The cerebral cortex (cortex of the brain) is the outer grey matter layer that completely covers the surface of the two cerebral hemispheres. It is about 2 to 4 mm thick and contains an aggregation of nerve cell bodies. This layer is thrown into complex folds, with elevations called gyri and grooves known as sulci.
The cerebral cortex is quite distinct from the cerebrum (forebrain) which describes the two cerebral hemispheres (right and left), the largest part of the brain. The cerebrum consists of the outer grey matter (cerebral cortex), an inner mass of white matter made up of myelinated axons, which forms the bulk of the deeper structures of the cerebral hemispheres, and subcortical structures which include the diencephalon, pituitary gland, limbic structures and the basal ganglia.
The cerebral cortex is organized into distinct functional areas made up of sensory, motor and association areas. It has a broad range of functions including perception and awareness of sensory information, planning, and initiation of motor activity. It also plays a key role in higher cognitive functions, such as decision making, motivation, attention, learning, memory, problem-solving, and conceptual thinking.
This article will discuss the anatomy and functions of the cerebral cortex.
|Definition||Outer gray matter layer of the cerebral hemispheres|
|Lobes||Each hemisphere is divided into six lobes: frontal, parietal, temporal, occipital, insular and limbic.|
Lateral sulcus (Sylvian fissure): Separates the temporal lobe from the frontal and parietal lobes
Central sulcus: Divides the frontal and parietal lobes
Parietooccipital sulcus: Separates the parietal and occipital lobes
Cingulate sulcus: Separates the limbic lobe from the frontal and parietal lobes
Collateral sulcus: Between the limbic lobe and temporal lobe
Frontal lobe: Precentral gyrus, superior, middle and inferior frontal gyri
Parietal lobe: Postcentral gyrus, superior parietal lobule, inferior parietal lobule (supramarginal and angular gyri)
Temporal lobe: Superior, middle and inferior temporal gyri
Occipital lobe: Superior, middle and inferior occipital gyri, cuneus, lingual gyrus
Insular lobe: Gyrus breves, gyrus longus
Limbic lobe: Subcallosal, cingulate, parahippocampal gyri
|Principal cortical areas/functional units||
Frontal lobe: Prefrontal cortex, premotor cortex, primary motor cortex (Brodmann area 6), Broca’s area (Brodmann areas 44 and 45)
Parietal lobe: Primary somatosensory cortex
Temporal lobe: Primary auditory cortex, Wernicke's area
Occipital lobe: Primary visual cortex (Brodmann Area 17)
Cortical branches of the anterior, middle and posterior cerebral arteries
|Functions||Control of voluntary movement, attention, learning, memory, motivation, planning decision making, problem-solving, conceptual thinking, perception of sensory stimuli, language processing, visual processing and comprehension, modulation of emotion|
- Principal gyri of the cerebral cortex
- Blood supply
The cerebral cortex is a dense layer of neuronal cell bodies that lines the outer surface of the cerebral hemispheres, just below the cranial pia mater. This layer has a convoluted appearance
with many elevated ridges of tissue called gyri, alternating with grooves called sulci. This structural conformation is an important feature of the cerebral cortex because it increases the surface area of the cortex, and thus the number of neurons within it, allowing larger processing and cognitive abilities within the cerebral hemispheres.
Lobes of the cerebral cortex
The cerebral cortex is divided into six lobes based on the organization of major sulci. Each lobe has gyri that contain neuronal cell bodies involved in specific functions. Four of these lobes, the frontal, parietal, temporal and occipital lobes take their names from the overlying cranial bones. The insular lobe is located deep to the lateral sulcus, while the limbic lobe is located on the medial aspect of the hemisphere. The boundaries of these lobes are defined by major sulci that separate one region of the cerebral cortex from the other.
