The diencephalon is the second part of the forebrain located in the midline. It contains the third ventricle and connects the cerebrum to the midbrain. The diencephalon is divided into dorsal and ventral parts by the hypothalamic sulcus. The dorsal part contains the thalamus, metathalamus, and epithalamus, while the ventral part contains the hypothalamus and subthalamus. The thalamus is the largest structure in the dorsal diencephalon and relays sensory and motor information to the cerebral cortex. It contains several nuclei that process different sensations and pathways. The metathalamus contains the medial and lateral geniculate bodies which
3. DIENCEPHALON
• Diencephalon is second part of forebrain which lies exactly in midline
• This structure is embedded in cerebralhemisphere, therefore it cannot be
seen from out side
• The diencephalon is a hollow structure, which contains inside third
ventricle
• This third ventricle above communicate with lateral ventricles and below
with cerebral aqueduct
• Thus it communicate the cerebrum with the midbrain
4. PARTS OF DIENCEPHALON
• The hypothalamic sulcus divides each half of the diencephalon into dorsal
and ventral parts
• Dorsal part: Thalamus, Metathalamus,Epithalamus
• Ventral part: Hypothalamus,Subthalamus
5. THALAMUS
• Large mass of grey matter in dorsal part of diencephalon
• Situated at the base but at dorsal side of third ventricle
• Forms Floor of lateral ventricle and postero-lateral boundary of third
ventricle
7. EXTERNAL FEATURES OF THALAMUS
• Thalamus has 2 ends and 4 surfaces
Ends:
• Anterior end: Narrow and forms posterior boundary of interventricular
foramen
• Posterior end: Expanded and known as pulvinar, It is directed postero-
laterally and related to the medical and lateral geniculate body
8. Surfaces
• Superior surface: Convex,
Outer part forms floor of lateral ventricle,
Inner part is related to tela—choroidea of third ventricle
• Inferior surface: Related with hypothalamus and Subthalamus
• Medial surface: Related with third ventricle
• Lateral surface: Related with internal capsule
9. INTERNAL FEATURES
Cross section of thalathalamus shows several small nuclei as –
1. Anterior nucleus: forms anterior end
2. Posterior nucleus: forms posterior end, also called as pulvinar
3. Medial nucleus: situated at medial side, Anterior Nucleus+Medial nucleus=
Pals thalamus
4. Lateral nucleus/ Ventral nucleus: Subdivided in ventral anterior,ventral lateral,
ventral posterior lateral, ventral posterior medial
5. Intra-laminar nucleus: situated between lateral and medial nuclei
There are two- lateral dorsal and lateral ventral nucleus
10.
11. IMPORTANCE OFTHALAMUS
• It is important station,where most of the afferent nerve tract gather
• Somatic sensations are brought to it by spino thalamic and trigemino thalamic nerve
tract
• Visual and auditory sensations are brought to it by medial and lateral geniculate
bodies
• Visceral sensations are brought to by hypothalamus
12. • All these afferent sensations are further conducted in cerebral cortex to
their respective centers
• Most of the efferent tracts from the cerebrum and cerebellum are
brought to it, thus It is important station in afferent and efferent nerve
tract
13. METATHALAMUS (PART OFTHALAMUS)
• This part of diencephalon is situated just behind and below theThalamus
and lies above the mid brain
• The Metathalamus consists of the medial and lateral geniculate bodies
14. MEDIAL GENICULATE BODY
• Oval elevation present just below the pulvinar of thalamus
• It is important station in the auditory nerve tract
• Afferents connection: lateral lamniscus, fibres of inferior colliculi, ascending
reticular pathway
• Efferents connection: auditory area of cortex, secondary somatosensory
area
15. LATERAL GENICULATE BODY
• It’s small oval elevation situated anterolateral to the medial geniculate
body, below theThalamus
• It is six layered structure
• It is covered by the temporal lobe
• It is important station in visual tract
• Afferents connection: Optic tract (lateral root)
• Efferents connection: Visual area of cortex
16. CLINICALANATOMY
• Lesions of thalamus:impairment of all types of sensations
• Thalamic syndrome: disturbance of sensations, hemiplegia or hemiparesis,
hyperaesthesia and severe spontaneous pain
• Choreoathetosis: abnormal movement
• Damage of medial nucleus of thalamus:Increase forgetfulness, decrease
anxiety and tension aggression
