Corpus Callosum

Table of Contents

What Is Corpus Callosum?

The corpus callosum is a thick and flat bundle of nerve fibres that connect the left and right hemispheres of the brain. It is a commissural region that is composed of almost 200 densely myelinated nerve fibres.

This structure is found only in placental mammals. It encompasses the longitudinal fissure of the brain, thus enabling communication between the two hemispheres. It is the largest white matter structure in the human brain. The main nerve tracts found in the corpus callosum are the rostrum, genu, trunk and splenium.

Structure

• The corpus callosum forms the base of the longitudinal fissure, a structure that separates the two hemispheres of the brain.
• A certain part of the corpus callosum is known to form the roof of the lateral ventricles.
• The four distinguishing parts of the corpus callosum include the genu, rostrum, trunk and splenium.
• Between the trunk and splenium is found a narrowed part that is known as the isthmus.
• Nerve bundles from the trunk and splenium are known as tapetum; they form the roof of each lateral ventricle.
• The genu, or the knee, is present towards the frontal lobes. It has a backward and downward curvature that slowly becomes thin.
• The rostrum, which is named so because of its similar appearance to a bird’s beak, stretches from the interventricular foramina to the optic stalk.
• The splenium is found towards the cerebellum; it is the thickest part that covers the third ventricle and midbrain and ends in a convex, thick border.
• The nerve fibres radiate from either side of the corpus callosum through the white matter into the cerebral cortices.
• The ones that curve forward from the genu towards the frontal lobes are called the forceps anterior or forceps minor.
• The ones that curve backwards from the splenium towards the occipital lobes are known as forceps posterior or forceps major.
• Between the forceps major and forceps minor is the tapetum with the main body of the nerve tract; it tends to extend laterally from either side of the temporal lobe covering the middle portion of the lateral ventricle.
• The anterior commissures and the tapetum share the function of connecting the two cerebral hemispheres.
• Myelination in the nerve fibres of the corpus callosum is directly linked to the functions they elicit; those with dense myelination are thick and fast conducting, whereas those with thin myelination are slow conducting.
• The thin axons from the genu connect the prefrontal cortex; these fibres arise from the tapetum from fork-like bundles of fibres.
• The thick axons arise from the trunk and connect the areas of the motor and visual cortex.
• The splenium functions to relay somatosensory information in the parietal and occipital lobes with the help of the fibres of the forceps major.

Corpus Callosum in Different Sexes

Major scientific studies have been carried out to find out the differences in corpus between men and women. An advanced MRI technique showed that the midsagittal corpus callosum is bigger in females than in males.

The rate of diffusion of molecules in and out of the tissues, known as anisotropy, has significant differences between the two sexes and also depends on the size and shape of the callosum.

Another study showed that people who are left-handed and ambidextrous have a bigger corpus callosum as compared to right-handed people. However, this study needs more research.

Clinical Significance

1. Marchiafava–Bignami disease: It is a progressive neurological disease that is characterised by loss of myelination and necrosis of the nerve fibres of the corpus callosum. Symptoms of the condition include depression, coma, ataxia and seizures. Significant lesions can also be seen in the corpus callosum. The main cause of the condition is alcoholism and sometimes nutritional deficiencies.
2. Epilepsy: Epilepsy is another neurological disorder that is characterised by recurrent seizures, which can lead to physical injuries. This condition is difficult to treat; however, some symptoms can be controlled by performing a corpus callosotomy lobotomy paralysis operation. It limits the spread of epileptic activity between the two halves of the brain.

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Also Read:

• Structure, Diagram, Parts of Human Brain
• Cerebrum: Anatomy, Function and Location
• Difference between Cerebellum and Cerebrum
• Hindbrain – Short Notes for NEET Biology
• MCQs on Human Brain for NEET 2022