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
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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
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
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:
Subdivisions of the hypothalamus
Divided into three zones
The periventricular and intermediate zones are often described together as medial zone
2- Intermediate zone
Lines the walls of 3rd ventricle, above the pituitary.
Divided into medial and lateral regions by the fornix.
1- Preoptic region:
Adjoins lamina terminalis which isalayer 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)
4- Mamillary region:
consists of mamillary body and area above it
Hypothalamus and nuclei within them
Supraoptic nucleusproduces vasopressin which increases water reabsorption by the kidney
Paraventricular nucleusproduces 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 thecapillary bed
concerned with the control of diurnal rhythm and sleep/awake cycle
Receives some afferent fibers directly from the retina
acts as satiety centre
Lesions cause polyphagia, polydipsia
Bilateral lesion of the medial part of the ventromedial nucleus causes hyperphagia and obesity .
Further lesion of the lateral part of the ventromedial nucleus in the same person produces complete cessation of food intake.
Part of the limbic system
Receive afferents from the hippocampusthrough fornix
Project to the:
Column of fornix
Superior & inferior colliculi
Hypothalamus also synthesizes releasing factors & release-inhibiting 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
Connections of the hypothalamus
-Hypothalamus is concerned with
-Connected to various parts of limbic
system, reticular formation, autonomic
centres in brainstem and spinal cord.
The hypothalamus recievesvisceral (including Taste) through spinal cord and brainstem.
Afferents from nucleus of tractussolitariusto hypothalamus carry taste sensation.
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.
In brainstem &
-Dorsal nucleus of vagus
Usually of cerebrovascular origin
Results in Hemiballism(sudden, forceful involuntary, violent or jerky, movements of the limbs) on the contralateral side
Plays an important role in normal functioning of basal ganglia