The diencephalon is the area surrounding the third ventricle of the brain. It contains several parts including the thalamus, hypothalamus, epithalamus, and subthalamus. The thalamus relays sensory information to the cortex and is involved in visual and auditory processing. The hypothalamus regulates autonomic functions and homeostasis through connections to the pituitary gland and autonomic nervous system. Lesions in the diencephalon can disrupt temperature regulation, appetite, water balance, and other homeostatic processes.

1. SABIHA M. HAQ
IIMC

2. Learning objectives
Describe the location and boundaries of
Diencephalon
Enumerate parts of Diencephalon and
describe each one briefly
Identify the location of these parts on
diagrams/models
Briefly describe the clinical effects of the
lesions of diencephalon

3. INTRODUCTION/LOCATION
It is the area which surrounds third
ventricle
It has two walls, a roof, ant wall and
floor
Posteriorly the roof and floor
converge. This is the point where third
ventricle meets the cerebral aqueduct

4. Anterior wall
Formed by lamina terminalis which is a thin layer
of grey matter
Its lower end meets the optic chiasma in an angle
called the optic recess
Behind its upper end is ant commissure (connects
the two temporal lobes, olfactory tracts and
amygdala)
Behind ant commissure are ant columns of fornix
Behind each ant column is interventricular
foramen connecting third and lat ventricles

5. Floor
It is actually the
floor of third
ventricle
It extends across
optic chiasma,
tuber cinerium,
infundibulum and
mamillary bodies to
posterior perforated
substance

6. Side walls
These are the
lateral walls of third
ventricle
Formed by
thalamus,
hypothalamic
groove or sulcus
and hypothalamus
itself

7. Roof
Roof is formed by
pia mater and
choroid plexus
of third ventricle

8. Parts of Diencephalon
Thalamus
Hypothalamus
Epithalamus
Subthalamus

9. Thalamus
Largest part
Wedge shaped

10. Thalamus
It has four surfaces, lateral, medial, superior and
inferior and two ends, anterior and posterior
Medial surface forms the lateral wall of third ventricle
& is lined by ependyma
It has an interthalamic connection
Posteriorly it diverges from the midline & ends in a
large convexity, the pulvinar
Lateral & medial geniculate bodies bulge out from
pulvinar

11. Thalamus
Lateral surface lies in contact with the internal
capsule
The ascending fibres from various tracts pass
through thalamic nuclei and leave the lateral
surface to join the internal capsule on their way
to the cortex
Superior surface is convex & triangular & tapers
anteriorly
A band of white matter called medullary stria
meets the stria from the other thalamus to form
U shaped habenular commissure
(The habenular nuclei are involved in pain processing, reproductive
behavior, nutrition, sleep-wake cycles, stress responses, and learning )

12. Thalamus
Inferior surface is narrow and joins the
hypothalamus medially
Posterolaterally it receives the lemnisci
from the midbrain
All four surfaces converge to the narrow
anterior pole which forms the posterior
boundary of interventricular foramen

13. Thalamic nuclei
A, Y shaped sheet of
white matter int
medullary lamina
divides the thalamus
into three parts
Anterior
Medial
Lateral
Each part contains
several nuclei

14. Thalamic nuclei
Anterior thalamic nuclei are concerned
with the emotional tone and recent
memory
Medial thalamic nuclei are concerned with
the behavior and expression
Lateral thalamic nuclei are connected to
sensory and motor pathways including
sense of taste and balance

15. Other thalamic nuclei
Medial geniculate
body concerned
with auditory relay
through inf colliculi
Lateral geniculate
body concerned
with visual relay
through superior
colliculi

16. Functions of thalamus
Plays an important part in the integration
of sensory and motor systems
Recieves precortical sensory input from all
the sensory systems except the olfactory
system
Centre for Visual reflexes
Centre for Auditory reflexes
Taste pathways

17. Hypothalamus
The floor of diencephalon is called
hypothalamus
It maintains the internal environment of
the body through 3 systems
Autonomic NS
Endocrine system
Limbic system

18. Hypothalamus
Parts of hypothalamus visible from the ventral
surface
Infundibulum
Mamillary bodies
Tuber cinereum
Median eminence which is responsible for the
production of neurosecretory substances which
control the ant pitutary
Posterior perforated substance
This is one of the few parts of brain which has no
blood brain barrier

19. Functions of hypothalamus
Thirst and water balance (supraoptic &
paraventricular nuclei)
Production of releasing factors for
Adenohypophysis
Precursors of ADH & Oxytocin
Hunger centre
Autonomic regulation centre
Temperature regulation centre

20. Subthalamus
This is the caudal part of thalamus,
contains
Subthalamic nucleus
Cranial part of red nucleus
Cranial part of substantia nigra
It is a part of basal ganglia and the
reticular activating system of brain (RAS)

21. Epithalamus
It consists of
Fornix
Habenular nuclei and commissure
Pineal gland
Posterior commissure (concerned with bilateral pupillary
reflex)
The pineal gland secretes Melatonin which sets
the day and night clock of the body
It becomes calcified in old age

22. Lesions of diencephalon cause:
Poor temperature control
Abnormal appetite
Lack of ADH causing polyuria and polydypsia
These lesions rarely ever occur alone. Usually they
occur in conjunction with cerebral lesions.

23. THE END