Complete guide to know central nervous system

Central Nervous System 
The central nervous system (CNS) consists of the brain and the spinal cord. The CNS is protected by bone: The brain occupies the cranial cavity, and the spinal card occupies the vertebral canal.
Brain 
The human brain is divided into the medulla oblongata, pons, midbrain, cerebellum, hypothalamus, thalamus, and cerebrum. The brain has four cavities, called ventricles: two lateral ventricles, the third ventricle, and the fourth ventricle. Interventricular foramina connect the lateral ventricles with the third ventricle. The third and fourth ventricles are connected by a small canal called the cerebral aqueduct (aqueduct of Sylvius).
Brain Stem 
The medulla oblongata, pons, and midbrain lie in a portion of the brain known as the brain stem. The medulla oblongata (me-dul'ah ob"long-gah'tah) lies between the spinal cord and the pons and is anterior to the cerebellum. It contains a number of vital centers for regulating heartbeat, breathing, and blood pressure. It also contains the reflex centers for vomiting, coughing, sneezing, hiccoughing, and swallovving. The medulla contains tracts that ascend or de­scend between the spinal card and the brain's higher centers.
The pons is a "bridge;" it contains bundles ofaxons traveling between the cerebellum and the rest of the CNS. In addition, the pons functions with the medulla to regulate breathing rate and has reflex centers con­cerned with head movements in response to visual and auditory stimuli.
The midbrain encloses the cerebral aqueduct. Aside from acting as a relay station for tracts passing between the cerebrum and the spinal cord or cerebellum, the midbrain has reflex centers for visual, auditory, and tac­tile responses.
Diencephalon 
The hypothalamus and thalamus are in a portion of the brain known as the diencephalon (di"en-sefah-lon), where the third ventricle is located. The hypothalamus (hi"po-thal'ah-mus), which forms the floor of the third ventricle, maintains homeostasis, or the constancy of the internal environment, and contains centers for regulating hunger, sleep, thirst, body temperature, water balance, and blood pressure. The hypothalamus controls the pituitary gland and thereby serves as a link between the nervous and endocrine systems.
The thalamus, in the lateral walls of the third ventri­cle, is the last portion of the brain for sensory input before the cerebrum. It serves as a central relay station for sensory impulses traveling upward from other parts of the body and brain to the cerebrum. It receives all sensory impulses (except those associated with the sense of smell) and channels them to appropriate regions of the cortex for interpretation.
The brain stem and the diencephalon contain reflex centers that are involved in controlling internal organs. and tracts that channel impulses into the brain or betvveen brain regions. The hypothalamus maintains homeostasis and controls the secretions of the pituitary gland.
Cerebellum 
The cerebellum (ser"e-bel'um), which lies below the pos­terior portion of the cerebrum, is separated from the brain stem by the fourth ventricleThe cerebellum has two ­parts called hemispheres that are joined by a constricted median portion. The surface of the cerebellum is gray matter, and the interior is largely white matter. The cere­bellum functions in muscle coordination, integrating impulses received from higher centers to ensure that all of the skeletal muscles work together to produce smooth and graceful motion. The cerebellum is also responsible for maintaining normal muscle tone and transmitting impulses that maintain posture. It receives information about body position from the inner ear and then sends impulses to the muscles, whose contraction maintains or restores balance.
The cerebellum controls balance and complex muscular movements. 
Cerebrum 
The cerebrum (ser'e-brum) is the largest and most superior part of the brain. It is the only area of the brain responsible for consciousness. The cerebrum is divided into halves known as the right and left cerebral hemispheres; each hemisphere contains a lateral ventricle.
The outer layer of the cerebrum, called the cortex, is gray and contains cell bodies and short fibers. The cortex has convolutions known as gyri, which are separated by shallow grooves called sulci and deep grooves called fissures. The cerebrum is almost divided by a deep, longitudinal fis­sure. At the base of this fissure lies the corpus callosum, a bridge of myelinated fibers that joins the two hemispheres.
Each cerebral hemisphere has four lobes: frontal, parietal (pah-ri'e-tal), temporal, and occipital (ok-sip'i-taI), which are named for the bones that cover them. Each lobe has particular functions.
These two areas in particular demonstrate how it is possi­ble to map the cerebrum by associating particular parts of the cerebrum with particular parts of the body. A momentary lack of oxygen during birth can damage the motor areas of the cerebral cortex so that the individual develops the symptoms of cerebral palsy, a condition charac­terized by a spastic weakness of the arms and legs.
The motor area for speech, called Broca's area, is lo­cated near the base of the primary motor area. Broca's area is usually only found in the left cerebral hemisphere. Damage to this area can interfere with a per­son's ability to understand words (written or spoken) and to communicate with others. This explains why a stroke is often accompanied by speech problems. Strokes occur when the blood supply to the brain is temporarily halted due to a burst blood vessel or to a blood clot in an artery. Electroencephalograms (EEGs), which record the brain's electrical activity, are examined in the Medical Focus reading on this page.
Basal Nuclei The basal nuclei constitute several masses of gray matter that lie deep within the white matter of the cere­brum. The precise function of the basal nuclei is not known, but they are a part of the limbic system discussed next. Also they must have some control over voluntary muscle action because when they are diseased, Parkinson disease may develop and there may be spastic movement of limbs.
Consciousness is under the control of the cerebrum, the most highly developed portion of the brain. It is responsible for higher mental processes, including the interpretation of sensory input and the initiation of voluntary muscular movements.
Limbic System 
The limbic system involves portions of both the unconscious and conscious brain. It lies just be­neath the cerebral cortex and contains neural pathways that connect portions of the frontal lobes, the temporal lobes, the thalamus, and the hypothalamus.
Stimulation of different areas of the limbic system causes the subject to experience rage, pain, pleasure, or sor­row. By causing pleasant or unpleasant feelings about experiences, the limbic system apparently guides the indi­vidual into behavior that is likely to increase the chance of survival.
The limbic system is also involved in learning and memory. Learning requires memory, and memory is stored in the sensory regions of the cerebrum, but just what permits memory development is not definitely known. The involvement of the limbic system in memory explains why emotionally charged events result in our most vivid memories. The fact that the limbic system communicates with the sensory areas for touch, smell, vi­sion, and so forth accounts for the ability of any particular sensory stimulus to awaken a complex memory.
The limbic system is involved in learning and memory, and in causing the emotions that guide behavior.