CEREBRUM - by vikas lodhi

Cerebrum

The cerebrum (Latin for brain), refers to the part of the brain comprising the cerebral cortex (of the two cerebral hemispheres), as well as several subcortical structures, including the hippocampus, basal ganglia, and olfactory bulb. In humans, the cerebrum is the superior-most region of the central nervous system (CNS). The telencephalon refers to the embryonic structure from which the mature cerebrum develops. In mammals, the dorsal telencephalon, or pallium, develops into the cerebral cortex, and the ventral telencephalon, or subpallium, becomes the basal ganglia. The cerebrum is also divided into approximately symmetric left and right cerebral hemispheres.

With the assistance of the cerebellum, the cerebrum controls all voluntary actions in the body.

Structure

The cerebrum is composed of the following regions:

*Cerebral cortex, or cortices of the cerebral hemispheres

*Basal ganglia, or basal nuclei

*Limbic System

The cerebrum comprises the largest part of the brain. It lies in front or on top of the brainstem and in humans is the largest and best-developed of the five major divisions of the brain. The cerebrum is the newest structure in the phylogenetic sense, with mammals having the largest and best-developed structures among all species. In larger mammals, the cerebral cortex is folded into many gyri (ridges) and sulci (furrows), which has allowed the cortex to expand in surface area without taking up much greater volume. The cerebral cortex is only present in mammals.

In humans, the cerebrum surrounds the older parts of the brain. The limbic, olfactory, and motor systems project fibers from the cerebrum to the brainstem and spinal cord. Cognitive and volitive systems project fibers from the cerebrum to the thalamus and to specific regions of the midbrain. The neural networks of the cerebrum facilitate complex behaviors such as social interactions, thought, judgement, learning, working memory, and in humans, speech and language.

Development

In the developing vertebrate embryo, the neural tube subdivides into four unseparated sections which then develop further into distinct regions of the CNS; these are the prosencephalon, the mesencephalon the rhombencephalon and the spinal cord. The prosencephalon develops further into the telencephalon (forebrain or cerebrum), and the much smaller diencephalon which develops into the optic vessels and the hypothalamus. The telencephalon then forms two lateral telencephalic vesicles which develop into the left and right cerebral hemispheres.

Functions

As the cerebrum is a gross division with many subdivisions and sub-regions, it is important to state that this section lists the functions that the cerebrum as a whole serves. See main articles on cerebral cortex and basal ganglia for more information. The cerebrum is a major part of the brain, controlling emotions, hearing, vision, personality and much more. It controls all voluntary actions.

Movement

The cerebrum directs the conscious or volitional motor functions of the body. These functions originate within the primary motor cortex and other frontal lobe motor areas where actions are planned. Upper motor neurons in the primary motor cortex send their axons to the brainstem and spinal cord to synapse on the lower motor neurons, which innervate the muscles. Damage to motor areas of cortex can lead to certain types of motor neuron disease. This kind of damage results in loss of muscular power and precision rather than total paralysis.

Language and communication

Speech and language are mainly attributed to the parts of the cerebral cortex. Motor portions of language are attributed to Broca's area within the frontal lobe. Speech comprehension is attributed to Wernicke's area, at the temporal-parietal lobe junction. These two regions are interconnected by a large white matter tract, the arcuate fasciculus. Damage to the Broca's area results in expressive aphasia (non-fluent aphasia) while damage to Wernicke's area results in receptive aphasia (also called fluent aphasia).