Human Anatomy - H. I. Koliadenko 2009

Nervous System
Autonomic (Vegetative) Nervous System

As already noted, The Nervous system is divided into the somatic (or animal) nervous system, which innervates striated Muscles, Skin, and the Skeletal System, and the Autonomic Nervous System, which innervates internal (vegetative) Organs—specifically, The Cardiovascular system, digestive, respiratory, and urogenital systems, Endocrine glands, as well as all smooth muscles and Glands of the body. Like the somatic system, the autonomic nervous system comprises central and peripheral divisions. The central division is located in the Brain AND SPINAL cord and consists of clusters of Nerve Cells (nuclei, centers). The peripheral division consists of ganglia and nerve fibers.

An important feature of the autonomic nervous system is that its activity occurs outside of human consciousness, and therefore it cannot consciously control the work of Internal Organs.

The nerve fibers of the autonomic nervous system differ from those of the somatic nervous system both morphologically and functionally. Each nerve fiber is interrupted along its length, dividing into two fibers. The first branch, originating from the processes of autonomic centers, emerges from the brain and Spinal Cord as part of the ventral roots of spinal or Cranial Nerves. These processes are called preganglionic fibers. They reach the peripheral autonomic ganglia, from which arise the processes of Neurons known as postganglionic fibers. These make direct contact with the innervated organ. Preganglionic fibers are covered with myelin and are therefore referred to as white, whereas postganglionic fibers are gray and unmyelinated.

A morphological feature of the autonomic nervous system is that The Cell bodies of effector neurons (both preganglionic and postganglionic), unlike in the somatic nervous system, are located not within the Central Nervous System, but closer to the innervated organ within peripheral ganglia.

The autonomic nervous system is divided into sympathetic and parasympathetic divisions. Internal organs are typically innervated by both divisions. Impulses from one division stimulate organ activity, while impulses from the other inhibit it. For example, the sympathetic division accelerates Heart rate, whereas the parasympathetic division slows it down. Conversely, the parasympathetic nervous system accelerates intestinal peristalsis, while the sympathetic system slows it down. Thus, these systems differ functionally from one another.

During excitation of the Sympathetic division of the autonomic nervous system, norepinephrine is released, whereas Acetylcholine is released during excitation of the parasympathetic division.

The sympathetic division of the autonomic (autonomic) nervous system (Fig. 176). Its centers are located in the lateral horns of the Gray matter of the spinal cord, extending from the VIII cervical to the III lumbar segment. The peripheral section of the sympathetic nervous system consists of ganglia that form the right and left sympathetic trunks, running along the sides of THE Vertebral Column from the Base of the Skull to the coccyx. The ganglia are interconnected by bundles of nerve fibers and are also linked via connecting branches to the ventral rami of somatic nerves. These are prevertebral ganglia.

Class="center">

Fig. 176. Sympathetic division of the autonomic nervous system. Preganglionic fibers are depicted by single lines, postganglionic fibers by double lines (diagram):

C_VIII — eighth cervical segment of the spinal cord; Th_І — first thoracic segment; Th_XI — twelfth thoracic segment; L_І, _ІІ, _ІІІ — first, second, and third lumbar segments; 1, 2, 3 — superior, middle, and inferior cervical ganglia of the Sympathetic trunk; 4 — cervicothoracic ganglion; 5 — postganglionic fibers to The Heart and Lungs; 6 — abdominal aortic plexus; 7 — postganglionic fibers to abdominal organs; 8 — pelvic plexus; 9 — postganglionic fibers to pelvic organs; 10 — postganglionic fibers to smooth muscles and glands of the HEAD; 11 — ganglion impar

In the cervical region, each trunk has three cervical sympathetic ganglia, 10–12 thoracic, 5 lumbar, 4 sacral, and 1 coccygeal. In the coccygeal region, both trunks join together.

The cervical ganglia are paired and include the superior, middle, and inferior ganglia, the largest of which is the superior ganglion. Cardiac branches originate from each of these ganglia and reach the cardiac plexus. Branches also extend from the cervical ganglia to Blood Vessels, forming vascular plexuses around them. Along these vessels, sympathetic nerves reach the organs. The superior cervical ganglion gives rise to the internal and external carotid nerves, which form plexuses around the Arteries of the same name.

The middle cervical ganglion is small and is occasionally absent in humans. The inferior cervical ganglion often merges with the first thoracic ganglion, forming a large cervicothoracic ganglion. The cervical sympathetic ganglia are connected to the cervical Spinal Nerves, forming the cervical and brachial plexuses.

Sympathetic nerve fibers pass from the cervical sympathetic ganglia to the Salivary Glands, Pharynx, Larynx, and eye pupils, causing the latter to dilate.

In the thoracic region, the ganglia lie on the heads of the Ribs. Two nerves emerge from them: the greater splanchnic nerve from the 6th–9th ganglia, and the lesser splanchnic nerve from the 10th–11th ganglia. Both nerves pass through the Diaphragm into the Abdominal cavity AND terminate in the celiac plexus. The celiac plexus includes numerous nerve ganglia, from which nerves extend to the abdominal organs. The right Vagus nerve connects with the celiac plexus.

