The brain is one of the most powerful organs of the body. The brain mainly consists of fat, water, protein, carbohydrates, and salts- Simple, isn’t it? As simple as it seems, the brain consists of numerous complex structures- one being the cerebral cortex- each responsible for highly complex processes. What is the cerebral cortex, where is it situated, and what does it do?
The cerebral cortex, or cerebral mantle, is the thin outermost layer of the cerebrum. The cerebral cortex consists of neural tissue (grey matter) holding approximately 15 billion neurons, allowing processes such as consciousness, attention, perception, emotions, thought, language, and memory.
The cerebral cortex is merely a few millimeters thick yet contains 14 to 16 billion nerve cells. This structure consists of many areas with various functions, several layers with unique characteristics, and complex structures regulating some parts of human existence. If you want to become more knowledgeable about the cerebral cortex’s positioning, structure, and function, you have come to the right place.
Where Is The Cerebral Cortex?
As previously established, the cerebral cortex is the brain’s outermost layer. This layer is merely 0.08 to 0.16 inches (two to four millimeters) thick and lies on top of the cerebrum. We must first examine the cerebrum’s basic structure to completely understand where and how the cerebral cortex positions itself in the human body.
The cerebrum is the largest part of the brain. It consists of two halves, called hemispheres, which communicate via a bundle of nerve fibers - the corpus callosum. The cerebral cortex consists of white matter (the inner mass of the cerebrum constructed from axons) and grey matter (the outer matter of the cerebrum made up of dendrites). The outer layer of grey matter is called the cerebral cortex.
The Structure Of The Cerebral Cortex
The cerebral cortex has a wrinkled, folded appearance to ensure maximum surface area exposure. The large surface area allows a more considerable amount of neurons to operate there, increasing the amount of information processed at a time. Many bulges called gyri (singular: gyrus), and grooves called sulci (singular: sulcus) achieve the characteristic folded appearance of the cerebral cortex.
Different levels of construction can explain the structure of the cerebral cortex. The first way to examine the structure of the cortex is in terms of the neocortex, which makes up 90 percent of the cerebral cortex, and the allocortex, which makes up the remaining 10 percent of the cortex.
The neocortex is a relatively new vertebrate evolution; therefore, the prefix “neo” is in its name. The neocortex contains six laminar layers of nerve cells: the molecular/plexiform, external granular, external pyramidal, internal granular, internal pyramidal, and the multiform/fusiform layer.
Secondly, we investigate the cerebral cortex’s structure in terms of the areas of the cerebral cortex (the sensory area, the motor area, and the association area) or, thirdly, in terms of the six different lobes of the brain (frontal, parietal, temporal, occipital, insular and limbic lobe).
Despite the complex structural levels of the cerebral cortex, all these structural components are integrated into a united whole and function cooperatively to regulate and optimize human functioning.
The Six Layers Of The Cerebral Cortex
The cerebral cortex contains billions of neurons, yet all are different combinations of only three morphological shapes. These shapes include pyramidal, stellate, granular, and fusiform cells. The other cells encountered in the cerebral cortex, such as the horizontal cells of Cajal-Retzius and cells of Martinotti (multipolar neurons), are merely modifications of one of the cells mentioned above.
The six layers are as follows:
- The molecular (plexiform) layer
- The external granular layer
- The external pyramidal layer
- The internal granular layer
- The internal pyramidal layer
- The multiform (fusiform) layer
Each layer has a characteristic distribution of different neurons. Each layer also uniquely connects with cortical and subcortical areas, which distinguishes it from the next layer.
The Molecular (Plexiform) Layer
The molecular (plexiform) layer is the outermost layer, thus the most superficial of the six layers. Cellular components poorly represent the molecular layer, and it only consists of a few horizontal cells of Cajal-Retzius (a transient population of cells critical for brain development). The most significant part of this layer actually consists of the processes of the underlying neurons and their synapses.
The External Granular Layer
The external granular layer is just beneath the molecular layer in the neocortex, and small stellate cells primarily make up this layer. These stellate cells give the layer a grainy or “granular” appearance. This layer also consists of small pyramidal cells.
The External Pyramidal layer
The external pyramidal layer of the neocortex, lying right beneath the external granular layer, in contrast, almost exclusively consists of pyramidal cells. As depth increases, the size of the pyramidal cells increases as well.
The Internal Granular Layer
The fourth layer comprises stellate cells known as the internal granular layer and a small number of pyramidal cells. The majority of the stimuli from the periphery arrive here; therefore, the internal granular layer is the primary input cortical station of the cerebral cortex. There is particular development in the sensory regions of the internal granular layer for this specific reason.
Internal Pyramidal Layer
The layer beneath the internal granular layer is known as the internal pyramidal layer of the cerebral cortex. This layer is the source of the output fibers and, therefore, primarily encountered in the motor cortex from which it sends fibers to regulate motor activities. Large and medium-sized pyramidal cells make up this layer.
The Multiform (Fusiform) Layer
The multiform (fusiform) layer is the cerebral cortex’s deepest layer. This layer lies directly above the white matter of the cerebrum and consists of fewer pyramidal cells and interneurons than the other layers. The multiform layer predominately consists of fusiform cells. The axons of these cells distribute fibers that end in the thalamus. Information relays in the thalamus before sending it to the cerebral cortex.
Areas Of The Cerebral Cortex And Its Functions
Three different areas of the brain characterize the cerebral cortex. These areas include the sensory area, the motor area, and the association area. These sensory areas are located in the cerebral cortex and receive and process sensory information from the sensory organs and the environment.
