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HYPOTHALAMUS &HYPOTHALAMUS & THALAMUS THALAMUS

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ObjectivesObjectivesAt the end of this presentation, student should be able to:At the end of this presentation, student should be able to:

1)1) List the components of the DiencephaloneList the components of the Diencephalone2)2) Identify the nuclei of the HypothalamusIdentify the nuclei of the Hypothalamus3)3) Know the multifaceted functions of the Know the multifaceted functions of the

hypothalamushypothalamus4)4) Relate hypothalamic functions to hypothalamic Relate hypothalamic functions to hypothalamic

nucleinuclei5)5) Know the afferent and efferent pathways traversing Know the afferent and efferent pathways traversing

the hypothalamusthe hypothalamus6)6) Identify the nuclei of the ThalamusIdentify the nuclei of the Thalamus7)7) Know the function of the ThalamusKnow the function of the Thalamus

ReferencesReferences FitzGerald MJT, Gruener G. and Muti E. (2007) FitzGerald MJT, Gruener G. and Muti E. (2007)

Clinical Neuroanatomy and Neuroscience. 5Clinical Neuroanatomy and Neuroscience. 5thth edition, international edition. Saunders Elsevier. edition, international edition. Saunders Elsevier. Chapters 26 & 27 (pp. 289-301).Chapters 26 & 27 (pp. 289-301).

Guyton, (2006) Chapter 58, pp. 730-734.Guyton, (2006) Chapter 58, pp. 730-734.

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DiencephalonDiencephalon Sits on top of the brain stemSits on top of the brain stem Enclosed by the cerebral Enclosed by the cerebral

hemisphereshemispheres Made of four parts:Made of four parts:

ThalamusThalamus HypothalamusHypothalamus EpithalamusEpithalamus SubthalamusSubthalamus

4Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Location of the Hypothalamus and Location of the Hypothalamus and Thalamus in the BrainThalamus in the Brain

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HYPOTHALAMUSHYPOTHALAMUS

Hypothalamus (Hypo means below) is the most ventral part Hypothalamus (Hypo means below) is the most ventral part of the diencephalonof the diencephalon

Less than 1% Less than 1% of total brain volume of total brain volume The main function of the Hypothalamus is to maintain The main function of the Hypothalamus is to maintain

HOMEOSTASIS by acting on 3 major systems HOMEOSTASIS by acting on 3 major systems Considered an Considered an integrative centerintegrative center that protects survival that protects survival

functions and propagation of the speciesfunctions and propagation of the species Inferior to the thalamus.Inferior to the thalamus. Consists of Consists of mammillary bodymammillary body, , median eminencemedian eminence, , infundibuluminfundibulum, and , and

a number of a number of nucleinuclei..

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HYPOTHALAMUS HYPOTHALAMUS FUNCTIONSFUNCTIONS

Homeostasis is maintained by the hypothalamus Homeostasis is maintained by the hypothalamus via:via:

1.1. Endocrine Secretions:Endocrine Secretions: pituitary hormones pituitary hormones2.2. Autonomic Function:Autonomic Function: through direct through direct

projections to preganglionic autonomic projections to preganglionic autonomic neurons located in the brain stem and spinal neurons located in the brain stem and spinal cordcord

3.3. Control of Emotions and DrivesControl of Emotions and Drives: numerous : numerous interconnections with the interconnections with the limbic systemlimbic system which generates behaviors involved in rage, which generates behaviors involved in rage, aggression, escape, sexual driveaggression, escape, sexual drive……etc. etc.

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Hypothalamic NucleiHypothalamic Nuclei

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1) ENDOCRINE SECRETION1) ENDOCRINE SECRETION

1.1. The The Parvocellular (small cells) Parvocellular (small cells) neuroneuroendocrineendocrine system (true neurons & system (true neurons & endocrine cells from Preoptic N., VMN, and endocrine cells from Preoptic N., VMN, and Arcuate N.)Arcuate N.)

