Human Anatomy - Kotsan I. Ya. 2009

Pathways of the brain and spinal cord
Commissural pathways

Commissural pathways connect corresponding centers (Gray matter) of the right and left cerebral hemispheres. They serve as the morphological substrate that ensures the Structural and functional unity of paired Brain activity. Passing from one hemisphere to the other, the fibers of the commissural pathways form the so-called cerebral commissures: the corpus callosum, anterior commissure, epithalamic (posterior) commissure, fornix commissure, and interthalamic adhesion.

The corpus callosum is the largest cerebral commissure, found exclusively in mammals. It contains fibers that connect newer, evolutionarily younger brain regions and the cortical centers of the right and left hemispheres. Here, the fibers diverge in a fan-like manner to form the radiation of the corpus callosum (radiatio corporis callosi).

Commissural fibers passing through the genu and rostrum of the corpus callosum interconnect the cortical areas of the frontal lobes of the right and left cerebral hemispheres. Curving anteriorly, these fiber bundles seemingly embrace the anterior part of the longitudinal cerebral fissure from both sides, forming the forceps minor (frontal forceps) (forceps (minor) frontalis).

The body (truncus) of the corpus callosum contains nerve fibers that connect the cortex of the central gyri, parietal lobes, and temporal lobes of both cerebral hemispheres.

The splenium of the corpus callosum consists of fibers connecting the cortex of the occipital lobes and the posterior PARTS OF THE parietal lobes of the right and left cerebral hemispheres. Curving posteriorly, these fiber bundles embrace the posterior parts of the longitudinal cerebral fissure, forming the forceps major (occipital forceps) (forceps (major) occipitalis).

The anterior cerebral commissure (comissura cerebri anterior) is a horseshoe-shaped bundle of fibers belonging to the olfactory pathway. Located anterior to the columns of the fornix, the anterior commissure consists of a smaller anterior part—whose fibers interconnect the olfactory bulb, olfactory tubercle, and anterior perforated substance of the right and left hemispheres—and a larger posterior part, which connects the anteromedial temporal lobes (not connected by corpus callosum fibers) and the parahippocampal gyri.

The epithalamic (posterior) commissure (comissura epithalamica (posterior)) is located in the region of the posterior wall of the Third ventricle. The fibers of this commissure interconnect the pulvinar thalami and link them with subcortical visual centers.

The commissure of the fornix (comissura fornicis), or hippocampal commissure, is a thin, triangular sheet of White matter situated between the Inferior surface of the splenium of the corpus callosum and the crura of the fornix. As an evolutionarily older Structure belonging to the olfactory system, the fornix commissure is composed of transverse fibers that interconnect the hippocampal structures of the right and left cerebral hemispheres. Research has shown that the hippocampus is involved not only in olfactory Functions but also in The formation of emotional responses (such as fear, rage, anger, and depression).

The commissural fibers of the Spinal Cord pass through the anterior white commissure (comissura alba anterior) and the posterior white commissure (comissura alba posterior).