Chapters 5 - Motor systems 05. The autonomic nervous system

05. The autonomic nervous system

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Besides the somatic nervous system [ 160 ] which is our relationship with the outside world and which we are largely aware, there is another system altogether involuntary ensures that the internal functioning of the various organs of the body. This is the autonomic nervous system [ 3 , 4 , 42 , 50 , 104 , 107 , 160 ] also said vegetative.

This system regulates the functioning of the heart, lungs, glands, digestive system, blood vessels [ 133 ] ... short of many organs which are not voluntary control.

The autonomic nervous system is divided into two main systems which have often antagonistic [share 3 , 52 , 133 ] in their different targets: The sympathetic nervous system (sympathetic) and the parasympathetic nervous system.

1. The sympathetic nervous system.

The first neurons of the sympathetic nervous system [ 3 ] have their nuclei in the lateral horn of the spinal gray matter [ 44 ]. They provide pre-ganglionic fibers that will end either in a ganglion of the sympathetic chain or in a peripheral ganglion [ 160 ]. These nodes are called from other postganglionic to reach the destination organs [fibers 3 , 4 ].

As in the parasympathetic system [ 133 ], the preganglionic neurons are cholinergic (their neurotransmitter is acetylcholine) [ 133 ]. While post-ganglionic neurons are often noradrenergic [ 71 ] (they secrete norepinephrine) or adrenergic (secreting epinephrine), these two molecules are part of catecholamines [ 52 ].

The sympathetic nervous system plays an important role in situations of stress and threat, where physical force is applied, where it needs attention and energy [ 82 ].

Thus, this system expands the pupil dilates the pulmonary bronchioles and increases respiratory rate, it also increases the rate and cardiac output, it raises blood pressure and stimulates the secretion of adrenaline (stress hormone) by the adrenal medulla [ 133 ]. It inhibits digestion, direct the blood to the muscles, stimulates the release of glucose by the time in the blood and inhibits the transmission of urine through the bladder.

There are several types of catecholaminergic receptors [ 136 ] which are distinguished based on their response to a preferential catecholamine or another. We therefore receptor alpha 1, alpha 2, beta 1, beta 2 and beta 3.

2. The parasympathetic nervous system:

The parasympathetic nervous system [ 3 ] is a native of cranial nerves: III (common oculomotor), VII (facial nerve), IX (glossopharyngeal) and X (vagus nerve) [ 38 ]. The latter is the main route of the parasympathetic system and the anterior branches of the last four sacral nerves.

Both pre and post-ganglionic neurons of the parasympathetic nervous system are cholinergic [ 107 ]. Acetylcholine stimulates nicotinic receptors in the autonomic ganglia and muscarinic receptors in target tissues [ 3 ].

The parasympathetic nervous system is involved in situations of calm, rest [ 82 ] and maintenance of energy [ 136 ]. Its action opposes almost point by point to the sympathetic system [ 3 , 52 , 133 ].

Thus, the overall effects of parasympathetic stimulation are: bradycardia (vagus nerve responsible for vasovagal syncope), increased intestinal peristalsis, increased gastric, salivary and intestinal secretions, releasing most of the sphincters of the gastrointestinal tract, miosis ( contraction of the iris) ...

Chapters 5 - Motor systems 05. The autonomic nervous system