notes by dr Claudio Italiano
The vegetative nervous system regulates visceral functions and sends nerve
bundles to the viscera (trachea, bronchi, esophagus, stomach, intestine) and
also to the heart and blood vessels; innervates the muscular laminae of all the
hollow viscera and influences the secretion of the external secretion glands and
internal secretion glands). There are mainly driving fibers for the smooth
muscles of organs and vessels, secretory fibers that induce the secretion of
glandular cells and trophic fibers that regulate the nutrition of organs and
tissues. The vegetative nervous system was improperly called autonomous: in fact,
the vegetative centers are located in the cerebro-spinal axis. The vegetative
nervous system consists essentially of two parts, the sympathetic or
sympathetic proper and the parasympathetic.
The simpatic consists of a chain of ganglia containing groupings of nerve cells, a chain located on both sides of the vertebral bodies, which takes place from the first cervical vertebrae up to the coccyx. Between ganglion and ganglion, a cord of fibers takes the name of intermediate cord or intergangliare. The ganglia, thanks to the so-called communicating branches, join the spinal nerves. Pre-marrow fibers of the marrow thus enter the sympathetic chain. From each ganglion, gray filaments, formed of postganglionic fibers, start at the internal organs, such as the heart, the lungs, the various segments of the digestive tract, the salivary glands and those with internal secretion (thyroid, hypophysis, etc.), the liver, the kidney. At the top the first cervical ganglion, thanks to numerous branches, binds to the internal carotid artery and in this way brings the sympathetic innervation to the meninges, to the encephalic vessels, to the eye, and to the lacrimal gland. The number of sympathetic ganglia is constant on each side: there are three ganglia in the cervical region, eleven or twelve ganglia in the thoracic region, five or four in the lumbar region, four or five in the sacral region, and one in coccygeal. However, their number is very variable because some ganglia often merge together.
Intertwining of fibers and peripheral ganglia form
the plexuses, such as the cardiac, which sends its ramifications to the heart
and the coronary arteries; celiac or sun, which innervates the stomach, liver
and spleen; the mesentery), which innervates the small intestine; the
hypogastric, which innervates the large intestine and the urinary bladder. The
sympathetic acts by contracting the muscular cells of the blood vessels; in the
heart, instead, it acts by dilating the coronary arteries. Also on the muscle
fibers of the bronchi it has a dilating action. Accelerates intestinal
peristalsis and dilates the pupil diaphragm (pupillary mydriasis).
The parasympathetic system is so called because it sends fibers coming from the cerebro-spinal axis to the organs already innervated by the sympathetic. The cell chain that compose it is completely independent of the osympathetic ganglia. Only in the depth of the viscera the two systems, through networks and plexuses, mix their fibers. Both the sympathetic and the parasympathetic do not possess only efferent fibers, ie fibers that carry impulses from the centers to the periphery, causing contraction or de-contraction of muscular fibers and activating secretion functions. It should not be forgotten, however, that the viscera are also made of afferent fibers and therefore do not lack a singular sensitivity (visceral sensitivity) and this because around the viscera and within their walls are nervous receptors able to bring to the centers stimuli psychics; maximum feelings of pain, tension and contraction. The two systems, the sympathetic and the parasympathetic, assure both, as stated above, the normal functioning of the organs of the feeding life and their physiological action is generally antagonistic. In fact, the excitation of the sympathetic produces the dilatation of the pupil, the acceleration of the heart, the contraction of the blood vessels; the excitation of the parasympathetic, on the contrary, restricts the pupil, slows down the heart and tends to dilate the blood vessels. So there is a balance between the sympathetic and the parasympathetic in the organism. This balance can be disturbed: if the action of the sympathetic predominates, sympathicotonia occurs, in the opposite case there is vagotonia. Tachycardic individuals, that is, with a fast-paced heart, and vagotonic, bradycardic ones, ie a slow-paced heart, are sympathetic.