Biology · Ch 9 — Control and Co-ordination
Cranial Nerves
Cranial Nerves
2. Peripheral Nervous System (PNS) - Cranial Nerves : Twelve pairs of cranial nerves, numbered I to XII with Roman numerals, arise from or terminate in the brain of every amniote (reptiles, birds and mammals, including humans), and are classified by function as sensory (I, II, VIII), motor (III, IV, VI, XI, XII) or mixed (V, VII, IX, X). Each has its own point of origin, the organs it innervates, and a specific job -- from the olfactory nerve (I) carrying smell, through the optic nerve (II) carrying vision, the oculomotor (III), pathetic/trochlear (IV) and abducens (VI) nerves that together move the six eye muscles, the large mixed trigeminal nerve (V, the 'dentist's nerve', with ophthalmic, maxillary and mandibular branches serving facial sensation and jaw movement), the facial nerve (VII, expression, taste, salivary and lacrimal secretion), the auditory/vestibulocochlear nerve (VIII, hearing and equilibrium), the glossopharyngeal (IX, taste, salivation, swallowing), the vagus (X, the only cranial nerve reaching internal organs, with the maximum branches and longest distribution, governing breathing, cardiac slowing and digestive-gland secretion), the spinal accessory (XI, neck/shoulder/pharynx/larynx movement) and the hypoglossal (XII, tongue movement). The full functional detail of every pair is set out in the accompanying table.
I. Olfactory -- Sensory -- Origin: olfactory bulb -- Innervates: epithelium of nose -- Function: smell.
II. Optic -- Sensory -- Origin: side of diencephalon -- Innervates: retina of eye -- Function: vision.
III. Oculomotor -- Motor -- Origin: floor of mid brain -- Innervates: 4 of 6 eye muscles -- Function: movement of eyeball.
IV. Pathetic (Trochlear) -- Motor -- Origin: floor of mid brain -- Innervates: 1 of 6 eye muscles, forehead scalp -- Function: rotation and movement of eyeball.
V. Trigeminal (Dentist's nerve; branches Ophthalmic-sensory, Maxillary-sensory, Mandibular-mixed and largest) -- Mixed -- Origin: ventral side of pons -- Innervates: nasal cavity, eyelids, forehead, scalp, conjunctiva, lacrimal gland, nose/palate mucosa, upper teeth and lip, lower teeth, cheek, muscles of mastication -- Function: sensation of skin/touch/taste, jaw movement.
VI. Abducens -- Motor -- Origin: pons -- Innervates: lateral rectus muscle of eyeball -- Function: movement of eye (smallest cranial nerve).
VII. Facial (bears geniculate ganglion) -- Mixed -- Origin: pons -- Innervates: facial/scalp/neck muscles, lacrimal, sublingual, submandibular, nasal and palatine glands -- Function: facial expression, neck movement, tear secretion, taste, salivary secretion.
VIII. Auditory (Vestibulo-cochlear: Vestibular + Cochlear) -- Sensory -- Origin: pons -- Innervates: internal ear -- Function: hearing and equilibrium.
IX. Glossopharyngeal -- Mixed -- Origin: side of medulla oblongata -- Innervates: pharynx, tongue, salivary glands -- Function: taste, salivation, swallowing. …
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