Cranial Nerves PDF

Cranial Nerves- Paired nerves branching off the brain serving a variety of sensory and motor (somatic and autonomic) functions. _________________________________________________________________________ I.​ CN I- The olfactory nerve. A.​ Position: 1.​ Adjacent to the...

Cranial Nerves- Paired nerves branching off the brain serving a variety of sensory and motor (somatic and autonomic) functions. _________________________________________________________________________ I.​ CN I- The olfactory nerve. A.​ Position: 1.​ Adjacent to the nasal cavity (sitting on the cribriform plate of the skull with projections actually through the bone and into the superior nasal cavity). Provides the sense of smell. B.​ Functions: 1.​ Close association with memory and emotion centers within the amygdala and hippocampus. II.​ CN II- The optic nerve A.​ Position: Originates in the central portion of the retina (optic disc). Each nerve travels posteromedially, then converges at the optic chiasm. 1.​ At this point 50% of the sensory information from one eye crosses over to the contralateral eye. From here the optic tract runs through the lateral geniculate nucleus of the thalamus, then to the occipital lobe for visual processing. B.​ Damage can result in monocular blindness and loss of the sensory limb of the pupillary light reflex. III.​ CN III- The oculomotor nerve A.​ Position: 1.​ Originates in the midbrain, travels through the superior orbital fissure, and serves somatic and autonomic motor function: B.​ Function: 1.​ Somatic - Will innervate the superior rectus, medial rectus, inferior rectus, inferior oblique, and levator palpebrae superioris muscles. 2.​ Visceral motor - Will innervate sphincter pupillae muscle (Iris) for pupillary constriction and ciliary body for lens accommodation. C.​ If damaged 1.​ Damage to CN III- mydriasis (fixed dilated pupil), ptosis (droopy eyelid), loss of accommodation reflex, limited eye movement. *Anisocoria- Notable difference in pupil size between the eyes. IV.​ CN IV-The trochlear nerve A.​ Position: 1.​ Originates in the dorsal aspect of the brainstem. B.​ Function 1.​ Innervates the superior oblique muscle, which causes the eyeball to move down and out. V.​ CN VI- The abducens nerve A.​ Position & Function: Originates in the pons, enters the orbit via the superior orbital fissure, and innervates the lateral rectus muscle, which abducts the eye  B.​ If damaged: Damage to CN VI may result in diplopia (double vision). VI.​ CN V-The trigeminal nerve - senses pain and temp anterior 2/3 A.​ Position: Originates on the lateral surface of the pons and has a large sensory root and a smaller motor root. Forms three main branches: 1.​ V1- Ophthalmic division- SENSORY BRANCH a)​ enters the orbit through the superior orbital fissure and provides sensory innervation to the orbit, cornea, and the skin of the bridge of the nose, scalp and forehead. 2.​ V2- Maxillary division- SENSORY BRANCH a)​ travels through the foramen rotundum into the pterygopalatine fossa. This provides sensory innervation to the skin between the lateral corners of the eye and corners of the mouth. V2 also provides general sensory innervation to the palate, nasal cavity, paranasal sinuses and the maxillary gums and teeth. 3.​ V3- Mandibular division- SENSORY AND MOTOR a)​ travels through the foramen ovale into the infratemporal fossa. This provides sensory innervation to the lower part of the face (including the anterior 2/3 of the tongue), the mandibular teeth and lateral sides of the scalp. b)​ V3 also provides the somatic motor innervation to the muscles of mastication (masseter, temporalis and the medial and lateral pterygoid muscles). VII.​ CN VII- The facial nerve - Sensory and Motor ; taste anterior ⅔ of tongue A.​ Position: 1.​ This originates from the brainstem and runs between CN VI and VIII. B.​ Function 1.​ Sensory: a)​ It provides innervation to the muscles of facial expression, autonomic innervation to the lacrimal and salivary glands, the special sense of taste to the anterior 2/3 of the tongue, and general sensation (pain/temperature) to a portion of the external acoustic meatus (canal) (POSTERIOR ⅓) 2.​ Motor: a)​ The facial nerve proper has temporal, zygomatic, buccal, mandibular, and cervical branches which innervate the muscles of facial expression. VIII.​ The greater petrosal nerve innervates the lacrimal gland and produces tears that wash and protect the eye and palatonasal glands that produce mucus to line the nasal cavity and palate. A.​ CN7 contributes to this?? IX.​ The chorda tympani nerve runs adjacent to CN V3 and will innervate the submandibular and sublingual glands to produce saliva. It will also deliver special sensory neurons to sense taste on the anterior 2/3 of the tongue. X.​ CN VIII- The vestibulocochlear nerve-  A.​ Position & Function: 1.​ Originates in the brainstem, albeit slightly inferior to CN VII. This contains a vestibular branch, which synapses on the semicircular canals providing a sense of balance, as well as a sense of acceleration and tilt of the head (equilibrium). The cochlear branch synapses on the cochlea and provides the sense of hearing. B.