What is the cerebrum?
The cerebrum or endbrain makes up the main part of the human brain. It consists of a right and a left half (hemisphere), the two connected by the bar (corpus callosum). Apart from the bar, there are other (smaller) connections (commissures) between the two halves of the brain.
External division of the cerebrum
The two cerebral hemispheres can each be divided into four lobes:
- Frontal lobe or frontal lobe (lobus frontalis)
- Parietal lobe or parietal lobe (lobus parietalis)
- temporal lobe or temporal lobe (lobus temporalis)
- Occipital lobe or occipital lobe (lobus occipitalis)
The surface of the two cerebral hemispheres is furrowed like a walnut and thus significantly enlarged. The numerous cerebral convolutions (gyri) are delimited from each other by furrows (sulci).
Internal structure of the cerebrum
The cerebral cortex is between two and five millimeters thick. It consists of the isocortex (or neocortex) and the underlying allocortex. The isocortex has six layers and makes up about 90 percent of the cerebral cortex. The allocortex is developmentally older and has a three-layered structure. The developmentally oldest part of the allocortex is called the paleocortex. Together with the somewhat younger archicortex, it forms the allocortex.
The cerebral cortex consists of the cell bodies of billions of neurons (including pyramidal cells) and glial cells. The neurons have long projections (axons) in all directions. The medulla of the cerebrum consists of these nerve cell processes, which allow communication even with distant cells.
What is the function of the cerebrum?
However, not all stimuli reach the cerebral cortex. Some information is processed very quickly and without reaching consciousness in “lower” brain regions. For example, the central regulation of breathing takes place in the medulla oblongata (extended spinal cord or afterbrain).
Each cerebral hemisphere is specialized for specific tasks: the left cerebral areas usually house language and logic, while the right cerebral areas house creativity and the sense of direction.
Homunculus (brain)
The cerebral cortex has various motor and somatosensitive areas that are assigned to specific body parts. Thereby, neighboring body parts are “mapped” onto neighboring brain areas. This results in the model of a small, size-distorted human, called a homunculus.
The function of different cerebral areas
The neocortex houses, among other things, the ability to learn, speak and think, as well as consciousness and memory.
In the parietal lobe or parietal lobe of the cerebrum is the body sensation sphere, represented by sensory pathways that originate in the skin and muscles and pass through the thalamus into the primary sensory cortical fields of the parietal lobe. Secondary sensitive cortical fields store memories of sensations that originated in the primary cortical fields.
In the temporal lobe or temporal lobe, the primary auditory center, the end of the auditory pathway, lies on the outer surface. Connected posteriorly is the secondary auditory center, the auditory memory center. Some sections of the auditory center scan the constant flood of sound that flows into the brain via the ear for familiar sounds and classify them accordingly.
In the temporal lobe, and to some extent in the parietal lobe, is the Wernicke area, which is especially crucial for understanding speech. The Wernicke and Broca areas form the language center in the brain.
Where is the cerebrum located?
The cerebrum is located under the skullcap. The frontal lobe is located in the anterior fossa, and the temporal lobe is located in the middle fossa.
What problems can the cerebrum cause?
Diseases and injuries in the cerebrum can have diverse consequences, depending on where in the cerebrum and how pronounced the damage is.
Irritation of the motor centers in the frontal brain causes convulsions (cortical epilepsy), and destruction of these centers initially leads to paralysis of the muscles on the other side of the body (hemiplegia). In the later course, neighboring cerebral fields and/or those of the opposite side can take over the function.
If Broca’s area is damaged, the patient can usually still understand speech, but has difficulty forming words and sentences by himself. In milder cases, affected individuals can still communicate in a staccato telegram style.
If the primary sensitive cortical fields of the parietal lobe are damaged, anesthesia, insensitivity, results. Injuries to the secondary sensitive cortical fields cause agnosia – the inability to detect objects by palpation. Disturbances on the left side, where the reading center with a memory of the meaning of characters is located, result in the inability to read (alexia).
A disturbance of the secondary auditory center in the temporal lobe of the cerebrum leads to the fact that earlier impressions are no longer remembered and thus words, sounds, music are no longer understood (the so-called soul deafness).
Destruction of certain districts of the cerebral cortex in the area of the visual center (brain) due to a tumor or stroke leads to visual field loss. Complete destruction of the visual cortex on both sides in the cerebrum results in so-called cortical blindness – affected persons are blind although their retina and visual pathway are intact. At best, they can still distinguish light from dark and recognize motion stimuli.
If the secondary visual center (brain) in the occipital lobe in the cerebrum is destroyed, soul blindness results. Affected persons cannot recognize objects again because memory is extinguished and comparison with earlier optical impressions is no longer possible.
