Hypothalamus (2)

DR NILESH KATE

MBBS,MD ASSOCIATE PROF

DEPT. OF PHYSIOLOGY

HYPOTHALAMUS.

OBJECTIVES Physiological

Anatomy. Functions of

Hypothalamus. Applied Aspects.

Monday, May 1, 2023

HYPOTHALAMUS Latin word – Hypo- below; Thalamus – room or

chamber Very small part of brain weighing about 4 gms. Regulate all vegetative & endocrine process. Main organ of integration of homeostasis. Bilateral diencephalic structure, diffuse nuclear

mass below the thalamus.

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HYPOTHALAMUS The most ventral part of diencephalon which lies

below the thalamus 4 gram in weight (whole brain wt 1400gms) 0.3 to 0.5% of total brain Sherrington regarded as head ganglion of ANS Nauta describes as the nodal region in the

maintenance of Homeostasis.

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Physiological Anatomy. External features. Subdivisions & Nuclei

of Hypothalamus. Connections of

Hypothalamus.

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External features. Boundaries.

Superior. Inferior Medial Lateral Anterior Posterior.

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Subdivisions & Nuclei of Hypothalamus.

Zones Medial zone & lateral

zone. Regions

Preoptic Supraoptic Tuberal Mammilary.

Nuclei. Preoptic N. Suprachiasmatic,

supraoptic anterior, paraventricular.

Dorsomedial, lateral, tuberal, ventromedial and arcuate nucleus.

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4.

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5.

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5.

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Region wise descriptions of Nuclei

A. Preoptic Region: Lies anterior to hypothalamus along with lamina terminalis between optic chiasma & ant.commissure

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Supra optic

Region:1. Supra optic Nucleus: Medial,

lateral and periventricular part. It is Sexually dimorphic Nuclei.

2. Suprachiasmatic: Involves circadian rhythm

3. Anterior Nucleus: Thirst Center

4. Paraventricular

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C. Tuberal Region1. Arcuate or

infundibular nucleus: composed of small neurons. Controls emotional behaviors and endocrine function

2. Ventromedial: Satiety centre

3. Ventrolateral4. Lateral nucleus:

feeding centre

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Mammilary Region1. Mammilary bodies: i) Medial intercalated N.:

small neurons. Forms the bulk of mammilary bodies.

ii) Lateral intercalated N.: Receive termination of fornix and provide origin to mamilothalamic tract and mamilotegmental tract

1. Posterior hypothalamic nucleus

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Connections of Hypothalamus. Afferent connections. Efferent connections.

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Afferent connections.

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Efferent connections.

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Functions of Hypothalamus.(AS-RESPECT)

Autonomic functions. Sleep –wake cycle. Reward & punishment

centre. Endocrinal functions. Sexual behaviour &

reproduction. Ph(F)ood intake regulation.

Emotional & Instinctual behaviour.

Circadian Rhythm control.

Temperature regulation.

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Autonomic functions. Sherrington –

describes as Head Ganglion.

Ant – Parasympathetic

Post – Sympathetic.

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AUTONOMIC FUNCTIONS. Cardiovascular

regulation.- Post & lat N stimulation – tachycardia ,HT & Cutaneous vasoconstriction.

Preoptic area opposite.

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AUTONOMIC FUNCTIONS. Pupil size – post & Lat –

dilatation. And Preoptic & supraoptic opposite.

Peristaltic & Secretomotor functions of GIT – POST & LAT N decreases secretions & motility.

Ant & medial opposite.

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Sleep –wake cycle. Ant hypothalamus –

sleep fascilitatory Post hypothalamus –

waking centre. Sleep – negative

Phenomenon. Inhibition of waking centre in post hypothalamus by ant hypothalamus – leads to sleep.

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Food intake regulation. Feeding Centre.

Lat Hypothalamic N. Stimulations increases

food intake. Its destruction –

anorexia.

Satiety Centre. Feeling of fulfillment after

food intake. Ventromedial N of

Hypothalamus. Stimulation causes fulfillment

– stop food intake Destruction – Hyperphagia.

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PRINCIPAL HYPOTHALAMIC POLYPEPTIDE.

Food intake increased by Neuropeptide Y. Orexin – A Orexin –B Melanin concentrating

hormone. (MCH) Ghrelin.

Food intake decreased by Cocacine &

amphetamine regulated transcript. (CART)

CRH.

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Endocrinal functions. Anterior Pituitary.(through

Tubero-infundibular tract & hypophyseal portal system)

Controls Thyroid G. Controls Metabolism through

adrenal gland. Keep gonads inhibited. Control formation of milk by

prolactin secretion.

Posterior Pituitary regulate water balance through ADH.

Regulation Of Uterine Contractility & regulation of Milk Ejection from breast through oxytocin.

