Diencephalon
DR ROHINI PUNJA
Competency
AN62.5 Describe boundaries, parts, gross relations, major nuclei
and connections of dorsal thalamus, hypothalamus,
epithalamus, metathalamus and subthalamus
Introduction
Situated cranial to midbrain
Surrounded by cerebrum
Cavity of diencephalon – 3rd Ventricle
(divides it into 2 halves)
Divisions of Diencephalon – (hypothalamic sulcus)
Pars dorsalis- thalamus (dorsal thalamus, metathalamus,
epithalamus
Pars ventralis- subthalamus (ventral thalamus),
hypothalamus
Parts of diencephalon
Dorsal part: Thalamus, Metathalamus & Epithalamus
Ventral part: Hypothalamus & Subthalamus
Thalamus
•Large ovoid mass of grey matter, Lies dorsal to the hypothalamic
sulcus.
•Two thalami situated on either side of 3rd ventricle, connected via
interthalamic adhesions
•Narrow pointed anterior end, wider posterior end (pulvinar)
Final relay station for all sensory pathway (except
olfactory) and is considered as the great gateway to
the cerebral cortex.
External features -Thalamus
•2 ends and 4 surfaces
•Anterior end-tubercle of thalamus, forms the posterior boundary of
interventricular foramen
•Posterior end- pulvinar, overhangs the geniculate bodies and superior
colliculi
•Superior surface- forms the floor of central part of lateral ventricle
•Inferior surface- anterior part fused with subthalamus, posterior part free
•Medial surface-lateral wall of 3rd ventricle
•Lateral surface- forms the medial boundary of the posterior limb of internal
capsule
Parts-Thalamus
•The internal medullary lamina- a
Y shaped sheet of white fibre
divides the thalamus into 3
parts- Anterior, medial and
lateral
•Each part consists of a number
of nuclei
ANTERIOR
L
DIA
E
M
AL
R
E
LAT
AALL
I
I
D
D
MEE
M
Nuclei of Thalamus
•Anterior nucleus
•Medial dorsal nucleus
Anterior nucleus
•Nuclei in the lateral
part
Dorsomedial nucleus
Internal medullary lamina
Lateral nucleus
Ventral nucleus
Geniculate bodies
Pulvinar
Lateral group
Dorsal tier
Ventral tier
VA
VL
VP
LD
LP
PULVINAR
Connections of Thalamus
•Anterior nucleus and its connections –attention
and recent memory (lesion loss of recent
memory)
•Medial dorsal nucleus- “mood” and “emotional
balance”
FUNCTIONS1) It acts as relay station of all sensory pathways
except for olfactory senses.
2) Concerned with crude sensations like pain and
temp
3)Significant role in the ARAS for arousal or
alertness
4) It regulates the activities of motor pathways.
Connections between cerebral cortex and
thalamus
-Reciprocal connections between cerebral
cortex &
thalamus form a fan shaped thalamic
radiation.
Clinical correlation
Lesions affecting the anterior nuclei leads to KORSAKOFF’S SYNDROME
with loss of recent memory.
Thalamic syndrome
 Blockage of thalamogeniculate branch of posterior
cerebral artery damages the postero ventral &
postero lateral nuclei of thalamus.
Symptoms
Somatic sensations – diminished
Threshold for touch pain & temperature – raised
Metathalamus
•Consists of medial and lateral geniculate bodies
•Small rounded elevations on the inferior aspect of the posterior
part of thalamus
•Relay stations for the auditory and visual pathways
•Medial geniculate –lies lateral to the superior colliculus (SC),
the inferior brachium runs upward and laterally to MG
(conveys auditory impulses )
SC
MG
LG
IC
•Lateral geniculate- receives retinal fibres through optic tract,
fibres of superior brachium are concerned with production of
visual reflexes.
*SLIM
Epithalamus
•Pineal gland (epiphysis cerebri) cone-shaped
reddish grey structure between the two
superior colliculi
•It has a stalk which divides into two laminaeventral (superior) continues with posterior
commissure & dorsal (inferior) continues with
habenular commissure
Pineal gland
•Neuroendocrine gland –pinealocytes and neuroglial
cells
•Secrete melatonin- inhibitory effect on other endocrine
glands and gonads
•Calcium phosphates and carbonates deposited in the
gland with age- Corpora arenacea (brain sand)
•Only part of brain no neural tissue & supplied by
nerve (nervus conari) outside the brain
Hypothalamus
•Part of diencephalon lies below the thalamus
•Regarded as the head ganglion of the autonomic
nervous system
collections of :
nerve cells in matrix of neuroglial tissue,
nerve fibres,
plexus of blood capillaries.
• Anatomically small but physiologically very
significant- controls endocrine and autonomic system
Anteriorly-Lamina terminalis
Posteriorly -subthalamus
Superiorly- thalamus
Inferiorly: floor of the third ventricle.
• OPTIC CHIASMA*
• INFUNDIBULUM
• TUBER CINERIUM- MEDIAN EMINENCE
• MAMMILLARY BODIES
• POSTERIOR PERFORATED SUBSTANCE
Laterally- internal capsule
Medially- cavity of 3rd ventricle
Boundaries
SUBDIVISIONS and NUCLEI
Preoptic region – preoptic nu
Supraoptic region- supraoptic
nu, anterior nu, paraventricular
nu
Tuberal region- arcuate
(infundibular) nu, ventromedial
nu, dorsomedial nu
Mamillary region- posterior nu,
mammillary nu
Connections
1)Hypothalamo –hypophyseal tract
Axons of supra optic and paraventricular nuclei
neurohypophysis transport vasopressin and
oxytocin
2) Hypothalamo-hypophyseal portal system
Axons of tuberal nuclei deliver neurosecretory
material to portal system of blood vessels controls
secretions of adenohypophysis
Functions
•Autonomic functions- anterior controls parasympathetic,
posterior sympathetic NS.
•Endocrine functions –regulates hormonal secretions
•Temperature regulation.
•Regulation of food and water intake.
•Sex regulation- influences the secretions of gonadotrophic
hormones by pituitary
• Influence on emotional behavior.
•Circadian rhythm- regulates the cyclical activities of body
(sleep wake cycle)