{"id":2276,"date":"2024-03-12T15:08:08","date_gmt":"2024-03-12T19:08:08","guid":{"rendered":"https:\/\/pressbooks.library.torontomu.ca\/assessmentnursingmain\/chapter\/introduction-to-cranial-nerves-2\/"},"modified":"2024-05-31T10:49:18","modified_gmt":"2024-05-31T14:49:18","slug":"introduction-to-cranial-nerves-2","status":"publish","type":"chapter","link":"https:\/\/pressbooks.library.torontomu.ca\/assessmentnursingmain\/chapter\/introduction-to-cranial-nerves-2\/","title":{"raw":"Introduction to Cranial Nerves","rendered":"Introduction to Cranial Nerves"},"content":{"raw":"In total, 12 paired cranial nerves<\/strong> originate within the brain and brainstem and extend into multiple branches (see Figure 6<\/strong>).<\/span>\r\n\r\nThe 12 cranial nerves are related to sensory<\/strong> and\/or motor<\/strong> functions (see Table 4<\/strong>). Sensory refers to senses such as seeing, hearing, tasting, smelling, and touching, while motor refers to movement. Innervation and associated responsibilities of the nerves can be affected when the nerve is damaged from a physical trauma (e.g., an accident), a surgical intervention, a [pb_glossary id=\"2403\"]brain lesion[\/pb_glossary] (related to a stroke, cerebral inflammation, tumour, aneurysm), or a condition resulting in [pb_glossary id=\"2405\"]demyelination [\/pb_glossary] (e.g., multiple sclerosis).<\/span>\r\n\r\nThe next section explores some of the most common approaches that nurses use to examine the 12 pairs of cranial nerves. Keep in mind that there are many ways to assess cranial nerves, and an abnormal finding may indicate damage to the nerve. These findings should be considered in the context of the complete neurological examination.<\/span>\r\n\r\n\"\"\r\n\r\nFigure 6<\/strong>: Cranial nerves.\r\n\r\n(This image is licensed under the Creative Commons<\/a> Attribution 2.5 Generic<\/a> license and taken from https:\/\/commons.wikimedia.org\/w\/index.php?curid=15108118<\/a>)\r\n\r\n \r\n\r\nTable 4<\/strong>: Cranial nerves.\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n
 \r\n\r\nNerves<\/strong><\/span><\/td>\r\n \r\n\r\nNeurological signs and symptoms (when CN is damaged)<\/strong><\/span><\/td>\r\n<\/tr>\r\n
 \r\n\r\nCN I (1) Olfactory nerves<\/span>\r\n\r\nSensory nerves<\/strong> related to smell.<\/span><\/td>\r\n \r\n
    \r\n \t
  • Hyposmia (partial loss of the sense of smell) or anosmia (complete loss of the sense of smell).<\/span><\/li>\r\n<\/ul>\r\n<\/td>\r\n<\/tr>\r\n
 \r\n\r\nCN II (2) Optic nerves<\/span>\r\n\r\nSensory nerves<\/strong> related to visual acuity (how well a person\u2019s eyes can identify shapes and details of an object at a specific distance) and visual fields (periphery of vision). This nerve is also responsible for sending a message to the brain when light is introduced to the eye when assessing pupillary light reflex to evaluate CN III.<\/span><\/td>\r\n \r\n
    \r\n \t
  • Partial or complete loss of central or peripheral vision.<\/span><\/li>\r\n<\/ul>\r\n<\/td>\r\n<\/tr>\r\n
 \r\n\r\nCN III (3) Oculomotor nerves<\/span>\r\n\r\nSensory nerves<\/strong> related to pupil innervation (pupillary constriction) and lens shape.<\/span>\r\n\r\nMotor nerves<\/strong> related to upper eyelid movement and eye muscle movement specific to four muscles (superior rectus, inferior rectus, medial rectus, and inferior oblique) controlling eye movements: diagonal upward (both inward and outward); diagonal downward-outward; horizontal inward.<\/span><\/td>\r\n \r\n
    \r\n \t
  • Loss of reactivity to light and pupillary dilation.<\/span><\/li>\r\n \t
  • Inability to track an object (follow with eyes).<\/span><\/li>\r\n \t
  • Inability to open eyelid or ptosis (drooping of the eyelid).<\/span><\/li>\r\n \t
  • Double vision.<\/span><\/li>\r\n<\/ul>\r\n<\/td>\r\n<\/tr>\r\n
 \r\n\r\nCN IV (4) Trochlear nerves<\/span>\r\n\r\nMotor nerves<\/strong> related to eye muscle movement specific to one set of muscles (superior oblique) controlling the diagonal downward-inward movement of the eye.<\/span><\/td>\r\n \r\n
