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1. neural.
2. unduly excitable or easily agitated.
nervous system the organ system that, along with the endocrine system, correlates the adjustments and reactions of an organism to internal and environmental conditions. It is composed of the brain, spinal cord, and nerves, which act together to serve as the communicating and coordinating system of the body, carrying information to the brain and relaying instructions from the brain. The system has two main divisions: the central nervous system, composed of the brain and spinal cord; and the peripheral nervous system, which is subdivided into the voluntary and autonomic nervous systems. (See color plates.)
The Nerve Cell. The basic unit of the nervous system is the nerve cell, or neuron. This highly specialized cell has many fibers extending from it which carry messages in the form of electrical charges and chemical changes. The fibers of some cells are only a centimeter or less long (a fraction of an inch), but those of others (for example, the sciatic nerve) may extend for half a meter to one meter (18 inches to more than 3 feet). These fibers reach into muscles and organs throughout the body and to the ends of the fingers and toes, and they cluster by the thousands in certain areas of the skin no larger than the head of a pin. The nerve fibers come together from the extremities of the body and gather into cables running to and from the brain. Along the length of the spinal cord are a number of junctions where impulses or messages are sorted or relayed to higher centers. The fibers of connecting nerve cells do not touch each other. Impulses are relayed from one to another by chemical means across the gap or synapse between them. In most cases an impulse must cross more than one synapse to cause the desired action.

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.
Autonomic and Voluntary Systems. The human peripheral nervous system evolved over many millennia, developing the ability to perform more and more complicated functions. It is divided into two specialized subsystems. The autonomic nervous system operates without conscious control as the caretaker of the body. The voluntary nervous system, which includes both motor and sensory nerves, controls the muscles and carries information to the brain.

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.)


1. Relating to a nerve or the nerves.
2. Easily excited or agitated; suffering from mental or emotional instability; tense or anxious.
3. Formerly, denoting a temperament characterized by excessive mental and physical alertness, rapid pulse, excitability, often volubility, but not always fixity of purpose.
[L. nervosus]


/ner·vous/ (ner´vus)
1. neural (1).
2. unduly excitable.


a. Of or relating to the nerves or nervous system: nervous tissue.
b. Stemming from or affecting the nerves or nervous system: a nervous disorder.
2. Easily agitated or distressed; high-strung or jumpy.
3. Marked by or having a feeling of unease or apprehension: nervous moments before takeoff.
4. Vigorous in style or feeling; spirited: "the nervous thrust of a modern creation" (Henry A. Kissinger).
5. Archaic Strong; sinewy.

nerv′ous·ly adv.
nerv′ous·ness n.


adjective Related to a nerve; neural.
adjective Related to anxiety; anxious; jittery, excitable.


1. Neural–neurology.
2. Excitable–psychology.


1. Relating to a nerve or the nerves.
2. Easily excited or agitated; suffering from mental or emotional instability; tense or anxious.
3. Formerly, denoting a temperament characterized by excessive mental and physical alertness, rapid pulse, excitability, often volubility, but not always fixity of purpose.
[L. nervosus]


1. pertaining to a nerve or nerves.
2. unduly excitable.

nervous acetonemia
in contrast to the more common form of this disease of cattle, the wasting form, this one is manifested by delirious signs of circling, head pushing, leaning, straddling, forceful licking including themselves, salivation and incoordination. There is a strong acetonuria and odor on the breath.
autonomic nervous system
the branch of the nervous system that works without conscious control. The voluntary nervous system governs the striated or skeletal muscles, whereas the autonomic governs the glands, the cardiac muscle, and the smooth muscles, such as those of the digestive system, the respiratory system and the skin. The autonomic nervous system is divided into two subsidiary systems, the sympathetic system and the parasympathetic system.
It is also divided into central and peripheral sections. The core of the central section is the hypothalamus which receives afferent input from many other parts of the brain including the cerebral cortex. Its efferent output goes to many lower centers in the nervous system that have visceral control as their functions, e.g. the respiratory center in the medulla. The peripheral section consists of nonmedullated nerve fibers that leave the central nervous system in the craniosacral outflow (parasympathetic system) or the thoracolumbar outflow (sympathetic) system, and terminate in effector organs after passing through a ganglion, visible paravertebral ganglia in the sympathetic system, or ganglia embedded in the wall of the target organ in the parasympathetic system.
central nervous system
the portion of the nervous system consisting of the brain and spinal cord. See also nervous, brain, cerebral.
nervous dysfunction
can occur in any of four ways: (1) Excitation or irritation, an increase in the number of electrical stimuli or facilitation in their passage. (2) Release phenomena, from the damping, modifying effects of higher centers; includes spasticity, exaggerated tendon jerks. (3) paralysis, due to reduction or cessation of transmission of nerve impulses. (4) Nervous shock, a temporary cessation of activity in the nervous system as a whole in response to an insult applied to a part of it.
nervous excitation
see nervous dysfunction (above).
nervous paralysis
see nervous dysfunction (above).
peripheral nervous system
the portion of the nervous system consisting of the nerves and ganglia outside the brain and spinal cord.
nervous release phenomena
see nervous dysfunction (above).
nervous shock
see nervous dysfunction (above).
nervous system
the organ system that along with the endocrine system, correlates the adjustments and reactions of an organism to internal and environmental conditions, comprising the central, peripheral and autonomic nervous systems.

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?

A. here is a quote from the National Fibromyalgia Association site:

"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?

A. Dysautonomia is any disease or malfunction of the autonomic nervous system. The symptoms of dysautonomia conditions are usually “invisible” to the untrained eye. The child can appear to be as healthy as other children. The manifestations are occurring internally, and although the symptoms are often are not visible on the outside. Symptoms can be unpredictable, may come and go, appear in any combination, and may vary in severity).There is no cure for dysautonomia. There are medications to assist in stabilization, but are often needed on a long-term basis.

More discussions about nervous
References in periodicals archive ?
When our waiter did appear with the side orders, he retracted nervously as a manager stepped in front of him to make the unnecessary gesture of topping up our already-full water glasses.
Pakistan secured their first Test win against Australia in 15 years after they nervously knocked off the 40 runs they required on the fourth morning at Headingley.
Some buried their heads nervously in newspapers, others studied their pints.
That means people like grandmother June Mills must wait nervously to see whether an operation carried out 150 miles away was successful.
The visitors began nervously and fell behind early on when Barry Conlon headed home his 12th of the season.
The result leaves Rovers 16th and looking nervously over their shoulders just three points above the relegation zone.
Moments later, however, one of the teens entered the store and began looking around nervously.
On the opposite wall, a perspiring artist (Smit himselfl is seen greeting guests at an opening, nervously playing the endless handshake and air-kiss game.
Before the concert began, people in the audience spoke nervously about living in a changed world.
RCIA candidates, many from the unfairly maligned Generation X, gather in church halls, perhaps nervously at first, wondering what they're getting themselves into, and later jubilantly when they celebrate with their fellow parishioners their full welcome as members of the Body of Christ.
Investors reacted nervously to the announcement, with the Dow Jones average losing an earlier 106-point gain almost immediately.
Preston reports with some glee that The Washington post botched its front-page story on the matter by stating, incorrectly, that the monkeys had "been destroyed as a precaution" at a time when they most emphatically had not been destroyed, and when quite a few scientists were nervously trying to figure out how to destroy them without contracting the disease.