​ If damaged: Damage to CN VIII can result in hearing impairment/deafness, as well as balance/equilibrium problems. Hypersensitivity can result in motion sickness XI.​ CN IX- The glossopharyngeal nerve (SENSE TO GAG) A.​ Position & Function: 1.​ This originates from the lateral aspect of the medulla oblongata, and provides motor innervation to the stylopharyngeus muscle (swallowing) and the parotid gland (salivation). This also transmits sensory information from the carotid body and sinus, the auditory tube (eustation tube), and taste from the posterior third of the tongue, sensation, touch, pain and temperature. Provides afferents for the gag reflex. 2.​ Contributes to homeostasis of blood Fluid volume, blood PH and pressure B.​ If damaged: Damage to CN IX may result in dry mouth (bcuz no parotid gland), dysphagia (trouble swallowing), loss of the gag reflex, loss of taste, and interruption of the gag reflex XII.​ CN X- The vagus nerve. (THE ACTUAL GAGGING) - BROAD RANGE A.​ Position and function: 1.​ Also originates from the lateral aspect of the medulla oblongata. This serves to innervate the muscles of the larynx, pharynx, and palate (swallowing), also contributes to the gag reflex (motor branch), and provides primary parasympathetic innervation to the heart, lungs and GI tract. Also transmits sensory info to the brain from carotid body chemoreceptors and stretch and chemoreceptors from the aortic arch. (kinda like CN 9; contributes to perception of blood pH and volume) 2.​ Forms branches such as the pharyngeal branch (swallowing), superior and recurrent laryngeal branches (swallowing and laryngeal/voice muscles) a)​ Production of speech B.​ Damage: 1.​ Damage to CN X can result in hoarseness, dysphagia, loss of gag reflex, inc heart rate and slowed GI peristalsis. XIII.​ CN XI- The spinal accessory nerve - Somatic motor A.​ Position & function: 1.​ Originates from the upper border of the spinal cord and provides motor innervation to the trapezius and sternocleidomastoid muscles. Turns the head and shrugging shoulders B.​ Damage:  1.​ Damage to this nerve can result in weakness in shoulder shrugging against resistance and weakness in turning the head to the opposite side. XIV.​ CN XII- The hypoglossal nerve. A.​ Position and function: 1.​ Originates from the “Hypoglossal Nucleus”, a 2cm cell column at the ventral region of the medulla oblongata. This nerve innervates the muscles that move the tongue (genioglossus, hyoglossus and styloglossus). B.​ Damage 1.​ Damage to this nerve will result in unilateral weakness of the muscles on the affected side, resulting in the tongue pointing towards the side of the damaged nerve. XV.​ **if there is a right sided stroke (right middle cerebral artery goes), the damage occurs on the left side*** __________________________________ I.​ The Orbit- Formed by the parietal, frontal, lacrimal, ethmoid, maxilla, zygomatic, and sphenoid bones. A.​ Supraorbital and infra orbital foramen for their corresponding nerves and vessels. B.​ Ant and Pos ethmoidal foramina transmit the ant and pos nerves and vessels to the nasal cavity, sphenoid, and ethmoid sinuses. C.​ Nasolacrimal canal drains tears from the eye to the inferior meatus in the nasal cavity. D.​ Optic canal transmits the optic nerve and ophthalmic artery. E.​ Superior orbital fissure transmits CN III, IV and V-1 along with ophthalmic veins F.​ Inferior orbital fissure transmits V-2 and the infraorbital artery and veins G.​ Lacrimal apparatus- The gland itself lies in the superolateral corner of the orbit serving to secrete tears that spread evenly over the eyeball through blinking and cleanse the eye of dust and foreign particles. 1.​ Tear drainage is via the nasolacrimal duct into the inferior nasal meatus of the nasal cavity. Innervation to the lacrimal gland is provided by the greater petrosal nerve (A branch of CN VII). H.​ Levator palpebrae superioris muscle elevates the eyelid and is innervated by CN III. The iris and ciliary muscles are also innervated by CN III. 1.​ Brief mention of Horner’s Syndrome. When individuals have damage to CNlll, (pupil is constricted, droopy eye) a)​ Caused by surgical error or injury or tumors b)​ See myosis, don't sweat on affected side of face, I.​ Closing the eye is via the orbicularis oculi muscle (and CN VII). Overview of the eye itself: I.​ Sclera- A.​ White fibrous covering of the eye that muscles insert. Continues anteriorly to form the……. II.​ Cornea-  A.​ A bulging transparent region which refracts light as it enters the eye. An anterior chamber lies posterior to the cornea. Deep to this is where the lens sits. The visual image is projected to the retina via the lens which accommodates via the action of the ciliary muscles (CN III). The suspensory ligaments support the lens within the eyeball. B.​ Ciliary muscles alters shape of lens depending on where the muscle is C.​ Astigmatism: cornea is mal shaped III.