Oracle IAS, the best coaching institute for UPSC/IAS/PCS preparation in Dehradun brings to you UKPCS Science Life Sciences (paper 6)-Central nervous system
The central nervous system (CNS) is the processing center for the nervous system. It receives information from and sends information to the peripheral nervous system. The two main organs of the CNS are the brain and spinal cord. The brain processes and interprets sensory information sent from the spinal cord. Both the brain and spinal cord are protected by a three-layered covering of connective tissue called the meninges.
Brain
The brain is the control center of the body. It has a wrinkled appearance due to bulges and depressions known as gyri and sulci. One of these furrows, the medial longitudinal fissure, divides the brain into left and right hemispheres. Covering the brain is a protective layer of connective tissue known as the meninges.
There are three main brain divisions: the forebrain, the brainstem, and the hindbrain. The forebrain is responsible for a variety of functions including receiving and processing sensory information, thinking, perceiving, producing and understanding language, and controlling motor function. The forebrain contains structures, such as the thalamus and hypothalamus, which are responsible for such functions as motor control, relaying sensory information, and controlling autonomic functions. It also contains the largest part of the brain, the cerebrum. Most of the actual information processing in the brain takes place in the cerebral cortex. The cerebral cortex is the thin layer of gray matter that covers the brain. It lies just beneath the meninges and is divided into four cortex lobes: frontal lobes, parietal lobes, occipital lobes, and temporal lobes. These lobes are responsible for various functions in the body that include everything from sensory perception to decision-making and problem solving. Below the cortex is the brain’s white matter, which is composed of nerve cell axons that extend from the neuron cell bodies of gray matter. White matter nerve fiber tracts connect the cerebrum with different areas of the brain and spinal cord.
The midbrain and the hindbrain together make up the brainstem. The midbrain is the portion of the brainstem that connects the hindbrain and the forebrain. This region of the brain is involved in auditory and visual responses as well as motor function.
The hindbrain extends from the spinal cord and contains structures such as the pons and cerebellum. These regions assist in maintaining balance and equilibrium, movement coordination, and the conduction of sensory information. The hindbrain also contains the medulla oblongata which is responsible for controlling such autonomic functions as breathing, heart rate, and digestion.
Spinal Cord
The spinal cord is a cylindrical shaped bundle of nerve fibers that is connected to the brain. The spinal cord runs down the center of the protective spinal column extending from the neck to the lower back. Spinal cord nerves transmit information from body organs and external stimuli to the brain and send information from the brain to other areas of the body. The nerves of the spinal cord are grouped into bundles of nerve fibers that travel in two pathways. Ascending nerve tracts carry sensory information from the body to the brain. Descending nerve tracts send information pertaining to motor function from the brain to the rest of the body.
Like the brain, the spinal cord is covered by the meninges and contains both graymatter and white matter. The interior of the spinal cord consists of neurons contained within an H-shaped region of the spinal cord. This region is composed of gray matter. The gray matter region is surrounded by white matter containing axons insulated with a special covering called myelin. Myelin functions as an electrical insulator that helps axons to conduct nerve impulses more efficiently. Axons of the spinal cord carry signals both away from and toward the brain along descending and ascending tracts.
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