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In a reflex, the impulse is relayed from one nerve to another by a shortcut that produces a reaction without involving the brain. The knee jerk is an example of the simplest sort of reflex reaction. When the knee is tapped, the impulse travels through the sensory nerve that receives the tap, crosses a single synapse, and activates the motor nerve that controls the quadriceps muscle in the thigh, causing the leg to jerk up automatically.
A very different sort of reflex is the conditioned reflex.Conditioning is the process of building links or paths in the nervous system. When an action is done repeatedly the nervous system becomes familiar with the situation and learns to react automatically. A new reflex has been built into the system. Hundreds of daily actions are conditioned reflexes. Walking, running, going up and down stairs, and even buttoning a shirt all involve great numbers of complex muscle coordinations that have become automatic.
The autonomic system is further specialized into two subsidiary systems: the sympathetic and the parasympathetic. The control centers of these systems lie in the hypothalamus. The sympathetic and parasympathetic nervous systems are continuously operative, functioning to adjust body processes to external and internal demands. (See also Plates.)
The sympathetic nervous system has in general an excitatory effect, and in response to danger or some other challenge, almost instantly puts body processes into high gear. This is done by the discharge of stimulating secretions at nerve junctions. These secretions, along with epinephrine discharged into the blood by the adrenal medulla, help start muscle action quickly. Glucose is released from the liver into the blood and thus is made available to all the body's muscles as a source of quick energy. The rates of heart and lung action increase, digestive activity slows down, blood vessels constrict, and sweating begins so that the body will be kept cool while under stress. Thus the body is prepared for an extraordinary effort.
The parasympathetic nervous system prevents body processes from accelerating to extremes. Acting more slowly than the sympathetic system, it causes the discharge of secretions that slow the heartbeat and lung action, restore digestive functioning, and limit the constriction of the blood vessels. Generally it acts as a damper, so that unless the challenge demands a prolonged effort, body processes will begin returning to normal.
The voluntary nervous system has nerves of two kinds, sensory and motor. The sensory nerves bring messages to the brain from all parts of the body. They are sorted in the spinal cord and sent on to the brain to be analyzed, acted upon, associated with other information and stored as memory. Messages from the brain, often in response to information received by way of the sensory nerves, are delivered to the muscles by the motor nerves. One motor nerve with its branching fibers may control thousands of muscle fibers.
The different parts of the nervous system are constantly interacting, and are so well coordinated that humans can think, feel, and act on many different levels and without serious confusion, all at the same time. (See also neurologic assessment.)
adjective Related to a nerve; neural.
adjective Related to anxiety; anxious; jittery, excitable.
Patient discussion about nervous
Q. Is fibromyalgia related to Central Nervous System? Is fibromyalgia related to Central Nervous System? Among men and women who is more prone to the symptoms of fibromyalgia?
"Little research has been conducted that measures the prevalence of fibromyalgia, and estimates vary widely as to the proportion of male versus female patients. A 1999 epidemiology study conducted in London found a female to male ratio of roughly three to one. However, a 2001 review of the research literature in Current Rheumatology Reports stated the ratio was nine to one."
Q. What is dysautonomia? My friend has dysautonomia. What does it mean? What are the symptoms? Is it curable?