Corpus Callosum

Corpus Callosum

Question 1. Enumerate the various commissures of the brain.
Answer:

The important commissures of the brain:

• Corpus callosum
• Anterior commissure
• Posterior commissure
• Hippocampal commissure
• Habenular commissure

Corpus callosum

Question 2. Describe the corpus callosum under the following headings:

1. Definition,
2. Parts,
3. The course of fibres,
4. Functions and
5. Applied anatomy.
   

Answer:

Corpus Callosum Definition: The corpus callosum is the largest commissure of the brain. It is 10 cm long, which is nearly half of the anteroposterior length of the cerebrum. It consists of 300 million fibres. The corpus callosum connects all the parts of the neocortex, except for the lower and anterior parts of the temporal lobes, which are connected by the anterior commissure.

Corpus Callosum Parts In the sagittal section, the corpus callosum is divided into four parts, from before to back:

• Rostrum
• Genu
• Body/trunk
• Splenium

The corpus callosum begins at the anterior commissure in the upper part of the lamina terminalis, which passes upwards and forwards as the rostrum, then bends sharply upwards and backwards to form the genu, and finally, it extends backwards as the body and ends posteriorly as a thick, massive extremity called the splenium.

Parts of the corpus callosum

• Its inferior surface is connected in the midline with the upper surface of the fornix by the septum pellucidum, which lies between the two lateral ventricles.
• Its superior surface is related to the indusium griseum and medial and lateral longitudinal striae.

The course of the fibres of the corpus callosum

• The fibres of the genu curve forwards on each side towards the frontal cortex, forming the forceps minor.
• The fibres of the body spread out laterally on each side to form the roof of the central part of the lateral ventricle. These fibres are intersected by the vertically running fibres of the corona radiata.
• The fibres of the splenium curve backwards on each side towards the occipital cortex, forming the forceps major. Its fibres form the upper part of the medial wall of the posterior horn of the lateral ventricle.

Corpus callosum functions

• The fibres of the posterior part of the brain, dyed together with some fibres from the splenium, extend laterally to form the roof of the posterior horn of the lateral ventricle and then turn downwards to form the lateral wall of both the posterior and inferior horns.

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Functions

• Interhemispheric transfer of learned/visual memory.
• Interhemispheric transfer of speech function.
• Coordination of activities of the two cerebral hemispheres for proper bilateral coordination and responses.

Corpus callosum lesion

Applied anatomy

• Patients with lesions of the corpus callosum respond as if they have two separate brains – a condition called the Split-brain effect/syndrome.
• A surgical section of the corpus callosum has been attempted in the past to prevent the spread of seizures.