cranial nerves

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HEAD AND NECK ANATOMY : 

HEAD AND NECK ANATOMY THE CRANIAL NERVES

The cranial nerves : 

The cranial nerves 12 in number Are part of the peripheral nervous system All exit the cranial cavity through foramina or fissures All originate from the brain except cranial nerve 11( Accessory nerve) Contain sensory, motor or both components

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-special sensory components are associated with hearing, seeing, smelling, balancing and tasting -special motor components include those that innervate muscles derived from the pharyngeal arches

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In utero, 6 pharyngeal arches are designated but the 5th never develops Each pharyngeal arch is associated with a developing cranial nerve or its branches

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1st arch- CN 5 (V3) 2nd arch- CN 7 3rd arch- CN 9 4th arch- Superior Laryngeal Branch of CN 10 6th arch- Recurrent Laryngeal Branch of CN 10

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Olfactory nerve-CN I Carries special afferents (SA) for smell Peripheral processes act as receptors in the nasal mucosa Receptors are located in the roof and upper parts of the nasal cavity Central processes return information to the brain Central processes enter cranial cavity through the Cribiform plate of ethmoid Terminate by synapsing with neurons in the olfactory bulb Lesions result in ANOSMIA

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Optic nerve-CN II Special afferents for vision Returns information from photoreceptors in the retina to the brain Optic nerve enter the cranial cavity through the optic canals Lesion leads to anopsia and loss of light reflex Oculomotor nerve- CN III Moves the eyeball in all directions Adduction is the most important action Constricts pupil (sphincter papillae) Accomodates (ciliary muscle) Raises eyelids (LPS)

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Oculomotor nerve- CN III Carries 2 types of fibers GSE innervating most of the extra ocular muscles (LPS,SR,IR,MR,IO) GVE part of the parasympathetic part of Autonomic Nervous System -synapse in the ciliary ganglion (pupillary constriction and accommodation) Exits the cranial cavity via the lateral wall of the cavernous sinus through the superior orbital fissure Lesion involves ptosis, external strabismus etc

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Trochlear nerve CN IV GSE to Superior Oblique muscle Enters the orbit via the lateral wall of the cavernous sinus Trigeminal nerve CN V General sensory of the head, motor innervation to muscles that move the lower jaw GSA-sensory input from the face, the scalp, mucous membrane of oral and nasal cavity ,PNS, part of the TM, eye and conjunctiva, dura mater in the anterior and middle cranial fossa

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2 roots- Large sensory - small motor Expands into a Trigeminal ganglion in the middle cranial fossa 3 divisions -V1 -V2 -V3

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Ophthalmic nerve (V1) exits the cranial cavity into the orbit via the lateral wall of the cavernous sinus and superior orbital fissure Sensory from the eyes, conjunctiva and orbital contents including the lacrimal gland

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Maxillary nerve Exits the cranial through foramen rotundum Sensory branches from anterior and middle cranial fossa, nasopharynx, palate, nasal cavity, teeth of the upper jaw, maxillary sinus, skin of the side of the nose, lower eyelid, cheek, upper lip

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Mandibular nerve Exits skull through foramen ovale Motor root of CNS also exits through foramen ovale and unites with the sensory component of V3 outside the skull Only division that contains a motor component Motor fibers innervate muscles of mastication, tensor tympani, anterior belly of digastric

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Sensory fibres from the skin of the lower face, cheek lower lip, ear, external auditory meatus and temporal region, anterior two thirds of the tongue, teeth of the lower jaw, teeth of the lower jaw, mastoid air cells, mucus membrane and dura in the middle cranial fossa Lesion involves loss of sensation, weakness in chewing, Jaw deviation towards the affected side, Trigeminal neuralgia

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Abducent nerve-CN VI GSE –Lateral Rectus in orbit Crosses the cavernous sinus as it enters the orbit through the superior orbital fissure Lesion-internal strabismus Facial nerve- CN VII Carries GSA,SA,GVE and BE GSA-sensory input from ext auditory meatus and small skin posterior to the ear SA-taste from anterior two thirds of the tongue

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GVE-parasympathetic part of Autonomic Nervous System -stimulate secretomotor activity in the lacrimal gland, submandibular and sublingual glands, mucus membranes of the nasal cavity, hard and soft palates BE-muscles of the face, scalp, stapedius, posterior belly of the digastric and stylohyoid muscles 2 roots- Large motor - Smaller sensory (the intermediate nerve)

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Intermediate nerve contains SA (taste), GVE (parasympathetic) and GSA Large motor root contains the BE fibres Both roots exit the posterior cranial fossa through the internal auditory meatus and fuse within the facial canal (petrous part of the temporal bone) ?facial nerve Expands into the geniculate ganglion Greater petrosal nerve ?preganglionic parasympathetic Nerve to stapedius and chorda tympani in the facial canal

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Exits the skulls through the stylomastoid foramen Chorda tympani carries taste (SA) fibres from the anterior two thirds of the tongue and preganglionic parasympathetic (GVE) to the submandibular ganglion. Vestibulocochlear nerve-CN VIII SA for hearing and balance 2 divisions -vestibular component for balance -cochlear component for hearing

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Glossopharyngeal nerve CN (IX) carries GVA, SA, GVE, and BE fibers: GVA fibers provide sensory input from the carotid body and sinus, posterior one-third of the tongue, palatine tonsils, upper pharynx, and mucosa of the middle ear and pharyngotympanic tube; SA fibers are for taste from the posterior one-third of the tongue; GVE fibers are part of the parasympathetic part of the autonomic division of the PNS and stimulate secretomotor activity in the parotid salivary gland BE fibers innervate the muscle derived from the third pharyngeal arch (the stylopharyngeus muscle)

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Tympanic nerve: branch from CN IX within the jugular foramen Forms part of the tympanic plexus within the middle ear cavity Contributes GVE which leaves tympanic plexus in the lesser petrosal nerve carrying preganlionic parasympathetic fibres to the otic ganglion? parotid

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PARASYMPATHETIC GANGLIA OF THE HEAD

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Vagus nerve- CN X carries GSA, GVA, SA, GVE, and BE fibers: GSA fibers provide sensory input from the skin posterior to the ear and the external acoustic meatus; GVA fibers provide sensory input from the aortic body chemoreceptors and aortic arch baroreceptors, and the mucous membranes of the pharynx, larynx, esophagus, bronchi, lungs, heart, and abdominal viscera in the foregut and midgut; SA fibers are for taste around the epiglottis

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GVE fibers are part of the parasympathetic part of the autonomic division of the PNS and stimulate smooth muscle and glands in the pharynx, larynx, thoracic viscera, and abdominal viscera of the foregut and midgut; BE fibers innervate one muscle of the tongue (palatoglossus), the muscles of the soft palate (except tensor veli palatini), pharynx (except stylopharyngeus), and larynx. Lesion- dysphagia, hoarseness, uvula points away from the affected side, loss of gag and cough reflex, Horner's syndrome

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Accessory nerve-CN XI BE fibres to the sternocleidomastoid and trapezius muscles Roots arise from the motor neurons in the upper 5 segments of the cervical spinal cord Turns head to opposite side/elevates and rotates scapula Lesion- shoulder droop, weakness turning head to opposite side

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Hypoglossal nerve- CN XII GSE- Intrinsic and most extrinsic muscles of the tongue Exits the cranial cavity through the hypoglossal canal Supplies the hyoglossus, styloglossus, genioglossus and all the extrinsic muscles of the tongue Lesion causes tongue to point towards affected side

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