Tuberoinfundibular tractTuberoinfundibular tract CaCa+2+2-dependent exocytosis of Releasing & Inhibiting -dependent exocytosis of Releasing & Inhibiting

Hormones to Anterior PituitaryHormones to Anterior Pituitary((CRH; TRH; GHRH; GHIH; PRH; PIH; LHRHCRH; TRH; GHRH; GHIH; PRH; PIH; LHRH))

2.2. The The Magnocellular (large cells) Magnocellular (large cells) neuroneuroendocrineendocrine system (from Paraventricular N. system (from Paraventricular N. and Supraoptic N.)and Supraoptic N.)

Hypothalamichypophyseal TractHypothalamichypophyseal Tract ADH (vassopressin) (water resorption) ADH (vassopressin) (water resorption) Oxytocin (lactation, Parturition, male-female bonding via Oxytocin (lactation, Parturition, male-female bonding via

Amygdale) Amygdale)

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Hypothalamic Hypothalamic NeuroNeuroendocrineendocrine cells cells (?) (?)

2 different 2 different hypothalamic-hypothalamic-hypophysial hypophysial communication communication systems:systems: Tuberoinfundibular Tuberoinfundibular

tract to Hypothalamic-tract to Hypothalamic-hypophysial hypophysial portal portal systemsystem to the Anterior to the Anterior Pituitary Pituitary (Adenohypophysis)(Adenohypophysis)

Hypothalamic-Hypothalamic-hypophysial hypophysial tracttract to to the Posterior Pituitary the Posterior Pituitary (Neurohypophysis)(Neurohypophysis)

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2) Control of Autonomic 2) Control of Autonomic CentersCenters

Hypothalamus projects to:Hypothalamus projects to: Parasympathetic Vagal nuclei in the brain stemParasympathetic Vagal nuclei in the brain stem Preganglionic sympathetic neurons through the Preganglionic sympathetic neurons through the

spinal cordspinal cord

Stimulation of the Stimulation of the AnteriorAnterior (Rostoral) (Rostoral) HypothalamusHypothalamus produces produces parasympatheticparasympathetic effects: effects: Slowing the heartSlowing the heart Constriction of the pupilConstriction of the pupil Salivary secretionSalivary secretion Intestinal peristalsisIntestinal peristalsis

Stimulation of the Stimulation of the PosteriorPosterior (Caudal) (Caudal) HypothalamusHypothalamus produces produces sympatheticsympathetic effects: effects: Increase heart rateIncrease heart rate Increase BPIncrease BP Dilation of PupilDilation of Pupil Intestinal stasisIntestinal stasis

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3) Other Functions3) Other FunctionsI.I. TemperatureTemperature Control Control

Rostral Hypothalamus (Heat Loss CenterRostral Hypothalamus (Heat Loss Center): warm blood, ): warm blood, antipyretics or stimulation of heat receptors cause antipyretics or stimulation of heat receptors cause vasodilatation and sweating vasodilatation and sweating reducesreduces body Temp. body Temp.

CaudalCaudal Hypothalamus (Heat Conservation Center): Hypothalamus (Heat Conservation Center): cool blood, cool blood, pyrogenics or stimulation of cold receptors pyrogenics or stimulation of cold receptors increasesincreases body body Temp.Temp.

II.II. Food IntakeFood Intake (i.e. hunger) (i.e. hunger) ApstatApstat is the is the AppetiteAppetite set point set point Apstat is set by Apstat is set by LateralLateral N. + N. + VentromedialVentromedial N N FEEDING CENTERFEEDING CENTER (Lateral N.) (Lateral N.) SATIETY CENTERSATIETY CENTER (Ventromedial N.) (Ventromedial N.) Fat cells in the overfed state will release a protein called Fat cells in the overfed state will release a protein called

leptinleptin or ( or (OBOB), after the gene name), which passes through ), after the gene name), which passes through the BBB, binds to Leptin Receptor A and B in the the BBB, binds to Leptin Receptor A and B in the hypothalamus, hypothalamus, reduces appetitereduces appetite and and stimulates metabolism stimulates metabolism

Leptin regulates the hypothalamic-pituitary-thyroid axis Leptin regulates the hypothalamic-pituitary-thyroid axis and the thyroid hormones (TH) metabolismand the thyroid hormones (TH) metabolism

Increased Leptin receptor density has recently been reported Increased Leptin receptor density has recently been reported in the astrocytes of the dorsomedial hypothalamus and Arcuate in the astrocytes of the dorsomedial hypothalamus and Arcuate Nucleus, suggesting a role for the astrocytes in obesity.Nucleus, suggesting a role for the astrocytes in obesity.

