Lecture Notes in Human Anatomy - Hryhorieva O.A., Svitlytskyi A.O. 2020

Splanchnology (splanchnologia)
Anatomy of the Nervous System
Peripheral Nervous System

Lecture Outline:

1. Cranial Nerves

2. Spinal Nerves.

3. Cervical plexus

4. Brachial Plexus

5. Lumbar plexus

6. Sacral Plexus

The Peripheral Nervous system includes 12 pairs of cranial nerves and 31 pairs of spinal nerves.

All cranial nerves emerge from the Base of the Brain, except for the IV pair, which exits from the DORSAL SIDE OF the brain. The numbering order reflects the sequence in which the nerves emerge. Cranial nerves are classified into sensory (I, II, VIII), motor (III, IV, VI, XI, XII), and mixed (V, VII, IX, X).

Pair I - Olfactory nerve, consists of olfactory filaments arising from olfactory receptors located in the mucosa of the superior nasal meatus and nasal septum, extending to the olfactory bulb, via the olfactory tract into the olfactory trigone, to the parahippocampal gyrus, where they terminate.

Pair II - Optic nerve, originates from multipolar retinal ganglion Cells, enters the cranial cavity, and anterior to the sella turcica forms an optic chiasm with the corresponding nerve of the opposite side, continuing along the optic tract to the subcortical visual centers.

Pair III - Oculomotor nerve, contains parasympathetic fibers running to the sphincter pupillae Muscle and the ciliary muscle; its Nucleus lies on the floor of the Midbrain aqueduct. The nerve emerges from the base of the brain, enters the Orbit, and innervates all extraocular Muscles except the superior oblique and lateral rectus muscles.

Pair IV - Trochlear nerve, its nucleus lies adjacent to the oculomotor nucleus; it innervates the superior oblique muscle of the eye.

Pair V - Trigeminal nerve, its nucleus is located in the pontine region, in the upper part of the Rhomboid fossa. The sensory part of the nerve features the trigeminal ganglion, from which three branches depart: the ophthalmic, maxillary, and mandibular nerves. Each branch consists of numerous rami that innervate the facial Skin, temporal region, palpebral conjunctiva, cornea, nasal mucosa, Tongue, gingiva, soft and hard palate, and the cranial dura mater. Parasympathetic and sympathetic fibers join the Branches of the trigeminal nerve to innervate the secretory Cells of the lacrimal gland, the Glands of the nasal and oral mucosa, and the major Salivary Glands. The motor ROOT originates from the motor nucleus located in the Hindbrain and joins the 3rd branch of the nerve, innervating the Muscles Attached to the Mandible.

Pair VI - Abducens nerve, its nucleus is located in the pontine region, in the upper part of the rhomboid fossa. The nerve emerges from the brain, enters the orbit, and innervates the lateral rectus muscle of the Eyeball.

Pair VII - Facial Nerve, contains motor, sensory, and parasympathetic fibers. The motor fibers originate from the motor nucleus in the tegmentum of the Pons and, within the thickness of the parotid gland, divide into 5–10 branches that innervate the facial muscles and part of the sublingual muscles. The sensory part consists of fibers of the gustatory analyzer. Parasympathetic fibers run to the submandibular and sublingual salivary glands and the glands of the lingual mucosa.

Pair VII - Vestibulocochlear nerve. The vestibular part conducts impulses that monitor HEAD and body position; the receptors for this nerve are located in the Inner ear, and axons reach the nuclei of the pons and Cerebellum without connecting to motor nuclei. The cochlear nerve part conducts auditory stimuli from the receptors of the spiral organ (organ of Corti) of the cochlea; axons reach the hindbrain nuclei, where they synapse onto the Auditory pathway.

Pair IX - Glossopharyngeal nerve, contains motor, sensory, and parasympathetic (secretory) fibers. Sensory fibers originate from the lingual mucosa, pharyngeal receptors, and the tympanic cavity. Secretory fibers innervate the parotid gland, and motor fibers innervate the pharyngeal muscles.

Pair X - Vagus nerve, contains motor, sensory, and parasympathetic fibers; it emerges from the Medulla Oblongata onto the base of the Skull via 10–20 fine, short rootlets that unite into a common nerve trunk, which leaves the cranial cavity through the jugular foramen and extends into the thoracic and abdominal cavities, branching out within the muscles, membranes, and Organs of the head, neck, Thorax, and abdomen. Parasympathetic and sympathetic fibers form numerous plexuses that continue as trunks in the Abdominal cavity.

Pair XI - Accessory nerve, innervates the laryngeal muscles, sternocleidomastoid, and trapezius muscles.

Pair XII - Hypoglossal nerve, innervates the Muscles of the tongue and the Infrahyoid muscles.

