DIENCEPHALON

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DIENCEPHALON
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• 4th year

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DIENCEPHALON

• Site- It is the part of the forebrain which lies
  above the midbrain between the lower parts of
  the 2cerebral hemispheres.
• It consists of
• Thalamus -the large oval mass of grey matter
• Subthalamus- it lies directly above midbrain
• hypothalamus lies infront of subthalamus
• Metathalamus formed by lateral medial
  geniculate body
• Epithalamus Formed of pineal body, 2 habenular
  nuclei commissures posterior commissure.
• The thalamus Is the main sensory relay station
  on the pathway of all sensations (except smell)
  to the cerebral cortex.

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The thalamus

• It consists of 2 ends 4 surfaces
• 1) Narrow anterior end behind the
  interventricular foramen
• 2)expanded posterior end called pulvinar
• The surfaces of the thalamus
• The superior surface is related medially to the
  tella choroida, fornix laterally it form the
  floor of the central part of the lateral
  ventricle
• The inferior surface ?anteriorly it lies on
  hypothalamus,
• ? on its middle part on the subthalamus but
• ? on the posterior part it is free and has
  lateral medial geniculate bodies.

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• c) The medial surface forms the upper part of
  the lateral wall of the 3rd ventricle it is
  separated from the hypothalamus by hypothalamic
  sulcus. Here the 2 thalami are connected by inter
  thalamic adhesion.
• d) The lateral surface related to the posterior
  limb of internal capsule separating it from the
  lentiform nucleus

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The internal structure of the thalamus

• It is divided by a Y-shaped sheet of white matter
• Called internal medullary lamina into 3 main
  parts. 1) anterior part between the 2 anterior
  limbs 2) medial part lying medial to the
  posterior limb of medullary lamina lateral part
  lying lateral to it.
• ?The thalamic nuclei
• The medial group in the medial part of the
  thalamus
• Anterior group in the anterior part
• The lateral part is divided by imaginary
  horizontal plane into
• a) small dorsal part
• b) Large ventral part
• ?nuclei of dorsal part
• a) lateral dorsal n.
• b) Lateral posterior n.
• Nuclei of ventral part 3 nuclei
• a) Ventral Anterior
• b) ventral Intermediate
• c) ventral Posterior

ventral Posterolateral n V. P. L.N
ventral Posteromedial n V. P. M.N
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The hypothalamus

• ??It lies anterior inferior to the thalamus.
• ??It form the floor lower part of the lateral
  wall of the third ventricle.
• ??It includes the following structure
• optic chiasma supra optic nuclei
• tuber cinerium infandibulum
• mammilary body
• posterior perforated substances

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SUBTHALAMUS

• It lies between the thalamus tegmentum of the
  midbrain
• It contains
• 1) 3 nuclei (upper end of red nucleus,
• upper end of substantia nigra
• subthalamic nuclei)
• 2) bundles of projection fibers

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THANK YOU