This document describes the external and internal features of the forebrain. It discusses the lobes, sulci, gyri and other surface features. It then describes the cortical areas including the primary motor, premotor, supplementary motor, frontal eye field, Broca's area, prefrontal cortex, primary somatosensory, secondary somatosensory, somatosensory association, and primary visual areas. It provides details on the location and functions of these different cortical regions.

1. By
Dr.Faris Al-Haddad
M.B.Ch.B, PhD Anatomy
College of Medicine,
Hawler Medical University
Arbil, Iraq
e-mail: farisurgeon@gmail.com

2. Forebrain
External features

3. SurfaceS :
1. Superolateral surface
2. Medial surface
3. Inferior surface

4. Sulci :
1. Central sulcus,
2. Lateral sulcus,
3. Parieto-occipital sulcus,

5. lobeS :
1. Frontal lobe (in front of the central sulcus
and above the lateral sulcus),
2. Temporal lobe(below the lateral sulcus),
3. Parietal lobe (behind the central sulcus and
above the lateral sulcus),
4. Occipital lobes (behind the parieto-occipital
sulcus).

7. Superolateral surface

8. 1. Lateral sulcus:

9. 2. Opercula:
Insula

10. Central Sulcus

11. 4. Frontal gyri:

12. 5. Temporal Gyrus:

13. 5. Parietal lobe :

14. 6. Occipital lobe:

15. 2. Medial surface :

16. 1. Corpus callosum

17. 2. The medial frontal gyrus

18. 3. Cingulate sulcus & Cingulate gyrus

19. 4. parieto-occipital sulcus
5. Calcrine sulcus
Paracentral
lobule
Precuneus
Cuneus
Lingual

20. 3. Inferior surface

21. Gyrus rectus
Olfactory sulcus
Olfactory
bulb
Olfactory
tract ,
Orbital gyri
& Sulci

22. Occipitotemporal
sulcus
Collateral sulcus
ParahipocampusLingual
LateralOccipitotemporal
Uncus

23. INTERNAL FEATURES

24. White Matter of the
Cerebral Hemispheres

25. • The white matter is composed of myelinatedmyelinated
nerve fibersnerve fibers supported by neuroglianeuroglia..
• The nerve fibers may be classified into three
groups according to their connections:
(1) Commissural fibersCommissural fibers,
(2) Association fibersAssociation fibers,
(3) Projection fibersProjection fibers.

26. 1. Commissure Fibers:
• connect corresponding regions of the two
hemispheres.
• They are as follows:
Corpus callosum,Corpus callosum,
Anterior commissure,Anterior commissure,
Posterior commissure,Posterior commissure,
Fornix,Fornix,
Habenular commissure.Habenular commissure.

27. A. Corpus callosum:
• the largest commissure of
the brain,
• connects the two cerebral
hemispheres.
• It lies at the bottom of the
longitudinal fissure.
• it is divided into :
1.1. RostrumRostrum :
is a thin part
of anterior end of corpus
callosum,
which is prolonged posteriorly
to be continuous with upper

28. 1.1. GenuGenu ::
is the
curved anterior end
of the corpus
callosum that bends
inferiorly in front of
the septum
pellucidum.
2.2. BodyBody ::
arches posteriorly
and ends as

29. • Forceps minor :
the fibers directed
laterally of the genu curve
forward into the frontal
lobes
• Radiation of CorpusRadiation of Corpus
CallosumCallosum
The fibers of the body
extend laterally.
• Forceps majorForceps major :
Traced
laterally, the fibers in the
splenium arch backward
into the occipital lobe and
form the.

30. Some of the fibers form the roof and lateral wallform the roof and lateral wall of the
posterior horn of the lateral ventricle and the lateral wall
of the inferior horn of the lateral ventricle; these fibers
are referred to as the Tapetum.

31. B. The anterior commissureThe anterior commissure :
is a small bundle
of nerve fibers
that
crosses the
midline in thein the
lamina terminalislamina terminalis.

32. C.Posterior Commissureosterior Commissure :
is a bundle of
nerve fibers that crosses
the midline immediately
above the opening of the
cerebral aqueductcerebral aqueduct into the
third ventricle.