The major sulci on the lateral surface of each cerebral hemisphere are the lateral sulcus (Sylvian fissure) which separates the temporal lobe from the frontal and parietal lobes, and the central sulcus which divides the frontal and parietal lobes. Notable sulci on the medial surface of the cerebral hemisphere include the parietooccipital sulcus which separates the parietal and occipital lobes, the cingulate sulcus which separates the limbic lobe from the frontal and parietal lobes, and the collateral sulcus which separates the limbic lobe from the temporal lobe. The insular lobe, which lies at the base of the lateral sulcus, is separated from the surrounding frontal, parietal, and temporal lobes by the circular sulcus of the insula.
Histology of the cerebral cortex
Microscopically, the cerebral cortex is composed of cell bodies of billions of neurons, their dendrites, myelinated and unmyelinated axons which altogether form a unique, multilayered arrangement. In addition, it contains a dense population of supporting glial cells which include oligodendrocytes, astrocytes, microglia, and ependymal cells, and blood vessels. The neuronal cells of the cortex consist of six main cell types. These are the pyramidal cells (the main output neurons of the cerebral cortex), fusiform cells, stellate (granular) cells, basket cells, horizontal cells of Cajal-Retzius and cells of Martinotti. Histologically, the cerebral cortex is organized into six layers or horizontal laminae based on the size and shape of the neuronal bodies. These layers are designated by Roman numerals, and from superficial (at the pial surface) to deep, they are the:
- Molecular (plexiform) layer (I): Contains mainly nerve axons and a few scattered horizontal cells of Cajal-Retzius
- External granular layer (II): Composed of a varying density stellate (granular) cells and pyramidal cells
- External pyramidal layer (III): Contains predominantly pyramidal cells of varying sizes
- Internal granular layer (IV): Consists mostly of the stellate cells and a smaller portion of the pyramidal cells. It is usually the narrowest layer
- Internal pyramidal layer (V): Contains mainly medium-sized to large pyramidal cells
- Multiform (fusiform) layer (VI): Composed different types of neuron types, mostly fusiform cells with less dominant pyramidal cells and interneurons
Columnar organization of the cerebral cortex
The cerebral cortex can also be functionally divided into vertical formations that are called columns. These represent the functional units of the cortex and are capable of memorizing relations and performing more complex operations than a single neuron. Each column is oriented perpendicular to the cortical surface and it consists of all of the 6 cellular layers. Neurons are tightly connected inside one column, but also share connections with the adjacent and distant columns, and with the subcortical structures as well, particularly the thalamus.
Functional areas of the cerebral cortex
Additionally, the cerebral cortex can be divided into three functional areas: primary, secondary and associative. The cortical areas responsible for the elementary functions of either motor or sensory are primary areas. Secondary areas are located around every primary area and receive afferent projections from the corresponding primary areas and the thalamus. They are responsible for integrating the raw signal from the primary areas with the information received from the thalamus, to refine the primary area stimuli. Association areas, on the other hand, are cortical areas that integrate, process and analyze different kinds of stimuli that reach the brain and are involved in mediating higher mental functions.
Phylogenetic types of cortex
Different regions of the cerebral cortex can be categorized based on evolutionary history and relationships into three groups, the allocortex, mesocortex, and neocortex (isocortex).
- The allocortex is the most ancient type of cortex and is composed of the archicortex and the paleocortex. It consists of three cellular layers: polymorphic, pyramidal and the molecular layer, and is associated with the limbic system. The paleocortex contains three to five layers of cells and mediates the sense of smell.
- The mesocortex is a transitional form between the allocortex and isocortex. It contains three to six layers and is found in the insula, cingulate and parahippocampal gyri.
- The neocortex, as its name suggests, is the most recent cortical region and makes up to 90% of the human cortex. It includes all of the lobes of the cortex except the limbic lobe and consists of six layers of cells or laminae.
