The diencephalon surrounds and forms the walls of the third ventricle. It contains the thalamus, hypothalamus, subthalamus, and epithalamus. The thalamus relays sensory information to the cortex and is involved in sensory and motor integration. The hypothalamus connects the nervous and endocrine systems and regulates autonomic functions and behaviors. The limbic system, which includes the hypothalamus, hippocampus, amygdala and limbic cortex, is involved in emotion, motivation and memory. The cerebral hemispheres are the largest part of the forebrain. They contain the cortex and underlying white matter. Sensory and motor areas of the cortex are involved in

1. SABIHA M. HAQ
IIMC

2. Learning objectives
 Describe the boundaries and contents of
diencephalon

3. INTRODUCTION
It is the area which surrounds third
ventricle
It has two walls, a roof, ant wall and
floor
Posteriorly the roof and floor converge.
This is the point where third ventricle
meets the cerebral aqueduct

4. Anterior wall
 Formed by lamina terminalis which is a thin
layer of grey matter
 Its lower end meets the optic chiasma in an
angle called the optic recess
 Behind its upper end is ant commissure
 Behind ant commissure are ant columns of
fornix
 Behind each ant column is interventricular
foramen

5. Floor
 It is actually the
floor of third
ventricle
 It extends across
optic chiasma, tuber
cinerium,
infundibulum and
mamillary bodies to
posterior perforated
substance

6. Side walls
 These are the lateral
walls of third
ventricle
 Formed by
thalamus,
hypothalamic
groove or sulcus and
hypothalamus itself

7. Roof
 Roof is formed by
pia mater of third
ventricle

8. Thalamus
Largest part
Wedge shaped

9. Thalamus
 It has four surfaces, lateral, medial, superior and
inferior and two ends anterior and posterior
 Medial surface forms the lateral wall of third ventricle
& is lined by ependyma
 It has an interthalamic connection
 Posteriorly it diverges from the midline & ends in a large
convexity, the pulvinar
 Lateral & medial geniculate bodies bulge out from
pulvinar

10. Thalamus
 Lateral surface lies in contact with the internal
capsule
 The ascending fibres from various tracts pass
through thalamic nuclei and leave the lateral
surface to join the internal capsule on their way
to the cortex
 Superior surface is convex & triangular & tapers
anteriorly
 A band of white matter called medullary stria
meets the stria from the other thalamus to form
U shaped habenular commissure

11. Thalamus
 Inferior surface is narrow and joins the
hypothalamus medially
 Posterolaterally it receives the lemnisci
from the midbrain
 All four surfaces converge to the narrow
anterior pole which forms the posterior
boundary of interventricular foramen

12. Thalamic nuclei
 A, Y shaped sheet of
white matter divides
the thalamus into
three parts
 Anterior
 Medial
 Lateral
 Each part contains
several nuclei

13. Thalamic nuclei
 Anterior thalamic nuclei are concerned with
the emotional tone and recent memory
 Medial thalamic nuclei are concerned with
the behavior and expression
 Lateral thalamic nuclei are connected to
sensory and motor pathways including
sense of taste and balance

14. Other thalamic nuclei
 Medial geniculate
body concerned
with auditory
relaythrough inf
colliculi
 Lateral geniculate
body concerned
with visual relay
through superior
colliculi

15. Functions of thalamus
 Plays an important part in the integration of
sensory and motor systems
 Recieves precortical sensory input from all
the sensory systems except the olfactory
system
 Centre for Visual reflexes
 Centre for Auditory reflexes
 Taste pathways

16. Hypothalamus
 The floor of diencephalon is called
hypothalamus
 It maintains the internal environment of the
body through 3 systems
 Autonomic NS
 Endocrine system
 Limbic system

17. Hypothalamus
Parts of hypothalamus visible from the ventral
surface
 Infundibulum
 Mamillary bodies
 Tuber cinereum
 Median eminence which is responsible for the
production of neurosecretory substances which
control the ant pitutary
 Posterior perforated substance
 This is one of the few parts of brain which has no
blood brain barrier

18. Functions of hypothalamus
 Thirst and water balance (supraoptic &
paraventricular nuclei)
 Production of releasing factors for
Adenohypophysis
 Precursors of ADH & Oxytocin
 Hunger centre
 Autonomic regulation centre
 Temperature regulation centre

19. Subthalamus
 This is the caudal part of thalamus, contains
 Subthalamic nucleus
 Cranial part of red nucleus
 Cranial part of substantia nigra
It is a part of basal ganglia and the
activating system of brain

20. Epithalamus
It consists of
 Fornix
 Habenular nuclei and commissure
 Pineal gland
 Posterior commissure
The pineal gland secretes Melatonin which sets the
day and night clock of the body
It becomes calcified in old age

21. Limbic system
 This is a system which controls the
emotional activities. This is also called the
Reward and Punishment centre. Following
parts of brain belong to limbic system
functionally
 Hypothalamus
 Hippocampus
 Amygdala
 Limbic cortex( parahippocampal gyrus)

