Human Anatomy: Part 2 - K. A. Diubenko, A. K. Kolomiitsev, Yu. B. Tchaikovsky 2008

Special Section
Autonomic nervous system, systema nervosum autonomicum
Autonomic plexuses — Brief overview of the innervation of certain organs

Class="center">Innervation of the Eyeball

Efferent somatic fibers to the striated Muscles of the eyeball run within Cranial Nerves III, IV, and VI. Afferent innervation is supplied by the first branch of the Trigeminal nerve.

Efferent parasympathetic fibers (preganglionic) travel within the Oculomotor nerve to reach the ciliary ganglion, where they terminate. Postganglionic fibers arising from the ganglion Neurons pass through the short ciliary nerves to the ciliary Muscle and the sphincter pupillae. Lesions of the parasympathetic efferent pathway lead to the loss of accommodation (the eye's ability to focus on near objects) and pupillary dilation (mydriasis).

Efferent sympathetic fibers (preganglionic) originate from Cells of the columna intermediolateralis of segments C_VIII-Th_II, passing via the top two or three white communicating rami to the superior cervical ganglion of the Sympathetic trunk, where they terminate. Postganglionic fibers reach the ciliary ganglion through the internal carotid nerve and plexus, and the ophthalmic plexus, passing through it in transit, and continue via the short ciliary nerves to the dilator pupillae and orbital muscle. Damage to the sympathetic efferent pathway results in pupillary constriction (miosis) and dilation of the ocular Blood Vessels.

Innervation of the Lacrimal and Major Salivary Glands

Sensory innervation of the lacrimal gland is supplied by the lacrimal nerve, n. lacrimalis (a branch of the n. ophthalmicus from the n. trigeminus). The submandibular and sublingual salivary glands are innervated by the lingual nerve, n. lingualis (a branch of the n. mandibularis from the n. trigeminus). The parotid gland is supplied by the auriculotemporal nerve, n. auriculotemporalis (a branch of the n. mandibularis from the n. trigeminus).

Efferent parasympathetic fibers (preganglionic) from the superior salivatory Nucleus run within the intermediate nerve, and subsequently within the greater petrosal nerve to the pterygopalatine ganglion, and via the chorda tympani and lingual nerve to the submandibular ganglion.

Postganglionic fibers from the pterygopalatine ganglion pass through the maxillary, zygomatic, and lacrimal nerves to reach the lacrimal gland, while those from the submandibular ganglion supply the submandibular and sublingual glands.

Preganglionic parasympathetic fibers from the inferior salivatory nucleus travel within the Glossopharyngeal nerve, and then via the tympanic and lesser petrosal nerves to the otic ganglion. From there, postganglionic fibers reach the Cytology/practical/97.html">Parotid salivary gland via the auriculotemporal nerve.

Stimulation of parasympathetic fibers enhances the secretory function of the respective glands (lacrimal and/or salivary), whereas transection leads to a reduction or complete cessation of secretion.

Efferent sympathetic fibers (preganglionic) from cells of the columna intermediolateralis of the upper thoracic segments pass to the superior cervical ganglion of the sympathetic trunk. Postganglionic fibers from this ganglion reach the lacrimal gland via the internal carotid nerve and plexus, ophthalmic plexus, and ciliary ganglion (in transit) through short ciliary nerves; they reach the submandibular and sublingual glands via the external carotid nerve and plexus, facial plexus, and submandibular ganglion (in transit); and they reach the parotid gland via the external carotid plexus, otic ganglion (in transit), and auriculotemporal nerve.

Stimulation of sympathetic fibers inhibits the secretory activity of the glands: tear production decreases, the cornea and conjunctiva become dry, saliva volume drops, the saliva becomes thicker, and a sensation of dry Mouth occurs.

