DIENCEPHALON
Dr. Zeenat Zaidi
Diencephalon

Paired structure
 Located between the
brain stem and the
cerebral hemisphere
 Continuous with the
rostral part of the
midbrain
 Forms the lateral wall of
the 3rd ventricle
C
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p
mo

Almost entirely
surrounded by the
cerebral hemispheres
 A little part seen
externally on the base
of the brain caudal to
optic chiasma, includes:
• Infundibulum
• Tuber cinerium
• Mamillary bodies
 Other parts seen on
sagittal & coronal
sections
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mb

On the medial
surface, the
diencephalon is
subdivided, by
hypothalamic
sulcus (indicated
by black line)
into:
 Dorsal part
 Ventral part
Fornix
CC
Dorsal
Ventral
Optic chiasma
Midbrain
Cerebral
aqueduct
Dorsal part
Thalamus & Epithalamus
H
Subthalamus & Hypothalamus
Ventral part
Relations
Dorsal:
Lateral
ventricle
Lateral:
Internal
capsule
Medial: 3rd
ventricle
Ventral: Exposed on
the base of the brain
EPITHALAMUS
Epithalamus

Relatively small
part, located in
most caudal and
dorsal region
 Lies immediately
rostral to superior
colliculus
 Consists of:
 Pineal gland &
 Habenular nuclei
Pineal Gland

An endocrine organ
 Synthesizes
melatonin
 Controls:
 Sleep/awake
cycle
 Regulation of
onset of puberty
Habenular nuclei

Located in habenular
triangle (area in the
posterior part of the
diencephalon, just
anterior to pineal gland)
 Have connections with
limbic system
 Serves autonomic
function and emotional
drives
THALAMUS
Thalamus

Large mass of grey matter, in shape and size, resembles
small hen’s egg
 Forms the lateral wall of the 3rd ventricle
 Separated from hypothalamus by hypothalamic sulcus
 May be connected to opposite thalamus by interthalamic
adhesion (massa intermedia)
thalamus
Interthalamic
adhesion
Hypothalamic
sulcus
Thalamus: In horizontal sections of brain
Lower
level
Higher
level
Thalamus has a narrow
anterior end called
tubercle of thalamus,
that lies in the posterior
boundary of the
interventricular foramen
The expanded posterior end,
called pulvinar, lies above the
superior colliculi
Relations
Dorsal: lateral ventricle
Lateral:
Internal
capsule
Anterior:
interventricular
foramen
Medial: 3rd
ventricle
Ventral: Subthalamus & Hypothalamus
Caudal: midbrain
Surfaces
4
•
•
•
•
Surfaces:
Superior
Inferior
Medial
Lateral
S
L M
l
Superior Surface

Bounded laterally by
caudate nucleus,
thalamostriate vein
and a nerve fiber
bundle called stria
terminalis
 Lateral part lies in the
floor of the lateral
ventricle & is covered
by ependyma
 Medial part is related
to the choroid plexus
of the 3rd ventricle
stria terminalis
caudate nucleus
LV
thalamostriate vein
choroid plexus
ependyma
Lateral Surface
 Related to the
internal capsule
Inferior Surface
 Rests on the
subthalamus &
hypothalamus
Medial Surface

Stria medullaris thalami
(a fascicle of nerve
fibers) courses along its
dorsomedial margin
 Below is limited by
hypothalamic sulcus
 Forms the upper part of
the lateral wall of the
3rd ventricle
 Covered by ependyma
Stria medullaris thalami
Hypothalamic sulcus
Internal Organization

Thalamus is composed
of grey matter,
interrupted by two
vertical sheaths of white
matter called medullary
laminae.

External medullary
lamina:

Located laterally,
separates reticular
nucleus from the rest of
the thalamic mass
 Contains thalamocortical
& corticothalamic fibers


Internal medullary
lamina
Y- shaped band, divides
thalamus into Anterior,
Medial & Lateral nuclear
groups
 Contains:
 Fibers connecting
thalamic nuclei with
one another
 Neuronal collections
called intralaminar
nuclei
Nuclear Groups


Anterior nuclear group
Lateral nuclear group:
Divided into:
 dorsal &
 ventral tiers
Medial nuclear group
Intralaminar nuclei
Reticular nucleus