​ Iris - A.​ Colored part of the eye. Varies in thickness depending on the amount of light present. / controls size of pupil?? 1.​ Made up of the following smooth muscles, sphincter pupillae muscle (CN III parasympathetic), dilator pupillae muscle (cervical ganglia sympathetic). IV.​ Deep to these structures is a liquid filled layer known as the vitreous chamber. Deep to this is the……… V.​ Retina A.​ The innermost layer of the eyeball. Its most central portion is the macula lutea which contains the fovea centralis. This has a high concentration of receptor cells known as cones, which aid in detailed, color vision. B.​ Slightly inferior to this is the optic disc (hole). This is the point where the retina travels posteriorly, and becomes the optic nerve and in the process, forms a blind spot in the visual field. C.​ Rods and cones VI.​ Extraocular movement is provided by six strap-like muscles, superior, inferior, medial and lateral rectus muscles, and the superior and inferior oblique. ___________________________________________________________________________ The Ear I.​ Anatomy A.​ External formed by the pinna/auricle (outer ear). Cup shaped to draw sound waves in. An external acoustic meatus (auditory canal) leads to a tympanic membrane. 1.​ This tympanic membrane is part of the sound wave conducting system. It transmits sound waves to a sequence of middle ear ossicles (malleus, incus and stapes). The tympanic membrane also divides the outer ear from the middle ear. B.​ The middle ear ossicles will in turn transmit sound wave vibrations to the (stapes is in contact with oval window) oval window at the vestibule of the cochlea. 1.​ The cochlea is a snail shaped structure within the inner ear that has a membrane of sensory hair cells that will transmit sound wave stimuli to CN VIII, which will deliver this stimuli to the auditory cortex for the sensation of hearing.  C.​ Please note the presence of the pharyngotympanic/eustachian tube within the middle ear. This along with the round window (located proximally in the tube) serve to equalize atmospheric pressure within the middle ear. D.​ Also present within the inner are the semicircular canals. These are fluid filled and ring shaped. They send information regarding balance, acceleration and tilt of the head (vestibular sense) to CN VIII. II.​ Abnormalities 1.​ Otitis externa - inflammation of outer ear 2.​ otitis media - inflammation in middle ear 3.​ tinnitus ________________________________________________________________ The nasal cavity I.​ Divided into two lateral compartments by a nasal septum. A.​ The cavities and septum are lined with a mucous membrane. 1.​ It is vascularized by branches of the maxillary (sphenopalatine and greater palatine arteries), facial, ophthalmic (anterior and posterior ethmoid) arteries. 2.​ The innervation comes from CN I, CN V-1 and V-2, and CN VII. The anterior border is formed by the nostrils, the posterior border is formed by the nasopharynx. 4.​ Its boundaries consist of a a)​ Roof- made of the nasal, frontal, sphenoid and ethmoid bones. This is where CN I is transmitted. b)​ Floor- formed by the maxilla and palatine bones c)​ Medial wall (nasal septum)- made up by the perpendicular plate of the ethmoid bone, the vomer bone and the septal cartilage. d)​ Lateral wall- formed by the superior, middle and inferior nasal conchae. The superior, middle and inferior meatus are the openings between the ridges formed by the conchae. e)​ Epistaxis- Nose bleeds B.​ Paranasal sinuses 1.​ These consist of the frontal, sphenoid, maxillary and ethmoid sinuses a)​ These sinuses are hollow cavities within the bones themselves. They serve to lessen the weight of the skull, resonate the sound produced through speech, and produce mucus. They communicate with the nasal cavities where mucus is drained. The ethmoid sinus is unique in that it is formed by a series of small cavities known as air cells. C.​ Sinusitis 1.​ Sinusitis infections usually have to be treated longer because their sight is alittle more secluded D.​ pituitary tumor surgery 1.​ Have to go through sphenoid sinus to get to sella turcica ______________________________________________________ I.​ Oral cavity- A.​ Separated from the nasal cavity by a hard and soft palate. B.​ The hard palate is made up of the palatine process of the maxillary bone and the horizontal plate of the palatine bone. C.​ The soft palate forms the soft posterior segment of the palate and is constructed by muscles (tensor veli palatini, levator veli palatine, palatoglossus) sheathed within a mucous membrane. 1.​ These muscles are innervated (motor) by CN X aside from the tensor veli palatine (CN III). 2.​ Other soft palate structures include the uvula, which serves to seal off the nasal cavity during swallowing; a)​ the palatoglossal and palatopharyngeal folds which aid the uvula b)​ palatine tonsils: a collection of lymphoid tissue serving immune function (1)​ You see the palatine tonsils c)​ Pharyngeal tonsils are in nasopharynx (superiorally)