Innervation of The Heart

The heart receives sensory, sympathetic, and parasympathetic innervation (Fig. 211). Efferent sympathetic fibers to the heart run within the sympathetic trunks and their branches (superior, middle, and inferior cervical cardiac nerves). They increase heart rate and myocardial contractility and dilate the coronary Arteries. Efferent parasympathetic fibers to the heart travel within the vagus nerves and their branches (superior and inferior cervical cardiac branches). They decrease heart rate and contractility and constrict the coronary arteries. Afferent fibers from receptors in the heart wall and its vessels run within both the sympathetic trunks and the vagus nerves, with the former primarily conducting pain sensations and the latter carrying other sensory modalities.

Upon approaching the heart, the nerve fibers form superficial (anterior) and deep (posterior) extraorgan cardiac plexuses. The former lies beneath the aortic arch, superior to the bifurcation of the pulmonary trunk, and is formed by Branches of the left Vagus nerve and the left superior cervical cardiac nerve (from the left superior cervical ganglion of the sympathetic trunk). The latter is located posterior to the aortic arch and anterior to the tracheal bifurcation, being formed by the left middle and inferior cervical cardiac nerves, all right and left thoracic cardiac nerves (from the corresponding sympathetic trunk ganglia), and branches of the right vagus nerve. Autonomic cardiac ganglia (ganglia cardiaca) are embedded within these extraorgan cardiac plexuses. One of the largest ganglia, described by Wrisberg*, is located on the anterior surface of the aortic arch near the paraaortic bodies.

Branches of the superficial and deep cardiac plexuses penetrate the heart wall along the medial wall of the SUPERIOR VENA CAVA, anterior and posterior to the ascending aorta, between the aorta and the pulmonary trunk, and posterior, left, and right of the pulmonary trunk. Intraorgan plexuses are formed in accordance with the layers of the heart: subepicardial, myocardial, and subendocardial. Some authors also distinguish a subendothelial plexus.

* Heinrich August Wrisberg (1739–1808) was a German anatomist renowned for his research on the Autonomic Nervous system. The cardiac ganglion (Wrisberg's ganglion), the intermediate nerve, and the cuneiform Cartilage are named after him.

Fig. 211. Diagram of The formation of extraorgan cardiac plexuses (after I. Ye. Kefeli)

Within the subepicardial plexus, V. P. Vorobyov described six secondary plexuses named after him. The left anterior plexus is located beneath the epicardium on the anterior surface of the left ventricle; the right anterior plexus lies beneath the epicardium on the anterior surface of the right ventricle; the anterior atrial plexus is situated beneath the epicardium on the anterior wall of both atria; the right posterior plexus lies beneath the epicardium on the posterior surface of the right atrium; the left posterior plexus is found beneath the epicardium on the posterior and lateral surfaces of the left ventricle along the oblique vein of the left atrium; and the posterior plexus of the left atrium is located beneath the epicardium on the upper part of the posterior surface of the left atrium.

Innervation of the Bronchi and Lungs

Efferent parasympathetic and sympathetic fibers to the lungs, as well as afferent fibers from the lungs, run within the vagus nerve and the sympathetic trunk. Around the ROOT of the lung, they form the anterior and posterior pulmonary plexuses, whose branches accompany the bronchi and bronchioles, reaching the elements of the acinus. These same plexuses serve as the source of innervation for the visceral Pleura. The parietal pleura receives sensory fibers from the intercostal and phrenic nerves.

Stimulation of sympathetic fibers leads to bronchodilation and vasoconstriction, whereas stimulation of parasympathetic fibers causes bronchoconstriction and mucus secretion.

Innervation of Abdominal Organs

The innervation of the Esophagus, Stomach, small and large intestines (down to the sigmoid colon), Liver, Pancreas, Spleen, Adrenal Glands, and Kidneys is organized as follows.