Spinal nerves. Corresponding to the segments of the Spinal Cord, 31 pairs of spinal nerves are formed: 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 1 coccygeal; all are mixed nerves, consisting of motor, sensory, and autonomic fibers. Upon exiting the intervertebral foramen, each spinal nerve branches into four rami: posterior, meningeal (recurrent), communicating, and anterior. The posterior rami run backward between the transverse processes of the vertebrae and innervate the muscles, periosteum, and skin of the posterior Regions of the head, neck, and trunk. The meningeal branches depart from the spinal nerve trunk and immediately re-enter the vertebral canal via the intervertebral foramen, innervating the dura mater and Blood Vessels of the spinal cord. The communicating rami arise from the 1st thoracic to the 2nd lumbar spinal nerves as part of the Sympathetic trunk and innervate Internal Organs and blood vessels. The anterior rami of all spinal nerves, except for the thoracic ones, participate in forming the cervical, brachial, and lumbosacral plexuses.

The cervical plexus is formed by the anterior rami of the upper four cervical nerves, located on the anterior surface of the cervical vertebrae and anteriorly covered by the sternocleidomastoid muscle. Its branches are divided into cutaneous, muscular, and mixed groups.

The brachial plexus consists of the anterior rami of the lower four cervical nerves and the first thoracic nerve, situated in the neck superior and posterior to the Subclavian Artery. The branches of the brachial plexus are divided into short and long groups. The short branches innervate muscles attached to the scapula and surrounding the shoulder joint, while the long branches descend along the upper limb and innervate its bones, skin, and muscles.

The lumbar plexus is formed by the anterior rami of the upper three lumbar nerves and the upper part of the 4th lumbar nerve, located anterior to the transverse processes of the vertebrae within the substance of the psoas major muscle, and innervates the iliopsoas muscle, quadratus lumborum, internal oblique, and transversus abdominis muscles, as well as the skin of the external genitalia.

The Lumbosacral plexus is formed by the branches of the lumbar, sacral, and coccygeal nerves.

The sacral plexus is formed by the Anterior branches of the last two lower lumbar nerves and the 3rd and 4th upper sacral spinal nerves, and is located on the anterior surface of the sacrum and the piriformis muscle. Its short branches innervate the pelvic muscles, while the long branches include the posterior femoral cutaneous nerve and the sciatic nerve.

Based on its functional principle, The Nervous System is divided into somatic and autonomic parts.

The somatic nervous system primarily performs the Functions connecting the body with the external environment, governing its sensitivity (via Sense Organs) and movement. It innervates voluntary (striated) skeletal muscles and certain internal organs—the tongue, Pharynx, Larynx, eyeball, and Middle ear—and provides sensory innervation to the entire body.

The Autonomic nervous system innervates all internal organs, Endocrine glands, involuntary muscles of the skin, Heart, and blood vessels—that is, the organs that carry out vegetative functions in the body (Digestion, Respiration, excretion, Blood Circulation, etc.) and constitute the internal environment. There are two PARTS OF THE autonomic nervous system: the sympathetic and the parasympathetic, which regulate The activity of internal organs, blood vessels, and Sweat Glands, as well as provide trophic innervation (nourishment) to skeletal muscles, receptors, and the nervous system itself.

The parasympathetic nervous system. Parasympathetic fibers originate from the midbrain and become part of the oculomotor nerve; these nerves innervate the circular muscle of the iris, and their excitation causes pupillary constriction. Parasympathetic fibers emerging from the medulla oblongata are incorporated into the facial, glossopharyngeal, and vagus nerves.

The parasympathetic fibers that are part of the facial and glossopharyngeal nerves innervate the salivary glands, and their excitation results in abundant salivation. The fibers of the vagus nerve branch out to innervate numerous internal organs: The Heart, Esophagus, Bronchi, alveoli, Stomach, Small Intestine, upper Large Intestine, and Spleen. Fibers of the pelvic nerve depart from the sacral region of the spinal cord to innervate the pelvic organs: the sigmoid colon, rectum, Urinary Bladder, and reproductive organs (except for the Uterus). The ganglia of the parasympathetic nervous system are located inside or near the organ they innervate.

The central component of the sympathetic nervous system is represented by Neurons in the lateral horns of the thoracic and lumbar segments of the spinal cord. The processes of these neurons (preganglionic neurons) emerge from the spinal cord and terminate in sympathetic ganglia, which form chains on both sides along the entire length of the spinal cord (sympathetic trunks). From there, postganglionic neurons extend toward the organs. The sympathetic nervous system innervates all organs and Tissues of the body, including skeletal (striated) muscles and the CNS.

As a rule, the sympathetic and parasympathetic Divisions of the autonomic nervous system exert opposing effects on organs.