22. Functions of limbic system
Feeding
Feeling
Fighting
Flight
Sexual drive

23. Dr. Sabiha M. Haq
IIMC

24. Cerebral hemispheres and Diencephalon
The fore brain consists of
Two cerebral hemispheres or
telencephalon
And diencephalon

25. The cranial fossae

26. Cerebral hemispheres
 Largest part of brain
 Outer cortex of grey matter
 Inner mass of white matter
 Buried in the white matter are masses of
grey nuclei called The basal Ganglia
 Two hemispheres are separated by a deep
fissure called the Great Longitudenal
Fissure

28. Cerebral hemispheres
 The great longitudinal fissure in life
accomodates the falx cerebri
 In the depth of the fissure lies the corpus
callosum
 This is an enormous sheet of transversely
running fibres, the commisural fibres which
connect the corresponding areas of cortex

29. Medial surface of the cerebrum

30. Cerebral hemispheres
The cortex is highly convoluted into
sulci and gyri
Some of these are permanent features
in every brain & are therefore named

31. The lateral surface of cerebrum
 Lateral fissure
 Parietooccipital sulcus
 Central sulcus
 Frontal lobe
 Parietal lobe
 Temporal lobe
 Occipital lobe

33. Cerebral hemispheres
 Pre central gyrus containing primary MOTOR
CORTEX
 Postcentral gyrus containing primary
SOMATOSENSORY CORTEX
 THE VISUAL CORTEX located in the occipital
lobe mostly on the medial surface
 THE AUDITORY CORTEX lying in the sup
temporal gyrus

34. Motor And Sensory Areas

37. Homunculi

38. 
The motor
humunculus

39. Internal str. of the hemispheres
 Fibres which pass to and from the cortex are
arranged in the shape of a fan called CORONA
RADIATA
 Deeper inside the hemisphere they are gathered
into a flat band on each side called the INTERNAL
CAPSULE
 The basal ganglia lie medial and lateral to the
internal capsule

40. Frontal lobe
 Precentral gyrus bw Central and Precentral
sulcus
 The area in front of precentral sulcus is
divided into
 Sup frontal gyrus
 Middle frontal gyrus
 Inf frontal gyrus

41. Cerebral Gyri And Sulci

42. Cerebral Gyri And Sulci
 Inf frontal gyrus is again divided into 3 by
the Anterior, Ascending and Posterior limbs
of the lateral sulcus. The three parts are:
 Orbital
 Triangular
 Opercular parts

43. The Insula
 The triangular part of the Inf frontal gyrus
with the adjacent part of parietal and
temporal lobes form the OPERCULA or the
lid.
 It overlies a buried part of the cortex called
the INSULA
 The insula is surrounded by circular sulcus
and has long and short gyri

45. Parietal lobe
 Postcentral gyrus
 Postcentral sulcus
 Behind the postcentral gyrus there is
 Superior parietal lobule
 Inferior parietal lobule
 Supramarginal gyrus around the post end of
lateral sulcus
 Angular gyrus around the posterior end of sup
temporal sulcus

46. Temporal lobe
 Two horizontal sulci
 Sup temporal sulcus
 Inf temporal sulcus
 Three gyri
 Sup temporal gyrus
 Middle temporal gyrus
 Inf temporal gyrus

47. Occipital lobe
 It does not have any important sulcus or
gyrus on the superolateral surface

48. The Medial Surface

49. The Medial and Inferior Surfaces of
Cerebrum

50. The Medial and Inferior Surfaces of
Cerebrum
 Corpus callosum is
the largest
commissure in the
brain
 Cingulate gyrus
starts above the ant
end of corpus
callosum and arches
above it all the way to
the posterior end

51. The Medial and Inferior Surfaces of
Cerebrum
 The Callosal sulcus
separates it from the
corpus callosum
 Cingulate sulcus
separates the cingulate
gyrus from the sup
frontal gyrus
 Calcrine sulcus

52. The Medial and Inferior Surfaces of
Cerebrum
 Paracentral lobule
surrounds the area
around the medial end
of central sulcus
 Its ant part is
continuous with pre
central gyrus & post.
part with the post
central gyrus on the
superolateral surface

53. The Medial and Inferior Surfaces of
Cerebrum
 Precuneus lies bw the
upturned post end of
cingulate sulcus & the
parieto occipital sulcus
 Cuneus is the
triangular area bw
parieto occipital sulcus
and the superomedial
margin

54. The Medial and Inferior Surfaces of
Cerebrum
 Collateral sulcus is
below and lateral to
calcrine sulcus
 Bw the above two
sulci is the Lingual
gyrus
 Anterior to lingual
gyrus is
Parahippocampal
gyrus which
terminates anteriorly
in Uncus

55. The Medial and Inferior Surfaces of
Cerebrum
 Lateral to collateral
sulcus is Med
Occipitotemporal gyrus
 Lateral to the above is
Occipitotemporal
sulcus & Lat
Occipitotemporal gyrus

56. The Medial and Inferior Surfaces of
Cerebrum
 The inf surface of
Frontal lobe shows the
Olfactory sulcus
containing the
Olfactory tract & bulb
 Medial to this is Gyrus
Rectus & lat to it are
many inferior orbital
gyri