Efferent parasympathetic and sympathetic fibers to the aforementioned organs, as well as sensory fibers from them, run within the vagus nerve, sympathetic trunk, celiac, superior, and inferior mesenteric plexuses. Within the organ walls, these nerve fibers form intramural plexuses (subserose, myenteric, and submucous). Most sympathetic preganglionic fibers pass through the sympathetic trunk ganglia in transit, synapsing instead within the ganglia of the celiac, superior, and inferior mesenteric plexuses. Notably, The adrenal medulla, which originates from sympathoblasts, represents a modified sympathetic ganglion. Consequently, the adrenal medulla is supplied not by postganglionic, but by preganglionic sympathetic fibers that terminate on chromaffin cells.

Stimulation of sympathetic fibers leads to the inhibition of gastrointestinal motility, contraction of sphincters, and vasoconstriction of abdominal blood vessels. Conversely, parasympathetic stimulation enhances peristalsis and glandular secretion, causes sphincter relaxation, and induces vasodilation.

Innervation of the Pelvic Organs

The innervation of the pelvic organs (sigmoid colon, rectum, Urinary Bladder, Prostate Gland, Seminal Vesicles, Testis, Ovaries, uterine tubes, Uterus, and Vagina) is organized as follows.

Efferent parasympathetic and sympathetic fibers to these organs, along with sensory fibers from them, run as part of the pelvic splanchnic nerves, the sympathetic trunk, the inferior mesenteric plexus, and the superior and inferior hypogastric plexuses. In addition, sympathetic fibers reach the testis and Ovary from the celiac plexus via the testicular or ovarian plexuses. The uterus receives parasympathetic innervation, which promotes its evacuation; therefore, stimulating therapy during childbirth is contraindicated for women with a predominance of the parasympathetic autonomic profile. The majority of sympathetic preganglionic fibers pass through the sympathetic trunk ganglia in transit, synapsing within prevertebral ganglia. Intramural plexuses are also formed within the walls of the pelvic organs.

Stimulation of sympathetic fibers results in the inhibition of pelvic organ motility, contraction of the internal anal sphincter and urinary bladder sphincter, relaxation of the detrusor muscle, and consequently, urinary retention. Conversely, parasympathetic stimulation enhances pelvic organ motility, relaxes the internal anal sphincter and urinary bladder sphincter, and contracts the detrusor muscle.

Innervation of Blood Vessels and Sweat Glands

Efferent sympathetic and parasympathetic fibers to blood vessels, as well as sensory fibers from them, travel within cranial nerves III, V, VII, IX, and X and respective branches of the sympathetic trunk (for Vessels of the HEAD region), Spinal Nerves and respective sympathetic trunk branches (for limb vessels), and branches of the vagus and pelvic splanchnic nerves alongside the sympathetic trunk (for vessels of the thoracic and abdominal cavities). Perivascular plexuses form around blood vessels, from which nerve fibers penetrate all layers of the vessel wall to establish intramural nerve plexuses.

Efferent nerve fibers of the intramural plexuses form terminals on myocytes within the walls of arteries, arterioles, and Veins. Sensory nerve fibers originate from mechanoreceptors and chemoreceptors that monitor the degree of vascular filling, pressure levels, blood flow velocity, and parameters of cardiovascular Homeostasis.

It should be noted that dual efferent innervation of blood vessels (sympathetic vasoconstrictor and parasympathetic vasodilator) is present only in certain organs, such as the salivary glands, Tongue, and corpora cavernosa of the Penis. The vast majority of blood vessels in other organs receive exclusively sympathetic vasoconstrictor nerve fibers. Skeletal Muscle arteries are supplied by sympathetic adrenergic (vasoconstrictor) fibers and sympathetic cholinergic (vasodilator) fibers, the latter of which contribute to muscle artery dilation during physical exertion.

Sweat glands are innervated exclusively by sympathetic nerve fibers. The majority of these fibers are cholinergic, mediating perspiration in response to elevated ambient temperatures (thermal sweating). A smaller portion are adrenergic, triggering sweat secretion during intense emotional stress (emotional sweating).