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VEGETATIVE (AUTONOMIC) SYSTEM Amanda Hess Borzacchini Group 20 2nd year, 1st semester Kursk 2012
The vegetative nervous system controls the activity of all organs concerned with the vegetative function of the body (respiration, fluid circulation, reproduction, excretion, nutrition) and accomplishes trophic innervation. The trophic function of the vegetative nervous system is responsible for the nutrition of the tissues and organs in conformity to their functioning under certain environmental conditions (adaptational-trophic function).
The vegetative nervous system is separated into two systems: the sympathetic and parasympathetic systems. The sympathetic system is mainly concerned with trophic functions. It is responsible for nutrient consumption, intensification of oxidation processes, respiration and increases the rate of cardiac activity and supply of oxygen to the muscles. The parasympathetic system carries a protective role, like constriction of the pupil in bright light, inhibition of cardiac activity, evacuation of the cavitary organs.
Comparison of the areas of distribution of the sympathetic and parasympathetic innervation discloses. Firstly some organs have the predominant role of one vegetative part over the other; e.g.: the urinary bladder receive mostly parasympathetic innervation and the sweat glands, the spleen, suprarenals are supplied only with the sympathetic innervation. Secondly, in organs with double innervation, the interaction of the sympathetic and parasympathetic nerves are antagonistic; e.g.: the stimulation of sympathetic nerves causes dilatation of the pupil, constriction of the vessels, increase in the rate of the cardiac Contractions; in contrast, the stimulation of parasympathetic nerves leads to constriction of the pupil, dilatation of the vessels, decrease in the rate of cardiac contractions.
The antagonism of the sympathetic and parasympathetic system are reciprocally affected, the relations between them alter dynamically in the different phases of the functioning of this or that organ; they can act both as antagonists and as synergists. The normal function of our organism is ensured by the coordination and regulation brought by the cerebral cortex. The sympathetic and parasympathetic are distinguished in the vegetative system according to the physiological and pharmacological data.
The sympathetic nervous system The central part of the sympathetic system is located in the lateral horns of the spinal cord between the level of C7 and Th1-L3 in the intermediolateral nucleus. It give rise to fibres innervating the smooth muscles of the viscera and the sensory organs (eyes), and the glands. Vasomotor, pilomotor and respiration centres are also located here.
The peripheral part of the sympathetic system is formed by two symmetrical right and left sympathetic trunks stretching on either side of the spinal from the base of the skull to the coccyx where the caudal ends of both trunks meet to form a single common ganglion.
Each sympathetic trunk is composed of a series of nerve ganglia of the first order connected by longitudinal interganglionic branches that consist of nerve fibres. The processes of cells located in the lateral horns of the thoracolumbar part of the spinal cord emerge from it through the anterior roots and pass in the white communicating branches to the sympathetic trunk.
From the white communicating branches the processes of the cells join by means of synapsis with the cells of the sympathetic trunk ganglia or pass through the ganglia without interruption and reach one of intermediate ganglia. This is the preganglionic pathway. From the ganglia of the sympathetic trunk or from the intermediate ganglia arise non- medullated fibres of the postganglionic pathways and pass to the blood vessels and viscera.
The sympathetic system has a somatic part, it is connected with the spinal nerves providing innervation of the soma. This connection is brought about by the grey communicating branches which are segment of postganglionic fibres stretching from the sympathetic trunk ganglia to a spinal nerve. As components of the grey communicating branches and spinal nerves the postganglionic fibres spread in the vessels, glands, and smooth muscles of the skin of the trunk and limbs, as well as in the striated muscles for whose nutrition and tonus they are responsible.
Thus, the SNS is connected with the somatic system by two types of communicating branches, white and grey. The white communicating branch (medullated) are the preganglionic fibres; they stretch from the centres of the sympathetic nervous system through the anterior roots of the ganglia of the sympathetic trunk. The centres are situated at the level of the thoracic and upper lumbar segments.
The grey communicating branch, the postganglionic fibres, provide the vasomotor and trophic processes in the soma. They connect the sympathetic trunk with the spinal nerves for its entire length. The cervical part of the sympathetic trunk is also connected with the cranial nerves. All the plexuses of the somatic nervous system contain therefore fibres of the sympathetic system in their bundles and nerve trunks.
