By

Dr.Faris Al-Haddad

M.B.Ch.B, PhD AnatomyCollege of Medicine,

Hawler Medical UniversityArbil, Iraq

e-mail: farisurgeon@gmail.com

Forebrain

External features

Surfaces :

1. Superolateral surface

2. Medial surface

3. Inferior surface

Sulci :

1. Central sulcus,

2. Lateral sulcus,

3. Parieto-occipital sulcus,

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).

Superolateral surface

1. Lateral sulcus:

2. Opercula:

Insula

Central Sulcus

4. Frontal gyri:

5. Temporal Gyrus:

5. Parietal lobe :

6. Occipital lobe:

2. Medial surface :

1. Corpus callosum

2. The medial frontal gyrus

3. Cingulate sulcus & Cingulate gyrus

4. parieto-occipital sulcus

5. Calcrine sulcus

Paracentrallobule

Precuneus

Cuneus

Lingual

3. Inferior surface

Gyrus rectus

Olfactory sulcus

Olfactory bulb Olfactory tract ,

Orbital gyri & Sulci

Occipitotemporal sulcus

Collateral sulcus

Parahipocampus

Lingual

Lateral Occipitotemporal

Uncus

INTERNAL FEATURES

White Matter of the Cerebral Hemispheres

• The white matter is composed of myelinated myelinated 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.

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.

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 end of the lamina terminalis.

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

3.3. SpleniumSplenium : thickened posterior

portion

• Forceps minor : the fibers directed laterally of the genu curve forward into the frontal lobes

• Radiation of Corpus Radiation 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.

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

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

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.

2. Association FibersAssociation Fibers :

• Association fibers are nerve fibers that essentially connect various cortical regions connect 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 :

• Uncinate Uncinate Fasciculus :Fasciculus : connects the first motor motor 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 occipital occipital

lobelobe, and is distributed to the temporal lobetemporal lobe.

TYPES OF ASSOCIATION FIBERS :

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.

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

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

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.

• 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.

Cortical AreasCortical Areas

Frontal Lobe

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.

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.

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.

The movement areas of the body are body are represented in represented 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.

• 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;

• 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.

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

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.

• The function of the premotor area is to program is to program activity of primary motor area. activity of primary motor area.

• It is particularly involved in controlling coarse controlling coarse postural movementspostural movements through its connections with the basal ganglia.

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 a a 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.

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.

• 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.

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.

• 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.

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.

• 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.

Parietal Lobe

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 posterior lateral ventral posterior lateral and ventral posterior medial nuclei of the thalamus. and ventral posterior medial nuclei of the thalamus.

S1

• 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.

• 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.

• 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.

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 smaller much smaller and less importantand less important than the primary sensory area.

S2

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

• It is believed that its main function is to receive and integrate different sensory receive and integrate different sensory modalitiesmodalities.

• For example, it enables one to recognize recognize objects placed in the hand without the help of objects placed in the hand without the help of vision. vision.

Occipital Lobe :

The primary visual area (Brodmann area 17)

• is situated in the walls of the posterior part of the walls 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 lateral geniculate bodygeniculate 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

• 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.

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.

Secondary visual area (Brodmann areas 18 & 19) :

• surrounds the primary visual area surrounds 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 the relate 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.

Occipital Eye Field :

• Is thought to exist in the secondary visual area exist 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.

Temporal Lobe

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 medial medial geniculate body geniculate body & form auditory radiationauditory radiation

of the internal capsule.

• 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.

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 interpretation necessary for the interpretation of soundsof sounds and for the association of the auditory input with other sensory information.

The sensory speech area of Wernicke

• is localized in the left left 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.

• 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.

Other Cortical Areas :• The taste area (Brodmann area 43) :

is situated at the lower end of the postcentral lower end of the postcentral gyrusgyrus in the superior wall of the lateral sulcus and in the adjoining area of the insulaadjoining area of the insula.

• Ascending fibers come from the nucleus solitarius ventral posteromedial nucleus of the thalamus, cortex.

The vestibular area :

• is believed to be situated nearsituated near the part of the the part of the postcentral gyrus concerned with sensations of postcentral 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.

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 articulatory planning or coordinating the articulatory movements necessary for speech.movements necessary for speech.

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.

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 cavernous cavernous sinussinus .

• 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.

Branches Of The Cerebral Portion Of Internal Carotid artery :

1. Ophthalmic artery

2. Posterior communicating artery3. Choroidal artery4. Anterior Cerebral Artery5. Middle Cerebral Artery

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.

Medial Surface

Lateral Surface

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 substance and supply the lentiform and caudate nuclei and the internal capsule.

Medial Surface

Lateral Surface

B. Vertebral Artery :• A branch of the first part of the subclavian

artery, • It enters the skull through the foramen magnum the 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 basilar form the basilar artery.artery.

Branches of the Cranial Portion1.The meningeal branches 2. The posterior spinal artery 3. The posterior inferior cerebellar artery

4. The medullary arteries5. The basilar artery.

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 two posterior cerebral posterior cerebral arteriesarteries.

Branches Of Basilar Artery :1. The pontine arteries2. The labyrinthine artery 3. The anterior inferior cerebellar artery 4. The superior cerebellar artery 5. The posterior cerebral artery

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.

Medial Surface

Lateral Surface

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

• 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.