Download Hypothalamus

Diencephalon
Hypothalamus
Objectives
1.Describe the structure of hypothalamus,
epithalamus , and subthalamus
2.List the nuclei of the hypothalamus
3.List the afferent connections of the
hypothalamus
4.List the efferent connections of the
hypothalamus
5.List the functions of hypothalamus
Hypothalamus
The hypothalamus lies in the
anterior portion of
the diencephalon, below the
thalamus and
above the pituitary gland.
It forms part of the
wall and floor of the third
ventricle.
The hypothalamus consists of
only 4 cm3 of neural tissue, or
0.3% of the total brain
Hypothalamus
.
Its functional
significance is
disproportionate to its
size.
It has been considered
as the head nucleus of
the ANS as it is the
principle autonomic
center in the brain.
• Most of the hypothalamus
is hidden except the inferior
surface, that can be seen on
the inferior surface of the
brain, cranial to the cerebral
peduncles
• Parts of hypothalamus seen
on the base of the brain
include:
– Preoptic area
– Infundibulum
– Tuber cinerium
– Mammillary bodies
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Subdivisions of the hypothalamus
Divided into three zones
Periventricular zone
Intermediate zone
Lateral zone
The periventricular and intermediate zones are often
described together as medial zone
Subdivisions of the hypothalamus
• From medial to lateral:
1-Periventricular zone
2- Intermediate zone
2-Lateral zone
Lines the walls of 3rd
ventricle, above the pituitary.
Divided into medial and
lateral regions by the fornix.
• The anterior column
of the fornix passes
vertically through the
substance of
hypothalamus (to
terminate in the
mamillary body) and
divides it into medial
and lateral zones
Subdivisions of the hypothalamus
• Anterior to posterior:
1- Preoptic region:
Adjoins lamina terminalis which is a
layer of gray matter in the brain
connecting the optic chiasma and the
anterior commissure
2- Suraoptic region:
Lies above optic chiasma
3-Tuberal region: (infundibulotuberal)
• -includes infundibulum
• tubercinereum
4- Mamillary region:
consists of mamillary body and area
above it
Hypothalamus and nuclei within them
Medial Zone
(Periventricular and
intermediate)
Preoptic region
Supraoptic region
Tuberal region
Mamillary or posterior
region
Mamillary body
Lateral Zone
Preoptic nucleus
Paraventricular nucleus
Periventricular cell grps
Suprachiasmatic nucleus
Intermediate cell group
Suprachiasmatic
nucleus
Dorsimedial nucleus
Ventrimedial nucleus
Lateral tuberal
Arcuate/infundibular nu. nucleus
Premamillary nucleus
Posterior nucleus
Tuberomamillary
nucleus
Mamillary nuclei
Medial Nuclei
Lateral Nuclei
Lateral part
• Lies medial and ventral
to the subthalamus
• Traversed by many fibers
including medial
forebrain bundle
(connecting the
hypothalamus with the
midbrain tegmentum
and the limbic system)
• Controls food and water
intake (feeding centre)
• Lesions cause aphagia
and adipsia
Medial part
• Forms lateral wall of the
3rd ventricle
• Contains:
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Anterior nucleus
Supraoptic nucleus
Preoptic nucleus
Paraventricular nucleus
Dorsomedial nucleus
Ventromedial nucleus
Posterior nucleus
Mammillary nuclei
Infundibular nucleus
(Arcuate)
Terms
Definitions and functions
Hypothalamic Nuclei Anterior
parasympathetic
Anterior Nuclei
Supraoptic, Paraventricular, Anterior,
Preoptic, Suprachiasmatic
Supraoptic Nuclei function
unmylenated axons which transport ADH
down the supraopticohypophyseal tract to
the posterior pituitary
Paraventricular Nuclei Function
Unmylenated axons which transport
oxytocin down the supraopticohypophyseal
tract to the posterior pituitary
Anterior Nuclei Function
several complex parasympathetic functions
Preoptic Nuclei Function
Thermoregulator when hot
Suprachiasmatic Nuclei Function
Circadial rhythms such as temperature,
sleep, light, feeding
Hypothalamic Nuclei Intermediate
parasympathetics
Intermediate Nuclei
Dorsomedial, Ventromedial, Arcuate, Tuber
Cinereum
Dorsomedial Nuclei function
GI parasympathetic control center
Ventromedial Nuclei function
Center for thirst and hunger gratification
"satiety center"
Arcuate Nuclei Function
Tuber Cinereum Nuclei Function
Contribute axons to the tuberoinfundibular
tract, which carries releasing factors for
hormones. Secretes hormones into the
perivascular space of the infundibular stalk.
Hormones are then carried to the anterior
pituitary by blood stream.
Undulating bulge between the infundibular
stalk and mammilary bodies.
TUBEROINFUNDIBULAR TRACT was named
for this!
Hypothalamic Nuclei Posterior
sympathetics
Posterior Nuclei
Mammilary Bodies, Posterior
Mammilary Bodies Function
short-term memory, influences
SNS activity.