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33 ) )Other FunctionsOther Functions

IV.IV. Water IntakeWater Intake (i.e. thirst) (i.e. thirst)(zona incerta neurons)(zona incerta neurons)

IV.IV. EmotionsEmotions (Rage and fear) (Rage and fear)V.V. Sleeping and WakingSleeping and Waking (superchiasmatic N. + (superchiasmatic N. +

Pineal gland)Pineal gland)VI.VI. Sexual ArousalSexual Arousal (INAH3 cells in the Preoptic (INAH3 cells in the Preoptic

N.)N.)VII.VII. MemoryMemory (Mammillothalmic tract to (Mammillothalmic tract to

Mammillary bodies of the limbic system )Mammillary bodies of the limbic system )VIII.VIII. Regulation of Plasma VolumeRegulation of Plasma Volume (i.e. via (i.e. via

Circumventricular feedback loop) see figureCircumventricular feedback loop) see figure Median eminence, neurhypophysis, lamina Median eminence, neurhypophysis, lamina

terminalsisterminalsis Subfornical organ, Pineal Gland, Area PostremaSubfornical organ, Pineal Gland, Area Postrema

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Overall, the hypothalamus controls theOverall, the hypothalamus controls the SET POINTSET POINT for:for:1.1. Blood pressureBlood pressure2.2. Body temperatureBody temperature3.3. Fluid and electrolyte balanceFluid and electrolyte balance4.4. Body weightBody weight

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Mapping the Functions of Mapping the Functions of Hypothalamus to its Individual Hypothalamus to its Individual

NucleiNucleiNoNo

.. AnteriorAnteriorMiddleMiddlePosteriorPosterior

11PreopticPreopticParaventriParaventricularcular

PosteriorPosterior

22SupraopticSupraopticDorsomediDorsomedialal

MammillaryMammillary

33SuperchiasSuperchiasmaticmatic

LateralLateralTuberomammiTuberomammillaryllary

44ParaventricParaventricular ular AnteriorAnterior

VentromedVentromedialial

DorsalDorsal

55ArcuateArcuate

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Localizing Hypothalamic Functions to Localizing Hypothalamic Functions to its Nucleiits Nuclei

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Hypothalamic Nuclei: Preoptic Hypothalamic Nuclei: Preoptic RegionRegion

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Hypothalamic Nuclei: Anterior Hypothalamic Nuclei: Anterior (Supraoptic) Region(Supraoptic) Region

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Hypothalamic Nuclei: Middle (Tuberal) Hypothalamic Nuclei: Middle (Tuberal) RegionRegion

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Hypothalamic Nuclei: Posterior (Mammillary) Hypothalamic Nuclei: Posterior (Mammillary) RegionRegion

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AfferentAfferent Projections to the Projections to the HypothalamusHypothalamus

Hypothalamic control of Homeostasis is maintained Hypothalamic control of Homeostasis is maintained through major afferents: (Vagus-RF-limbic-eye-through major afferents: (Vagus-RF-limbic-eye-blood) blood)

1.1. Nucleus Tractis SolitarisNucleus Tractis Solitaris (visceral sensory (visceral sensory from the Vagus)from the Vagus)

2.2. Reticular Formation (skin temperature is Reticular Formation (skin temperature is relayed to the hypothalamus)relayed to the hypothalamus)

3.3. Limbic SystemLimbic System: Amygdala, hippocampus, and : Amygdala, hippocampus, and olfactory cortico-hypothalamic projections via olfactory cortico-hypothalamic projections via the fornix regulate eating and reproductionthe fornix regulate eating and reproduction

