Human Anatomy Part 2 - K. A. Diubenko, A. K. Kolomiitsev, Yu. B. Chaikovskyi 2008

Special Part
Nervous system, systema nervosum - Special Part
Pallium

The surface of the hemispheres is covered by the mantle, pallium, which is formed by Gray matter—the Cerebral Cortex, cortex cerebralis. The cerebral hemispheres correspond in shape to the Skull. Three surfaces are distinguished in each hemisphere:

- the Superolateral surface of the cerebral hemisphere, facies superolateralis hemispherii cerebri;

- the Medial surface of the cerebral hemisphere, facies medialis hemispherii cerebri;

- the Inferior surface of the cerebral hemisphere, facies inferior hemispherii cerebri.

The superolateral surface of the hemisphere is convex in all directions and conforms to the shape of the skull bones. The medial surface is flat, faces the medial surface of the opposite hemisphere, and they are separated from each other superiorly by the falx cerebri of the dura mater. The inferior surface lies on the cranial base, adjoining it anteriorly, and touching the tentorium cerebelli posteriorly. The surface of the hemispheres is divided by numerous cerebral sulci, sulci cerebri, of varying depth and length, between which lie the gyri, giving the hemispheres a folded appearance. The sulci divide the hemispheres into regions called lobes of the cerebrum. There are five lobes in each hemisphere:

- frontal lobe, lobus frontalis;

- parietal lobe, lobus parietalis;

- temporal lobe, lobus temporalis;

- occipital lobe, lobus occipitalis;

- insula, insula*.

Along with the surfaces, several poles are distinguished in the hemispheres: the frontal pole, polus frontalis, the occipital pole, polus occipitalis, and the temporal pole, polus temporalis.

The superolateral surface of the cerebral hemisphere, facies superolateralis hemispherii cerebri (Fig. 151).

On the superolateral surface of the hemisphere is the lateral sulcus, sulcus lateralis, or Sylvian fissure**, which extends from the Base of the Brain as a deep cleft and divides into three branches: two short ones—the anterior branch, ramus anterior, and the ascending branch, ramus ascendens—and a long posterior branch, ramus posterior, which is directed posteriorly and superiorly.

Running from top to bottom across the middle of the superolateral surface is the central sulcus, sulcus centralis, or Rolando's***, which does not reach the lateral sulcus. Anterior to the central sulcus and superior to the lateral sulcus lies the region of the hemisphere belonging to the frontal lobe. Posterior to the central sulcus is the parietal lobe, bounded anteriorly by the central sulcus, inferiorly by the posterior branch of the lateral sulcus, and posteriorly by two sulci: superiorly by the parieto-occipital sulcus, sulcus parietooccipitalis, and inferiorly by the transverse occipital sulcus, sulcus occipitalis transversus. Inferior to the lateral sulcus lies the temporal lobe, which transitions into the occipital lobe. The occipital lobe is located posterior to the parieto-occipital and transverse occipital sulci. The boundary between the temporal and occipital lobes is considered to be the line extending downward from the transverse occipital sulcus.

Frontal lobe, lobus frontalis.

In the posterior part of the frontal lobe runs the precentral sulcus, sulcus precentralis. Extending longitudinally at a right angle from the precentral sulcus are the superior and inferior frontal sulci, sulci frontales superior et inferior. These sulci divide the frontal lobe into the following gyri:

- precentral gyrus, gyrus precentralis;

- superior frontal gyrus, gyrus frontalis superior;

- middle frontal gyrus, gyrus frontalis medius;

- inferior frontal gyrus, gyrus frontalis inferior.

* Some anatomists consider the insula as the insular lobe, lobus insularis, or the island of Reil (Johann Christian Reil (1759–1813), professor of anatomy in Germany).

** François Sylvius (Franciscus Sylvius (1614–1672)) — professor of medicine in Holland.

*** Luigi Rolando (Luigi Rolando (1773–1831)) — professor of anatomy in Italy.

The function of the frontal lobe is associated with voluntary movements, coordination of motor mechanisms, articulate speech or linguistic communication, as well as 'creative' or critical thinking.

Parietal lobe, lobus parietalis.

Parallel to the central sulcus on the superolateral surface of the hemispheres lies the postcentral sulcus, sulcus postcentralis. This sulcus originates at the superior margin of the hemisphere, and its inferior margin continues into the intraparietal sulcus, sulcus intraparietalis, which runs parallel to the superior margin of the hemisphere. In the anterior part of the parietal lobe, There is a gyrus located parallel to the precentral gyrus, or the motor cortex. This is the postcentral gyrus, or the primary somatosensory cortex (areas 3, 1, and 2).

The parietal lobe is divided by the intraparietal sulcus into the superior and inferior parietal lobules, lobuli parietales superior et inferior. The inferior parietal lobule arches over the ends of the posterior ramus of the Sylvian fissure and the superior temporal sulcus. The region of the parietal lobe bounded by the end of the posterior ramus of the lateral sulcus is called the supramarginal gyrus, gyrus supramarginalis, while the region around the superior end of the temporal sulcus is the angular gyrus, gyrus angularis.

The function of the parietal lobe is associated with somatic sensation, language- and learning-related memory, and spatial orientation. The inferior parietal lobule (the supramarginal gyrus, which is the praxia analyzer, and the angular gyrus, the written language analyzer) is closely linked to language mechanisms, as damage to this cortical area in the left hemisphere leads to impaired language comprehension. Although The Role of the parietal lobe in spatial orientation is not yet fully understood, patients with lesions of the right parietal lobe exhibit impaired spatial orientation.

