Motor portion: Originates in the midbrain and passes through the superior orbital fissure.
Innervates the superior oblique muscle, an extrinsic eyeball muscle; Functions: Proprioception.
Somatic motor function: Movement of the eyeball; Clinical application: In trochlear nerve paralysis diplopia and gaze downward strabismus occur. V.
Trigeminal nerve (mixed). (Fig. 5.3, 5.4.). Nuclei: a) motor nucleus of trigeminal nerve (locates in upper part of pars dorsalis pontis; b) superior sensory nucleus of trigeminal nerve (same as that of previous nucleus, laterally of it); c) nucleus of spinal tract of trigeminal nerve (continuation of previous one along the length of medulla oblongata); d) mesencephalic nucleus of trigeminal nerve (tegmentum of cerebral peduncle lateral of aqueduct of midbrain); Site where nerve leaves the brain or enters in; Anteriad of middle cerebellar peduncle; Site of exit from the cranium: Ophthalmic nerve, superior orbital fissure, maxillary nerve – foramen rotundum, mandibular nerve – foramen ovale; Sensory portion: Consists of three branches, all of which end in the pons.
The ophthalamic nerve contains axons from the skin over the upper eyelid, eyeball, lacrimal glands, nasal cavity, side of nose, forehead, and anterior half of scalp that pass through superior orbital fissure.
The maxillary nerve contains axons from the mucosa of the nose, palate, parts of the pharynx, upper teeth, upper lip, and lower eyelid that pass through the foramen rotundum.
The mandibullar nerve contains axons from the anterior two-thirds of the tongue (somatic sensory axons but not axons for the special sense of taste), the lower teeth, skin over mandible, cheek and mucosa deep to it, and side of head in front of ear that pass through the foramen ovale; Motor portion: It’s part of the mandibular branch, which originates in the pons, passes through the foramen ovale, and innervates muscles of mastication (masseter, temporal is, medial pterygoid, lateral pterygoid, anterior belly of digastric, and mylohyoid muscles); Functioins: Sensory: Conveys impulses for touch, pain, and temperature sensations and proprioception.
Motor: Chewing; Clinical application: Neuralgia (pain) of one or more branches of the trigeminal nerve is called trigeminal neuralgia (tic douloureux).
Injury of the mandibullar nerve may cause paralysis of the chewing muscles and a loss of the sensations of touch, temperature, and proprioception in the lower part of the face. “Trismus” is a tonic spasm of the masticatory muscles caused by acute encephalitic lesions in the pons, by rabies, by tetanus, or by other conditions.
Because of the strong abnormal tension in these muscles, the patient is not able to open his mouth. Figure 5.3.
Anatomy of nucleus of III, IV, VI cranial nerves (A.A.
Skoromets, 1995) Figure 5.4.
Inervation of facial skin and head skin (A.A.
Skoromets, 1995) VI.
Abducens nerve (mixed, mainly motor) Nuclei: Nucleus of abducens nerve (locates in dorsal portion of pons, in region of facial colliculus); Site where nerve leaves the brain or enters in: posterior edge of pons in sulcus between pons and pyramid; Site of exit from the cranium: superior orbital fissure; Sensory portion: Consists of axons from proprioceptors in the lateral rectus muscle, which passes through the superior orbital fissure and ends in the pons; Motor portion: Originates in the pons, passes through the superior orbital fissure, and innervates the lateral rectus muscle, an extrinsic eyeball muscle; Function: Proprioception.
Movement of the eyeball; Clinical application: With damage to this nerve, the affected eyeball cannot move laterally beyond the midpoint, and the eye usually is directed medially.
All three motor nerves of one eye are interrupted, the eye looks straight ahead and cannot be moved in any direction, and its pupil is wide and does not react to light (ophthalmoplegia totalis).
Bilateral paralysis of the eye muscles is usually the result of the nuclear damage.
The most frequent causes of nuclear paralysis are encephalitis, neurosyphilis, multiple sclerosis, circulatory condition, hemorrhages, and tumors.
The most frequent causes of peripheral eye muscle palsies are meningitis, sinusitis, cavernous sinus thrombosis, aneurysm of internal carotid artery or posterior communicating artery, fractures, tumors of the cranial base as well as of the orbit, diphtheria, and botulism.
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