Autonomic nervous systemThis is a featured page

Nervous sysyem

The autonomic nervous system is responsible for maintaining and controlling the involuntary effectors of the human body. This means that smooth muscles and involuntary actions, such as the heart, are regulated by the part of the nervous system that requires no conscious thought, but still receives directive from the brain. The human brain need not think about the heart beat, it happens because there is a specified section of the brain known as the autonomic nervous system.

Every portion of the body, whether controlled by conscious thought or hormonal release, is technically controlled by brain function. In the case of autonomic nervous system elements, variables and adjustments are made via the brain’s response to stimuli. The brain sends a signal to the heart during strenuous exercise, explaining that it requires the heart to beat faster with more force in order to sustain the body’s health during this level of activity.

The autonomic nervous system is not entirely independent of the central nervous system or the peripheral nervous system even though it does function without intentional decision or thought by the brain. The involuntary effectors which are dependant upon the autonomic nervous system include the cardiac muscle, visceral smooth muscle tissue, and glandular epithelium which is cell which secrete substances such as sweat, mucous, milk, wax, and saliva. This can mean that the variances of the diverse effectors might be part of visceral organs, blood vessels, or specialized functions that are adherent to other organs. In some cases, only part of an organ is controlled via the autonomic nervous system.

Autonomic nervous system


The autonomic nervous system uses somatic motor innervation to maintain the involuntary control and effects associated with involuntary action. This is in stark contrast to the entire system the voluntary skeletal muscles are controlled. The majority of somatic motor control is typically conducted along a single axiom, the necessary information passing along the spinal cord to be intercepted by the neuromuscular junction. However, the autonomic motor system in this instance relies on two neurons which follows a predetermined pathway and adheres to the motor transmission of impulses. One cell of the motor neuron begins in the brain’s gray matter or in the top of the spinal cord. The first motor neuron joins a second motor neuron and exchanges information within the bounds of an autonomic ganglion. The ganglion is defined as a cluster of cells which linger just outside the central nervous system.

To illustrate this further, the first cell is referred to either as preganglionic or presynaptic. The postganglionic cell then follows its own axon to the effector organ to help the process of carrying out the brain’s commands.

The origination point of the preganglionic neuron begins in either the mid or hindbrain as well as the spinal cord stemming from the fourth sacral portions. It does not begin however, between the area or the spinal cord known as areas L3 and S1. The clusters of cells known as autonomic ganglia are located in the abdomen as well as the head and neck. Long links of the autonomic ganglia run alongside both sides of the spinal cord, parallel to its path.

Skeletal muscles can not function without the assistance of the appropriate motor nerves and in fact will become flaccid and paralyzed if communication with the motor nerves is lost. In contrast, involuntary effects can remain in a state of chronic motion for en extended period of time despite a lack of communication with the autonomic motor nerves. While the involuntary effects can not adjust to stimuli without the motor nerves, the ability to maintain a reasonable rate of motion is present. Smooth muscles have the ability to retain a level of tension despite a lack of nerve stimulus. In the event the nerve itself becomes damaged, the involuntary effects can often become more sensitive to stimulation. The built in muscle tone helps these muscles achieve this ability. Not excluding other muscles, the cardiac muscle is able to retain a natural rhythm. The nerves are also able to obtain and retain a reasonable resting rate, despite lack of communication for a period of time.

The autonomic nervous system is a built in, never ending, battery power for those muscles and organs that require constant action or activity without demanding the conscious brain endure the constant reminding of these effectors to maintain themselves.

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Organs included in Autonomic nervous system
Adrenal glands
Adrenergic stimulation
Cardiac muscle
Cholinergic stimulation
Dual innervation
Hypothalamus
Neurotransmitters
Parasympathetic division
Peripheral ganglia
Smooth muscle
Sympathetic division
Visceral effector organs
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Autonomic nervous system

The autonomic nervous system controls involuntary (visceral) functions and has three divisions. The sympathetic and parasympathetic divisions consist of two-neuron chains that connect the central nervous system with the smooth muscles and glands of the viscera, blood vessels, and skin.


The enteric division is a largely independent system that lies in the walls of the gastrointestinal tract and controls many digestive functions. The sympathetic system organizes the involuntary responses that anticipate maximal exertion (the fight-or-flight reaction). Conversely, the parasympathetic system organizes the involuntary responses that generally reflect visceral function in a state of relaxation.

Sympathetic and parasympathetic ganglia are innervated by preganglionic neurons in the spinal cord. Sympathetic preganglionic axons arise from neurons in the thoracic and upper lumbar spinal cord. The preganglionic neurons that innervate the head and thoracic organs are in the upper and middle thoracic segments, and those that innerate the abdominal and pelvic organs are in the lower thoracic and upper lumbar segments. The parasympathetic preganglionic axons arise from neurons in the brainstem and sacral spinal cord. Many organs--including the salivary glands, heart, bladder, and sex organs--receive inputs from both the sympathetic and parasympathetic systems. Other targets receive only sympathetic innervation, including the sweat glands, the adrenal medulla, the piloerector muscles of the skin, and most blood vessels.


The neurons innervated by the preganglionic sympathetic axons are mostly found in the sympathetic chain ganglia, whereas the parasympathetic motor neurons are located in ganglia within the organs they control. The enteric nervous system, although it receives sympathetic and parasympathetic innervation, acts to some degree independently of the rest of the autonomic system. A rich intrinsic circuitry of sensory neurons, interneurons, and motor neurons interconnects different levels of the gut and coordinates activity along its length.


The enteric system governs gut motility, secretion, and the transfer of substances across the gut epithelium. Sensory inputs from the viscera modulate autonomic activity. Like other primary sensory neurons, the relevant cell bodies lie in dorsal root and cranial nerve ganglia; the visceral sensory axons that enter the spinal cord terminate mainly in the intermediate gray matter, near the preganglionic neurons of the thoracolumnar and sacral cord. Those that enter the brainstem (in cranial nerves VII, IX, and X) terminate in the nucleus of the solitary tract. Sensory fibers that travel in the sympathetic nerves convey visceral sensations, usually pain. Other fibers, including most of those that travel in the parasympathetic nerves to the nucleus of the solitary tract, convey information that does not reach consciousness, but which is important for reflex integration (for example, arterial baroreceptors and chemoreceptors).



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Latest page update: made by Trimurtulu , Oct 5 2007, 1:25 AM EDT (about this update About This Update Trimurtulu Edited by Trimurtulu


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