The temporal lobe, lobus temporalis.

The lateral surface of the temporal lobe features two longitudinal sulci: the superior and inferior temporal sulci, sulci temporales superior et inferior, which divide the temporal lobe into three gyri. The course of the temporal sulci runs parallel to the lateral sulcus of the hemisphere. The lateral sulcus and the superior temporal sulcus bound the superior temporal gyrus, gyrus temporalis superior.

The superior and inferior temporal sulci bound the middle temporal gyrus, gyrus temporalis medius. Located between the superolateral surface and the base of the brain is the inferior temporal gyrus, gyrus temporalis inferior.

The temporal lobe is associated with the perception of auditory sensations, participates in language function through auditory monitoring of speech, and plays a role in spatial evaluation and memory function. It is known that the transverse temporal gyrus (area 41) is the primary auditory center. A small area (42) bordering this gyrus is considered an "associative" or "interpretive" auditory center. Area (22) of the left hemisphere is also linked to language function, as lesions in this region lead to the loss of The ability to understand the meaning of words. There is also evidence indicating that the temporal lobe is associated with vestibular sensitivity (the sense of balance). Memory function and dreaming are also sometimes associated with the temporal lobes.

The occipital lobe, lobus occipitalis.

The occipital lobe is divided on its lateral surface into corresponding gyri by the transverse occipital sulci, sulci occipitalis transversi. On the inferolateral surface, there is a depression: the preoccipital notch, incisura preoccipitalis. It serves as a landmark for drawing an imaginary boundary between the occipital lobe posteriorly, and the parietal and temporal lobes anteriorly.

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Fig. 151. Superolateral surface of the cerebral hemisphere (after R. D. Sinelnikov)

Fig. 152. Medial surface of the cerebral hemisphere (after R. D. Sinelnikov)

The occipital lobe is known to be the cortical area associated with Vision. The visual cortex is located along the calcarine sulcus, fissura calcarina.

The insula, insula.

The insula is a triangular-shaped invagination of brain tissue located deep within the lateral (Sylvian) sulcus. It is bounded by the circular sulcus of the insula, sulcus circularis insulae. The surface of the insula is divided by sulci into short gyri, gyri breves insulae. The margin of the lateral sulcus of the hemispheres that covers the insula is called the operculum. The function of the insular cortex is not fully understood. Its stimulation produces visceral effects: belching, increased salivation, gastric peristalsis, and nausea.

The inferior surface of the cerebral hemisphere, facies inferior hemispherii cerebri.

On the inferior surface of the hemispheres, facies inferior hemispherii, lies the region of the frontal lobe located anterior to the lateral sulcus. In this region, running parallel to the longitudinal cerebral fissure, is the olfactory sulcus, sulcus olfactorius. This sulcus is occupied by the olfactory bulb and olfactory tract. Between the olfactory sulcus and the longitudinal fissure lies the straight gyrus, gyrus rectus; lateral to the olfactory sulcus are several orbital sulci, sulci orbitales, which bound the orbital gyri, gyri orbitales.

The region of the inferior surface of the hemispheres located posterior to the lateral sulcus belongs to the temporal and occipital lobes. The lateral sulcus on the inferior surface of the temporal lobe is the occipitotemporal sulcus, sulcus occipitotemporalis, which, together with the inferior temporal sulcus, bounds the inferior temporal gyrus, gyrus temporalis inferior.

Running parallel to the occipitotemporal sulcus is the collateral sulcus, sulcus collateralis. Between these sulci lies the lateral occipitotemporal gyrus, gyrus occipitotemporalis lateralis. Medial to the collateral sulcus is the medial occipitotemporal gyrus, gyrus occipitotemporalis medialis, bounded by the collateral and calcarine sulci, sulcus calcarinus. The lateral and medial occipitotemporal gyri are connected via transitional gyri to the parahippocampal gyrus, gyrus parahippocampalis.

The medial surface of the cerebral hemisphere, facies medialis hemispherii cerebri (Fig. 152)

The medial surface of the hemisphere is flat and is virtually divided by the corpus callosum into superior and inferior regions. In the area above the corpus callosum lies the sulcus of the corpus callosum, sulcus corporis callosi, which arches around the corpus callosum and continues into the hippocampal sulcus, sulcus hippocampi.

Above the sulcus corporis callosi runs the cingulate sulcus, sulcus cinguli, which continues as the subparietal sulcus, sulcus subparietalis. Above the cingulate gyrus in the anterior part of the hemisphere lies the medial part of the superior frontal gyrus, the posterior boundary of which is considered to be the paracentral sulcus, sulcus paracentralis. Between the paracentral sulcus and the posterior end of the gyrus cinguli lies the paracentral lobule, lobus paracentralis. Posterior to this lobule is a quadrate-shaped Structure, the precuneus. Behind the precuneus lies the cuneus, which belongs to the occipital lobe. The cingulate sulcus and the sulcus of the corpus callosum bound the cingulate gyrus, gyrus cinguli, which continues at its narrowed portion (the isthmus, isthmus) into the parahippocampal gyrus, gyrus hippocampi*. This gyrus terminates anteriorly as the uncus. It is bounded medially by the sulcus collateralis. The transition zone from the cingulate gyrus to the parahippocampal gyrus is located posterior to the splenium of the corpus callosum, splenium corporis callosi. Within the hippocampal sulcus lies the dentate gyrus, gyrus dentatus, which is part of the limbic system structures.