White matter of cerebrum dr.gosai

Ojvensha E learning Resources-Prepared by Dr.B.B.Gosai

White matter of Cerebrum Introduction:

White matter of cerebrum is formed by nerve fibers in the cerebrum.

Types of Fibers forming white matter of Cerebrum: (*****Important - Viva)

Commissural fibers: These fibers connect two cerebral hemispheres passing across the midline. Example: Corpus Callosum

Association fibers: These fibers connect different parts of same cerebral hemisphere. Example: Superior longitudinal bundle

Projection fibers: These fibers connect cortex of cerebral hemisphere to any lower centers. Example: Internal capsule containing corticospinal tract

(No need to draw this diagram- only for understanding)


Commissural Fibers (*****Important - Viva)

Definition: These fibers connect two cerebral hemispheres passing across the midline.

Examples:

1. Corpus Callosum

2. Anterior commissure

3. Posterior commissure

4. Habenular commissure

5. Commissure of fornix

Corpus Callosum (*****Most Important Short note - Viva) Definition: Corpus Callosum is largest commissure of brain which connects all the parts

of two cerebral hemispheres passing across the midline except anteroinferior part of temporal lobe.

Parts of Corpus Callosum:

1. Rostrum

2. Genu

3. Trunk (Body)

4. Splenium

Draw this Diagram for the short note)


Rostrum: This part runs downwards and backwards from Genu and tapers to continue with Lamina terminalis.

Relations of Rostrum:

• Inferiorly: Anterior cerebral artery

• Superiorly : Lateral ventricle (Anterior horn)

Genu: This part is bend between the rostrum and trunk. It is located 4 cms behind the frontal pole.

Relations of Genu:

• Antriorly: Anterior cerebral artery

• Poseriorly : Lateral ventricle (Anterior horn)

Trunk (Body): This large part located between the genu and splenium. Its superior surface is concavo-convex

Relations of Trunk (Body):

• Superiorly : Anterior cerebral artery, Falx cerebri and Inferior sagittal sinus

• Inferiorly: Lateral ventricle (Anterior horn and central part)

Splenium: This part is posterior most part of corpus callosum. It is located 6 cms in front of the occipital pole.

Relations of Splenim:

• Poseriorly : Pineal gland

Fibers in Corpus Callosum:

1. Forceps minor: These fibers connect two frontal lobes and forms small fork.

2. Forceps major: These fibers connect two occipital lobes and forms larger fork.

3. Tapetum: These fibers connect two temporal lobes and forms strip like fibers and do not interdigitate with corona radiate fibers.

4. Rest of the fibers connect two parietal lobes and interdigitate with corona radiate fibers


(Draw this Diagram for the short note)

Function of Corpus Callosum:

1. Coordination of activities of two cerebral hemispheres especially for the steriognosis (Identification of objects with closed eye).

Applied Anatomy of Corpus Callosum:

1. Corpus callosum can be congenitally absent without causing any abnormal effects as both hemispheres learn to keep steriognosis

2. Due to this finding many neurological operations are planned by cutting the corpus callosum.

3. Such operative procedures in blind leads to miserable dependent life as Steriognosis is lost (Asteriognosis: Inability to identify objects with closed eyes). Steriognosis is most important for blind for their all day to day activities.

4. Postoperative advice to any person when corpus callosum is cut is to accompany while moving in the dark location.


Other commissures

1. Anterior commissure: located in upper part of lamina terminalis connecting anteroinferior part of temporal lobe

2. Posterior commissure: located in lower stalk of pineal gland connecting pretectal region

3. Habenular commissure: located in upper stalk of pineal gland connecting hebenular nuclei

4. Commissure of fornix: located in the posterior part of fornix connecting two hippocampal nuclei

Association Fibers (***Important - Viva)

Definition: These fibers connect different parts of same cerebral hemisphere.

Types of Association Fibers:

Short Association Fibers: These fibers connect adjacent gyri of same hemisphere.

Long Association Fibers: These fibers connect distant areas of same hemisphere.

Examples:

1. Superior longitudinal Bundle: Connect Frontal lobe with occipital lobe

2. Inferior longitudinal Bundle: Connect Temporal lobe with occipital lobe

3. Fasciculus Uncinatus: Connect Frontal lobe with temporal lobe

4. Cingulum (Seen on Medial surface within Cingulate gyrus): Connect parts of limbic system


Projection fibers: These fibers connect cortex of cerebral hemisphere to any lower centers. Example: Internal capsule containing corticospinal tract

Internal capsule: (*****Most Important Short note - Viva)

Definition: Internal capsule consists of projection fibers connecting cortex of cerebrum to any lower centers.

Location: Located between Lentiform nucleus (L) (Laterally) and Caudate nucleus (C) and Thalamus (Th) (Medially).

Shape: “V” shape in Horizontal section of cerebrum



Parts of Internal capsule:

1. Anterior limb

2. Posterior limb

3. Genu

4. Retrolentiform part (Optic radiation)

5. Sublentiform part (Auditory Radiation) (Cannot be seen in Horizontal Section)

(No need to draw this diagram- only for understanding)



Anterior limb: located between Lentiform nucleus laterally and Caudate nucleus medially.

Fibers in the anterior limb:

• Afferent fiber: Thalamocortico radiation

• Efferent fiber : Corticopontine fibers

Genu: located between anterior and posterior limb.

Fibers in the Genu:

• Efferent fibers:

• Corticonuclear fibers

• Corticospinal tract for upper limb and upper half of trunk

Posterior limb: located between Lentiform nucleus laterally and Thalamus medially.

Fibers in the posterior limb:

• Afferent fiber: Thalamocortico radiation

• Efferent fiber :

• Corticospinal tract for lower limb and lower part of trunk

• Corticorubral tract

• Corticopontine fibers


Retrolentiform part (Optic radiation): located behind Lentiform nucleus.

Fibers in the retrolentiform part:

• Afferent fiber: Optic radiation-part of visual pathway from lateral geniculate body to visual area of occipital lobe

Sublentiform part (Auditory radiation): located below Lentiform nucleus.

Fibers in the sublentiform part:

• Afferent fiber: Auditory radiation-part of auditory pathway from medial geniculate body to auditory area of temporal lobe

Blood supply of Internal Capsule:

1. Anterior limb (Upper part): Middle cerebral Artery (Internal Carotid Artery).

2. Anterior limb (lower part): Anterior cerebral artery (Internal Carotid Artery).

3. Genu (Upper part): Middle cerebral Artery (Internal Carotid Artery).

4. Genu (lower part): Recurrent branch of Anterior cerebral artery (Heubner’s Artery)

5. Posterior limb (upper part): Charcot’s artery of cerebral hemorrhage (Lenticulostriate branch of Middle cerebral artery)

6. Posterior limb (lower part): Anterior choroidal artery (Internal Carotid Artery).

7. Retrolentiform part: Posterior cerebral artery (Basilar artery)

8. Sublentiform part: Anterior choroidal artery (Internal Carotid Artery).

Applied Anatomy of Internal capsule:

1. Fibers in the internal capsule are compactly arranged. Hence even a small lesion (damage) can lead to wide spread effects.

2. The common lesion is due to cerebral hemorrhage or cerebral thrombosis. It results in complete hemiplegia on the opposite side (contralateral hemiplegia).

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White matter of cerebrum dr.gosai