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Cerebral Cortex

Cortex cerebri

For medical students2 min readUpdated 2026-10-10

The cerebral cortex (cortex cerebri) is a highly differentiated layer of gray matter covering the cerebral hemispheres. Depending on its evolutionary age, it is divided into several types that differ in structural complexity, number of cell layers, and functional significance.

Neocortex VolumeThe neocortex accounts for approximately 96% of the total surface area of the cerebral hemispheres in adult humans.
Layered StructureMorphologically, the neocortex is divided into 6 distinct cellular layers.
CytoarchitectonicsThe branch of anatomy that studies the cellular structure of specific cortical fields.

Phylogenetic Types of the Cortex

The evolutionary development of the central nervous system has led to the formation of several types of cortical matter, each with distinct morphological features.

The most simply structured is the paleocortex (paleocortex). Topographically, it is located on the inferomedial surface of the temporal lobe. Its structures include the olfactory tubercle with adjacent areas, as well as the anterior perforated substance. Physiologically, this part of the brain primarily serves the olfactory system.

Appearing slightly later in phylogenesis is the archicortex (archicortex). Its key morphological distinction from the paleocortex is that it is clearly separated from subcortical centers by a specialized cortical plate. However, in the adult human, the archicortex still retains a single-layered structure. It includes the hippocampus, which lies deep within the hippocampal sulcus, and the dentate gyrus (gyrus dentatus). Functionally, these zones are closely linked to memory formation and the limbic system.

The transitional link between evolutionarily old and new formations is the mesocortex (mesocortex). It is generally divided into two key zones:

Topographically, these intermediate zones occupy parts of the insular lobe, parahippocampal gyrus, and inferior regions of the limbic area.

The pinnacle of brain development is the neocortex (neocortex). This is the most highly differentiated part, which in humans accounts for about 96% of the total surface area of the hemispheres. It is characterized by a complex multi-layered cellular organization.

Layered Structure of the Neocortex

The neocortex is distinguished by a complex multi-layered structure. Based on the morphological characteristics of cells and fibers, six lamina are classically distinguished in the adult neocortex. These layers are arranged from the surface of the hemisphere inward toward the white matter:

  1. Molecular layer (lamina molecularis or plexiformis).
  2. External granular layer (lamina granularis externa).
  3. External pyramidal layer (lamina pyramidalis externa).
  4. Internal granular layer (lamina granularis interna).
  5. Internal pyramidal layer (lamina pyramidalis interna or ganglionaris).
  6. Multiform layer (lamina multiformis).

Principles of Cortical Architectonics

The cerebral cortex is not uniform throughout its extent. Its structure exhibits marked variations across different regions of the hemispheres. These structural variations affect:

Rigorous morphofunctional analysis has allowed researchers to identify specific cortical fields. Each such field possesses individual structural features and is responsible for performing specific functions.

Systematization of these data forms the basis of two disciplines:

The result of these studies has been the creation of detailed maps of the cerebral cortex fields, establishing fundamental principles of its organization.

Mnemonic

To remember the 6 neocortex layers: "M-E-E-I-I-M" — Molecular, External granular, External pyramidal, Internal granular, Internal pyramidal, Multiform.

Frequently asked questions

What types of neurons form the molecular layer of the neocortex?

The molecular layer of the neocortex is formed predominantly by small neurons — Cajal–Retzius cells. Overall, this layer contains relatively few cells.

  • Cajal–Retzius cells — play a major role in establishing the laminar structure of the cerebral cortex. They secrete the specific protein reelin, which coordinates the movement of migrating neurons.

Some of these cells degenerate immediately after cortical development is complete. Additionally, the dendrites of Cajal–Retzius cells run tangentially within this layer.

In which neocortical layer are giant Betz pyramidal cells located?

Giant Betz pyramidal cells are located in the fifth layer of the neocortex — the internal pyramidal layer (lamina pyramidalis interna), also known as the ganglionic layer.

  • Betz cells — the largest cells of the cortex, localized exclusively in the precentral gyrus.

The axons of these giant pyramids are wrapped in a thick myelin sheath and form the corticonuclear and corticospinal (pyramidal) tracts running to the spinal motor neurons. These cells exhibit high conduction velocities and fire during movement.

Which cells and fibers form the internal granular layer?

The internal granular layer (lamina granularis interna) contains nerve fibers running tangentially to form the outer band of Baillarger. In agranular cortex, this layer contains a high density of pyramidal cells.

What Brodmann cytoarchitectonic areas exist and where are they localized?

According to the Brodmann cytoarchitectonic map, there are 52 cortical fields. The primary areas and their localizations include:

  • Areas 3, 1, 2 — primary somatosensory cortex (postcentral gyrus, part of the precentral gyrus, and paracentral lobule).
  • Area 4 — primary motor cortex (precentral gyrus).
  • Areas 6 (6aα, 6aβ), 8 — premotor cortical areas.
  • Areas 9, 10, 11, 12, 44, 45, 47 — prefrontal cortical areas (frontal lobe).
  • Area 17 — primary visual cortex (occipital lobe).
  • Areas 41, 42 — primary auditory cortex.

Topographically, these fields do not strictly correspond to gyral boundaries and may partially overlap.

What is the morphological difference between the archicortex and the paleocortex?

Unlike the paleocortex, the archicortex is separated from deep subcortical structures by a specialized cortical plate, although it remains a single-layered structure in the adult human.

What structures belong to the paleocortex?

Structures of the paleocortex (paleocortex) include the olfactory tubercle, the cortex surrounding it, and a portion of the anterior perforated substance.

What is the mesocortex and where is it located?

The mesocortex is the intermediate cortex, serving as a transitional zone between the old/ancient cortex and the neocortex. It is located in the region of the insular lobe, parahippocampal gyrus, and inferior regions of the limbic area.

What serves as the basis for creating cortical field maps?

The basis for mapping cortical fields is data from cytoarchitectonics (cellular structure) and myeloarchitectonics (myelin fiber distribution).

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