Explain the functionality of Central Nervous System ?

The central nervous system is the center of the nervous system, receiving impulses from, and sending impulses to, the peripheral nervous system. It consists of the brain and the spinal cord, which are heavily protected by bone, connective and elastic tissue. Dense bone forms the skull and the vertebral column that protects the spinal cord. Beneath the bones are three layers of dense connective tissue called meninges. Within the outer layer, the dura mater, lie blood vessels and nerves. The middle layer is a delicate membrane called the arachnoid layer (from the Greek term meaning "cobweb like") enclosing the brain and spinal cord. The thin third layer, adhering to the brain and spinal tissue, is called the pia mater. Between the arachnoid and the pia mater is the subarachnoid space, containing cerebrospinal fluid that serves as a shock absorber for the central nervous system. The cerebrospinal fluid is produced within cavities in the brain called ventricles.

The Brain :  We now look at the human brain, the part of the body which most makes you unique as an individual. Scientists have been able to localize brain functions by studying the effects on behavior of people with accidentally damaged brains, and by applying electrodes to certain parts of brains of humans and animals. They found that there is much overlapping of function, but certain areas are principally involved with separate functions. The human brain, as well as that of other vertebrates, can be divided into three sections -- the forebrain, midbrain, and hindbrain, each involved with different functions.

The forebrain contains two major parts: the telencephalon and the diencephalon. The anterior part, the telencephalon, is highly developed in humans. It contains the cerebrum, which is divided by a fissure into left and right cerebral hemispheres, and the cerebral cortex, the outer layer of the cerebrum. The convoluted surface of the cerebrum - the gray matter, is composed of unmyelinated nerve cells, interspersed with myelinated fibers. The myelinated part of the cerebrum, or white matter, connects the bases of the cerebral hemispheres with each other. The largest bundle of axons of myelinated cells connecting the two hemispheres is called the corpus callosum. Each hemisphere of the cerebrum is separated by deep grooves into four lobes, the frontal, parietal, temporal, and occipital. The frontal lobe is the site of complex reasoning, speech, and voluntary muscle movement. The parietal lobe interprets messages from sensory cells such as touch, the temporal lobe is associated with hearing, and the occipital lobe with visual imaging. Impulses from the left side of the body tend to be processed in the right brain, and vice versa.

The diencephalon is the posterior part of the forebrain, containing the thalamus, which regulates sensory information, the posterior lobe of the pituitary gland, which is described in the discussion of the endocrine system, and the limbic system. The limbic system, located below the thalamus, controls emotional states, and possibly memory. It is composed of the hypothalamus, amygdala, and hippocampus. The hypothalmus controls hormonal and nervous interactions, including constriction and dilatation of blood vessels, adjustment of water balance, blood sugar, and to some extent metabolism of carbohydrates and fats, regulation of body temperature, discharge of sweat, and other functions concerned with the autonomic nervous system. The amygdala is associated with emotional states such as fear and pleasure. The hippocampus is thought to control rage, sexual arousal, and memory.

The midbrain consists of the superior colliculi, bumps on the brainstem surface, which control reflexes of eyes and eyelids, and inferior colliculi, which are concerned with hearing. The midbrain is proportionally much smaller in humans than in animals, but it contains the reticular formation, an important center consisting of a network of nerves that extends into the lower part of the forebrain and into the hindbrain. It serves to distinguish between incoming impulses, selecting the ones requiring immediate attention and screening out unimportant noises and other stimuli. This allows the cerebrum to better concentrate on important tasks.

The hindbrain includes the cerebellum, medulla oblongata, and pons. The cerebellum is concerned with equilibrium and movement. It receives sensory input from eyes, ears, and muscles, and sends motor impulses in response to inhibit or promote activity in the target organs. The medulla oblongata is an enlargement of the spinal cord as it enters the brain. It contains clusters of neuron cell bodies that receive input associated with autonomic or reflex functions, such as breathing, swallowing, and blood vessel constriction. The pons, located above the medulla, connects the cerebrum to the cerebellum, and controls sleep states.

The midbrain, medulla, pons, and the diencephalon, are joined to form a region referred to as the brain stem, connecting the cerebrum with the spinal cord. Information may be processed and modified here.

The Spinal Cord :  The spinal cord of nervous tissue extends from the medulla to the end of the vertebral column. As in the brain, there is gray matter composed of cell bodies of cells concerned with reflex activities, and white matter made up of bundles of myelinated axons carrying information to the brain and other parts of the spinal cord. The rapid response to pain that we call a reflex is controlled by a reflex arc, a pathway of at least two neurons, one sensory and one motor. The cell bodies of these nerves have their origin in the spinal cord. There may also be one or more interneurons located between the sensory and motor neuron. The simple structure of the reflex arc makes it possible for the body to respond to a stimulus faster than if the impulse had to go to the brain for processing.