Cranial Nerves.docx

8 Pages
Unlock Document

Western University
Anatomy and Cell Biology
Anatomy and Cell Biology 3319
Kem Rogers

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
More Less

Related notes for Anatomy and Cell Biology 3319

Log In


Don't have an account?

Join OneClass

Access over 10 million pages of study
documents for 1.3 million courses.

Sign up

Join to view


By registering, I agree to the Terms and Privacy Policies
Already have an account?
Just a few more details

So we can recommend you notes for your school.

Reset Password

Please enter below the email address you registered with and we will send you a link to reset your password.

Add your courses

Get notes from the top students in your class.