Cranial Nerves.docx

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School
Western University
Department
Anatomy and Cell Biology
Course
Anatomy and Cell Biology 3319
Professor
Kem Rogers
Semester
Fall

Description
Cranial Nerves • 12 pairs of cranial nerves • Part of peripheral nervous system (PNS) • Attach to brain and pass through various foramina in skull • Nerves are numbered I through XII in a rostral to caudal direction • First two pairs attach to forebrain, & the rest to the brain stem • Except for vagus nerve (X), which extends into the abdomen, cranial nerves innervate only head & neck structures • Following mnemonic phrase: Oh, Oh, Oh, To Touch And Feel Very Good Velvet, Ah! • Classification o Motor:  Muscles of the head and neck o General sensory:  Touch, pain & temperature o Special sensory:  Olfaction, vision, taste & hearing o Parasympathetic Roman Name Name Somatic or Visceral Function Parasympathetic Numeral Pneumonic (Sensory or Motor) Pneumonic I. Olfactory Oh VS Some II. Optic Oh SS Say III. Oculomotor Oh SM & VM Marry P IV. Trochlear To SM Money V. Trigeminal Touch SS & SM But VI. Abducens And SM My VII. Facial Feel SS, VS, SM, VM Brother P VIII. Vestibulocochlear Very Some SM Says IX. Glossopharyngea Good SS, VS, SM, VM Big P l X. Vagus Velvet SS, VS, SM, VM Boobs P XI. Accessory A SM Matter XII. Hypoglossal H! SM More Olfactory Nerve (I) • Sensory function: afferent nerve for sense of smell and visceral sensory • Origin: olfactory receptors cells (bipolar neurons) in the olfactory epithelium of nasal cavity • Odor enters nose and is detected by nerve • Passes through cribriform foramina of ethmoid bone to synapse in olfactory bulb • Fibres of olfactory bulb neurons extend posteriorly beneath frontal lobe as olfactory tract • Terminate in the primary olfactory cortex • Clinical Application: Anosia o Fracture of ethmoid bone or lesions of olfactory fibres may result in partial or total loss of smell Optic Nerve (II) • Sensory function: afferent nerve for vision • Origin: Light enters eye – detected by retina • Passes through the optic canal of sphenoid bone • Optic nerves converge to form optic chiasma where fibres partially cross over, then continue as optic tracts to synapse in the thalamus • Thalamic fibres project to & terminate in primary visual cortex in occipital bone • Clinical Application: Optic Nerve Damage o Damage to an optic nerve results in blindness in the eye served by the nerve o Damage to visual pathway distal to optic chiasma results in partial visual losses o Visual defects are called: Anopsias Oculomotor Nerve (III) • Somatic Motor Function o Innervate four extrinsic eye muscles that direct the eyeball  Superior rectus  Medial rectus  Inferior rectus  Inferior oblique muscles o Innervate levator palpebrae superioris muscle that elevates upper eyelid o Afferent proprioceptor fibres return from extrinsic eye muscles • Visceral Motor Function (parasympathetic) o Constrictor muscles of the iris constrict the pupil (sphincter papillae) o Ciliary muscle controls lens shape (focus) - rounding lens for near vision • Origin: Oculomotor nuclei in ventral midbrain • Passes through superior orbital fissure to enter the orbit • Parasympathetic fibre from brain stem synapse with post ganglionic neurons in ciliary ganglion that innervate iris & ciliary muscle • Clinical Application: Oculomotor Nerve Paralysis o Because actions of the two extrinsic eye muscles not served by cranial nerve III are unopposed – eye cannot be moved up or inward o At rest eye turns laterally (external strabismus) o Upper eyelid droops (ptosis) o Person has double vision Trochlear Nerve (IV) • Somatic Motor Function o Innervate the superior oblique muscle o Muscle passes through ligamentous pulley at the roof of orbit, trochlea o Afferent proprioceptor fibres return from superior oblique • Note: only cranial nerve to decussate & emerge from the dorsal brainstem • Left trochlear nerve innervates right superior oblique • Origin: trochlear nuclei in the dorsal midbrain • Pathway: pass ventrally around the midbrain & pass through superior orbital fissure to enter the orbit • Clinical Application: Trochlear Nerve Damage o Damage to trochlear nerve results in double vision & reduced ability to rotate eye inferolaterally Trigeminal Nerves (V) • Large trigeminal nerve forms three divisions (trigeminal = threefold) o Mixed nerve is general somatic sensory nerve of the face for touch, temperature & pain o Ophthalmic (V ) 1  Sensory: anterior scalp & forehead, upper eyelid, nose, nasal cavity mucosa, cornea & lacrimal gland o Maxillary (V2)  Sensory: skin of cheek region, upper lip, lower eyelid, nasal cavity mucosa, palate, upper teeth o Mandibular (V 3  Sensory: skin of chin, lower cheek, temporal region of scalp, anterior 2/3 tongue & lower teeth  Motor: muscles of mastication: temporalis, masseter, pterygoids, anterior belly of diagastric • Origin: sensory receptors in skin & mucosa of face • Motor fibres from trigeminal motor nucleus in pons • Pathway o Cell bodies of sensory neurons of all three divisions located in large trigeminal ganglion o Fibres extend to trigeminal nuclei in pons • Clinical Application: Anesthesia for Upper & Lower Jaws o Dentists desensitize upper & lower jaws by injecting local anesthetics (such as Novocain) into alveolar branches of maxillary & mandibular divisions of trigeminal nerve o Blocks pain-transmitting fibres from teeth & surrounding tissues become numb Through the Skull Cutaneous Branch V1– superior orbital fissure Supraorbital foramen V2– foramen rotundum Intraorbital foramen V3– foramen ovale Mental foramen mandibular foramen Abducens Nerve (VI) • Somatic Motor Function o Innervate lateral rectus muscle – abducts the eye o Afferent proprioceptor fibres return from lateral rectus • Origin: abducens nuclei in inferior pons • Pathway: passes through superior orbital fissure to enter orbit Facial Nerve (VII) • Mixed nerve: chief somatic motor nerve to facial muscle • Sensory function o Special visceral sensory from taste bunds on anterior 2/3 of the tongue o General somatic sensory from small patch of skin on the ear • Somatic motor function o 5 branches  Temporal  Zygomatic  Buccal  Mandibular  Cervical o Inner
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