Human Anatomy - A Course of Lectures - Kostylenko Yu.P. 2015

Autonomic part of the peripheral nervous system

Lecture Plan

10.1. General characteristics of the Autonomic Nervous system.

10.2. Sympathetic division of the Autonomic Nervous System.

10.3. Parasympathetic division of the Autonomic Nervous System.

10.4. CHARACTERISTICS OF THE Main Autonomic plexuses.

10.1 General Characteristics of the Autonomic Nervous System

As is well known, The Human Body can, with a certain degree of convention, be divided into two main parts: the body proper (soma) and The system of Internal Organs (viscera). The first part is represented by The Musculoskeletal System, which serves for purposeful actions and coordinated movement of the body in space, while the second part—the visceral—ensures the vital Functions of the Organism.

The part of The Nervous System that regulates the contractile activity of skeletal Muscles is called the animal or somatic division, whereas the one regulating the work of internal organs is termed the vegetative or autonomic division.

Thus, the autonomic or vegetative part of the nervous system, which will be discussed in this chapter, is an integral part of the human nervous system. It innervates The Heart, Blood and Lymphatic vessels, and internal organs, and performs tissue trophism. Autonomic nerves activate or inhibit organ function and glandular secretion, and alter vascular lumen.

The autonomic nervous system possesses several morphofunctional features:

1. The function of the autonomic nervous system is not entirely under conscious control.

2. The autonomic nervous system contains only the efferent link of the reflex arc; the afferent link is shared with the somatic division of the nervous system.

3. Autonomic nerve fibers either entirely lack a myelin sheath or have a poorly developed one, which is why their diameter is relatively small (5–6 µm) and the impulse conduction velocity along them is low (about 10 m/s compared to 100 m/s in the somatic division).

4. Both the central and peripheral Divisions of the autonomic nervous system are distributed unevenly throughout the human body, forming distinct clusters or centers.

5. The Cell body of the final neuron in the autonomic reflex arc is located in the periphery; together, they form autonomic ganglia.

6. NERVES OF THE autonomic nervous system form plexuses along the course of Blood Vessels.

Despite these listed features, the general structural principle of the autonomic nervous system is the same as that of the nervous system as a whole. It comprises central and peripheral divisions. The central division includes:

1. Suprasegmental centers (located in the Cerebral Cortex, Hypothalamus, reticular formation, Cerebellum, and limbic system).

2. Segmental centers (parasympathetic nuclei of the III, VII, IX, and X cranial nerve pairs; sacral parasympathetic nuclei located in Spinal Cord segments S₂-S₄; and sympathetic nuclei—lateral intermediate nuclei in spinal cord segments C₈ - L₃).

The Peripheral Division of the Autonomic Nervous System includes autonomic ganglia, autonomic branches and nerves, and autonomic plexuses.

In turn, the autonomic nervous system is subdivided into sympathetic and parasympathetic divisions.

Almost all Tissues and organs (without exception) receive sympathetic innervation, meaning it is widespread throughout the body. Parasympathetic innervation is not received by blood vessels (except for coronary vessels), Sweat Glands, pilomotor muscles, skeletal muscles, and The adrenal medulla. In organs with dual autonomic innervation (both sympathetic and parasympathetic), opposite functional effects are observed in most cases. For example, sympathetic nerves accelerate heart rate and constrict blood vessels, whereas parasympathetic nerves slow down heart rate and dilate blood vessels.

Recently, A number of researchers have distinguished a third part within the autonomic nervous system—the enteric (or metasympathetic) division. This refers to extensive nerve plexuses and microscopic ganglia located in the walls of hollow organs endowed with motility (Esophagus, Stomach, intestines, Urinary Bladder, Gallbladder and Bile ducts, and fallopian tubes).

Thus, the structural formations of the metasympathetic nervous system provide the capability for isolated, autonomous operation of internal organs, which is why organ transplantation surgeries have been successfully performed in recent times.