Branches from the thoracic ganglia also extend to the Organs of the posterior Mediastinum, as well as to the aortic, cardiac, and pulmonary plexuses.

Fibers pass from the ganglia of the abdominal part of the sympathetic trunk to the Abdominal Aorta and lumbar nerves.

Fibers extend from the sacral division of the sympathetic trunk, which consists of 4 ganglia, to the sacral and coccygeal nerves. In the lesser pelvis, There is a hypogastric plexus formed by Branches of the sympathetic trunk. Nerve fibers extend from it to the pelvic organs.

Parasympathetic division of the autonomic nervous system (Fig. 177). The centers of the parasympathetic nervous system are located in the Midbrain and Medulla Oblongata, as well as in the sacral section of the spinal cord (from segments II to IV).

Fig. 177. Parasympathetic division of the autonomic nervous system.

Preganglionic fibers are depicted by single lines, postganglionic fibers by double lines (diagram):

1 — mesencephalic region; 2 — bulbar region; 3 — sacral region; 4 — Oculomotor nerve; 5 — ciliary ganglion; 6 — postganglionic fibers to the sphincter pupillae Muscle and ciliary muscle of the eye; 7 — Facial Nerve; 8 — Glossopharyngeal nerve; 9 — vagus nerve; 10 — sacral nerves; 11–14 — ganglia of the facial, glossopharyngeal, and vagus nerves; 15 — ganglia of the celiac plexus; 16 — ganglia of the hypogastric plexus; 17 — fibers to the lacrimal gland and Oral Cavity glands; 18 — fibers to the parotid gland; 19 — fibers to the submandibular and sublingual glands; 20, 21 — fibers to thoracic organs; 22 — fibers to abdominal organs; 23 — fibers to pelvic organs

From the brain, parasympathetic nerve fibers run as part of four pairs of cranial nerves—III, VII, IX, and X. Parasympathetic fibers to the smooth Muscles of the Eyeball run alongside the III pair of cranial nerves, the oculomotor nerve. Along its path, the preganglionic fiber enters the ciliary ganglion. A postganglionic fiber originates from this ganglion, and its impulses cause pupil constriction.

Fig. 178. Nerves and plexuses of the cervical and thoracic PARTS OF THE autonomic nervous system:

1 — External Carotid Artery; 2 — Hypoglossal nerve; 3 — external maxillary artery; 4 — lingual artery; 5, 6, 11 — superior thyroid artery; 7 — common carotid artery; 8 — Trachea; 9 — brachiocephalic trunk; 10 — SUPERIOR VENA CAVA; 12 — pulmonary branches of the vagus nerve; 13 — Esophagus; 14 — lung; 15 — esophageal plexus; 16 — Thoracic Aorta; 17 — diaphragm; 18 — Stomach; 19 — anterior gastric plexus; 20 — celiac artery; 21 — Pancreas; 22 — celiac plexus; 23, 32 — sympathetic trunk; 24 — intercostal nerves; 25 — communicating branches; 26 — intercostal arteries and Veins; 27 — azygos vein; 28 — thoracic ganglion of the sympathetic trunk; 29 — Subclavian Artery; 30 — stellate ganglion; 31 — Brachial Plexus; 33 — superior cervical ganglion of the sympathetic trunk; 34 — occipital artery; 35 — sternocleidomastoid muscle; 36 — Internal Carotid Artery

Along with the VII cranial pair—the facial nerve—originates a parasympathetic nerve, the chorda tympani, which innervates the submandibular and sublingual salivary glands. Preganglionic fibers approach the pterygopalatine and submandibular ganglia, from which postganglionic fibers of the parasympathetic nervous system proceed directly to the salivary glands. As part of the greater superficial petrosal nerve, parasympathetic fibers innervate the lacrimal gland and the mucous glands of the nasal and oral cavities.

As part of the IX pair (glossopharyngeal nerve), along with the lesser superficial petrosal nerve, parasympathetic fibers innervate the Cytology/practical/97.html">Parotid salivary gland. The fiber synapses in the ganglion of the same name.

An important parasympathetic nerve is the X pair—the vagus nerve, which innervates the organs of the neck, Thorax, and abdominal cavity. In these cavities, the vagus nerve forms numerous plexuses with sympathetic nerves (cardiac, bronchial, pulmonary, celiac). From the sacral region of the spinal cord, preganglionic fibers of the parasympathetic nervous system pass to the hypogastric plexus, which gives rise to postganglionic nerve fibers innervating the descending colon, sigmoid colon, rectum, Urinary Bladder, and internal and external genitalia.

A characteristic feature of the parasympathetic nervous system is that its ganglia are located near the organ it innervates or within its wall; therefore, postganglionic nerve fibers are considerably shorter than preganglionic ones. It is believed that parasympathetic fibers are absent in the smooth muscles of the skin and skeletal muscles, Adrenal Glands, and Spleen.

The higher centers of the autonomic nervous system are the tuber cinereum of the Diencephalon and the corpus striatum of the cerebral hemispheres. Centers of the Cerebral Cortex that influence the Functions of the autonomic nervous system have also been identified. The functional connection between the CEREBRAL CORTEX AND internal organs ensures cortical regulation of their activity, including that of the heart and blood vessels (Fig. 178).