Components of the Central Nervous System (CNS)

Autonomic Nervous System The autonomic nervous system (ANS) is the part of what is called the peripheral nervous system that acts as a control system to maintain the normal and harmonious function (homeostasis) of the entire human body. Also known as involuntary nervous system, the ANS functions without voluntary or conscious control. Because the ANS supplies nerves to the cardiac muscle, smooth muscle, and several endocrine glands; it also influences the activity of most tissues and organ systems in all parts of the body. Thus, the ANS makes a significant contribution in maintaining the normal functioning of the entire body. The regulation of blood pressure, gastrointestinal responses to food, contraction of the urinary bladder, regulation of body temperature are some of many homeostatic functions regulated by the ANS. The regulation of blood pressure, gastrointestinal responses to food, contraction of the urinary bladder, regulation of body temperature are some of many homeostatic functions regulated by the ANS. The system modulates heart rate, digestion, respiration rate, salivation, and perspiration, urination, and sexual arousal. The main components of the ANS include the sensory system and the motor system of the parasympathetic nervous system and sympathetic nervous system. Sympathetic Nervous System The sympathetic nervous system is a component of the autonomic nervous system. It originates from the thoracic and lumbar regions of the spinal cord. Just like other divisions of the nervous system, the sympathetic nervous system operates through a series of interconnected nerve cells, called neurons. Sympathetic neurons of the central nervous system communicate with peripheral sympathetic neurons through a mass of nerve tissue known as sympathetic ganglia. The sympathetic nervous system is in charge of regulating most of the homeostatic mechanisms in the human body. Best known for mediating the neuronal and hormonal stress response, commonly known as the ‘fight-or-flight’ response, the sympathetic system supplies energy to every organ system in the human body. The sympathetic nervous system promotes the "fight or flight" response, through acute energy generation and inhibition of digestion by diverting blood flow away from the gastro-intestinal (GI) tract and skin, by constricting the blood vessels, enhancing blood flow to the lungs and skeletal muscles, by facilitating greater alveolar oxygen exchange, and by dilating bronchioles of the lung, These activities provide the mechanism for enhanced blood flow to skeletal muscles by increasing the heart rate and the contractility of cardiac muscles, dilating the coronary blood vessels of the heart, and allowing more light to the eye by dilating and relaxing the lens of the eyes. Parasympathetic Nervous System The parasympathetic nervous system is another important component of the autonomic nervous system. It originates from the brain stem and the lower part of the spinal cord. In general, the parasympathetic nervous system opposes the physiological effects of the sympathetic nervous system. It promotes the "rest and digest" response, promotes calms of the nerves, enables the human body to return to regular function, and enhances digestion. The parasympathetic nervous system increases intestinal activity and stimulates digestive secretions, slows the heart rate, relaxes sphincter muscles, constrict the pupils, and dilate blood vessels. During unusual conditions of anxiety and/or fear, the parasympathetic system causes spontaneous responses such as urination, excessive secretion of gastric and salivary juices, including nausea or vomiting.