4.4. RetinaRetina: optic nerve to the superchiasmtic N. : optic nerve to the superchiasmtic N. which regulates circadian rhythmswhich regulates circadian rhythms

5.5. BloodBlood (Hypothalamic Thermoreceptors, (Hypothalamic Thermoreceptors, Osmoreceptors; Glucose and Hormone levels Osmoreceptors; Glucose and Hormone levels sensors)sensors)

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EfferentEfferent Projections from the Projections from the HypothalamusHypothalamus

The two main outputs for the hypothalamus are:The two main outputs for the hypothalamus are:

1.1. Neural signals to the Autonomic Nervous System:Neural signals to the Autonomic Nervous System: Lateral hypothalamus projects to Autonomic Vagal Lateral hypothalamus projects to Autonomic Vagal

Parasympathetic centers in the lateral MedullaParasympathetic centers in the lateral Medulla Lateral hypothalamus projects to the preganglionic Lateral hypothalamus projects to the preganglionic

nuclei in the spinal cordnuclei in the spinal cord Controls heart rate, vasoconstriction, digestion, Controls heart rate, vasoconstriction, digestion,

sweatingsweating 2.2. Endocrine Signals to the pituitary:Endocrine Signals to the pituitary:

Stimulation of Anterior/Posterior Pituitary glandStimulation of Anterior/Posterior Pituitary glandTherefore, the Therefore, the hypothalamus maintains homeostasis by hypothalamus maintains homeostasis by

controling: controling: Every gland, Every gland, Blood pressureBlood pressure Body temperatureBody temperature Sexual driveSexual drive MetabolismMetabolism

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ThalamusThalamus Largest component of the Largest component of the

diencephalone diencephalone Large ovoid mass of gray Large ovoid mass of gray

matter.matter. THE THE RelayRelay Area of almost all Area of almost all

sensory neurons in the brainsensory neurons in the brain Lateral Geniculate (Latin Lateral Geniculate (Latin

for Knee-looking structure) for Knee-looking structure) (vision)(vision)

Medial Geniculate Medial Geniculate (hearing)(hearing)

““GatewayGateway to cerebral cortex to cerebral cortex”” Cell station to all main Cell station to all main sensorysensory system except the system except the olfactory pathway.olfactory pathway.

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Thalamic Nuclei & their Thalamic Nuclei & their RelaysRelays

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Thalamic Nuclei & their Thalamic Nuclei & their Relays in 3DRelays in 3D

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ThalamusThalamus 55 specific (relay) nuclei are specific (relay) nuclei are

reciprocally connected to reciprocally connected to motormotor or or sensorysensory areas of the cerebral cortex areas of the cerebral cortex

66 associationassociation nuclei are reciprocally nuclei are reciprocally connected to association areas of the connected to association areas of the cortexcortex

Non specific nuclei not connected with Non specific nuclei not connected with any specific motor or sensory nucleiany specific motor or sensory nuclei

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THALAMIC THALAMIC FUNCTIONSFUNCTIONS

1.1. Most Most sensory (Vision, hearing, taste, and sensory (Vision, hearing, taste, and touchtouch ))stimuli project to the thalamus, stimuli project to the thalamus, which in turn which in turn projects to the cerebrumprojects to the cerebrum..

2.2. Injury to the thalamus can cause Injury to the thalamus can cause deafness, blindness, or loss of any other deafness, blindness, or loss of any other sense, except smell.sense, except smell.

3.3. Thalamus also influences moods and Thalamus also influences moods and activities associated with strong emotion.activities associated with strong emotion.

4.4. The thalamus is believed to The thalamus is believed to PROCESSPROCESS and and RELAYRELAY information information

5.5. Regulation of Regulation of sleep and wakefulness. and wakefulness. 6.6. The physical site for The physical site for consciousness believed to exist through believed to exist through

strong Thalamic nuclei reciprocal connections with the cerebral strong Thalamic nuclei reciprocal connections with the cerebral cortex, forming cortex, forming thalamo-cortico-thalamic circuits