October 29 - Cranial Nerves.docx

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Western University
Anatomy and Cell Biology
Anatomy and Cell Biology 3319

October 29, 2013 Cranial Nerves Pg. 431-439 Cranial Nerves - 12 pairs of cranial nerves - First 2 pairs attach to the forebrain - The rest attach to the brain stem o Except for cranial nerve X (vagus nerve) – extends to abdomen - How to remember names: Oh, Oh, Oh, To Touch And Feel Very Good Velvet, AH! Cranial nerves Sensory function Motor function Somatic Visceral Somatic Visceral motor: sensory (SS) sensory (VS) motor (SM) parasympathetic (VM) I Olfactory Smell II Optic Vision III Oculomotor SM VM IV Trochlear SM V Trigeminal General SM VI Abducens SM VII Facial General General; taste SM VM VIII Hearing; Some Vestibulocochlear equilibrium IX General General; taste SM VM Gloddopharyngeal X Vagus General General; SM VM tissue XI Accessory SM XII Hypoglossal SM - How to remember function: Some Say Marry Money But My Brother Says Big Boobs Matter More - Cranial nerves contain the sensory and motor nerve fibers that innervate the head - Cell bodies of the sensory neurons lie either in receptor organs or within cranial sensory ganglia, which lie along some cranial nerves - Cell bodies of most cranial motor neurons occur in cranial nerve nuclei in the ventral gray matter of the brain stem - Primarily or exclusively sensory nerves: CN1, 2 and 8 o Contain special sensory fibers for smell (1), vision (2), and hearing and equilibrium (8) - Primarily motor nerves: CN 3, 4, 6, 11, 12 o Contain somatic motor fibers to skeletal muscles of the eye, neck and tongue - Mixed (motor and sensory) nerves: CN 5, 7, 9, 10 o Supply sensory innervation to the face (through general somatic sensory) and to the mouth and viscera (general visceral sensory), including the taste buds of the sense of taste (special visceral sensory) o These nerves also innervate pharyngeal arch muscles (somatic motor), such as chewing muscles (CN5) and the muscles of facial expression (CN7) - Parasympathetic division of the ANS: CN 3, 7, 9, 10 o Contain visceral motor fibers that regulate visceral muscle and glands throughout much of the body 1 Olfactory nerve: - Origin and course: fibers arise from olfactory receptor cells located in olfactory epithelium of nasal cavity and pass through to synpase in olfactory bulb o Fibers of olfactory bulb neurons extend posteriorly as olfactory tract, which runs beneath frontal lobe to enter cerebral hemispheres and terminates in primary olfactory cortex - Function: purely sensory o Carry special visceral afferent impulses for sense of smell 2 Optic nerve: - Origin and course: Fibers arise from retina of eye to form optic nerve o The optic nerves converge to form the optic chiasm, where fibers partially cross over, continue on as optic tracts, enter the thalamus, and synapse there o Thalamic fibers run (as the optic radiation) to the occipital cortex, where visual interpretation occurs - Function: purely sensory o Carry special somatic afferent impulses for vision 3 Oculomotor nerve: - Origin and course: fibers extend from ventral midbrain (near its junction with pons) and pass through bony orbit to eye - Function: primarily motor o Contain a few proprioceptive afferents o Each nerve includes:  Somatic motor fibers to 4 of the 6 extrinsic eye muscles:  Inferior oblique  Superior, inferior, and medial rectus muscle that help direct eyeball  And to levator palpebrae superioris muscle, which raises upper eyelid  Parasympathetic motor fibers  To constrictor muscles (spincter papillae) of iris, which cause pupil to constrict  And to ciliary muscle, which controls lens shape for focusing.  Cell bodies of ganglionic parasympathetic neurons are in the ciliary ganglion  Sensory (proprioceptor) afferents, which run from same 4 extrinsic eye muscles to midbrain 4 Trochlear nerve: - Origin and course: fibers emerge from dorsal midbrain and course ventrally around midbrain to enter orbit along with oculomotor nerve o The only cranial nerve to decussate and emerge from the dorsal brainstem - Function: primarily motor o Supply somatic motor fibers to, and carry proprioceptor fibers from, one of the extrinsic eye muscles, the superior oblique muscle 5 Trigeminal nerve: - Largest of cranial nerves - Fibers extend from pons to face, and form 3 divisions: o Opthalamic, maxillary and mandibular divisions - As major general somatic sensory nerves of face, transmit afferent impulses from touch, temperature, and pain receptors - Mandibular division also contains motor fibers that innervate chewing muscles Opthalamic Maxillary Mandibular Division (V )1 Division (V 2 Division (V )3 Function - Sensory fibers - Sensory fibers - General sensory from skin of from skin of cheek, fibers from anterior scalp, upper lip, lower anterior 2/3 upper eyelid, and eyelid tongue, lower nasal region teeth/cheek, skin of chin, temporal
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