The brain (latin: cerebrum, greek: enképhalos) is the central anatomical part of the nervous system responsible for integrating most sensory information and coordinating body functions, both consciously and unconsciously, and providing complex functions such as thinking and feeling. The brain is an organ of neural tissue grossly composed of the brainstem, the cerebellum and two cerebral hemispheres.
The brain is contained within the cranial cavity and thus mechanically protected by the bones of the skull. Within the skull three connective tissue layers called the meninges cover the brain, and these are the dura mater, pia mater, and arachnoid mater.
The human brain weighing about 1.2 to 1.4 kg on average composes about 2% of the total body weight, and the tissue of the brain use approximately 20% of the total energy expenditure of the human body. The brain tissue is constructed mainly by two types of cells: neurons - the functional units of the neural tissue, and the supportive glial cells.
Major anatomical parts of the brain include the medulla oblongata, pons, cerebellum, midbrain, diencephalon (including thalamus and hypothalamus), and cerebrum. The medulla oblongata, pons and midbrain together form the portion of the brain known as the brainstem, which continues rostrally with the spinal cord.
The medulla oblongata is the lower part of the brain that appears as a swelling at the upper end of the spinal cord. Besides being a conduit for fibers running between the spinal cord and higher regions of the brain, it contains control centers for involuntary functions such as blood pressure, breathing, swallowing, and vomiting.
Just above the medulla are the pons and cerebellum. The pons is a part of the brainstem between the medulla and the midbrain that relays information between higher regions of the brain, while the cerebellum, which is located behind the pons, processes sensory information and helps coordinate body movements.
The next segment of the brain, the midbrain is located above the pons below the diencephalon and is primarily associated with regulating eye movements, hearing functions, as well as sleep/wake cycles among other functions.
Above the midbrain lies the diencephalon, which includes two major brain regions: the thalamus and hypothalamus. The thalamus processes and integrates all sensory information going to the higher regions of the brain, while the hypothalamus is critical for homeostasis, the maintenance of the body`s internal environment. The hypothalamus influences nervous control of all internal organs and also serves as the master regulator of endocrine functions by its control over the pituitary gland via the hypophyseal-pituitary axis.
The highest region of the brain is the cerebrum, which is divided into two almost symmetric cerebral hemispheres. The gray matter of the cerebrum is formed by neuronal cell bodies and includes both the cerebral cortex that is visible on the outside of the brain and several subcortical structures, including the basal nuclei and hippocampus. The white matter is formed by nerve fibers (myelinated axons of neurons) that lies deep to the cortex. The cerebrum is responsible for such processes as conscious sensation and voluntary movement, as well as advanced functions such as thinking, learning, and emotion.
The cerebral cortex (latin: cortex cerebri) is a layer of gray matter forming the outer part of the cerebral hemispheres. The surface of the cerebral cortex creates folded bulges called gyri and deep fissures called sulci. These cerebral folds increase the surface area of the cerebral cortex, thus increasing the amount of information that can be processed.
Functionally, the cerebral cortex may be divided into motor, sensory and association areas. Sensory areas receive sensory input, motor areas execute voluntary control over muscle movements, and association areas provide more complex functions such as thinking, learning and decision making, as well as complex movements like writing and speaking.
Anatomically, a deep fissure called the central sulcus separates the precentral gyrus anteriorly and postcentral gyrus posteriorly. These two folds correspond to the primary motor and sensory areas. Other areas and anatomical landmarks of the cerebral cortex also correspond with different brain functions.
The main functional areas of the cerebral cortex are as following: