Human Anatomy - H. I. Koliadenko 2009

Nervous System
Peripheral Nervous System
Cranial Nerves

There are twelve pairs of Cranial Nerves, which are divided into three groups: sensory, motor, and mixed.

The sensory nerves include: pair I — Olfactory nerve, pair II — Optic nerve, pair VIII — Vestibulocochlear nerve.

The motor nerves include: pair IV — Trochlear nerve, pair VI — Abducens nerve, pair XI — Accessory nerve, pair XII — Hypoglossal nerve.

The mixed nerves include: pair III — Oculomotor nerve, pair V — Trigeminal nerve, pair VII — Facial Nerve, pair IX — Glossopharyngeal nerve, pair X — Vagus nerve.

The olfactory nerve (n. olfactorius) lies on the Base of the Brain in the region of the frontal lobe (Fig. 171) and consists of the olfactory bulb and the olfactory tract, which transitions into the olfactory trigone bounded by the anterior perforated substance. From the Cells of the olfactory bulb, 15–25 fine trunks extend, passing through the openings in the cribriform plate of the Ethmoid bone to the mucous membrane of the Nasal cavity. The olfactory nerve transmits impulses from the olfactory receptors of the nasal cavity to the brain: first to the mamillary bodies of the Diencephalon, and then via the fornix to the uncus of the hippocampus, where the cortical center of the olfactory analyzer is located. This is where olfactory sensations arise.

The optic nerve (n. opticus) originates from specific cells of the retina, passes through the optic canal located at the base of the lesser wings of the Sphenoid bone, anterior to the sella turcica, forms the optic chiasm with the corresponding nerve of the opposite hemisphere, and continues as the optic tract. Its fibers run to the thalamus, where the third neuron of the visual pathway originates; this neuron connects the thalamus with the visual center located in the calcarine sulcus of the occipital lobe of the Cerebral Cortex (see Fig. 171).

Some fibers of the optic nerve are also connected by the lateral geniculate bodies with the superior colliculi of the Midbrain tectum. This connection makes it possible to direct the eyes toward the object being viewed, while The connection between the optic nerves and the tectospinal tract regulates reflexive motor responses to the received information.

The oculomotor nerve (n. oculomotorius) emerges from the midbrain through the superior orbital fissure, enters the orbital cavity, and innervates the superior, inferior, and medial rectus Muscles of the eye, as well as the inferior oblique Muscle and the levator palpebrae superioris muscle. It contains an autonomic branch (parasympathetic fibers) that enters the ciliary ganglion and promotes constriction of the sphincter pupillae muscle and contraction of the ciliary body muscles of the Eyeball.

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Fig. 171. Base of the brain. Sites of emergence of the cranial nerves:

1 — olfactory nerve (olfactory tract); 2 — optic nerve; 3 — oculomotor nerve; 4 — trochlear nerve; 5 — trigeminal nerve; 6 — abducens nerve; 7 — facial nerve; 8 — vestibulocochlear nerve; 9 — glossopharyngeal nerve; 10 — vagus nerve; 11 — accessory nerve; 12 — hypoglossal nerve; 13 — Spinal Cord; 14 — decussation of pyramids; 15 — Medulla Oblongata; 16 — pyramid of medulla oblongata; 17 — olive; 18 — Pons; 19 — large ROOT of trigeminal nerve; 20 — small root of trigeminal nerve; 21 — cerebral peduncle; 22 — mamillary body; 23 — optic tract; 24 — optic chiasm; 25 — Pituitary Gland; 26 — olfactory bulb

The trochlear nerve (n. trochlearis) exits the cranium through the superior orbital fissure, enters the orbital cavity, and innervates the superior oblique muscle of the eyeball. Its Nucleus, like that of the oculomotor nerve, is located in the midbrain.

The trigeminal nerve (n. trigeminus) emerges from the brain substance by two roots: a larger sensory root and a smaller motor root. In the cranial cavity, the sensory root forms the trigeminal ganglion, from which three major branches extend: the ophthalmic, maxillary, and mandibular nerves (Fig. 172).

The ophthalmic nerve passes through the superior orbital fissure into the Orbit and innervates the eyeball, upper eyelid, Skin of the forehead region, mucous membrane of the nasal cavity, and the dorsum of the Nose (Fig. 173).

The maxillary nerve exits the cranial cavity through the foramen rotundum of the greater wing of the sphenoid bone, enters the pterygopalatine fossa, and gives off branches to the maxillary Teeth. In addition, this nerve innervates the skin of the lower eyelid, nose, upper lip, part of the nasal mucosa, part of the cheek skin, and the oral mucosa.

Fig. 172. Trigeminal nerve:

1 — lacrimal gland; 2 — branch of oculomotor nerve; 3 — inferior oblique muscle of eyeball; 4 — inferior rectus muscle of eyeball; 5 — infraorbital nerve; 6 — superior posterior alveolar nerves; 7 — maxillary artery; 8 — mandibular nerve; 9 — maxillary nerve; 10 — trigeminal ganglion; 11 — oculomotor nerve; 12 — ophthalmic nerve; 13 — levator palpebrae superioris muscle; 14 — superior rectus muscle of eyeball; 15 — lateral rectus muscle of eyeball

The mandibular nerve exits the cranial cavity through the foramen ovale along with the motor nerve. The motor branches of this nerve innervate all the Muscles of Mastication and partially the digastric muscle. Its sensory branches innervate the skin of the external acoustic meatus and the temporal region, the buccal mucosa, the submandibular and sublingual Salivary Glands, the mandibular teeth, the anteroinferior region of facial skin, and the mucosa of the dorsum of the Tongue. The largest sensory Branches of the mandibular nerve are the lingual, inferior alveolar, and auriculotemporal nerves.

Closely associated with the trigeminal nerve are the autonomic ganglia: the ciliary, pterygopalatine, otic, and submandibular ganglia. Each of these receives sympathetic and parasympathetic fibers from the trigeminal nerve. For example, parasympathetic fibers (chorda tympani) run within the lingual nerve and perform the secretory function for the submandibular and sublingual salivary glands.

Fig. 173. Ophthalmic nerve:

1 — ophthalmic nerve; 2 — maxillary nerve; 3 — infraorbital nerve; 4 — chorda tympani; 5 — parotid duct; 6 — inferior alveolar nerve; 7 — lingual nerve; 8 — sublingual gland; 9 — external maxillary artery; 10 — submandibular gland; 11 — sternocleidomastoid muscle (retracted); 12 — External Carotid Artery; 13 — medial pterygoid muscle; 14 — facial nerve; 15 — external acoustic meatus; 16 — lateral pterygoid muscle; 17 — maxillary artery; 18 — mandibular nerve; 19 — trigeminal ganglion; 20 — roots of trigeminal nerve

The abducens nerve (n. abducens) emerges from the cranial cavity through the superior orbital fissure and innervates the lateral rectus muscle of the eyeball. The Nucleus of this nerve is located in the floor of the Rhomboid fossa within the region of the pons.

The facial nerve (n. facialis; Fig. 174) and the intermediate nerve enter the internal acoustic meatus of the Temporal bone and exit through the stylomastoid foramen, entering the substance of the parotid gland. The facial nerve branches out into terminal twigs that innervate all the Muscles of facial expression and the platysma. The branching of the facial nerve on the face is referred to as the pes anserinus major (goose's FOOT). Additionally, the facial nerve gives off branches to the stylohyoid muscle and the posterior belly of the digastric muscle. The facial nerve also contains parasympathetic fibers for the lacrimal gland, as well as the submandibular and sublingual salivary glands.

Fig. 174. Facial nerve:

1 — frontal muscle; 2 — orbicularis oculi muscle; 3 — infraorbital nerve; 4 — submandibular gland; 5 — platysma; 6 — sternocleidomastoid muscle; 7 — branches of the Cervical plexus; 8 — parotid gland; 9 — facial nerve; 10 — pes anserinus major

The nervus intermedius is a mixed nerve containing secretory fibers that innervate the lacrimal gland via the pterygopalatine ganglion (greater petrosal nerve), as well as the submandibular and sublingual salivary glands (chorda tympani). Through the submandibular and sublingual ganglia, the fibers of the chorda tympani also innervate the taste buds of the anterior two-thirds of the tongue.

The vestibulocochlear nerve (n. vestibulocochlearis) is the nerve of Hearing and Equilibrium. It emerges from the cranial cavity through the internal acoustic meatus, located just inferior to the facial nerve, and enters the internal auditory canal where it divides into two parts: vestibular and cochlear. The vestibular part innervates the semicircular canals and the vestibule. Both nerve processes originate from the vestibular ganglion and transmit statokinetic impulses that enable spatial orientation.

The cochlear part of this nerve contains the spiral ganglion, which consists of Nerve Cells whose peripheral processes extend to the Cytology/practical/79.html">Spiral organ of Corti, while their central processes form the cochlear component of the vestibulocochlear nerve.

The glossopharyngeal nerve (n. glossopharyngeus) emerges from the cranial cavity through the jugular foramen, runs anteriorly and inferiorly, and branches out within the Pharynx, the base of the tongue, the palatine Tonsils, and the faucial pillars. It innervates the muscles and mucous membrane of the pharynx and the vallate papillae of the tongue, while its secretory fibers supply the Parotid salivary gland. The nuclei of this nerve are located in the medulla oblongata.

The vagus nerve (n. vagus) exits the cranial cavity through the jugular foramen and comprises motor, sensory, and secretory fibers. It courses down the neck within the neurovascular bundle, giving off branches to the pharynx, Larynx, and Heart. Entering the thoracic cavity anterior to the Subclavian Artery, it sends branches to the Trachea, Bronchi, Esophagus, and Pericardium. In the esophageal region, branches of the vagus nerve, combined with fibers from the Sympathetic trunk, form the anterior and posterior esophageal plexuses.

Within the Abdominal cavity, the branches of the vagus nerve distribute to the wall of The Stomach, forming the anterior and posterior gastric plexuses. Furthermore, the vagus nerve contributes branches to the celiac plexus, Liver, Spleen, and Kidneys, and forms enteric nerve plexuses within the walls of the intestines. The vagus nerve innervates the majority of the gastrointestinal tract, excluding only the left half of the colon starting from the left colic flexure, as well as the pelvic Organs.

The accessory nerve (n. accessorius) emerges from the cranial cavity through the jugular foramen. It is formed by spinal roots that enter the cranium through the foramen magnum and exit through the jugular foramen. This nerve innervates the trapezius and sternocleidomastoid muscles.

The hypoglossal nerve (n. hypoglossus) exits the cranial cavity through the jugular foramen and innervates all muscles of the tongue. It gives off a descending branch that supplies the anterior Infrahyoid muscles of the neck (Fig. 175).

The nuclei of the IX, X, XI, and XII pairs of cranial nerves are located in the floor of the rhomboid fossa of the medulla oblongata.

Fig. 175. NERVES OF THE neck:

1 — hypoglossal nerve; 2 — external carotid plexus; 3 — external carotid artery; 4 — common carotid plexus; 5 — common carotid artery; 6 — superior cervical cardiac nerve; 7 — vagus nerve; 8 — Internal Carotid Artery; 9 — sympathetic trunk; 10 — superior cervical ganglion; 11 — glossopharyngeal nerve; 12 — Internal jugular vein