Posterior Nuclei function
Thermoregulator when cold
• Supraoptic nucleus produces
vasopressin which increases
water reabsorption by the
kidney
• Paraventricular nucleus
produces oxytocin
• The axons of cells in
supraoptic and paraventricular
nuclei pass to the
neurohypophysis in the
hypothalamo-hypophyseal
tract
• The hormones are transported
in this tract and released into
the capillary bed
• Suprachiasmatic nucleus:
• concerned with the
control of diurnal rhythm
and sleep/awake cycle
• Receives some afferent
fibers directly from the Bilateral lesion of the medial
retina
part of the ventromedial
• Ventromedial nucleus: nucleus causes hyperphagia
and obesity .
• acts as satiety centre
Further lesion of the lateral
• Lesions cause polyphagia,part of the ventromedial
nucleus in the same person
polydipsia
produces complete cessation
of food intake.
• Mammillary nuclei:
• Part of the limbic
system
• Receive afferents from
the hippocampus
through fornix
• Project to the:
Anterior nucleus of thalamus through mammillothalamic tract
Brainstem through the mamillotegmental tract
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Optic tract
Mamillary body
Column of fornix
Thalamus
Superior & inferior
colliculi
6. Caudate nucleus
7. Anterior commissure
8. Mamillothalamic tract
• Hypothalamus also synthesizes releasing factors & releaseinhibiting factors, that control the release of hormones by
the adenohypophysis
• These factors are released from the terminals of
hypothalamic neurones into the capillary bed of the
pituitary portal system, which conveys the release agents to
the anterior pituitary
Functions
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Co-ordination of homeostatic mechanism
Controls the release of hormones from the pituitary gland.
Center for regulation of autonomic activity --- controls medulla oblongata nuclei
for cardiovascular, respiration
 Activation of posterior region associated with sympathetic responses
 Activation of anterior region associated with parasympathetic responses
The mammillary nuclei are associated with the emotional behaviour and
memory
The suprachiasmatic nucleus is concerned with diurnal rhythm & sleep/waking
cycle
The lateral hypothalamus & the ventromedial nucleus regulate feeding and
drinking
Center for Feeding reflexes—licking, swallowing, etc.
Controls subconscious skeletal muscle movements—facial expressions, sexual
movements
Coordinates autonomic response to conscious input—thought of fear produces
accelerated heart rate, etc.
Connections of the hypothalamus
-Hypothalamus is
concerned with
visceral function
-Connected to various
parts of limbic
system, reticular
formation, autonomic
centres in brainstem and
spinal cord.
Afferent connections
The hypothalamus recieves visceral
(including Taste) through spinal
cord and brainstem.
Afferents from nucleus of tractus
solitarius to hypothalamus carry
taste sensation.
Neocortex
Thalamus
Hypothalamus
Somatic afferents reach through
collaterals of major ascending tracts
Afferents from olfactory pathway
and limbic system.
Anterior perforated substance,
septal nuclei Amygdaloid complex,
hippocampus, piriform cortex.
Limbic system
Visual input
Ascending
Somatosensory
pathway
Visceral centres
In brainstem &
Spinal cord.
Efferent connections
• The hypothalamus sends fibres to autonomic
centres in brain and spinal cord
• In brainstem:-Nucleus of solitary tract
-Dorsal nucleus of vagus
-Nucleus ambigus
-Parabrachial nucleus
Epithalamus
• Relatively small
part, located in
most caudal and
dorsal region
• Lies immediately
rostral to superior
colliculus
• Consists of:
 Pineal gland &
 Habenular nuclei
Pineal Gland
• An endocrine organ
• Synthesizes
melatonin
• Controls:
 Sleep/awake
cycle
 Regulation of
onset of puberty
Habenular nuclei
• Located in habenular
triangle (area in the
posterior part of the
diencephalon, just
anterior to pineal gland)
• Have connections with
limbic system
 Serves autonomic
function and emotional
drives
SUBTHALAMUS
• Region of
diencephalon
located below the
thalamus &
dorsolateral to
hypothalamus
• Continues caudally
with the midbrain
Th
Hypothalamus
Contents
• Rostral extension of:
– Red nucleus
– Substantia nigra
– Brainstem reticular formation as Zona incerta
• Long tracts passing through brain stem and heading
toward thalamus
– Spinothalamic & Trigeminothalamic tracts
– Medial lemniscus
– Dentatothalamic fibers
• Pallidothalamic fibers (fasciculus lenticularis, Ansa
lenticularis & thalamic fascicle)
• Subthalamic nucleus
Subthalamic Nucleus
• Resembles a
biconvex lens in
shape
• Located in the
ventrolateral part of
the subthalamus
• Lies against the
medial surface of the
internal capsule
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Connections
• Has reciprocal
connections with
ipsilateral:
 Globus pallidus
via subthalamic
fasciculus, which
passes through
the internal
capsule
 Substantia nigra
Lesions
Functions
• Plays an
important role in
normal
functioning of
basal ganglia
• Rare
• Usually of cerebrovascular
origin
• Results in Hemiballism
(sudden, forceful
involuntary, violent or
jerky, movements of the
limbs) on the contralateral
side
Zona Incerta
• Rostral extension
of the brainstem
reticular formation
• Enveloped by
pallidothalamic
fibers (lies
between the
lenticular fascicle
and the thalamic
fascicle)