Cerebrum is the largest part of the brain. Together with diencephalon it forms the forebrain. Cerebrum is sometime also referred to as diencephalon, which is the embryonic structure from which the mature cerebrum develops.
Cerebrum is composed of two cerebral hemispheres that are connected by a mass of grey matter called the corpus callosum. The hemispheres are separated by a deep cleft called the longitudinal fissure, into which projects the falx cerebri. Each hemisphere extends from the frontal to the occipital bone above the anterior and middle cranial fossae and posteriorly above the tentorium cerebelli.
The surface layer of the entire cerebrum is composed of gray matter and is called the cortex. It is thrown into folds (gyri) separated by fissures (sulci). The gyri and sulci increase the surface area of the cortex by many times.
Several of the large sulci conveniently subdivide the surface of each hemisphere into lobes. These lobes are named according to the cranial bones under which they lie.
- Frontal lobe: It is anterior to the central sulcus and above the lateral sulcus.
- Parietal lobe: It is posterior to the central sulcus and above the lateral sulcus.
- Occipital lobe: It lies below the parieto-occipital sulcus.
- Temporal lobe: It lies below the lateral sulcus.
Some of the gyri of cerebrum show distinct functional characteristics, as described below:
- Precentral gyrus:
It lies immediately anterior to the central sulcus and is commonly known as the motor area. It contains large motor nerve cells that control the voluntary movements of the opposite side of the body.
- Postcentral gyrus:
It lies immediately posterior to the central sulcus and is commonly known as the sensory area. It contains small nerve cells that receive and interpret sensations of pain, temperature, touch and pressure from the opposite side of the body.
- Superior temporal gyrus:
It lies immediately below the lateral sulcus and is concerned with reception and interpretation of sound. It is therefore called the auditory area.
- Motor speech area (Broca’s area):
It lies just above the lateral sulcus and is concerned with control of movements employed in speech. It is dominant in the left hemisphere of right-handed people and right hemisphere of left-handed people.
- Visual area:
It lies on the posterior pole of the cerebral hemisphere towards the medial aspect, in the region of the calcarine sulcus. It is the receiving area for visual impressions.
They are part of the ventricular system of the brain, the largest of the ventricles. They represent the cavity within each cerebral hemisphere. They communicate with the third ventricle through the interventricular formina of Monro.