The nervous system is the system of the body that coordinates all the activities of the body to maintain homeostasis and effectiveness The human adult nervous system is usually divided into two large structural division , namely, thee central nervous system (CNS )and the peripheral nervous system(PNS): 1, The CNS: The common subdivisions of the CNS are the brain and the spinal cord(SC) The parts of the brain are cerebrum, diencephalon, brain stem, and cerebellum The spinal cord is somewhat flattened cylinder of nervous tissue about 17" long and about the diameter of a the average finger. Its inner gray matter surrounds a central canal , and the outer white matter is arranged in bundles or funiculi of myelinated fibers 2. The PNS comprises the peripheral receptors, cranial nerves, spinal nerves, peripheral plexuses and ganglia Functional operations of the nervous system The nervous system receives information about changes in the body and the external environment through sensory receptors and sense organs and transmit the information as neural impulses to the CNS. I the CNS integration and interpretation takes place : the bran and or spinal cord compares the information with past experience and determines the appropriate response for the extant circumstances.. The CNS the sends instructions to the effector organs --chiefly muscles and glands to execute the instructions ; The usual functional division of the PNS is as follows : 1. The sensory or afferent division; carriessensory signals from various sense receptors around the body to te CNS The somatic sensory division transmits impulses from receptors in skin muscle and joints\ Visceral sensory division carries signals from the viscera of the thoracic and abdominal cavities e.g. heart lungs, stomach and urinary bladder. The motor or efferent division carries impulses from the CNS to effectors--glands and muscle cells Somatic afferent division carries impulses from CNS to voluntary skeletal muscles that cause them to contract on command. This is voluntary action because it is under the control of the human individual The visceral motor division or Autonomic Nervous System carries instructions to glands , smooth muscles, cardiac muscles;. There is no voluntary control over the activities of these effectors Subdivisions of the ANS are the Sympathetic subdivision and the parasympathetic subdivision The sympathetic division is call the "fight or flight" division. It function is to arouse the body for action; It has effects like increasing heart beat and raising blood pressure and respiratory rate. However, it inhibits motility of the GI tract. The parasympathetic division tends to oppose the actions of the sympathetic division. It is sometime called the "rest and digest" division; it slows heart rate, reduces respiratory rate and depth and stimulates digestive tract activity.
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These sub-classes can be partitioned , structurally as follows: Cerebrum : cerebral cortex, white matter of cerebrum, basal ganglia Diencephalon: Thalamus, hypothalamus, epithalamus Brain Stem: midbrain, pons, medulla oblongata Cerebellum Other structures of the CNS are the lateral, second third ventricles, the choroid plexus and the meninges: dura mater, arachnoid mater and the pia mater which protect the brain and spinal cord. The cerebrospinal fluid (CSF) which flows in th aqueductal system of the brain and the central canal of the spinal cord protects the brain against physical blows and shocks.