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The autonomic nervous system The autonomic nervous system is the part of the peripheral nervous system that regulates the basic visceral processes needed for the maintenance of normal bodily functions.
It operates independently of voluntary control, although certain events, such as stress, fear, sexual excitement, and alterations in the sleep-wake cycle, change the level of autonomic activity. Schematic representation of the autonomic nervous system, showing distribution of sympathetic and parasympathetic nerves to the head, trunk, and limbs.
The autonomic system usually is defined as a motor system that innervates three major types of tissue: However, it also relays visceral sensory information to the central nervous system and processes it so that alterations can be made in the activity of specific autonomic motor outflows, such as those Nervous breakdown help control the heartblood vessels, and other visceral organs.
It also stimulates the release of certain hormones involved in energy metabolism e. These integrated responses maintain the normal internal environment of the body in an Nervous breakdown help state called homeostasis. The autonomic system consists of two major divisions: These often function in antagonistic ways.
The motor outflow of both systems is formed by two serially connected sets of neurons. The first set, called preganglionic neuronsoriginates in the brainstem or the spinal cordand the second set, called ganglion cells or postganglionic neuronslies outside the central nervous system in collections of nerve cells called autonomic ganglia.
Parasympathetic ganglia tend to lie close to or within the organs or tissues that their neurons innervate, whereas sympathetic ganglia are located at more distant sites from their target organs. Both systems have associated sensory fibres that send feedback into the central nervous system regarding the functional condition of target tissues.
A third division of the autonomic system, the enteric nervous system, consists of a collection of neurons embedded within the wall of the gastrointestinal tract and its derivatives.
This system controls gastrointestinal motility and secretion.
Sympathetic nervous system The sympathetic nervous system normally functions to produce localized adjustments such as sweating as a response to an increase in temperature and reflex adjustments of the cardiovascular system.
Under conditions of stress, however, the entire sympathetic nervous system is activated, producing an immediate, widespread response called the fight-or-flight response. This response is characterized by the release of large quantities of epinephrine from the adrenal glandan increase in heart rate, an increase in cardiac outputskeletal muscle vasodilation, cutaneous and gastrointestinal vasoconstriction, pupillary dilation, bronchial dilation, and piloerection.
The overall effect is to prepare the individual for imminent danger. Sympathetic preganglionic neurons originate in the lateral horns of the 12 thoracic and the first 2 or 3 lumbar segments of the spinal cord.
For this reason the sympathetic system is sometimes referred to as the thoracolumbar outflow. The axons of these neurons exit the spinal cord in the ventral roots and then synapse on either sympathetic ganglion cells or specialized cells in the adrenal gland called chromaffin cells. Sympathetic ganglia Sympathetic ganglia can be divided into two major groups, paravertebral and prevertebral or preaorticon the basis of their location within the body.
Paravertebral ganglia generally are located on each side of the vertebrae and are connected to form the sympathetic chainor trunk. There are usually 21 or 22 pairs of these ganglia—3 in the cervical region, 10 or 11 in the thoracic region, 4 in the lumbar region, and 4 in the sacral region—and a single unpaired ganglion lying in front of the coccyxcalled the ganglion impar.
The three cervical sympathetic ganglia are the superior cervical ganglion, the middle cervical ganglion, and the cervicothoracic ganglion also called the stellate ganglion. The superior ganglion innervates viscera of the head, and the middle and stellate ganglia innervate viscera of the neck, thorax i.
The thoracic sympathetic ganglia innervate the trunk region, and the lumbar and sacral sympathetic ganglia innervate the pelvic floor and lower limbs.
All the paravertebral ganglia provide sympathetic innervation to blood vessels in muscle and skin, arrector pili muscles attached to hairs, and sweat glands.
The three preaortic ganglia are the celiac, superior mesenteric, and inferior mesenteric. Lying on the anterior surface of the aortapreaortic ganglia provide axons that are distributed with the three major gastrointestinal arteries arising from the aorta. Thus, the celiac ganglion innervates the stomachliverpancreasand the duodenumthe first part of the small intestine; the superior mesenteric ganglion innervates the small intestine ; and the inferior mesenteric ganglion innervates the descending colonsigmoid colonrectumurinary bladderand sexual organs.
Neurotransmitters and receptors Upon reaching their target organs by traveling with the blood vessels that supply them, sympathetic fibres terminate as a series of swellings close to the end organ.
Because of this anatomical arrangement, autonomic transmission takes place across a junction rather than a synapse.
The distance between pre- and postsynaptic elements can be quite large compared with typical synapses. For instance, the gap between cell membranes of a typical chemical synapse is 30—50 nanometres, while in blood vessels the distance is often greater than nanometres or, in some cases, 1—2 micrometres 1,—2, nanometres.
Owing to these relatively large gaps between autonomic nerve terminals and their effector cells, neurotransmitters tend to act slowly; they become inactivated rather slowly as well. To compensate for this inefficiency, many effector cells, such as those in smooth and cardiac muscle, are connected by low-resistance pathways that allow for electrotonic coupling of the cells.
In this way, if only one cell is activated, multiple cells will respond and work as a group. At a first approximation, chemical transmission in the sympathetic system appears simple:The autonomic nervous system is the part of the peripheral nervous system that regulates the basic visceral processes needed for the maintenance of normal bodily functions.
It operates independently of voluntary control, although certain events, such as stress, fear, sexual excitement, and. Recording. The recording was financed by Greg Ginn with proceeds he had earned from his mail-order ham radio electronics business, Solid State Tuners (SST).
Through Spot, then an apprentice engineer whom Ginn had already known from living in Hermosa Beach, California, the band found Media Art, a studio that had recently completed construction..
The recording was originally supposed to be. Functions of the human nervous system.
The human nervous system differs from that of other mammals chiefly in the great enlargement and elaboration of the cerebral hemispheres. Much of what is known of the functions of the human brain is derived from observations of the effects of disease, from the results of experimentation on animals, particularly monkeys, and from neuroimaging studies of.
breakdown - Translation to Spanish, pronunciation, and forum discussions. The signs and symptoms of your nervous breakdown are an indication that you've reached your limit.
You may feel like you're falling apart, but I promise you - you're not going mad. You're not 'mental'! Nervous breakdown and mental breakdown are dated terms describing emotional or physical stress that temporarily makes someone unable to function in day-to-day life.