10.2 Sympathetic Division of the Autonomic Nervous System

The sympathetic division of the autonomic nervous system is conventionally divided into central and peripheral parts. The segmental centers of the sympathetic nervous system are located in the intermediolateral Nucleus of the spinal cord Gray matter (extending from the 8th cervical to the 2nd–3rd lumbar segments). This is THE ORIGIN OF preganglionic sympathetic fibers, which emerge from the spinal cord as part of the anterior roots of the Spinal Nerves.

From the anterior roots, these fibers pass into the trunks of the spinal nerves, but soon leave them to form the white communicating rami.

The peripheral part of the sympathetic division is represented by the paired Sympathetic trunk, autonomic ganglia, and the nerves branching off from them.

The sympathetic trunk consists of a chain of ganglia located on either side of THE Vertebral Column, interconnected by longitudinal and transverse interganglionic rami. Typically, the sympathetic trunk comprises 3 cervical, 10–12 thoracic, 2–5 lumbar, and 3–5 sacral ganglia.

Caudally, the entire chain terminates in the unpaired ganglion impar (coccygeal ganglion). The majority of preganglionic sympathetic fibers terminate in the ganglia of the sympathetic trunk. Some preganglionic fibers pass through the sympathetic trunk in transit without synapsing within it, continuing onward to prevertebral ganglia. Postganglionic fibers, which innervate the internal organs, originate from the efferent Neurons of the sympathetic trunk (Fig. 10.1).

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Fig. 10.1. Sympathetic Innervation of the internal organs:

1 - superior cervical ganglion of the sympathetic trunk; 2 - middle cervical ganglion of the sympathetic trunk; 3 - inferior cervical ganglion of the sympathetic trunk; 4 - white communicating rami; 5 - intermediolateral nucleus of the spinal cord; 6 - external carotid plexus; 7 - internal carotid plexus; 8 - cervical and thoracic cardiac nerves; 9 - abdominal plexus.

The cervical portion of the sympathetic trunk consists of 3 ganglia: superior, middle, and inferior.

The superior cervical ganglion lies at the level of the transverse processes of the II–III cervical vertebrae. A number of branches arise from this ganglion: 1) jugular nerve; 2) internal carotid nerve; 3) external carotid nerves; 4) superior cervical cardiac nerve; 5) pharyngeal branches; 6) gray communicating rami to the I–IV cervical spinal nerves.

The jugular nerve extends to the ganglia of the glossopharyngeal and vagus nerves, and its fibers travel along the branches of these nerves to the Pharynx, Larynx, and other neck organs.

The internal carotid nerve runs to the artery of the same name, forming the internal carotid plexus around it. This plexus extends into the cranial cavity and distributes along the Branches of the Internal Carotid Artery, providing sympathetic innervation to the cerebral blood vessels, Pituitary Gland, lacrimal gland, and the Glands of the nasal and palatine mucous membranes. One of the branches of the internal carotid plexus joins the ciliary ganglion, with its fibers innervating the dilator pupillae Muscle. Consequently, damage to the superior cervical ganglion results in pupillary constriction (miosis) on the affected side.

The external carotid nerves give rise to a plexus surrounding the External Carotid Artery. The Meninges, major Salivary Glands, and Thyroid Gland receive their innervation from the external carotid plexus.

The superior cervical cardiac nerve descends into the thoracic cavity, contributing to The formation of the cardiac plexus.

The pharyngeal branches supply sympathetic fibers to the pharynx and throat.

The middle cervical ganglion lies at the level of the transverse process of the VI cervical vertebra; it is relatively small in size and may occasionally be absent. It gives rise to gray communicating rami to the V–VI cervical spinal nerves, branches to the common carotid plexus, the inferior thyroid artery plexus, and the middle cervical cardiac nerve.

In the majority of cases (75–80%), the inferior cervical ganglion fuses with one or two upper thoracic ganglia, resulting in the Formation of the cervicothoracic (stellate) ganglion. This ganglion is frequently called stellate because nerve branches radiate from it in all directions, making it star-shaped.