The sympathetic trunk Sympathetic trunk is a r (or abdominal) and pair formation, situated sacral (or pelvic). at flanks of the spinal cord, consists of 20-25 ganglions connected with interganglionic branches. Each of the two sympathetic trunk is subdivided into four parts: cervical, thoracic, lumba
The cervical part stretches from the base of the skull to the neck of the first rib, lies behind the carotid arteries on the deep muscles of the neck. It has three cervical sympathetic ganglia: superior, middle and inferior. Superior cervical ganglion is the largest ganglion of the sympathetic trunk, lies on the level of the 2nd and part of the 3rd cervical vertebrae behind the internal carotid artery and medial to the vagus nerve. Middle cervical ganglion is small and usually located at the intersection of the inferior thyroid artery with the carotid artery. Inferior cervical ganglion is situated behind the initial part of the vertebral artery, it is often fused with the 1st and sometimes with the 2nd thoracic ganglion to form a common inferior cervical ganglion.
The cervical ganglia send nerves to the head, neck and chest; can be divided into an ascending group passing to the head, a descending group stretching to the heart, and a group running to the organs of the neck almost immediately from the site of origin.
Ascending group: the nerves of the head arise from the superior and inferior cervical ganglia and separate into a group of nerves that penetrate the cranial cavity and a group of nerves that reach the head from outer surface. 1st group is represented by the internal carotid nerve, from the superior cervical ganglion and the vertebral branch of the inferior cervical ganglion. Both nerves form plexuses around them, internal carotid plexus and the vertebral plexus.
Together with the arteries passing through the the nerves enter the cranial cavernous sinus. cavity where they anastomose with one another and send branches to the cerebral vessels, the meninges, the hypophysis, the trunk of the 3rd, 4th, 5th and 6th pairs of cranial nerves and to the tympanic nerve. The internal carotid plexus is continuous with the cavernous plexus which surrounds the internal carotid artery in the part
2nd group, external, consists of salivary), and to the muscle two branches of the superior which dilates the pupil (m. cervical ganglion, the external dilatator pupillae). carotid nerves, which form plexuses around the external carotid artery and then pass in attendance to its ramifications on the head. The plexus sends a small ramus to the optic ganglion, the facial plexus gives off a branch accompanying the facial artery and passing to the submandibular ganglion. The superior cervical plexus sends fibres to the vessels (vasoconstrictors) and the glands of the head (sweat, lacrimal, mucous and
Descending group: is formed by the cardiac branches of the superior, middle and inferior cervical ganglia; and together with the cardiac branches of the sympathetic thoracic ganglia and branches of the vagus nerve contribute to the formation of the cardiac plexuses.
The thoracic part lies in ganglia and participates in front of the neck of the ribs the formation of the cardiac and is covered by pleura. It plexus. consists of 10 to 12 ganglia. The thoracic part is characterized by the presence of white communicating branches which connect the anterior roots of the spinal nerves with the sympathetic trunk ganglia. The five branches are: 1.Cardiac branch arises from the superior thoracic
2.Grey communicating branches are non- medullated fibres supplied to the intercostal nerves. 3.Pulmonary branches pass to the lungs to form the pulmonary plexus. 4.Aortic branches form a thoracic aortic plexus, partly on the oesophagus, oesophageal plexus, and on the thoracic duct.
5.Greater and lesser splanchnic nerves: The greater splanchnic nerve originates as several roots from the 5th to 9th thoracic ganglia, which pass medially to the level of the 9th thoracic vertebra where they fuse into one common trunk which is transmitted through the space between the muscular bundles of the diaphragmatic crura into the abdominal cavity in which becomes a component of the coeliac plexus. The lesser splanchnic nerve arises from the 10th and 11th thoracic ganglia, penetrates the diaphragm together with the greater splanchnic nerve or is separated from it by a few muscular bundles, and also becomes a component of the coeliac plexus.
The lumbar (or abdominal) part consists of four ganglia. Both sympathetic trunks come closer to each other in the lumbar part, as a result of which the ganglia lie on the anterolateral surface of the lumbar vertebrae on the medial border of the psoas major muscle. Along its entire distance the lumbar part sends off a great number of branches which, together with the greater and lesser splanchnic nerves and the abdominal segments of the vagus nerve, form the largest unpaired coeliac plexus. The coeliac plexus lies on the anterior semicircunference of the abdominal aorta behind the pancreas and surrounds the initial parts of the coeliac trunk and the superior mesenteric artery.
Coeliac trunk occupies anarea between the renalarteries, the suprarenalglands, and the aorticopening of the diaphragmand includes the pairedganglion of the coeliacartery – coeliacganglion, and sometimesthe unpaired ganglion ofthe superior mesentericartery- superiormesenteric ganglion lyingunder the root of thisartery.
