toronto.

Ask a homework question - tutors are online