Check out our videos, articles, illustrations and quizzes in these study units to learn more about the histology of the cerebral cortex:
The cerebral cortex is divided into smaller areas structurally by sulci based on its histological structure and cellular organization. The resulting smaller regions are known as Brodmann areas. There are a total of 52 areas which have been shown to have distinct neuronal organization and have also been correlated to various cortical functions.
|Frontal lobe||Primary motor cortex (Area 4), premotor cortex and supplementary motor cortex (Area 6), frontal eye field (Area 8), prefrontal cortex (Areas 9, 10)|
|Parietal lobe||Primary somatosensory cortex (Areas 1, 2, 3), somatosensory association cortex (Areas 5, 7), angular and supramarginal gyri (Areas 39, 40)|
|Temporal lobe||Primary auditory cortex (Areas 41, 42), secondary auditory cortex (Area 22)|
|Occipital lobe||Primary visual cortex (Area 17), secondary visual cortex (Area 18), associative visual cortex (Area 19)|
|Special Brodmann areas||Wernicke’s area (22, 39, 40) - language comprehension
Broca’s area (44, 45) - motor speech
The Brodmann areas can sometimes be challenging to understand! Take advantage of the videos, articles, illustrations and quizzes included in this study unit to learn the material from different perspectives.
Principal gyri of the cerebral cortex
The cerebral cortex has several notable gyri on each lobe which carry out its multitude of functions.
The frontal lobe is the largest lobe of the cortex and contains four main gyri located on its lateral surface: the precentral gyrus, superior, middle and the inferior frontal gyri. The precentral gyrus lies between the central and precentral sulci. It contains the primary motor cortex (Brodmann area 4), and is involved in integrating signals from different brain regions to modulate voluntary movement to the body and limbs on the contralateral side.
The superior frontal gyrus lies anterior to the precentral sulcus while the middle frontal gyrus lies between the superior and the inferior frontal sulci. The inferior frontal gyrus lies in the inferolateral surface of the frontal lobe below the inferior frontal sulcus, which separates it from the middle frontal gyrus. It is divided into three parts, a pars opercularis, pars triangularis, and pars orbitalis. In the dominant hemisphere, this region contains the Broca’s speech area and is important in the motor component of speech production.
The parietal lobe contains the postcentral gyrus, superior and inferior parietal lobules. The postcentral gyrus is known as the somatosensory cortex (Brodmann area 3,1,2). It lies between the central and postcentral sulci and is the region of the cerebral cortex that receives and integrates sensory information related to touch and the sensing of body position and movement. The inferior parietal lobule (Brodmann area 39,40) consists of two gyri, the supramarginal gyrus and the angular gyrus. The supramarginal gyrus is located superior to the posterior aspect of the lateral fissure. The angular gyrus lies just posterior to the supramarginal gyrus. Both gyri are involved in auditory and visual perception and form part of Wernicke’s area, which is a functional unit of the cerebral cortex that plays an important role in the comprehension of spoken language.
The superior parietal lobule (Brodmann area 5,7) is separated from the inferior parietal lobule by the intraparietal sulcus. This region is involved in integrating sensory and motor functions and provides input to the premotor cortex.
The temporal lobe consists of the superior, middle and inferior temporal gyri, separated by superior and inferior temporal sulci. The superior temporal gyrus contains a specialized region called the transverse temporal gyri of Heschl, which is also known as the primary auditory area (Brodmann area 41, 42). This region of the cerebral cortex is primarily responsible for the reception of auditory information. Posterior to the primary auditory area in the superior temporal gyrus, lies the auditory association area (Brodmann area 22), which is responsible for the interpretation of sounds and for the association of the auditory input with other sensory information. The posterior part of this region, in the dominant hemisphere (usually the left), contributes to Wernicke’s area, which is important in the comprehension of language. The middle temporal gyrus is associated with the perception of movement within the visual field, while the inferior temporal gyrus plays a role in facial recognition.
The occipital lobe forms the caudal aspect of the cerebral hemisphere. Its lateral surface often exhibits significant variability in the sulci resulting in either two or three occipital gyri (superior, middle and inferior). On the medial surface of the occipital lobe, the calcarine sulcus separates the cuneus which lies above the sulcus from the lingual gyrus below. The regions of both gyri adjacent to the calcarine sulcus form the primary visual cortex (Brodmann area 17), which is responsible for the integration and perception of visual information.
