2. Subthalamus & Hypothalamus
DIENCEPHALON
Subthalamus & Hypothalamus
Dr Zeenat Zaidi

3. SUBTHALAMUS

4. SUBTHALAMUS
Region of diencephalon located below the thalamus & dorsolateral to hypothalamus
Continues caudally with the midbrain Th
Hypothalamus

5. 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

6. 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 IC

7. Connections Has reciprocal connections with ipsilateral:
Globus pallidus via subthalamic fasciculus, which passes through the internal capsule
Substantia nigra

8. Lesions Functions Rare Usually of cerebrovascular origin
Results in Hemiballism (sudden, forceful involuntary, violent or jerky, movements of the limbs) on the contralateral side
Lesions
Plays an important role in normal functioning of basal ganglia
Functions

9. Zona Incerta Rostral extension of the brainstem reticular formation
Enveloped by pallidothalamic fibers (lies between the lenticular fascicle and the thalamic fascicle)

10. HYPOTHALAMUS

11. 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

12. Parts of hypothalamus seen on the base of the brain include:
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 oc tc I mb P

13. 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

14. Medial Nuclei
Lateral Nuclei

15. 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

16. Medial part Forms lateral wall of the 3rd ventricle Contains:
Anterior nucleus
Supraoptic nucleus
Preoptic nucleus
Paraventricular nucleus
Dorsomedial nucleus
Ventromedial nucleus
Posterior nucleus
Mammillary nuclei
Infundibular nucleus

17. 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

18. 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

19. 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

20. Optic tract
Mamillary body
Column of fornix
Thalamus
Superior & inferior colliculi
Caudate nucleus
Anterior commissure
Mamillothalamic tract

21. 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

22. Functions 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.

23. 3rd Ventricle: The cavity of the Diencephalon

24. 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 p ac H oc

25. Roof: Ependyma stretching between the two stria medullaris thalami

26. Floor: Anteroposteriorly: optic chiasma Infundibulum tuber cinerium
mammillary bodies
tegmentum of midbrain
Cavity is crossed by interthalamic adhesion (black arrow) 5 4 1 3 2

27. Recesses Are extensions of the cavity: Supraoptic Infundibular Pineal
Suprapineal

28. Communications
Rostrally: communicates on each side with the lateral ventricle through interventricular foramen of Monro
Caudally: with 4th ventricle through cerebral aqueduct

29. Interventricular Foramen of Monro
Paired foramina
Each bounded:
Anteriorly by column of fornix
Posteriorly by anterior pole of the thalamus
Communicate 3rd ventricle with the two lateral ventricles

30. 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

31. 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

32. Thank You & Good Luck