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HYPOTHALAMO-HYPOPHYSIAL TRACT The

hypothalamus is a neuroendocrine area which acts as a "transducer" to convert neuronal activity into hormonal secretions

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Controls anterior pitutary Several trophic factors or

hormones are released that influence the production of hormones in adenohypophysis.

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Neuro-secretory cells

1. Receive and process stimuli from

all parts of the CNS,

2. Conduct action potentials along their axons, and

3. Synthesize and release hormones into the circulatory system.

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Neuro-secretory cells4. produce peptide Prohormones

by mRNA on ribosomes in their nerve cell bodies, and then convert these Prohormones to

active hormones during the process of axoplasmic transport along axon filaments.

5. They store the hormones in vesicular granules at their axon terminals until depolarization of the plasma membrane causes Exocytosis.

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HORMONES RELEASED

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CONTROLS POSTERIOR PITUTARY It controls Neurohypophysis

through HYPOTHALAMO-HYPOPHYSEAL tract.

Approx. 100,000 Nonmyelinated fibers extend from the SON & PVN of the hypothalamus to the fenestrated capilary bed of the Neurohupophysis.

These fibers convey 2 peptide hormones; ADH & oxytocin

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Circadian Rhythm control. Common rhythmic

variations in Secretion of ACTH. Secretion of Growth

Hormone. Secretion of melatonin. Sleep wake cycle. Body-temp rhythm. Rhythmic Gonadotrophins

secretion.

Basis of circadian rhythm. Supra-chiasmatic N. main

site Biological clock

Receives inputs from Eye – retinohypothalamic

fibres. Lateral geniculate N.

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Circadian Rhythm control. Effect of

environmental factors on circadian rhythm.(HINTS) Light dark cycle Temperature. Meal timing.

Physiological significance. Enables homeostatic

mechanism to be used immediately & automatically.

Have effect on body’s resistance to drugs.

Disturbance of circadian rhythm. Speed jet travel – Jet lag.

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Temperature regulation. Heat loss centre.

Anterior Hypothalamus, Preoptic area.

Stimulation causes Cutaneous vasodilatation & sweating.

Lesion – abolishes response.

Heat gain centre. Posterior

hypothalamus. Stimulation –

Cutaneous vasoconstriction & shivering.

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SEXUAL BEHAVIOUR & REPRODUCTION.

Given by Brookhart & dey (1941)

Pathway-Amygdala – Stria terminalis - Preoptic area – Tuberal region.

Connection maintains basal secretion of GnRH.

Stimulation of Preoptic – cyclical surge – Ovulation.

Lesion – prevents Ovulation.

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Emotional & Instinctual behaviour.

Limbic cortex. Concerned with

affective nature of sensory impulses.

Whether pleasant or unpleasant.

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Reward & Punishment centre. Site Reward centre –

Lateral & Ventromedial N.

Punishment centre – Medial Hypothalamus.

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ROLE OF REWARD & PUNISHMENT CENTRE.

Controllers of our bodily activities, drives, aversions & motivation.

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RAGE Rage – violent & aggressive

emotional state by strong stimulation of Punishment Centre.

Kept in check by counterbalancing activity of Ventromedial N of hypothalamus, hippocampus, amygdala & ant portion of limbic cortex.

Characterized by – Development of

defense posture. Extension of limbs Lifting of tail. Hissing & splitting Piloerection. Wide openings of eye. Pupil dilation.

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SHAM RAGE. Outburst of rage on

mild peripheral stimulation.

Due to release of hypothalamus from cortical control.

Emotions are not associated with it.

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REGULATION OF WATER BALANCE.

Through thirst centre Through

osmoreceptors in supraoptic nucleus.

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Decreased Body water

Plasma Hypertonicity.

Thirst Center Osmoreceptors in supraoptic nucleus

Raised water injestion Post pituitary

ADH

Decreased urinary water

NORMAL RESTORATION OF BODY WATER.

APPLIED ASPECTS. Lesions of Hypothalamus. Disturbances in Hypothalamic lesions. Clinical conditions in hypothalamic lesions.

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LESIONS OF HYPOTHALAMUS. Tumour. Inflammation or

encephalitis. Ischemia. Damage due to

surgical operation

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DISTURBANCES IN HYPOTHALAMIC LESIONS.

Disturbance of all hypothalamic functions.

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CLINICAL CONDITIONS IN HYPOTHALAMIC LESIONS.

Diabetes Insipidus- supraoptic N damage. Deficiency of ADH Excessive thirst &

Polydipsia. Narcolepsy.

Sudden attack of unresistable desire of sleep during day time.

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Clinical conditions in hypothalamic lesions.

Cataplexy. Sudden emotional

outburst of anger, fear & excitement associated with narcolepsy.

Consciousness is not lost.

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