The diencephalon is the deep part of the forebrain located above the midbrain. It consists of four key parts: the thalamus, hypothalamus, epithalamus, and subthalamus. The thalamus acts as a relay station for all sensory systems except smell. The hypothalamus regulates functions like thirst, hunger, autonomic functions, and temperature. The epithalamus contains the pineal gland which regulates circadian rhythms. The subthalamus connects to motor control areas and the reticular activating system.

1. DIENCEPHALON
DR SANA YASEEN
ANATOMY DEPARTMENT
KIMS

2. • Is the deep part of the fore brain (procencephalon)
• Forms the central core of the brain. Located above
the midbrain, in lower parts of the two cerebral
hemispheres.
• EXTENSION:
Posteriorly – 3rd ventricle becomes continuous with
cerebral aqueduct
Anteriorly – till interventricular foramen

4. KEY PARTS:
It consists of four key parts:
• Thalamus
• Hypothalamus
• Epithalamus
• Subthalamus
• Except for these main four parts, some other segments and structures build up
the “interbrain” or, scientifically, diencephalon.
• Those include the pineal gland, the Stria medullaris thalami, the anterior
paraventricular nuclei, the posterior paraventricular nuclei, the posterior
commissure, the medial habenular nuclei, and the lateral habenular nuclei.

5. BOUNDARIES
SUPERIORLY: tela choroidea and fornix
INFERIORLY: anterior to posterior – optic chiasma with optic tract on either side ,
infundibulum with tubercenereum, mammillary bodies
ANTERIORLY: fornix, lamina terminalis, anterior commisure and interventricular
foramen
POSTERIORLY: habenular commisure, stalk of pineal gland, posterior commisure,
LATERALLY: internal capsule
MEDIALLY: thalamus and hypothalamus in between two hypothalamic sulcus

6. FORNIX
TELA CHOROIDEA
OPTIC
CHIASMA
INFUNDIBULUM
WITH
TUBERCENAREUM
MAMMILLARY
BODIES
CEREBRAL AQUEDUCT

7. FORNIX
ANTERIOR
COMMISSURE
LAMINA
TERMINALIS
HABENULAR COMMISSURE
PINEAL GLAND STALK
POSTERIOR
COMMISSURE

8. THALAMUS
• Is large ovoid mass of gray matter
• Is the largest comonent of the diencephalon
• Act as the relay station for all the sensory
systems except olfactory pathway.
• Anterior end is narrow and rounded and
forms the posterior boundary of the
interventricular foramen
• Posterior end is expanded to form pulvinar
which over hangs superior colliculus and
superior brachium

9. RELATIONS
• Superiorly: covered by tela choroida
and fornix medially, ependyma and
forms the floor of lateral ventrical
laterally
• Inferiorly: tegmentum of the mid
brain
• Laterally: choroid plexus of lateral
ventricle
• Medially: forms superior part of
lateral wall of srd ventricle , passes
interthalamic connection

10. HYPOTHALAMUS
• Is a sheath of gray matter with multiple nuclei covering the right
and left and the inferior surface of the third ventricle.
• Located below the hypothalamic sulcus on lateral wall of the 3rd
ventricle

11. Parts of hypothalamus visible from the ventral surface;
 infundibulum
Mamillary bodies
Tubercinereum
Median eminence : responsible for the production of neurosecretory
substances which control anterior pitituary
Posterior perforated substance

12. RELATIONS
• Antriorly: it extends up to optic chiasma to lamina terminalis and
anterior commissure. This area is also known as pre optic area.
• Caudally: merges into tegmentum of midbrain
• Superiorly: thalamus
• Inferolaterally : subthalamus
• Inferiorly: anterior to posterior
• Optic chaisma, optic tract, tubercenereum, infundebulum, mamillary
bodies`

14. FUNCTIONS:
• Thirst and water balance centre (superior optic and para
ventricular nuclei)
• Production of releasing factor for adenohypophysis
• precursors for ADH and oxytocin
• Hunger centre
• Autonomic regualtion centre
• Temperature regulation centre

15. EPITHALAMUS
• The epithalamus forms the roof of the
diencephalon and consists of the pineal
gland (an endocrine gland involved in
circadian rhythms and the onset of puberty)
and the pair of habenular nuclei inter
connected by habenular commissure.
• whose functions are associated with the
limbic system, as it connects to the septal
nuclei via a tract called the stria terminalis
thalami.
• Pineal gland secrets melatonin which sets the
day and night clock of the body. It becomes
calcified in the old age

17. SUB THALAMUS
• This is the caudal part of the thalamus and is located dorsolateral to the
hypothalamus (between thalamus and tegmentum of midbrain).
It contains:
• Subthalamus nucleus connecting with corpus striatum (control muscle activity)
• Cranial part of red nucleus
• Cranial part of substantia nigra
• It is the part of basal ganglia and the reticular activating system of brain

19. • In order to understand its anatomical position and
functions we describe its borders. First of all, it has a roof,
the lateral walls, as well as anterior and posterior walls.