Transcript 12. DIENCEPHALON II

DIENCEPHALON
Subthalamus
&
Hypothalamus
Dr Zeenat Zaidi
SUBTHALAMUS
SUBTHALAMUS
 Region
of
diencephalon
located below
the thalamus &
dorsolateral to
hypothalamus
 Continues
caudally with the
midbrain
Th
Hypothalamus
Contents

Rostral extension of:
 Red nucleus
 Substantia nigra
 Brainstem reticular formation as Zona incerta
 Long tracts passing through brain stem and
heading toward thalamus
 Spinothalamic & Trigeminothalamic tracts
 Medial lemniscus
 Dentatothalamic fibers
 Pallidothalamic fibers (fasciculus lenticularis,
Ansa lenticularis & thalamic fascicle)
 Subthalamic nucleus
Subthalamic Nucleus
 Resembles
a
biconvex lens in
shape
 Located in the
ventrolateral part of
the subthalamus
 Lies against the
medial surface of
the internal capsule
I
C
Connections
 Has


reciprocal
connections
with ipsilateral:
Globus pallidus
via subthalamic
fasciculus,
which passes
through the
internal capsule
Substantia
nigra
Lesions
Functions

Plays an
important role in
normal
functioning of
basal ganglia

Rare
 Usually of
cerebrovascular origin
 Results in Hemiballism
(sudden, forceful
involuntary, violent or
jerky, movements of the
limbs) on the
contralateral side
Zona Incerta

Rostral extension
of the brainstem
reticular
formation
 Enveloped by
pallidothalamic
fibers (lies
between the
lenticular fascicle
and the thalamic
fascicle)
HYPOTHALAMUS
Hypothalamus

Most ventral part of
diencephalon
 Lies beneath the
thalamus and
ventromedial to the
subthalamus
 Forms the floor and
lower part of the
lateral wall of the 3rd
ventricle
CC
F
TH
H

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:
 Infundibulum
 Tuber cinerium
 Mammillary bodies
I
The anterior column of the fornix passes vertically through
the substance of hypothalamus (to terminate in the
mamillary body) and divides it into medial and lateral zones
F
mb
Medial Nuclei
Lateral Nuclei
Lateral part

Lies medial and
ventral to the
subthalamus
 Traversed by many
fibers including medial
forebrain bundle
 Controls food and
water intake (feeding
centre)
 Lesions cause
aphagia and adipsia
Medial part

Forms lateral wall of
the 3rd ventricle
 Contains:
•
•
•
•
•
•
•
Suprachiasmatic
nucleus
Supraoptic nucleus
Paraventricular
nucleus
Dorsomedial nucleus
Ventromedial nucleus
Posterior nucleus
Mammillary nuclei

Supraoptic nucleus produces
vasopressin which increases
water reabsorption by the
kidney
 Paraventricular nucleus
produces 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
the capillary bed
Suprachiasmatic
nucleus:
•concerned with the
control of diurnal
rhythm and
sleep/awake cycle
•Receives some
afferent fibers
directly from the
retina
Ventromedial nucleus:
• acts as satiety centre
•Lesions cause
polyphagia, polydipsia

Mammillary nuclei:
• Part of the limbic
system
• Receive afferents
from the
hippocampus
through fornix
• Project to the:
Anterior nucleus of thalamus through
mammillo-thalamic tract
Brainstem through the mamillotegmental tract

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
Functions
1.
2.
3.
4.
5.
6.
7.
8.
9.
Co-ordination of homeostatic mechanism
Controls the release of hormones from the pituitary gland.
Center for regulation of autonomic activity --- controls medulla oblongata nuclei for
cardiovascular, respiration

Activation of posterior region associated with sympathetic responses

Activation of anterior region associated with parasympathetic responses
The mammillary nuclei are associated with the emotional behaviour and memory
The suprachiasmatic nucleus is concerned with diurnal rhythm & sleep/waking
cycle
The lateral hypothalamus & the ventromedial nucleus regulate feeding and drinking
Center for Feeding reflexes—licking, swallowing, etc.
Controls subconscious skeletal muscle movements—facial expressions, sexual
movements
Coordinates autonomic response to conscious input—thought of fear produces
accelerated heart rate, etc.
3rd Ventricle: The cavity of the
Diencephalon
Boundaries

Anterior: Lamina
terminalis, a membrane
stretching between
anterior commissure (ac)
& optic chiasma (oc)
 Posterior: Pineal gland
 Lateral walls:
 medial surface of
thalamus above &
 hypothalamus below
the hypothalamic
sulcus
TH
ac
H
oc
p
 Roof:
Ependyma
stretching
between the
two stria
medullaris
thalami

Floor:
Anteroposteriorly:
1. optic chiasma
2. Infundibulum
3. tuber cinerium
4. mammillary bodies
5. tegmentum of
midbrain
 Cavity is crossed by
interthalamic
adhesion (black
arrow)
5
1
3
2
4
Recesses
 Are
extensions
of the cavity:
 Supraoptic
 Infundibular
 Pineal
 Suprapineal
Communications
 Rostrally:
communicates on
each side with the
lateral ventricle
through
interventricular
foramen of Monro
 Caudally: with 4th
ventricle through
cerebral aqueduct
Choroid Plexus of 3rd ventricle





Tuft of capillaries enclosed
within ependyma
Invaginates from its roof
Extends rostrally till the
interventricular foramen
Continues laterally with the
choroid plexus of lateral
ventricle
Produces cerebrospinal
fluid
Clinical Anatomy

Obstruction of cerebral
aqueduct leads to
dilatation of 3rd ventricle
and both lateral ventricles
 Unilateral/bilateral
obstruction of
interventricular foramen
leads to dilatation of one
or both lateral ventricles
respectively
 In both cases symptoms
and signs of
Hydrocephalus develop
Thank You & Good Luck