33. 2. Association FibersAssociation Fibers :
• Association fibers are nerve fibers that
essentially connect various cortical regionsconnect various cortical regions
within the same hemispherewithin the same hemisphere and may be
divided into :
A.A. The shorT associaTion fibersThe shorT associaTion fibers
B. The long associaTion fibersThe long associaTion fibers :

35. • UncinateUncinate
Fasciculus :Fasciculus :
connects the
first motormotor
speech areaspeech area
and the gyri on
the inferior
surface of the
frontal lobefrontal lobe with
the cortex of the
pole of the
temporal lobetemporal lobe.
• Inferior Longitudinal Fasciculus :Inferior Longitudinal Fasciculus :
runs anteriorly from the occipitaloccipital
lobelobe, and is distributed to
the temporal lobetemporal lobe.
YPES OF ASSOCI ATI ON FI BERS :

36. Cingulum :Cingulum :
is a long,
curved fasciculus lying within the white matter of the
cingulate gyrus. It connects the frontal and parietal
lobes with parahippocampal and adjacent temporal
cortical regions.

37. • Superior Longitudinal Fasciculus :Superior Longitudinal Fasciculus :
is the
largest bundle of nerve fibers. It
connects the anterior part of theanterior part of the
frontal lobefrontal lobe to the occipitaloccipital and
temporal lobestemporal lobes.

38. • Fronto-occipital Fasciculus :Fronto-occipital Fasciculus :
connects the frontal lobefrontal lobe to
the occipitaloccipital and temporal lobestemporal lobes.

39. 3. Projection FibersProjection Fibers :
• Afferent and efferent nerve fibers passing to and from
the brainstem to the entire cerebral cortex must travel
between large nuclear masses of gray matter within
the cerebral hemisphere.
• At the upper part of the brainstemupper part of the brainstem, these fibers form a
compact band known as the internal capsule,
which is flanked medially by the caudate nucleus and
the thalamus and laterally by the lentiform nucleus.
Because of the wedge shape of the lentiform nucleus,
as seen on horizontal section, the internal capsule is
bent to form an anterior limbanterior limb and a posterior limbposterior limb,
which are continuous with each other at the genuthe genu.

40. • Once the nerve fibers have emerged superiorly
from between the nuclear masses, they radiate
in all directions to the cerebral cortex. These
radiating projection fibers are known as the
corona radiatacorona radiata.
• The nerve fibers of the internal capsule that
radiate toward the calcarine sulcus are known
as the optic radiationoptic radiation.

42. Cortical AreasCortical Areas

43. fronTal lobe

44. The precenTral area
• Includes the anterior wall of the central sulcus and
the posterior parts of the superior, middle, and
inferior frontal gyri;
• it extends over the superomedial border of the
hemisphere into the paracentral lobule.

45. The precenTral area
may be divided inTo :
• Primary motor area
(Brodmann area 4) :
The posterior region of
precentral area, its the motor
area, occupies the precentral
gyrus extending into the
paracentral lobule.
• Premotor area
(Brodmann area 6 and parts
of areas 8, 44, and 45) :It
occupies the anterior part of
the precentral gyrus and the
posterior parts of the superior,
middle, and inferior frontal gyri.

47. The primary moTor area
If electrically stimulated, produces:
• movements on the opposite side of the body
• contraction of muscle groups concerned with
the performance of a specific movement.
• Bilateral movements of extraocular muscles,
muscles of the upper part of the face, tongue,
and mandible, and larynx and pharynx also
occur.

48. The movement areas
of the body arebody are
represented inrepresented in
inverted forminverted form in the
precentral gyrus:
• Starting from below
and passing
superiorly are
structures involved in
swallowing and the
tongue, jaw, lips,
larynx, eyelid, and
brow.

49. • The next area is an
extensive region for
movements of the
fingers, especially
the thumb, hand,
wrist, elbow,
shoulder, and trunk.
• The movements of
the hip, knee, and
ankle are represent
-ed in the highest
areas of precentral
gyrus;

50. • the movements of
the Toes are
situated on the
medial surface of
the cerebral
hemisphere in the
paracentral lobule.
• The movements of
the anal and vesical
sphincters are also
located in the
paracentral lobuleparacentral lobule.

51. • The area of cortex controlling a particular
movement is proportional to the skill involved inis proportional to the skill involved in
performing the movementperforming the movement and is unrelated to
the mass of muscle participating in the
movement

52. The premoTor area
• which is wider superiorly than below and
narrows down to be confined to the anterior
part of the precentral gyrus.
• Electrical stimulation of the premotor area
produces muscular movements similar to those
obtained by stimulation of the primary motor
area; however, stronger stimulation is
necessary to produce the same degree of
movement.

53. • The function of the premotor area is to programis to program
activity of primary motor area.activity of primary motor area.
• It is particularly involved in controlling coarsecontrolling coarse
postural movementspostural movements through its connections
with the basal ganglia.