The Sensory Area
The sensory areas are responsible for receiving and processing incoming sensory information from the sensory organs and external stimuli. The sensory regions consist of the following:
- The visual cortex. This area receives and processes visual input.
- The auditory cortex. This area takes responsibility for auditory input.
- The somatosensory cortex. This area deals with tactile information (touch).
- The gustatory cortex. This area perceives tastes and flavors.
The Motor Area
The motor area is mainly responsible for initiating and regulating voluntary movements of the body. The motor area consists of the primary motor cortex, associated with coordination, the premotor cortex, which assures the preparation, selection, and execution of limb movements, and the supplementary cortex, which assists in planning and controlling complex bodily movements.
The Association Areas
Deep sulci bury the human brain’s most significant part of the cerebral cortex. These deep sulci also form the divisions between the brain lobes, which we will get to in a moment. The association areas of the cerebral cortex integrate information from these different lobes and connect sensory and motor areas to organize the data depending on the particular function of each lobe.
Lobes Of The Cerebral Cortex And Its Functions
Each lobe of the brain is responsible for unique processes. The four best-known lobes of the cerebral cortex are the frontal lobes, the parietal lobes, the temporal lobes, and the occipital lobes. Teachers in schools and lecturers in universities commonly teach these four lobes of the brain as the only lobes that play a critical role in high-level human functioning and tend to ignore the insular and limbic lobes.
The Frontal Lobes
The most prominent lobes of the cerebral cortex are called the frontal lobes. It lies at the very front of the brain. The frontal lobes primarily take responsibility for decision-making processes, conscious thinking, problem-solving, attention, and regulating emotions and behavior—for example, the individual’s ability to distinguish appropriate from non-appropriate behavior in specific scenarios or environments.
The frontal lobes also contain Broca’s Area, which plays a crucial role in language production. Reciprocally influenced, the frontal lobe acts as the storage unit of the personality and also houses intelligence.
The Occipital Lobes
In contrast to the frontal lobes, the occipital lobes are the tiniest of the four main lobes. It is positioned the furthest away from the frontal lobe - at the lower back of the brain.
The occipital lobes are primarily responsible for visual input, interpretation, and processing. They thus receive information from the eye’s retina and process the data in terms of color, orientation, and motion. Therefore, these lobes also assess distance and depth for visual world mapping and recognizing faces and other objects.
The Parietal Lobes
The parietal lobes of the cerebral cortex lie behind the frontal lobes, before the occipital lobes- more to the top of the head. The primary function of the parietal region is integrating sensory information to understand the environment around us regarding the temperature, pressure, pain, position, vibration, and the perception of touch.
The parietal lobes also aid in spatial processing and manipulation, thus making sense of what is happening around us. Its focus is on understanding the three-dimensional space we live in to navigate ourselves around our neighborhoods or towns.
The Temporal Lobes
The temporal lobes lie between the frontal and occipital lobes but more to the bottom of the brain. The right temporal lobe is responsible for memorizing non-verbal information, recognizing information, and controlling and determining facial expressions associated with different emotions.
The left temporal lobe is usually more dominant in humans. The left temporal lobe is responsible for memorizing verbal information and comprehending language. It also aids with learning processes and speech production. This lobe and the right lobe are vital in converting sounds into images to make sense of verbal input and ensure successful communication.
Insular Lobe And The Limbic Lobe
Although the frontal, parietal, temporal, and occipital lobes are much more well-known and thoroughly covered in studying the brain and its structures, the cerebral cortex contains two more lobes, including the insular and limbic lobes. These lobes also play a crucial role in human functioning as well, but their function is often underemphasized.
The Insular Lobe
The insular lobe compartment of the cerebral cortex folds into the fissure, which separates the temporal lobe from the frontal and parietal lobes. The insular lobe controls consciousness and aid in functioning emotions such as compassion and empathy. More of its functions includes its influence on tastes, perceptions, motor control, interpersonal skills, cognition, and self-awareness.
The Limbic Lobe
The limbic lobe is a complex, C-shaped combination of a structure composed of portions of each cerebral lobe. The limbic lobe is commonly referred to as the primitive part of the brain because of its involvement with unconscious processes such as compulsions, addiction, and mental illnesses. The limbic lobe also involves a range of hormones that actively affect these structures.
Despite the earlier belief of the limbic lobe’s primitive function, it contributes to many uniquely human processes such as emotions, self-awareness, and social skills. The limbic lobe also plays a vital role in memory, motivation, learning as well as the functioning of the endocrine system in regulating adrenaline-based responses.
Conclusion
The cerebral cortex is only a few millimeters thick, yet the most prominent site of neural integration in the central nervous system, and contains billions of nerve cells. This thin structure plays a crucial role in human functioning by integrating its complex layers, structures, and areas with various functions into a unified whole to regulate consciousness, language and information-processing, and many more.
The brain is not only our most powerful and influential organ but also one of the human body’s most complex, finely integrated structures. The cerebral cortex makes up only 40 percent of the fully-functioning human brain. Yet, it fulfills some of the most complex conscious and unconscious processes humans cannot live without.
References
https://www.simplypsychology.org/what-is-the-cerebral-cortex.html
https://my.clevelandclinic.org/health/articles/23073-cerebral-cortex
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3774067/
https://www.kenhub.com/en/library/anatomy/cortical-cytoarchitecture