The 2nd main source of ganglion whose innervation of the abdominal postganglionic fibres pass to organs is the aortic the pelvis as components of plexus, formed by two trunks the hypogastric nerves. arising from the coeliac plexus and branches running from the lumbar ganglia of the sympathetic trunk. Aortic plexus gives rise to the inferior mesenteric plexus for the transverse, descending, and sigmoid colon, and upper part of the rectum. At the origin of the inferior mesenteric plexus lies the inferior mesenteric
Aortic plexus is relation to the penis and continuous with the motor in relation to the unpaired hypogastric uterus and the sphincter plexus which bifurcates urethrae muscle. at the promontory of the sacrum and is in turn continuous with the pelvic plexus. Fibres derived from the superior lumbar segments are functionally vasomotor (vasoconstrictor) in
The sacral (or pelvic) part, part usually has four ganglia. Lying on the anterior surface of the sacrum along the medial margin of the anterior sacral foramen, both trunks converge to terminate as one common unpaired ganglion impar on the anterior surface of the coccyx. The ganglia of the pelvic part are connected both by small longitudinal and transverse trunks.
The parasympathetic system The central part of the parasympathetic system consists of the cranial nerves ( III, VII, IX and X); III, VII and IX carry parasympathetic fibers to structures within the head and neck only, whereas X (the vagus nerve) also innervates thoracic and most abdominal viscera; and spinal (or sacral) nerves S2 to S4, sacral parasympathetic fibers innervates inferior abdominal viscera, pelvic viscera and the arteries associated with erectile tissues of the perineum. The centres give rise to the efferent fibres of the posterior horns which cause dilation of the vessels and inhibition of contraction of the smooth muscles of the hair on the trunk and limbs.
The cranial part consists ciliaris) of centres lodged in the mesencephalic part and in the bulbar part (pons and medulla oblongata). 1.Mesencephalic part is represented by the accessory nucleus of the oculomotor nerve and by the median unpaired nucleus which are responsible for the innervation of the smooth muscles of the eye (m. sphincter pupillae and m.
2.Bulbar part is represented by the superior salivary nucleus of the facial nerve, the inferior salivary nucleus of the glossopharyngeal nerve, and the dorsal nucleus of the vagus nerve.
The nucleus of the sacral part lie in the spinal cord, in the intermediolateral nucleus of the lateral horn at the level of the 2nd to 4th sacral segments.
The peripheral part of the cranial parasympathetic system consist of: 1.Preganglionic fibres passing in the III, VII, IX and X pairs of cranial nerves. 2.Terminal ganglia lying close to the organs, the ciliary, sphenopalatine, submandibular, and optic ganglia.
3. Postganglionic fibres which either stretch independently, e.g. the short ciliary nerves arising from the ciliary ganglion, or pass in some other nerves, e.g. postganglionic fibres originating from the optic ganglion and running in the auriculotemporal nerve.
The peripheral part of the sacral parasympathetic system consists of fibres which run in the anterior roots of the 2nd, 3rd and 4th sacral nerves, in their anterior branches forming the sacral plexus (somatic plexus) and finally enter the true pelvis.
In the pelvis they leave the sacral plexus and as the pelvic splanchnic nerves pass to the pelvis plexus together with which they innervate the pelvic organs (the rectum with the sigmoid colon, the urinary bladder, and the external and internal genitalia). Stimulation of the pelvic splanchnic nerves causes contraction of the rectum and bladder with relaxation of their sphincter muscles. The fibres of the sympathetic hypogastric plexus, in contrast, delay the evacuation of these organs; they stimulate uterine contractions, while the pelvic splanchnic nerves inhibit it.
The pelvic splanchnic nerves also contain vasodilator fibres for the cavernous bodies of the penis and clitoris which are responsible for the erection. The parasympathetic fibres arising from the sacral segment of the spinal cord extend to the pelvic plexuses not only in the erigentes and pelvic splanchnic nerves but also in the pudental nerve (the preganglionic fibers). The pudental nerve is a complex nerve containing in addition to somatic fibres; vegetative (sympathetic and parasympathetic) fibres that form part of the inferior hypogastric plexus. The intramural nervous system also belongs to the PNS. (intramural system are the walls of some hollow organs that contain nerve plexuses of small ganglia with ganglionic cells and non-medullated fibres).
Autonomic nervous system disorder Dysautonomia (autonomic dysfunction) is a broad term that describes any disease or malfunction of the autonomic nervous system. This includes: postural orthostatic tachycardia syndrome (POTS), inappropriate sinus tachycardia (IST), vasovagal syncope, pure autonomic failure, neurocardiogenic syncope (NCS), neurally mediated hypotension (NMH), orthostatic hypertension, autonomic instability. And a number of lesser-known disorders such as cerebral salt-wasting syndrome. Dysautonomia is associated with multiple system atrophy (Shy-Drager syndrome), Ehlers-Danlos syndrome (EDS), and Marfan syndrome for reasons that are not fully