Cerebrum (telencephalon)

The human cerebrum, or telencephalon, is the largest and most conspicuous portion of the central nervous system. It consists of two longitudinal halves, which are called cerebral hemispheres. They occupy most of the cranial cavity as they lie above the cerebellum and brainstem. The right and left cerebral hemisphere are joined together into one functional organ by a thick, white bundle of myelinated fibers, which is called corpus callosum. Each one of the cerebral hemisphere consists of an external cortex of grey matter and an inner mass of white matter. The grey matter is made up of nerve cell bodies, while the white matter consists of myelinated axons that get together to form fibers. The myelin is a white sheath of fat that envelops each one of the axon; the axon in turn is the neuron's longest, hair-like, branching process (outgrowth of tissue).

The grey matter, or cerebral cortex structure, is composed of six layers of neurons and their support cells, which are called neuroglia. They communicate with one another, and with lower neurons in the brainstem and spinal cord, through synapse, forming a complex network of afferent and efferent nerve impulses that travel through axons and dendrites (nerve cell branches). The white matter, on the other hand, consists of billions of myelinated axons (a neuron longest branch) that get together to form nerve fibers and these white fibers in turn cluster together to form thick bundles called fasciculi (plural of fasciculus). These bundles link up every region of the cerebral cortex (grey matter) with one another; the largest one being the aforementioned corpus callosum; the longest one being the superior longitudinal fasciculus; and the most important ones, from the human and language point of view, being the uncinate and the arcuate fasciculus respectively (see association fibers in the brain).

Externally, the cerebral cortex is characterized by a series of grooves (called sulci) which divide each cerebral hemisphere into lobes and gyri (plural of gyrus). The deepest and most conspicuous grooves are the Sylvian fissure (also known as lateral fissure), the fissure of Rolando (also called central sulcus), and the calcarine fissure. These three fissures divide the cortex into four lobes: the frontal, temporal, parietal, and occipital lobe. The Sylvian, or lateral, fissure separates the temporal lobe from the frontal and parietal lobe, which lie above. The fissure of Rolando divides the frontal lobe from the parietal one, while the calcarine fissure divides the parietal from the occipital lobe. Each one of the cerebral lobes, in turn, is further divided into gyri by secondary sulci (grooves). Thus, a gyrus is a fold of the cerebral cortex delimited by two or more sulci. Each cerebral hemisphere lobe contains two, three or four gyri.

The most primitive parts of the cerebrum are the allocortex, which comprises the paleocortex and the olfactory bulb and tract, the hippocampus, and amygdala; these are centers of emotion and primitive impulses. The allocortex is located on the inferior side of each cerebral hemisphere; the hippocampus lies within the temporal lobe, while the amygdala is located in the medial temporal lobe at the end of the caudate nucleus of basal ganglia. The white matter of the cerebrum contains a number of subcortical structures; they are grey nuclei which are called basal ganglia. These are replicated and embedded within each cerebral hemispheres. They are grey in color because they also consists of constellation of neurons. The most important of these ganglia are the caudate nucleus, the putamen, and the globus pallidus. These nuclei control and modulate activities of the motor cortical areas located in the frontal lobe.

Both the cerebrum and cerebellum are tightly enveloped by three meninges: the dura mater, the arachnoid, and the pia mater. The space between them, like the brain cavities (ventricles), is filled with cerebrospinal fluid.

Function

The cerebrum is the center of superior perception of reality, complex executive function through efferent fibers, which means superior modulated behavior to successfully adapt to the physical and social environment. It is also the center of analysis (it sees and understands the difference between the parts that make up an object, and of synthesis (it puts the pieces that make up a whole together to see the purpose of the whole).

Blood Supply

The human cerebrum receives oxygenated blood through two main blood vessels: the internal carotid artery and the basilar artery. The internal carotid arises from the common carotid, while the basilar artery is the union of the two vertebral arteries, which in turn originates from each of the subclavian.

Right cerebral hemisphere of human cerebrum. As you can see, it lies right above the cerebellum and brainstem.