The hypothalamus is a very small, but

extremely important part of the diencephalon

that is involved in the mediation of :

endocrine,

autonomic and

behavioural functions.

General information

Part of diencephalon

Weighs about 4 grams

The whole brain weighs 1 400 grams

Occupies the bottom and infero-lateral walls of the 3rd

ventricle

The hypothalamus is the ventral-most part of the

diencephalon.

the hypothalamus is on either side of the third

ventricle,with the hypothalamic sulcus delineating its

dorsal border.

The ventral aspect of the hypothalamus is exposed

on the base of the brain.

It extends from the rostral limit of the optic chiasma

to the caudal limit of the mammillary bodies.

The Diencephalon

hypothalamus

thalamus Epithalamus

(Pineal &

Habenula)

The Diencephalon

subthalamus

pituitary

Mammillary

body

Optic chiasm

Anterior

commissure

Hypothalamus

Hypothalamic

sulcus

Lamina

terminalis

Optic

chiasma

Mamillary body

Hypothalamus

2. Anterior:

lamina terminalis

Position: lies ventral to thalamus

1. Superiorly: hypothalamic sulcus

Boundaries

3. Posterior:

continues

with

midbrain

tegmentum

4. Inferiorly: i. optic chiasma,ii. tuber cinereum,

infundibulum, and iii. mamillary body

i ii iii

2. Anterior:

lamina terminalis

2. Anterior:

lamina terminalis

2. Anterior:

lamina terminalis

2. Anterior:

lamina terminalis

2. Anterior:

lamina terminalis

2. Anterior:

lamina terminalis

2. Anterior:

lamina terminalis

2. Anterior:

lamina terminalis

2. Anterior:

lamina terminalis

A large number of nuclei and fiber tracts have

been described in the hypothalamus.

Some of these are ill-defined and have no

known function,

while others have been studied in detail both

anatomically and physiologically.

Organization

Composed of lateral and medial zones divided by fornix.

Nuclei of the lateral zone concerned with feeding (center of

hunger) and drinking (center of thirst).

Nuclei of the medial zone grouped in 3 regions:

1. Anterior,

2. Middle or tuberal and

3. Posterior or mamillary.

Three rostral to caudal regions are distinguished in the hypothalamus that correspond to

three prominent features on its ventral surface:

1) The supraoptic or anterior region at the level of the

optic chiasm,

2) the tuberal or middle region at the level of the tuber

cinereum (also known as the median eminence—the

bulge from which the infundibulum extends to the

hypophysis), and

3) the mammillary or posterior region at the level of the

mammillary bodies

Chiasma opticum

Infundibulum (median

eminence)

Tuber cinereum

Mamillary body

Optic tract

Hypothalamus

1

2

3

Ventral view

Divisions of the Hypothalamus

The hypothalamus can be divided into lateral, medial & periventricular zones :

3rd

VENTRICLE

Pre

op

tic

PO SO Tub Post

5 3 2

Medial Zone

Is divided in to :

1. ANTERIOR OR SUPRAOPTIC REGION

2. MIDDLE OR TUBERAL REGION

3. POSTERIOR OR MAMILLORY REGION

Damage to the anterior hypothalamus

blocks the production of ADH,

resulting in diabetes insipidus,

which is characterized by

rapid water loss from the kidneys.

Diabetes Insipidus

Section through the supra optic region

Preoptic Nucleus Control of parasympathetic function

Supraoptic Nucleus Synthesis and secretion of vasopressin. Damage

causes diabetes insipidus.

Suprachiasmatic

Nucleus

Fibers from the retina; fibers to the pineal body.

Controls circadian rhythms.

Anterior

Nucleus

Controls temperature and sexual behavior.

Paraventricular

Nucleus

Synthesis and secretion of oxytocin (milk

secretion & uterine contraction). Controls food

intake

Anterior ( Supraoptic ) Region

Dorsomedial Nucleus

- center of satiety

- on stimulation rage, cruelty

Ventromedial Nucleus

- center of satiety

- on stimulation depression of appetite

Arcuate Nucleus

- periventricular in tuber cinereum

- secretes releasing-factors

- dopaminergic neurons, inhibit release of prolactin

Middle or Tuberal

The lateral part, which is more loosely organized, is

termed the lateral hypothalamic area (LHA).

The medial forebrain bundle, which is described below,

courses through the LHA.