54. The supplemenTary moTor
area
• is situated in the medial frontal gyrus on the
medial surface of the hemisphere and anterior
to the paracentral lobule.
• Stimulation of this area results in movements of
the contralateral limbs, but aa stronger stimulusstronger stimulus
is necessary than when the primary motor area
is stimulated.
• Removal of the supplementary motor area
produces no permanent loss of movementno permanent loss of movement.

55. Frontal EyE
FiEld
• extends forward from
facial area of the
precentral gyrus into
middle frontal gyrus
(parts of Brodmann
areas 6, 8, and 9).
• Electrical stimulation
of this region
causes conjugate
movements of the
eyes, especially
toward the opposite
side.

56. • It controls voluntary scanning movements of
the eye and is independent of visual stimuli.
• thE involuntary Following oF moving
objEcts by thE EyEs : involves the visual
area of the occipital cortex to which the frontal
eye field is connected by association fibers.

57. thE motor spEEch
arEa oF broca
• is located in the inferior
frontal gyrus between
the anterior & ascending
rami and the ascending
and posterior rami of the
lateral fissure (Brodmann
areas 44 and 45).
• In the majority of
individuals, this area is
important on the left or
dominant hemisphere,
and ablation will result in
paralysis of speech.

58. • In those individuals in whom right
hemisphere is dominant, the area on the right
side is of critical importance. The ablation of
broca region in the nondominant hemisphere
( left side in this example) has no effect on
speech.
• brings about the formation of words by its
connections with the adjacent primary motor
areas; the muscles of the larynx, mouth,
tongue, soft palate, and the respiratory muscles
are appropriately stimulated.

59. thE prEFrontal cortEx
• Is an extensive area that lies anterior to the
precentral area.
• It includes the greater parts of the superior,
middle, and inferior frontal gyri; the orbital gyri;
most of the medial frontal gyrus; and the
anterior half of the cingulate gyrus (Brodmann
areas 9, 10, 11, and 12).
• Large numbers of afferent and efferent
pathways connect the prefrontal area with other
areas of the brain.

60. • The prefrontal area is concerned with the
makeup of the individual's
pErsonality.
• As the result of the input from many cortical
and subcortical sources, this area plays a role
as a
regulator of the person's depth of feeling.
• It also exerts its influence in determining the
initiative and
judgmEnt oF an individual.

61. pariEtal lobE

62. thE primary somEsthEtic arEa
(primary somatic sEnsory
cortEx s1)
• occupies the postcentral gyrus on the lateral surface
of the hemisphere and the posterior part of the
paracentral lobule on the medial surface (Brodmann
areas 3, 1, and 2).
• The primary somesthetic areas of the cerebral cortex
receive projection fibers from the ventral posteriorventral posterior
lateral and ventral posterior medial nuclei of thelateral and ventral posterior medial nuclei of the
thalamus.thalamus. S1

63. • The opposite 1/2 of
body is represented
as inverted :
• The pharyngeal
region, tongue, and
jaws are represented
in the most inferior
part of the postcentral
gyrus;
• this is followed by the
face, fingers, hand,
arm, trunk, and thigh.

64. • The leg and the foot
areas are found on
the medial surface of
the hemisphere in
the posterior part of
the paracentral
lobule.
• The anal and genital
regions are also
found in paracentral
lobule.

65. • The apportioning of the cortex for a particular
part of the body is related to its functional
importance rather than to its size. The face,
lips, thumb, and index finger have particularly
large areas assigned to them.

66. thE sEcondary somEsthEtic arEa
(sEcondary somatic sEnsory
cortEx s2)
• is in the superior lip of the posterior limb of the
lateral fissure.
• The secondary sensory area is much smallermuch smaller
and less importantand less important than the primary sensory
area.
S2

67. thE somEsthEtic association
arEa
• occupies the superior parietal lobule extending
onto the medial surface of the hemisphere
(Brodmann areas 5 and 7).
• This area has many connections with other
sensory areas of the cortex.
5 & 7

68. • It is believed that its main function is to
receive and integrate different sensoryreceive and integrate different sensory
modalitiesmodalities.
• For example, it enables one to recognizerecognize
objects placed in the hand without the help ofobjects placed in the hand without the help of
vision.vision.

