The thalamus is a paired, symmetrical structure located in the center of the brain near the brainstem. Each half is roughly the size and shape of a walnut. The thalamus acts as the main relay center for sensory information in the brain, receiving input from various sensory systems and projecting it to the appropriate areas of the cerebral cortex. It also plays an important role in regulating states of consciousness and sleep/wake cycles. The hypothalamus is located anterior to the thalamus and helps control autonomic functions like cardiovascular regulation, thirst, hunger, and temperature control through its connections to the sympathetic and parasympathetic nervous systems. It also regulates endocrine functions through connections to the pituitary gland.

1. THALAMUS
Anatomy & Physiology
Dr SHAROJ KHAN

2. THALAMUS ANATOMY
 The thalamus is a paired and symmetrical structure in the
brain ,
 The thalamus is perched on top of the brainstem,
near the center of the brain, with nerve fibers projecting ou
t to the cerebral cortex in all directions.
It surrounds the third ventricle.

3. THALAMUSMORPHOLOGY:
 Both parts of this structure of the brain in the huma
n are each about the size and shape of a waln
ut.
 About three centimeters in length,
 At the widest part 2.5 centimeters across.
 About 2 centimeters in height.
 The two halves of the thalamus are prominent bul
bshaped masses.
 About 5.7 cm in length, located obliquely (about 30
°) and symmetrically on each side of the third ventri
cle

5.  Thalamus is most important sensory relay station.
 Ascending fibers synapse in thalamus and are then
projected to the cortical sensory areas.
 It also receives impulses from the ascending
Reticular formation which it relays to widespread
areas of cerebral cortex.
 The two thalami form the floor and lateral walls of
the third ventricle of brain.

6. NUCLEI OF THALAMUS
 Functionally the nuclei of thalamus are divided into
two main groups:-
 Extrinsic nuclei or relay nuclei
 1. postero ventral nucleus
 Postero lateral Ventral(PLV)
 Postero Medial Ventral (PMV)
 2. Ventro lateral nucleus (VLN)
 Anterior nuclear mass
 Medial Geniculate bodies
 Lateral Geniculate bodies

7.  Intrinsic Nuclei or diffuse projection nuclei
 1. Midline nuclei
 2. Intralaminar nuclei
 3. Dorsomedial nucleus
 4. Lateral dorsal nucleus (LD)
 5. Lateral post. Nucleus (LP)
 6. Pulvinar
 7. Reticular nuclei

9. FUNCTIONS
 1. Relay of sensory signals
 Thalamus is most important relay center that relays:
 Somatic sensations
 Special sensations
 Visceral sensations

10.  2. The thalamus also plays an important role in
regulatingstates of sleep and wakefulness.
 Thalamic nuclei havestrong reciprocal connections
with the cerebral cortex,forming thalamo-cortico-
thalamic circuits that are believed to be involved
with consciousness.
 The thalamus plays amajor role in regulating
arousal, the level of awareness,and activity.
 Damage to the thalamus can lead toPermanent
coma.

11.  3. It helps as centre for integration of motor
function.
 4. It helps as centre for emotional expression and
behavior
 5. Centre for Crude sensation:
 Thalamus determines the affective nature of the
sensations i.e. whether the sensation is pleasant or
unpleasant
 6. Thalamus helps in processing of sensory
information i.e. modification and integration of
sensory information (impulses) before projecting
them to specific areas of brain.

12. HYPOTHALAMUS

13.  It constitutes the anterior part of diencephalon and
lies anterior to the thalamus.

16. FUNCTIONS OF HYPOTHALAMUS
 1. controls the activities of Autonomic Nervous
system.
 Posterior and lateral nuclei of hypothalamus Control
sympathetic division by controlling the sympathetic
activity through hypothalamic afferents to the level of
sympathetic outflow.
 Control of parasympathetic division by anterior group of
nuclei

17.  2. Control of Visceral and Vegetative functions:
 Regulation of cardiovascular functions:
 Posterior and lateral hypothalamus cause increase in heart
rate and increase in B.P. ( sympathetic activity)
 Anterior hypothalamic and preoptic areas cause decrease in
heart rate and decrease in H.R and decrease in B.P.
(Parasympathetic effect)
 Regulation of body water:
 Thirst center:
 Is present on lateral hypothalamus. Osmoreceptors are
present in this center. These are very sensitive to changes
in osmolality of ECF

18.  Decrease in ECF Volume
 Increase in osmolality of ECF
 Stimulation of Osmoreceptors
 Activation of thirst center

19.  ADH mechanismIncrease in osmolality also stimulates the
supra optic nucleus and cause release of ADH.
 Increase in osmolality Release of ADH Retention of water due to increase
reabsorption by renal tubules.
 Decrease in osmolality Supression of ADH Increase of water loss due to decreased
reabsorption by renal tubule

20.  Regulation of food intake and Gastro-intestinal
functions:
 Food intake is regulated by 2 centers present in the
hypothalamus:
 Feeding centers- present in lateral hypothalamus.. Activation
leads to hunger and food intake. Normally remains active but
inhibited after food intake due to stimulation of satiety center.
 Satiety center- present in ventromedial nucleus of
hypothalamus. Gets stimulated after food intake. Main cause
is rise in glucose level which stimulates the glucoreceptors
present in this centre.

21.  Regulation of uterine contraction & Milk ejection.
 Hypothalamus releases oxytocin which is released in
large quantity at full term of pregnancy that causes
strong uterine contractions and parturition i.e. delivery of
baby.
 When the baby sucklesthe breast of the mother,
oxytocin causes contraction of myo-epithelial cells
around thereby causes ejection of milk.

22.  Regulation of body temperature:
 Overall hypothalamic temperature control mechanism is also called
hypothalamic thermostat.
Preoptic area (ant.)
Central thermoreceptors
Posterior
hypothalamus
Temp changes in
blood (increase in
temperature
Peripheral Thermoreceptors
(mainly cold)
Final Efferent Signals
Heat loss mechanism
-Sweating
-- Vasodilatation
Heat gain mechanism
-Shivering
-Vasoconstriction
-Epinephrine secretion

23.  Control of Endocrine function:
 Hypothalamus control most of the endocrine functions
through the anterior pituitary gland. The Anterior
pituitary receives venous blood which has first flown
througyh lower part of hypothalamus.
 It controls posterior pituitary gland through
hypothalamo-hypophyseal tract.

24.  Circadian rhytm
 Rhythmic secretion of ACTH
 Body Temperature rhythm
 Sleep wakefulness cycle
 Maintainence of Millieau Interior
 By maintaining the normal fluid volume, temperature,
pH, O2, CO2, etc of the ECF