Mamillary Nucleus

- impulses from hippocampal formation via fornix

- impulses from tegmental nuclei, nuclei raphae via mamillary peduncle

- projections to anterior thalamic nucleus via mamillothalamic peduncle

Nucleus posterior

- controls thermoregulation (preserving temperature and producing heat)

- damage causes poikilothermia – inability of thermoregulation

Posterior or Mamillary Region

Crossed by Medial forebrain bundle

Contains two nuclei:

1. lateral preoptic Nucleus

2. lateral hypothalamic Nucleus

Clinical Correlate

- when stimulated feeling of hunger

- when destroyed anorexia nervosa and

fast

Lateral zone

MAJOR CONNECTIONS OF HYPOTHALAMUS

LIMBIC SYSTEM

1. MEDIAL FOREBRAIN BUNDLE

septal nuclei, olfactory regions HYPOTHALAMUS & brain stem

2. FORNIX

Hippocampal Complex Mammillary Bodies of Hypothalamus

3. STRIA TERMINALIS

Amygdala Hypothalamus

4. MAMMILLOTHALAMIC TRACT

Hypothalamus Thalamus (anterior nucleus)

AUTONOMIC CONNECTION

5. DORSAL (posterior) LONGITUDINAL FASCICULUS

Hypothalamus Brain Stem Reticular Formation

Hypothalamus Brain Stem Nucleus (e.g. vagus)

Intermediolateral Cell Column

ENDOCRINE CONNECTIONS

6. HYPOTHALAMOHYPOPHYSIAL TRACT

Hypothalamus Neurohypophysis

7. Tuberoinfundibular Tract

Tuberal Nuclei Sinusoids, Portal Veins Adenohypophysis

Arcuate nucleus

SO & PVN

Primary capillary bed

Sec capillary bed

Hypothalamus

Posterior pituitarySystemic venous outflow

Anterior pituitary

Hypothalamo-hypophysealportal system

Systemic arterial inflow

= Hypophysiotropic hormone = Anterior pituitary hormone

35

Pituitary-Hypothalamic Relationship

Functions of the Hypothalamus

Autonomic nervous system regulation

Hormone production

Endocrine regulation

Circadian rhythm regulation

Limbic system interaction

Various Temperature regulation

Feeding

Functions of the Hypothalamus

1. Autonomic nervous system regulation

Anterior area influences PSNS through projections to brainstem PSNS nuclei

Posterior area influences SNS through projections to the lateral gray horn

Functions of the Hypothalamus

2. Hormone production

Supraoptic and paraventricular nuclei produce oxytocin and vasopressin (ADH)

Transported via axonal transport systems (hypothalamohypophysial tract) to neurohypophysis

Released in circulation

Clinical Correlate

Damage to supraoptic n. diabetes insipidus

Functions of the Hypothalamus

3. Endocrine regulation

Stimulating or inhibiting hormones are transported via the tuberoinfundibular tract and released in to the pituitary portal system and ultimately to the adenohypophysis

Functions of the Hypothalamus

4. Circadian rhythm regulation

Input from retina to suprachiasmatic nucleus is then sent through poorly defined projections to the pineal gland

Functions of the Hypothalamus

5. Limbic system interaction

Preservation of species securing food,

defense mechanisms, sexual behavior

Emotions

Affective behavior

Memory

Motivation

Mammillary body

Functions of the Hypothalamus

6. Various

Temperature regulation

Feeding

Temperature

Posterior n. conserves heat

Anterior n. dissipates heat

Fever starts – sweating

Fever ends – chills

Feeding

Lateral n. induces eating

Ventromedial n. inhibits eating

Ant. Hypothalamus

Asexual

VM.Hypothalamus

Very Much Hungary Lateral Hypothalamus

Lack Hunger

3rd Ventricle

Neurotransmitters in the Hypothalamus The hypothalamus has been referred to as a “pharmacological museum” by virtue of the plethora of neurotransmitters that it contains.

Some of these neurotransmitters are found in the terminals of

axons that originate from neurons outside the hypothalamus, but

most are synthesized within the hypothalamus itself.

The list of putative neurotransmitters includes: the “classical” transmitters ACh, GABA, glutamate, serotonin, dopamine, and norepinephrine as well as literally dozens of

peptides that have been identified in recent years.

While the overwhelming number of transmitters may create

headaches for scientists and students, their presence offers

hope for pharmacological intervention in the large number of

different medical problems that are thought to involve the

hypothalamus.

Lesion of lateral hypothalamic

area leads to starvation Lesions of VMN leads

to morbid obesity

The hypothalamus is supplied with blood by

small branches of the Circle of Willis