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The corpus callosum, also callosal commissure, is a wide, thick nerve tract, consisting of a flat bundle of commissural fibers, beneath the cerebral cortex in the brain. The corpus callosum is only found in placental mammals. It spans part of the longitudinal fissure, connecting the left and right cerebral hemispheres, enabling communication between them. It is the largest white matter structure in the human brain, about ten centimetres in length and consisting of 200–300 million axonal projections.
The vertebrate cerebrum (brain) is formed by two cerebral hemispheres that are separated by a groove, the longitudinal fissure. The brain can thus be described as being divided into left and right cerebral hemispheres. Each of these hemispheres has an outer layer of grey matter, the cerebral cortex, that is supported by an inner layer of white matter. In eutherian (placental) mammals, the hemispheres are linked by the corpus callosum, a very large bundle of nerve fibers. Smaller commissures, including the anterior commissure, the posterior commissure and the fornix, also join the hemispheres and these are also present in other vertebrates. These commissures transfer information between the two hemispheres to coordinate localized functions.
The cingulate cortex is a part of the brain situated in the medial aspect of the cerebral cortex. The cingulate cortex includes the entire cingulate gyrus, which lies immediately above the corpus callosum, and the continuation of this in the cingulate sulcus. The cingulate cortex is usually considered part of the limbic lobe.
The fornix is a C-shaped bundle of nerve fibers in the brain that acts as the major output tract of the hippocampus. The fornix also carries some afferent fibers to the hippocampus from structures in the diencephalon and basal forebrain. The fornix is part of the limbic system. While its exact function and importance in the physiology of the brain are still not entirely clear, it has been demonstrated in humans that surgical transection – the cutting of the fornix along its body – can cause memory loss. There is some debate over what type of memory is affected by this damage, but it has been found to most closely correlate with recall memory rather than recognition memory. This means that damage to the fornix can cause difficulty in recalling long-term information such as details of past events, but it has little effect on the ability to recognize objects or familiar situations.
The longitudinal fissure is the deep groove that separates the two cerebral hemispheres of the vertebrate brain. Lying within it is a continuation of the dura mater called the falx cerebri. The inner surfaces of the two hemispheres are convoluted by gyri and sulci just as is the outer surface of the brain.
In neuroanatomy, the cingulum is a nerve tract – a collection of axons – projecting from the cingulate gyrus to the entorhinal cortex in the brain, allowing for communication between components of the limbic system. It forms the white matter core of the cingulate gyrus, following it from the subcallosal gyrus of the frontal lobe beneath the rostrum of corpus callosum to the parahippocampal gyrus and uncus of the temporal lobe.
The posterior cerebral artery (PCA) is one of a pair of arteries that supply oxygenated blood to the occipital lobe, part of the back of the human brain. The two arteries originate from the distal end of the basilar artery, where it bifurcates into the left and right posterior cerebral arteries. These anastomose with the middle cerebral arteries and internal carotid arteries via the posterior communicating arteries.
Brodmann area 33, also known as pregenual area 33, is a subdivision of the cytoarchitecturally defined cingulate region of cerebral cortex. It is a narrow band located in the anterior cingulate gyrus adjacent to the supracallosal gyrus in the depth of the callosal sulcus, near the genu of the corpus callosum. Cytoarchitecturally it is bounded by the ventral anterior cingulate area 24 and the supracallosal gyrus (Brodmann-1909). The pregenual area 33 is heavily involved in emotions, especially happy emotions.
The tuber cinereum is a hollow eminence of the middle–ventral hypothalamus, specifically the arcuate nucleus, situated between the mammillary bodies and the optic chiasm. In addition to the ventral hypothalamus, the tuber cinereum includes the median eminence and pituitary gland. Together with the hollow itself, it is sometimes referred to as the pituitary stalk.
The commissural fibers or transverse fibers are axons that connect the two hemispheres of the brain. In contrast to commissural fibers, association fibers connect regions within the same hemisphere of the brain, and projection fibers connect each region to other parts of the brain or to the spinal cord.
In the human brain, the entorhinal cortex appears as a longitudinal elevation anterior to the parahippocampal gyrus, with a corresponding internal furrow, the external rhinal sulcus, separating it from the inferiolateral surface of the hemisphere close to the lamina terminalis. It is analogous to the collateral fissure found further caudally in the inferior part of the temporal lobe.
The indusium griseum, consists of a thin membranous layer of grey matter in contact with the upper surface of the corpus callosum and continuous laterally with the grey matter of the cingulate cortex.
The chiasmatic cistern is formed as the interpeduncular cistern extends forward across the optic chiasm and onto the upper surface of the corpus callosum – the arachnoid stretches across from one cerebral hemisphere to the other immediately beneath the free border of the falx cerebri, and thus leaves a space in which the anterior cerebral arteries are contained. The "leaf" or extension of the chiasmatic cistern above the chiasma, which is separated from the optic recess of the third ventricle by the thin lamina terminalis, has been called the suprachiasmatic cistern. As spaces filled with freely circulating cerebrospinal fluid, cisterns receive little direct study, but are mentioned in pathological conditions. Cysts and tumors of the lamina terminalis extend into the suprachiasmatic cistern, as can pituitary tumors, or the cistern can be partially or completely effaced by injury and hematoma or by blockage of the cerebral aqueduct.
A nerve tract is a bundle of nerve fibers (axons) connecting nuclei of the central nervous system. In the peripheral nervous system this is known as a nerve, and has associated connective tissue. The main nerve tracts in the central nervous system are of three types: association fibers, commissural fibers, and projection fibers. A tract may also be referred to as a commissure, decussation, pathway or fasciculus. A commissure connects the two cerebral hemispheres at the same levels, while a decussation connects at different levels.
The cingulate gyrus commences below the rostrum of the corpus callosum, curves around in front of the genu, extends along the upper surface of the body, and finally turns downward behind the splenium, where it is connected by a narrow isthmus with the parahippocampal gyrus.
The subparietal sulcus or suprasplenial sulcus is a sulcus, or crevice, on the medial surface of each cerebral hemisphere, above the splenium of the corpus callosum. It separates the precuneus from the posterior part of the cingulate gyrus. It is the posterior continuation of the cingulate sulcus. The cingulate sulcus actually "terminates" as the marginal sulcus of the cingulate sulcus. It extends posteriorly toward the calcarine sulcus.
This article describes anatomical terminology that is used to describe the central and peripheral nervous systems - including the brain, brainstem, spinal cord, and nerves.