Midline nuclei



Functional Organization

All the nuclei of the
thalamus except
reticular nucleus,
project to ipsilateral
cerebral cortex
 The whole of the
cerebral cortex
receives input from
the thalamus
 All thalamic nuclei
receive corticofugal
fibers in a basically
reciprocal fashion
 Based
on their connection with the
cerebral cortex, the thalamic nuclei are
divided into:
Specific nuclei
Nonspecific nuclei
 Specific nuclei:
 Have well-defined
sensory and motor
functions
 Have highly organized
point-to-point connection
with sensory & motor
regions of cerebral cortex
 Lie within the ventral
group of the lateral
nuclear group


Non-specific Nuclei:
Receive less functionally
distinct afferent input
 Connect with wider area
of cortex, including
associative and limbic
regions
 Include nuclei of the
dorsal tier of lateral
group, and whole of the
anterior and medial
group
Lateral Nuclear Group
Ventral Tier
•
Ventral anterior
• Ventral lateral
• Ventral posterior:
• (VPL)
• (VPM)
•
Lateral geniculate
• Medial geniculate
Ventral Anterior Nucleus
Influences motor activity
Ipsilateral globus
pallidus &
substantia nigra
Motor cortex
Premotor &
supplementary
motor cortex
Ventral Lateral Nucleus
Influences motor activity
Ipsilateral globus pallidus &
substantia nigra
Contralateral dentate nucleus
Primary motor cortex
Primary motor cortex
Ventral Posterior Nucleus
Chief sensory relay station
General sensory
afferents from the
contralateral half
of the Head &
neck (VPM) and
Body (VPL)
Primary
somatosensory
cortex
Lateral Geniculate Body
Part of the Visual Pathway
Ipsilateral temporal
hemiretina
Contralateral nasal
hemiretina
Optic radiation
to the primary
visual cortex
Medial Geniculate Body
Part of the Auditory Pathway
Inferior
colliculus
Auditory
radiation to the
primary auditory
cortex
Lateral Nuclear Group
Dorsal Tier
•
•
•
Lateral Dorsal
Lateral Posterior
Pulvinar
Lateral dorsal
nucleus
 Part of Limbic
System
Hippocamus
Cingulate gyrus
Lateral posterior
nucleus
sensory association cortex
of parietal lobe
Pulvinar: Sensory
association cortices of
parietal, temporal &
occipital lobes
Medial Nuclear Group
Integrates emotion, thought, and judgment
Mediodorsal nucleus
& Nucleus reuniens
Hypothalamus,
amygdala, other
thalamic nuclei,
prefrontal cortex
Prefrontal cortex &
limbic structures
Anterior Nuclear Groups
Functionally part of the limbic system. Involved
in control of instinctive drives, emotional aspect
of behaviour and in memory

3 parts:

Anteroventral
Anteromedial
Anterodorsal


•
Mammillary body of
hypothalamus via
mammillothalamic tract
cingulate gyrus
Midline Nuclei

Located
between
medial nuclear
group and the
ependyma of
3rd ventricle
 Important in
visceral
functions
Brainstem
reticular
formation
Cingulate
gyrus and
hypothalamus
Intralaminar Nuclei

Located within the
internal medullary
lamina
 Main nuclei:
Centromedian &
Parafascicular
 Function as activator
of the cerebral
cortical mantle
 Lesions reduce the
perception of pain
and level of
conciousness
Reticular formation,
spinothalamic &
trigeminothalamic
systems
Widespread regions
of cerebral cortex,
caudate & putamen of
the basal ganglia
Reticular Nucleus
Regulates the activity of thalamus

Located between the
external medullary
lamina & the internal
capsule
Collaterals of both
Thalamocortical &
Corticothalamic fibers
Other thalamic nuclei
Functions of the thalamus

Receives and analyses all the sensory information
(except olfactory) from the body
 Having extensive connections with the basal ganglia and
the motor cortices, it plays a pivot role in voluntary
motor activity. Thalamotomy (VA, VL) was once used
to treat basal ganglia disorders
 Connections with the limbic system makes it important
in the control of mood, emotional and sexual behavior,
and memory
Thalamic Lesions

Cerebrovascular lesions or tumors of thalamus lead to:
 Loss of sensation in the contralateral side of face and
body followed by distressing discomfort, & burning
and diffuse pain in the anaesthetic areas (thalamic
pain)
 Thalamic syndrome: Abnormal voluntary movements
(chorea or hemiballismus) with hemisensory
disturbance
THANK YOU