The branches of the cervicothoracic ganglion include: 1) inferior cervical cardiac nerve; 2) vertebral nerve, which forms the vertebral plexus around the corresponding artery; 3) branches to the Subclavian Artery, forming the subclavian plexus; 4) gray communicating rami to the VII–VIII cervical and I–II thoracic spinal nerves; 5) communicating branch to the phrenic nerve; 6) branches to the aortic arch, forming the aortic arch plexus.

The thoracic portion of the sympathetic trunk contains 10 or 11, and occasionally 12, ganglia. Gray communicating rami pass from all the ganglia to the thoracic spinal nerves.

The upper thoracic ganglia give rise to 2–3 thoracic cardiac nerves, as well as branches that form the thoracic aortic plexus. These fibers pass through the cervicothoracic ganglia.

The lower thoracic ganglia give rise to the greater and lesser splanchnic nerves. The greater splanchnic nerve originates from the V–IX ganglia, while the lesser splanchnic nerve arises from the X–XI ganglia. Both nerves pass through the hiatus separating the crura of the Diaphragm into the Abdominal cavity, where they participate in forming the abdominal plexus. A renal branch emerges from the last thoracic ganglion to provide renal innervation.

The lumbar sympathetic ganglia vary in number, ranging from two to five on each side. Branches of the lumbar ganglia contribute to the formation of the Autonomic plexuses of the abdominal cavity. Lumbar splanchnic nerves extend from the upper two ganglia to the abdominal plexus, while branches from the lower ganglia participate in forming the abdominal aortic plexus.

The sacral portion of the sympathetic trunk is located on the pelvic surface of the sacrum. The branches of the sacral ganglia are: 1) gray communicating rami to the sacral spinal nerves; 2) sacral splanchnic nerves leading to the superior and inferior hypogastric plexuses.

10.3 Parasympathetic Division of the Autonomic Nervous System

The parasympathetic nervous system is likewise divided into central and peripheral parts. Based on the localization of its centers, this division of the nervous system is subdivided into cranial and sacral parts.

The cranial division, in turn, includes the mesencephalic (Midbrain), pontine, and bulbar parts (Fig. 10.2).

Fig. 10.2 Parasympathetic innervation of internal organs:

1 - ciliary ganglion; 2 - pterygopalatine ganglion; 3 - submandibular ganglion; 4 - otic ganglion; 5 - accessory nucleus of the Oculomotor nerve; 6 - superior salivatory nucleus; 7 - inferior salivatory nucleus; 8 - dorsal nucleus of the Vagus nerve; 9 - preganglionic parasympathetic fibers to internal organs as part of the vagus nerve; 10 - sacral division of the parasympathetic nervous system.

The mesencephalic part is represented by the accessory nucleus of the oculomotor nerve (pupillary nucleus, Edinger-Westphal nucleus, or Yakubovich's nucleus). Preganglionic fibers run as part of the oculomotor nerve to the ciliary ganglion located in the Orbit. Postganglionic fibers from the Cells of the ciliary ganglion enter the Eyeball and innervate the sphincter pupillae muscle, as well as the ciliary muscle, which provides eye accommodation. A lesion of the oculomotor nerve nucleus or the administration of atropine into the eye, which blocks impulse transmission along parasympathetic fibers, results in pupil dilation and impaired eye accommodation.

The pontine part includes the parasympathetic nucleus of the Facial Nerve — the superior salivatory nucleus. Preganglionic fibers run within the intermediate nerve to the geniculate ganglion; here they pass into the greater petrosal nerve, which terminates in the pterygopalatine ganglion. From there, postganglionic fibers reach the glands of the soft and hard palate, the mucous membrane of the Nasal cavity, and the lacrimal gland.

