2. DIENCEPHALON
Dr. Zeenat Zaidi

3. 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 mb p C mo

4. 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 tc I mb

5. Fornix
On the medial surface, the diencephalon is subdivided, by hypothalamic sulcus (indicated by black line) into:
Dorsal part
Ventral part CC
Dorsal
Ventral
Midbrain
Optic chiasma
Cerebral aqueduct

6. Thalamus & Epithalamus
Dorsal part
Thalamus & Epithalamus
Subthalamus & Hypothalamus
Ventral part H

7. Relations Lateral: Internal capsule Dorsal: Lateral ventricle
Medial: 3rd ventricle
Ventral: Exposed on the base of the brain

8. EPITHALAMUS

9. Epithalamus
Relatively small part, located in most caudal and dorsal region
Lies immediately rostral to superior colliculus
Consists of:
Pineal gland &
Habenular nuclei

10. Pineal Gland An endocrine organ Synthesizes melatonin Controls:
Sleep/awake cycle
Regulation of onset of puberty

11. 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

12. THALAMUS

13. 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

14. Thalamus: In horizontal sections of brain
Higher level
Lower level

15. 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

16. Relations Dorsal: lateral ventricle Anterior: interventricular foramen
Medial: 3rd ventricle
Lateral: Internal capsule
Ventral: Subthalamus & Hypothalamus
Caudal: midbrain

17. Surfaces
4 Surfaces:
Superior
Inferior
Medial
Lateral S L M l

18. 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
caudate nucleus
stria terminalis LV
thalamo-striate vein
ependyma
choroid plexus

19. Lateral Surface
Related to the internal capsule
Inferior Surface
Rests on the subthalamus & hypothalamus

20. Medial Surface
Stria medullaris thalami
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
Hypothalamic sulcus

21. 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

22. 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

23. Nuclear Groups Anterior nuclear group
Lateral nuclear group: Divided into:
dorsal &
ventral tiers
Medial nuclear group
Intralaminar nuclei
Reticular nucleus
Midline nuclei

24. 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

25. Based on their connection with the cerebral cortex, the thalamic nuclei are divided into:
Specific nuclei
Nonspecific nuclei

26. Specific nuclei: Non-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

27. Lateral Nuclear Group Ventral Tier
Ventral anterior
Ventral lateral
Ventral posterior:
(VPL)
(VPM)
Lateral geniculate
Medial geniculate

28. Ventral Anterior Nucleus
Influences motor activity
Ipsilateral globus pallidus & substantia nigra
Motor cortex
Premotor & supplementary motor cortex

29. Ventral Lateral Nucleus
Influences motor activity
Ipsilateral globus pallidus &
substantia nigra
Contralateral dentate nucleus
Primary motor cortex
Primary motor cortex

30. 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

31. Lateral Geniculate Body
Part of the Visual Pathway
Ipsilateral temporal hemiretina
Contralateral nasal hemiretina
Optic radiation to the primary visual cortex

32. Medial Geniculate Body
Part of the Auditory Pathway
Inferior colliculus
Auditory radiation to the primary auditory cortex

33. Lateral Nuclear Group Dorsal Tier
Lateral Dorsal
Lateral Posterior
Pulvinar

34. 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

35. Medial Nuclear Group Integrates emotion, thought, and judgment
Mediodorsal nucleus & Nucleus reuniens
Hypothalamus, amygdala, other thalamic nuclei, prefrontal cortex
Prefrontal cortex & limbic structures

36. 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

37. Mammillary body of hypothalamus via mammillothalamic tract
cingulate gyrus

38. Midline Nuclei
Located between medial nuclear group and the ependyma of 3rd ventricle
Important in visceral functions
Brainstem reticular formation
Cingulate gyrus and hypothalamus

39. 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

40. Reticular formation, spinothalamic & trigeminothalamic systems
Widespread regions of cerebral cortex, caudate & putamen of the basal ganglia

41. 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

42. 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

43. 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

44. THANK YOU