Cranial Nerves Flashcards
Name/number: I. Olfactory
Origin/course
• Fibers arise from olfactory receptors in the nasal mucosa and synapse with the olfactory bulbs (which, in turn, send fibers to the olfactory cortex)
Function
• Purely sensory; carries impulses for the sense of smell
Test
• Subject is asked to sniff and identify aromatic substances, such as oil of cloves or vanilla
Name/number: II. Optic
Origin/course
• Fibers arise from the retina of the eye and form the optic nerve. The two optic nerves form the optic chiasma by partial crossover of fibers; the fibers continue to the optic cortex as the optic tracts
Function
• Purely sensory; carries impulses for vision
Test
• Vision and visual field are tested with an eye chart and by testing the point at which the subject first sees an object (finger) moving into the visual field; eye interior is viewed with an ophthalmoscope
Name/number: III. Oculomotor
Origin/course
• Fibers run from the midbrain to the eye
Function
• Supplies motor fibers to four of the six muscles (superior, inferior, and medial rectus, and inferior oblique) that direct the eyeball; to the eyelid; and to the internal eye muscles controlling lens shape and pupil size
Test
• Pupils are examined for size, shape, and size equality; pupillary reflex is tested with a penlight (pupils should constrict when illuminated); eye convergence is tested, as is the ability to follow moving objects
Name/number: IV. Trochlear
Origin/course
• Fibers run from the midbrain to the eye
Function
• Supplies motor fibers for one external eye muscle (superior oblique)
Test
• Tested in common with cranial nerve III for the ability to follow moving objects
Name/number: V. Trigeminal
Origin/course
• Fibers emerge from the pons and form three divisions that run to the face
Function
• Conducts sensory impulses from the skin of the face and mucosa of the nose and mouth; also contains motor fibers that activate the chewing muscles
Test
• Sensations of pain, touch, and temperature are tested with a safety pin and hot and cold objects; corneal reflex tested with a wisp of cotton; motor branch tested by asking the subject to open mouth against resistance and move jaw from side to side
Name/number: VI. Abducens
Origin/course
• Fibers leave the pons and run to the eye
Function
• Supplies motor fibers to the lateral rectus muscle, which rolls the eye laterally
Test
• Tested in common with cranial nerve III for the ability to move each eye laterally
Name/number: VII. Facial
Origin/course
• Fibers leave the pons and run to the face
Function
• Activates the muscles of facial expression and the lacrimal and salivary glands; carries sensory impulses from the taste buds of anterior tongue
Test
• Anterior two-thirds of tongue is tested for ability to taste sweet, salty, sour, and bitter substances; subject is asked to close eyes, smile, whistle, etc.; tearing of eyes is tested with ammonia fumes
Name/number: VIII. Vestibulocochlear
Origin/course
• Fibers run from the equilibrium and hearing receptors of the inner ear to the brain stem
Function
• Purely sensory; vestibular branch transmits impulses for the sense of balance, and cochlear branch transmits impulses for the sense of hearing
Test
• Hearing is checked by air and bone conduction, using a tuning fork
Name/number: IX. Glossopharyngeal
Origin/course
• Fibers emerge from the medulla and run to the throat
Function
• Supplies motor fibers to the pharynx (throat) that promote swallowing and saliva production; carries sensory impulses from taste buds of the posterior tongue and from pressure receptors of the carotid artery
Test
• Gag and swallowing reflexes are checked; subject is asked to speak and cough; posterior tongue may be tested for taste
Name/number: X. Vagus
Origin/course
• Fibers emerge from the medulla and descend into the thorax and abdominal cavity
Function
• Fibers carry sensory impulses from and motor impulses to the pharynx, larynx, and the abdominal and thoracic viscera; most motor fibers are parasympathetic fibers that promote digestive activity and help regulate heart activity
Test
• Tested in common with cranial nerve nine because they both serve muscles of the throat
Name/number: XI. Accessory
Origin/course
• Fibers arise from the superior spinal cord (C1–C5)* and travel to muscles of the neck and back
Function
• Mostly motor fibers that activate the sternocleidomastoid and trapezius muscles
Test
• Sternocleidomastoid and trapezius muscles are checked for strength by asking the subject to rotate head and shrug shoulders against resistance
Name/number: XII. Hypoglossal
Origin/course
• Fibers run from the medulla to the tongue
Function
• Motor fibers control tongue movements; sensory fibers carry impulses from the tongue
Test
• Subject is asked to stick out tongue, and any position abnormalities are noted