69. occipital lobE
:

70. thE primary visual arEa
(brodmann arEa 17)
• is situated in the walls of the posterior part of thewalls of the posterior part of the
calcarine sulcuscalcarine sulcus and occasionally extends around the
occipital pole onto the lateral surfaceoccipital pole onto the lateral surface of the
hemisphere.
• The visual cortex receives afferent fibers from the
lateral geniculate bodylateral geniculate body. The fibers first pass forward in
the white matter of the temporal lobe and then turn
back to the primary visual cortex in the occipital lobe.
17

71. • The visual cortex receives fibers from the
temporal half of the ipsilateral retinatemporal half of the ipsilateral retina and the
nasal half of the contralateral retinanasal half of the contralateral retina.
• The right half of the field of vision, therefore, is
represented in the visual cortex of the left
cerebral hemisphere and vice versa.
• It is also important to note that the superior
retinal quadrants (inferior field of vision) pass to
the superior wall of the calcarine sulcus, while
the inferior retinal quadrants (superior field of
vision) pass to the inferior wall of the calcarine
sulcus.

72. Macula Lutea :
• which is the central area of the retinacentral area of the retina and the
area for most perfect visionmost perfect vision,
• is represented on the cortex in the posterior
part of area 17 and accounts for one-third of
the visual cortex.
• The visual impulses from the peripheral parts of
the retina terminate in concentric circles
anterior to the occipital pole in the anterior
part of area 17.

73. sEcondary visual arEa
(brodmann arEas 18 & 19) :
• surrounds the primary visual areasurrounds the primary visual area on the medial
and lateral surfaces of the hemisphere.
• This area receives afferent fibers from area 17
and other cortical areas as well as from the
thalamus.
• The function of the secondary visual area is to
relate the visual information received by therelate the visual information received by the
primary visual area to past visual experiences,primary visual area to past visual experiences,
thus enabling the individual to recognize and
appreciate what he or she is seeing.

74. Occipital Eye Field :
• Is thought to exist in the secondary visual areaexist in the secondary visual area
in humans.
• Stimulation produces conjugate deviation of the
eyes, especially to the opposite side.
• The function of is believed to be reflex and
associated with movements of the eye when
it is following an object.

75. tEmporal lobE

76. thE primary auditory arEa
(brodmann arEas 41 and 42)
• includes gyrus of
Heschl and is situ-
ated in the inferior
wall of the lateral
sulcus.
• Projection fibers to
auditory area arise
principally in medialmedial
geniculate bodygeniculate body &
form auditory radiationauditory radiation

77. • The anterior part of the primary auditory area
is concerned with the reception of sounds of
low frequencylow frequency
• The posterior part of the area is concerned
with the sounds of high frequencyhigh frequency.
• a unilatEral lEsion oF thE auditory
arEa produces partial deafness in both ears,
the greater loss being in the contralateral ear.

78. thE sEcondary auditory arEa
(auditory association cortEx)
(brodmann arEa 22) :
• Is situated posterior
to the primary audit-
ory area in the later-
al sulcus and in the
superior temporal
gyrus
• Is thought to be necessary for the interpretationnecessary for the interpretation
of soundsof sounds and for the association of the
auditory input with other sensory information.

79. thE sEnsory spEEch arEa oF wErnickE
• is localized in the leftleft
dominant hemispheredominant hemisphere,
• mainly in the superior
temporal gyrus, with
extensions around the
posterior end of the
lateral sulcus into the
parietal region.
• Is connected to the Broca area by a bundle of
nerve fibers called the arcuate fasciculus.

80. • It receives fibers from the visual cortexvisual cortex in the
occipital lobe and the auditory cortexauditory cortex in the
superior temporal gyrus.
• The Wernicke area permits the understanding
of the written and spoken language
• So, it enables a person to read a sentence,
understand it, and say it out loud .
• Since the Wernicke area represents the site on
the cerebral cortex where somatic, visual, and
auditory association areas all come together,
it should be regarded as an area of very great
importance.

81. Other Cortical Areas :
• thE tastE arEa (brodmann arEa 43) :
is situated at the lower end of thelower end of the
postcentral gyruspostcentral gyrus in the superior wall of the
lateral sulcus and in the adjoining area of theadjoining area of the
insulainsula.
• Ascending fibers come from the nucleus
solitarius ventral posteromedial nucleus of
the thalamus, cortex.

82. The vesTibular area :
• is believed to be situated nearsituated near the part of thethe part of the
postcentral gyrus concerned with sensations ofpostcentral gyrus concerned with sensations of
the facethe face and lies opposite the auditory area in
the superior temporal gyrus.
• The vestibular area and the vestibular part of
the inner ear are concerned with appreciation
of the positions and movements of the head
in space.
• Influenced in the maintenance of posture.