    \r\n \t
  • Inability to track an object downward and inward.<\/span><\/li>\r\n \t
  • Double vision.<\/span><\/li>\r\n<\/ul>\r\n<\/td>\r\n<\/tr>\r\n
 \r\n\r\nCN V (5) Trigeminal nerves<\/span>\r\n\r\nSensory nerves<\/strong> related to the sense of touch on facial [pb_glossary id=\"2407\"]dermatomes[\/pb_glossary] (forehead, maxillary, mandible) and the cornea.<\/span>\r\n\r\nMotor nerve<\/strong> related to the innervation of the temporal and masseter muscles of the face.<\/span><\/td>\r\n \r\n
    \r\n \t
  • Asymmetrical, decreased, or no sensation\/feeling to forehead, cheeks, and jaw region.<\/span><\/li>\r\n \t
  • Delayed or absent [pb_glossary id=\"2409\"]corneal reflex[\/pb_glossary].<\/span><\/li>\r\n \t
  • Asymmetry in jaw clenching movement and decreased strength.<\/span><\/li>\r\n<\/ul>\r\n<\/td>\r\n<\/tr>\r\n
 \r\n\r\nCN VI (6) Abducens nerves<\/span>\r\n\r\nMotor nerves<\/strong> related to eye muscle movement specific to one set of muscles (lateral rectus) controlling the horizontal outward movement of the eye.<\/span><\/td>\r\n \r\n
    \r\n \t
  • Inability to track an object outward on a horizontal plane.<\/span><\/li>\r\n \t
  • Double vision.<\/span><\/li>\r\n<\/ul>\r\n<\/td>\r\n<\/tr>\r\n
 \r\n\r\nCN VII (7) Facial nerves<\/span>\r\n\r\nSensory nerves<\/strong> related to taste on the dorsal side of the tongue on the anterior two-thirds (at the front of the tongue).<\/span>\r\n\r\nMotor nerves<\/strong> related to movement of the facial muscles (i.e., facial expressions).<\/span><\/td>\r\n \r\n
    \r\n \t
  • Alteration in taste (decreased or absent).<\/span><\/li>\r\n \t
  • Asymmetry of facial muscles such as flattening of the nasolabial fold or flattening of forehead wrinkles.<\/span><\/li>\r\n \t
  • Inability to close eyes.<\/span><\/li>\r\n \t
  • Decreased or inability to smile or show teeth.<\/span><\/li>\r\n<\/ul>\r\n<\/td>\r\n<\/tr>\r\n
 \r\n\r\nCN VIII (8) Vestibulocochlear nerves<\/span>\r\n\r\nSensory nerves<\/strong> related to balance (vestibular) and hearing (cochlear). This is a set of two nerves including the vestibular nerves and the cochlear nerves (with some motor function).<\/span><\/span><\/td>\r\n \r\n
    \r\n \t
  • Issues with proprioceptive sensation, balance issues, dizziness, and nausea.<\/span><\/li>\r\n \t
  • Difficulty or absent ability to hear sounds or voices.<\/span><\/li>\r\n<\/ul>\r\n<\/td>\r\n<\/tr>\r\n
 \r\n\r\nCN IX (9) Glossopharyngeal and CN X (10) Vagus nerves<\/span>\r\n\r\nThese nerves work together: CN IX carries afferent messages to the brain and CN X carries efferent messages to the affected area.<\/span>\r\n\r\nSensory nerves<\/strong> (CN IX) related to taste on the dorsal side of the tongue on the posterior third (toward the back of the tongue)\u00a0<\/span>\r\n\r\nMotor nerves<\/strong> related to movement of the soft palate, uvula, and pharynx, and some muscles of the tonsillar pillars, swallowing, and speech.\u00a0<\/span><\/td>\r\n \r\n
    \r\n \t
  • Decreased or absent taste (CN IX).<\/span><\/li>\r\n \t
  • Diminished or absent gag reflex.<\/span><\/li>\r\n \t
  • Asymmetrical or lack of movement of palate and uvula.<\/span><\/li>\r\n \t
  • Dysphagia.<\/span><\/li>\r\n \t
  • Dysphasia.<\/span><\/li>\r\n \t
  • Hoarseness.<\/span><\/li>\r\n<\/ul>\r\n<\/td>\r\n<\/tr>\r\n
 \r\n\r\nCN XI (11) Spinal accessory nerves<\/span>\r\n\r\nMotor nerves<\/strong> that innervates and controls the sternocleidomastoid and trapezius muscles.<\/span><\/span><\/td>\r\n \r\n
    \r\n \t
  • Asymmetry and atrophy of neck muscles.<\/span><\/li>\r\n \t
  • Misaligned levelling of shoulders.<\/span><\/li>\r\n \t
  • Decreased range of motion of neck or shoulders on one or both sides<\/span><\/li>\r\n \t
  • Decreased muscle resistance of neck or shoulders on one or both sides.<\/span><\/li>\r\n<\/ul>\r\n<\/td>\r\n<\/tr>\r\n
 \r\n\r\nCN XII (12) Hypoglossal nerves<\/span>\r\n\r\nMotor nerves<\/strong> related to tongue movement and strength.<\/span><\/td>\r\n \r\n