The insular lobe is buried deep to the lateral fissure. It contains a group of short gyri in its rostral region called short gyri (gyri breves) and another group of long gyri in its caudal region called long gyri (gyri longi). These sets of gyri are separated from each other by the central sulcus of the insula. The insular cortex is involved in receiving and processing and integration of various types of information, including taste sensation, visceral sensation, pain sensation, and vestibular function.
The limbic lobe is a ring of cortex on the medial aspect of each hemisphere that surrounds the corpus callosum. It forms part of the larger limbic system which is involved in emotional and behavioral expression. The limbic lobe is composed of the subcallosal, cingulate, and parahippocampal gyri.
- The subcallosal gyrus lies below the rostrum of the corpus callosum. This area also corresponds with sections of Brodmann areas 24, 25, and 32, and is believed to be involved in depression.
- The cingulate gyrus lies directly above the corpus callosum. It continues anteriorly around the genu of the corpus callosum, blending with the subcallosal gyrus. Posteriorly, the cingulate gyrus wraps around the splenium of the corpus callosum. It is separated from the corpus callosum by callosal sulcus, while the cingulate sulcus separates it from the frontal and parietal lobes. The cingulate gyrus is involved in modulating emotion, as well as in visceral motor processes.
- The parahippocampal gyrus lies between the parahippocampal sulcus and the collateral sulcus which continues anteriorly as the rhinal sulcus. It contains the hippocampal formation and extends anteromedially as the uncus which contains the amygdala. The parahippocampal gyrus provides a path of communication between the hippocampus and all cortical association areas through which afferent impulses enter the hippocampus.The anatomy of the brain can be quite challenging. Learn neuroanatomy faster with our brain quizzes and diagrams!
The anatomy of the brain can be quite challenging. Learn neuroanatomy faster with our brain quizzes and diagrams!
The cerebral cortex receives its blood supply from cortical branches of the anterior, middle, and posterior cerebral arteries. The anterior and middle cerebral arteries arise as terminal branches of the internal carotid artery, while the posterior cerebral artery is a terminal branch of the basilar artery. The middle cerebral artery supplies mainly the lateral surface of the cerebral hemisphere, whereas the occipital lobe and the inferior temporal gyrus receive blood supply from the posterior cerebral artery. Branches from all three arteries supply the medial and inferior surfaces of each hemisphere.
The cerebral cortex is organized into different functional areas/units that process various stimuli and are responsible for specific brain functions including sensory, motor and higher intellectual functions. Its neurons receive input from several subcortical structures conveyed by the thalamus as well as from other cortical regions via association fibers. Neuronal fibers from the cerebral cortex, in turn, project to several structures in the central nervous system including other cortical areas, the thalamus, basal nuclei, brainstem nuclei, pontine nuclei, cerebellum and spinal cord. These functional areas are located in the various lobes of the cerebral cortex.
- The frontal lobe contains the prefrontal cortex, premotor cortex, primary motor cortex (Brodmann area 6), Broca’s area (Brodmann areas 44 and 45). This lobe is responsible for the control of voluntary movement, and is involved in attention, short term memory tasks, motivation, planning and also contributes to personality traits.
- The parietal lobe is responsible for integrating proprioceptive and mechanoceptive stimuli, and also plays a role in language processing. It contains the primary somatosensory cortex (Brodmann areas 3,2,1), somatosensory association cortex (Brodmann areas 5, 7), and the inferior parietal lobule which forms part of the Wernicke’s area.
- The occipital lobe contains the primary visual cortex (Brodmann Area 17) and is the center for visual processing.
- The temporal lobe is involved in decoding sensory input into derived meanings for retention of visual memory and language comprehension. It contains the primary auditory cortex and Wernicke's area.
- The insular cortex plays a role in the processing and integration of taste sensation, visceral and pain sensation and vestibular functions.
- The limbic lobe contains areas that are concerned with the modulation of emotions, modulation of visceral and autonomic functions, learning, and memory.
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