83. The insula :
• is an area of the cortex that is buried within the
lateral sulcus and forms its floor.
• It can be examined only when the lips of the
lateral sulcus are separated widely.
• Its fiber connections are incompletely known.
• It is believed that this area is important for
planning or coordinating the articulatoryplanning or coordinating the articulatory
movements necessary for speech.movements necessary for speech.

84. Blood Supply of the Brain
1. Arteries of the Brain :
• The brain is supplied by the two internal carotid
and the two vertebral arteries.
• The four arteries lie within the subarachnoid
space,
• their branches anastomose on the inferior
surface of the brain to form the circle of Willis.

85. 1. Internal Carotid Artery :
• It ascends the neck
and perforates the
base of the skull
by passing through the
carotid canal of the
temporal bone.
• The artery then runs
horizontally forward
through the cavernouscavernous
sinussinus .

86. • It now enters the subarachnoid space by
piercing the arachnoid mater and turns to
the region of the medial end of the lateral
cerebral sulcus.
Here, it divides into :
• Anterior Cerebral arteries
• Middle Cerebral arteries.

87. Branches Of The Cerebral Portion Of
Internal Carotid artery :
1. Ophthalmic artery
2. Posterior communicating artery
3. Choroidal artery
4. Anterior Cerebral Artery
5. Middle Cerebral Artery

88. Anterior Cerebral Artery :
The cortical branches supply all the medial
surface of the cerebral cortex as far back as
the parieto-occipital sulcus.
• They also supply a strip of cortex about 1 inch
(2.5 cm) wide on the adjoining lateral surface.
• The anterior cerebral artery thus supplies the
“leg area” of the precentral gyrus.
• A group of central branches pierces the anterior
perforated substance and helps to supply parts
of the lentiform and caudate nuclei and the
internal capsule.

90. Medial Surface

91. Lateral Surface

92. Middle Cerebral Artery :,
• the largest branch of the internal carotid, runs
laterally in the lateral cerebral sulcus.
• Cortical branches supply the entire lateral
surface of the hemisphere, except for the
narrow strip supplied by the anterior cerebral
artery, the occipital pole, and the inferolateral
surface of the hemisphere, which are supplied
by the posterior cerebral artery.
• This artery thus supplies all The
moTor area excepT The “leg
area.”
• Central branches enter the anterior perforated

93. Medial Surface

94. Lateral Surface

95. B. Vertebral Artery :
• A branch of the first part of the subclavian
artery,
• It enters the skull through the foramen magnumthe foramen magnum
and pierces the dura mater and arachnoid to
enter the subarachnoid space.
• At the lower border of the pons, it joins the
vessel of the opposite side to form the basilarform the basilar
artery.artery.

96. Branches of the Cranial Portion
1.The meningeal branches
2. The posterior spinal artery
3. The posterior inferior cerebellar artery
4. The medullary arteries
5. The basilar artery.

97. Basilar Artery :
• formed by the
union of the two
vertebral arteries,
ascends in a
groove on the
anterior
surface of
pons .
• At the upper
border of pons,
it divides into
the two posteriortwo posterior
cerebral arteriescerebral arteries.

98. Branches Of Basilar Artery :
1. The pontine arteries
2. The labyrinthine artery
3. The anterior inferior cerebellar artery
4. The superior cerebellar artery
5. The posterior cerebral artery

99. The posterior cerebral artery :
• Curves laterally and backward around the midbrain
and is joined by the posterior communicating
branch of the internal carotid artery.
• Cortical branches supply the inferolateral and
medial surfaces of the temporal lobe and the lateral
and medial surfaces of the occipital lobe.
• Thus, the posterior cerebral artery supplies the
visual cortex.
• Central branches pierce the brain substance and
supply parts of the thalamus and the lentiform
nucleus as well as the midbrain, the pineal, and the
medial geniculate bodies.

100. Medial Surface

101. Lateral Surface

102. Circle of Willis
• The circle of Willis lies in the interpeduncular
fossa at the base of the brain. It is formed
by the anastomosis between the two internal
carotid arteries and the two vertebral arter-
ies.
• The circle is formed by :
1. anterior cerebral arteries,
2. The anterior communicating arteries,
3. internal carotid arteries,
4. posterior communicating arteries,
5. posterior cerebral arteries
6. basilar artery

103. • The circle of Willis allows blood that enters by
either internal carotid or vertebral arteries to be
distributed to any part of both cerebral
hemispheres. Cortical and central branches
arise from the circle and supply the brain
substance.
• Variations in the sizes of the arteries forming
the circle are common, and the absence of one
or both posterior communicating arteries has
been reported.