Part of the autonomic fibers running within the intermediate nerve pass into the chorda tympani, and then reach the submandibular ganglion. Postganglionic fibers from this ganglion proceed to the submandibular and sublingual salivary glands, as well as the minor salivary glands of the vestibule and the floor of the Oral Cavity.

The bulbar part also contains two parasympathetic nuclei: the inferior salivatory nucleus and the posterior nucleus of the vagus nerve. Preganglionic fibers from the inferior salivatory nucleus emerge with the Glossopharyngeal nerve, continue into the tympanic nerve and its terminal branch — the lesser petrosal nerve, which terminates in the otic ganglion. Postganglionic fibers innervate the parotid gland.

All parasympathetic nerves are secretory for the salivary glands; upon their stimulation, a large amount of watery saliva is secreted.

The posterior nucleus of the vagus nerve gives rise to parasympathetic fibers that run as part of this nerve to most visceral organs (from the neck region down to the sigmoid colon). They innervate the mucosa of the pharynx, larynx, Trachea, and Bronchi, the thyroid, parathyroid, and Thymus glands, the esophagus, Lungs, heart, stomach, and intestines down to the descending colon. The vagus nerve also provides parasympathetic innervation to the Liver, Pancreas, Spleen, Adrenal Glands, Kidneys, and Ureters.

The vagus nerve stimulates the secretion of digestive and bronchial glands, enhances the MOTOR FUNCTION OF The Stomach and intestines, and causes constriction of the small bronchi. On the heart, the vagus nerve exerts an inhibitory effect, reducing the rate and force of contractions and slowing impulse conduction through the cardiac conduction system.

The sacral division of the Parasympathetic part of the nervous system is represented by sacral parasympathetic centers localized in the gray matter of the spinal cord corresponding to the S2–S4 spinal segments.

Preganglionic fibers emerge as part of the anterior roots of the sacral spinal nerves and enter the Sacral Plexus, but then branch off from it as the pelvic splanchnic nerves. These nerves join the pelvic plexus, extending further along its branches. The area of their innervation covers the pelvic Organs of the Urogenital System. Parasympathetic nerves enhance the motility of the distal PARTS OF THE intestine, cause contraction of the urinary bladder, and dilate the Blood vessels of the genitalia.

10.4 Main autonomic plexuses of the thoracic and abdominal cavities

Important autonomic plexuses include the following: the thoracic aortic, abdominal aortic, superior mesenteric, and superior hypogastric plexuses. As a rule, both sympathetic and parasympathetic nerve fibers participate in their formation.

The thoracic aortic plexus is located along the course of the Thoracic Aorta and its visceral branches, uniting the following plexuses: the cardiac plexus, located along the course of the ascending aorta, aortic arch, pulmonary trunk, and Pulmonary Veins; the esophageal plexus, located in the adventitial coat of the esophagus; and the pulmonary plexus, located around the bronchi and Vessels of the roots of the right and left lungs. The thoracic aortic plexus, together with the aorta, penetrates into the abdominal cavity, where it continues into the abdominal aortic plexus.

The abdominal aortic plexus is located along the course of the Abdominal Aorta and its visceral branches. The largest plexus formed from the aortic plexus is the celiac (solar) plexus, located at the Base of the celiac trunk, posterior to the pancreas.

In the formation of the celiac plexus, In addition to the abdominal aortic plexus, branches of the greater, lesser, and lumbar splanchnic nerves, the vagus and phrenic nerves, as well as the thoracic aortic plexus, take part.

Inferiorly, the abdominal aortic plexus passes into the superior hypogastric plexus. The superior hypogastric plexus is located on the anterior surface of the vertebral column between the common iliac Arteries. At the level of the second sacral vertebra, the plexus divides into two branches and continues into the paired right and left inferior hypogastric plexuses, located on the posterolateral walls of the lesser pelvis. The inferior hypogastric plexus gives rise to the following visceral plexuses: middle rectal, inferior rectal, prostatic, Ductus deferens, and uterovaginal.