Cn Ii

CN V3f lesser petrosal nerve

Middle meningeal artery; epidural hemorrhage occurs as a result of a fracture in this area

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Posterior cranial fossa

8. Internal acoustic meatus

9. Jugular foramen

10. Hypoglossal canal

11. Foramen magnum

CN VII, VIII

Discharge of CSF from the external acoustic meatus (otorrhea) occurs as a result of fracture of the mastoid process and dural tear

CN IX, X, XI, sigmoid sinus; a mass in the jugular foramen causes difficulty in swallowing (dysphagia) and speaking (dysarthria), paralysis of the uvula, and inability to shrug the shoulders CN XII

Medulla of the brain stem, CN XI, vertebral arteries

<4 Figure 20-6. (A) Base of the skull (interior aspect), showing the foramina within the anterior (/I), middle (M), and posterior (P) cranial fossae. The anterior cranial fossa includes the cribriform plate (7); the middle cranial fossa contains the optic canal (2), the superior orbital fissure (3), the foramen rotundum (4), the foramen ovale (5), the foramen spinosum (6), and the foramen lacerum (7); and the posterior cranial fossa includes the internal acoustic meatus (8), the jugular foramen (9), the hypoglossal canal (10), and the foramen magnum (11). In a clinical vignette question, first identify the clinical features mentioned in the question, then match the features with the appropriate structures transmitted and the foramen (table), and finally identify the foramen in the figure. Common clinical situations are indicated in the table (e.g., rhinorrhea, epidural hemorrhage, otorrhea, mass in the jugular foramen). (B) Lateral and (C) frontal views of gross specimens, showing the falx cerebri and tentorium cerebelli.The anatomy of the falx cerebri and tentorium cerebelli is important in understanding various brain herniations (see VII A). A = anterior cranial fossa; CH= cerebral hemisphere; CR = cerebellum; FC = falx cerebri; M= middle cranial fossa; Md= midbrain; SS = straight sinus; SSS = superior sagittal sinus; TC- tentorium cerebelli; TS = transverse sinus. (A adapted with permission from Moore KL: Clinically Oriented Anatomy 3rd ed. Baltimore, Williams & Wilkins, 1992; B and C adapted with permission from Gosling JA, Harris PF, Humpherson JR, et al: Human Anatomy: Color Atlas and Text, 3rd ed. London, Mosby-Wolfe, 1996, pp 7.48, 7.49.)

Tentorium Crani Nerves

Cranial Nerve Clinical Features

I Mediates sense of smell (olfaction).

II Mediates sense of sight (vision).

III Lesion [e.g., transtentorial (uncal) herniation] causes a droopy upper eyelid due to paralysis of levator palpebrae muscle. The eye looks down and out due to paralysis of superior, medial, and inferior rectus muscles and inferior oblique muscle together with the unopposed action of superior oblique muscle (CN IV) and lateral rectus muscle (CN VI). Double vision (diplopia) occurs when patient looks in direction of the paretic muscle. The pupil is fixed and dilated due to paralysis of sphincter pupillae muscle. Accommodation is lost (cycloplegia) due to paralysis of ciliary muscle.

IV Innervates superior oblique muscle.

Lesion causes extortion of eye; vertical diplopia, which increases when looking down (e.g., reading a book); and head tilting to compensate for extorsion.

V Provides sensory innervation tc face and motor innervation to muscles of mastication.

Lesion causes hemianesthesia of face, loss of afferent limb of corneal reflex, loss of afferent limb of oculocardiac reflex, paralysis of muscles of mastication, deviation of jaw to injured side, hypoacusis due to paralysis of tensor tympani muscle, and tic douloureux (recurrent, stabbing pain).

Innervates lateral rectus muscle.

Lesion causes convergent strabismus, inability to abduct eye, and horizontal diplopia when patient looks toward paretic muscle.

<4 Figure 20-7. The base of the brain, with locations of CN I—XII. In a clinical vignette question, first identify the clinical features mentioned in the question, then match the features with the appropriate cranial nerve, and finally identify the cranial nerve in the figure.

VII Provides motor innervation to muscles of facial expression; mediates taste, salivation, and lacrimation.

Lesion causes paralysis of muscles of facial expression (upper and lower face), loss of efferent limb of corneal reflex, hyperacusis due to paralysis of stapedius muscle, and crocodile tears syndrome (tearing during eating) as a result of aberrant regeneration after trauma.

Cranial Nerve Clinical Features

VIII Mediates equilibrium and balance (vestibular) and hearing (cochlear).

Vestibular lesion causes disequilibrium, vertigo, and nystagmus; cochlear lesion (e.g., acoustic neuroma) causes hearing loss and tinnitus.

IX Mediates taste, salivation, swallowing, and input from the carotid sinus and carotid body.

Lesion causes loss of afferent limb of gag reflex, loss of taste from posterior third of tongue, and loss of sensation from pharynx, tonsils, fauces, and back of tongue.

X Mediates speech and swallowing, and innervates viscera in thorax and abdomen.

Lesion causes paralysis of pharynx and larynx, deviation of uvula to opposite side of injured nerve, loss of efferent limb of the gag reflex, and loss of efferent limb of oculocardiac reflex.

XI Innervates sternocleidomastoid and trapezius muscles.

Lesion causes inability to turn head to opposite side of injured nerve and inability to shrug ipsilateral shoulder.

Innervates intrinsic and extrinsic muscles of tongue.

Lesion causes deviation of tongue to same side of injured nerve.

Gag Reflex Levator

Inferior oblique

Muscle Nerve Clinical Test* or Function

Levator palpebrae

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