Sulci and gyri of the brain

Relief of the superolateral surface

Key structures governing movement, perception, and speech are located on the outer surface of the hemispheres.

• Central sulcus (sulcus centralis) separates the frontal and parietal lobes. Anterior to it lies the precentral gyrus (gyrus precentralis), the primary motor cortex controlling voluntary movements. Posteriorly lies the postcentral gyrus (gyrus postcentralis), where the primary somatosensory cortex is localized.
• Intraparietal sulcus (sulcus intraparietalis) divides the parietal lobe into superior and inferior parietal lobules. Spatial analysis and integration of various senses occur here.
• Superior temporal sulcus (sulcus temporalis superior) and the corresponding gyrus are responsible for hearing, and in the dominant hemisphere, for sensory speech.

Medial and inferior surfaces

The inner and inferior aspects of the hemispheres are closely linked with the limbic system, vision, and olfaction.

On the medial surface, the parietooccipital sulcus (sulcus parieto-occipitalis), involved in visuospatial analysis, and the paracentral lobule (termination of the central sulcus), which controls movement and sensation of the lower limb, are distinguished. On the inferior surface, the orbital sulci and gyri integrate autonomic reactions with olfaction, while the parahippocampal gyrus and uncus (uncus) are responsible for emotions.

Phylogenetic types of the cortex

The cerebral cortex is heterogeneous in origin and structure. Several types are distinguished:

1. Paleocortex (paleocortex). The simplest in organization. Occupies a region of the inferomedial surface of the temporal lobe. Includes the olfactory tubercle, the surrounding cortex, and a portion of the anterior perforated substance. Functionally related to olfaction.
2. Archicortex (archicortex). Appears later in evolution than the paleocortex. Remains single-layered in the adult human. Includes the hippocampus (located deep within the hippocampal sulcus) and the dentate gyrus. Closely linked with the limbic system and memory.
3. Mesocortex (mesocortex). Occupies a transitional position. Divided into periarchicortical (transition from archicortex to neocortex) and peripaleocortical (transition from paleocortex to neocortex) zones. Located in the insular lobe and parahippocampal gyrus.
4. Neocortex (neocortex). The most developed in humans, multi-layered, and highly differentiated. Constitutes about 96% of the hemisphere surface.

Relationship of gyri with projection pathways

Cortical gyri serve as terminal or initial points for numerous nerve tracts:

• Impulses from the ventrolateral nuclei of the thalamus (via the medial and trigeminal lemniscs, as well as the central thalamic radiation) are directed to the cortex of the postcentral gyrus.
• Cortex of the occipital lobe in the area of the calcarine sulcus receives the optic radiation (radiatio optica).
• The middle part of the superior temporal gyrus (Heschl's gyri) is the site of termination of the acoustic radiation.
• Frontal lobe and the anterior part of the cingulate gyrus receive signals through the anterior thalamic radiation.
• Descending pathways, such as the striate radiation, connect the extrapyramidal areas of the frontal and parietal lobes with the basal nuclei (caudate and lentiform).

Gray matter of the telencephalon

Gray matter (substantia grisea telencephali) represents clusters of neuronal cell bodies, their unmyelinated processes, neuroglia, and blood vessels. In the hemispheres, it forms three complex systems:

• Cerebral cortex (cortex cerebri, pallium) — the folded surface of the hemispheres.
• Basal nuclei (nuclei basales) — subcortical clusters at the base of the hemispheres.
• Rhinencephalon (rhinencephalon) — phylogenetically ancient structures.

All these systems have extensive interconnections that are carried out through the white matter of the hemispheres.

Class and exam questions

What else to study on this topic

• Ascending spinal cord pathways: spinoreticular and spinotectal tracts
• Proprioceptive pathways: gracile (Goll) and cuneate (Burdach) fasciculi
• Thalamic radiations and their projections to the cerebral cortex
• Ascending auditory and visual pathways of the brainstem
• Cerebellar pathways: spinocerebellar and olivocerebellar tracts

Other topics in the "CNS" section

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