The 12 Cranial Nerves: An In-Depth Look Flashcards
Olfactory I:
Sensory Only
o Origin & Course: Rise from cribiform plate of ethmoid bone, which runs from the frontal lobe.
o Function: Purely Sensory; carry afferent impulses for sense of smell.
Optic II:
Sensory Only
o Origin & Course: Innervate with the retina of the eye, form optic chiasma which continues to optic tracts and go to occipital lobe where sight is perceived.
o Function: Purely Sensory, carry afferent impulses for vision.
Oculomotor III:
Motor Only
o Origin & Course: Fibers extend from ventral midbrain and pass through bony orbit, via superior orbital fissure, to eye.
o Function: Chiefly motor nerves contain a few proprioceptive afferents. Each nerve includes the following:
• Somatic motor fibers to four of six extrinsic eye muscles that help direct eyeball, and raise upper eyelid.
• Parasympathetic (autonomic) motor fibers to sphincter pupillae, causes pupil to constrict. Also controls lens shape for visual focusing.
• Sensory (proprioceptor) afferent fibers, which run from same four eye muscles to midbrain.
Trochlear IV:
Motor Only
o Origin & Course: Fibers emerge from dorsal midbrain and course ventrally around midbrain to enter orbit through superior orbital fissure along with oculomotor nerves.
o Function: Primarily motor nerves; supply somatic motor fibers to one of the extrinsic eye muscles, the superior oblique.
Trigeminal V:
Sensory and Motor
o Origin & Course:
• Ophthalmic Division: Fibers run from face to pons via superior orbital fissure.
• Maxillary Division: Fibers run from face to pons via foramen rotundum.
• Mandibular Division: Fibers pass through skull via foramen ovale.
o Function:
• Ophthalmic Division: Conveys sensory impulses from skin of anterior scalp, upper eyelid, and nose, and from nasal cavity mucosa, cornea, and lacrimal gland.
• Maxillary Division: Conveys sensory impulses from nasal cavity mucosa, palate, upper teeth, skin of cheek, upper lip, lower eyelid.
• Mandibular Division: Conveys sensory impulses from anterior tongue, lower teeth, skin of chin, temporal region of scalp. Supplies motor fibers to, and carries proprioceptors from, muscles of mastication.
Abducens VI:
Motor Only
o Origin & Course: Fibers leave inferior pons and enter orbit via superior orbital fissure to run to eye.
o Function: Primarily Motor; supply somatic motor fibers to lateral rectus muscle. Convey proprioceptor impulses from same muscle to brain.
Facial VII:
Sensory and Motor
o Origin & Course: Fibers issue from pons, just lateral to abducens nerve, enter temporal bone via internal acoustic meatus, and run within bone before emerging through stylomastoid foramen. Nerve then courses to lateral aspect of face.
o Function:
• Convey motor impulses to skeletal muscles of face, except for chewing muscles served by trigeminal nerves, and transmit proprioceptor impulses from muscles to pons.
• Transmit parasympathetic motor impulses to lacrimal (tear) glands, nasal and palantine glands, and submandibular and sublingual salivary glands. Some of the cell bodies of these parasympathetic motor neurons are in pterygopalatine and submandibular ganglia of trigeminal nerve.
• Convey sensory impulses from taste buds of anterior two-thirds of tongue; cell bodies of these sensory neurons are in geniculate ganglion.
Vesibulocochlear VIII:
Sensory and Motor
o Origin & Course: Fibers arise from hearing and equilibrium apparatus located within inner ear of temporal bone and pass through internal acoustic meatus to enter brain stem at pons-medulla border. Afferent fibers from hearing receptors in cochlea form the cochlear division; those from equilibrium receptors in semicircular canals and vestibule form the vestibular division. The two divisions merge to form vestibulocochlear nerve.
o Function: Mostly Sensory. Vestibular branch transmits afferent impulses for sense of equilibrium, and sensory nerve cell bodies are located in vestibular ganglia. Cochlear branch transmits afferent impulses for sense of hearing, and sensory nerve cell bodies are located in spiral ganglion within cochlea. Small motor component adjusts the sensitivity of sensory receptors.
Glossopharyngeal IX:
Sensory and Motor
o Origin & Course: Fibers emerge from medulla and leave skull via jugular foramen to run to throat.
o Function:
• Mixed Nerves: Innervate part of tongue and pharynx. Provide somatic motor fibers to, and carry proprioceptors from, a superior pharyngeal muscle that elevates the pharynx for swallowing. Prove parasympathetic motor fibers to parotid salivary glands.
• Sensory Fibers: Conduct taste and general sensory impulses from pharynx and posterior tongue, from chemoreceptors in the carotid body and from baroreceptors of carotid sinus. Sensory neuron cell bodies are located in superior and inferior ganglia.
Vagues X:
Sensory and Motor
o Origin & Course: The only cranial nerves to extend beyond head and neck region. Fibers emerge from medulla, pass through skull via jugular foramen, and descend through neck region into thorax and abdomen.
o Function: Mixed nerves. Nearly all motor fibers are parasympathetic efferents, except those serving skeletal muscles of pharynx and larynx. Parasympathetic motor fibers supply heart, lungs, and abdominal viscera and are involved in regulating heart rate, breathing, and digestive system activity. Transmit sensory impulses from thoracic and abdominal viscera, from the aortic arch baroreceptors and the carotid and aortic bodies, and taste buds on the epiglottis. Carry proprioceptor fibers from muscles of larynx and pharynx.
Accessory XI:
Motor Only
o Origin & Course: Unique in that they form from rootlets that emerge from the spinal cord, not the brain stem. These rootlets arise laterally from superior region of spinal cord, pass upward along spinal cord, and enter the skull as the accessory nerves via foramen magnum. The accessory nerves exit from skull through jugular foramen together with the vagus nerves, and supply two large neck muscles.
o Function: Mixed nerves, but primarily motor in function. Supply motor fibers to trapezius and sternocleidomastoid muscles, which together move head and neck, and convey proprioceptor impulses from same muscles.
Hypoglossal XII:
Motor Only
o Origin & Course: As their name implies, hypoglossal nerves mainly serve the tongue. Fibers arise by a series of roots from medulla and exit from skull via hypoglossal vanal to travel to tongue.
o Function: Mixed nerves, but primarily motor in function. Carry somatic motor fibers to intrinsic and extrinsic muscles of tongue, and proprioceptor fibers from same muscles to brain stem. Hypoglossal nerve control allows tongue movements that mix and manipulate food during chewing, and contribute to swallowing and speech.
Cranial Nerves Involved in Parasympathetic Actions:
o Oculomotor III, Facial VII, Glossopharyngeal IX, Vagus X
