Cranial Nerves- Gilland Flashcards
What are the sensory, motor, and mixed cranial nerves?
Special Senses: olfactory, optic, vestibulocochlear nerve
Motor: oculomotor, trochlear, abducens, Hypoglossal nerve
Mixed: Facial, Vagus, Glossopharyngeal nerve
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Accessory nerve innervates SCM and trapezius.
What are the 3 major cranial special sense organs?
CN I: olfactory (nose)
CN II: optic (eyes)
CN VIII: Vestibulocochlear (ears)
What are the 4 somatic motor nerves that move the eyes and tongue?
CN III: Oculomotor
CN IV: trochlear
CN VI: Abducens
CN XII hypoglossal
What are the 4 mixed branchial nerves that move and sense jaws, face, pharynx, and larynx?
CN V: trigeminal
CN VII: facial
CN IX: glossopharyngeal
CN X: vagus
mixed nerves, each with one or more sensory ganglia (in the DRG)
What is the one special motor nerve that is cranial only in a roundabout way and innervates the sternocleidomastoid and trapezius muscles?
CN XI: Spinal accesory
What kind of fibers are sympathetic and parasympathetic fibers?
efferent fibers; GVE
What is a neurogenic placode?
an area of thickening of the epithelium in the embryonic head ectoderm layer that gives rise to neurons and other structures of the sensory nervous system
From what neurogenic placodes do the 3 cranial nerves serving special sense organs derive?
CN I: olfactory –> olfactory placode: central projecting sensory cells
CN II: optic (eyes) —> optic vesicle (diencephalon wall): sensory cells and ganglion cells
CN VIII: Vestibulocochlear (ears)–> Otic placode: auditory and vestibular sensory haircells and ganglion cells
CN I: Olfactory
-consists of central projecting axons in the olfactory epithelium that traverse cribriform plate of the ethmoid bone and synapse on second order neurons in the olfactory bulb
CN II: Optic
- optic nerves begin at retina, extend to optic chiasma where 1/2 of optic fibers cross over to the other side; fibers continue to the lateral geniculate nuclei of the thalamus (second order neurons)
- optic nerve is NOT as peripheral nerve but an optic TRACT in the CNS because the retina and optic nerves arise from the wall of the embryonic diencephalon
- most of the axons of optic nerve are from retinal ganglion cells
CN VIII: Vestibulocochlear
- Vestibulocochlear are two nerves (Cochlear and vestibular) that enter the brain at the pontomedullary junction
- the nerve fibers pass peripherally into the temporal bone via the internal acoustic meatus; they accompany the facial nerve here
- the cochlear nerve afferent fibers project to the lowest order brainstem auditory centers; the dorsal and ventral cochlear nuclei; cochlear nerve efferent axons in the superior olivary nuclei form the olivocochlear bundle
- the vestibular afferent fibers project to the vestibular nuclei (superior, medial, lateral, and descending) and to the vestibulocerebellum
Major central vestibular pathways include what?
-medial longitudinal fasciculus (MLF) and vestibulospinal tracts leading to extraocular and cervical motor nuclei controlling eye and head movements
How do you test the function of the CN I and CN VIII?
CN I: expose the patient to test odorants
CN VIII: vestibular fxn is tested by observing eye movements during introduction of cool or warm water into the external ear canal; this is a caloric test that inducing nystagmus (alternating eye movements); the caloric-vestibulo-ocular reflex is very useful in testing brainstem function in comatose patients
The somatomotor cranial nerves have only efferent components.
- have no affiliated sensory ganglia
- sensory fibers in the periheral parts of these nerves act as “hitch-hikers” from nearby mixed nerves
What is the only cranial nerve to exit the brain dorsally and decussate?
CN IV: trochlear
What is a complication of the oculomotor nerve?
-it also has parasympathetic components to the smooth muscles of the eye
What are the embryonic origins of striated cranial muscles innervated by somatomotor cranial nerves?
CN III, IV, VI, XII
- extraocular muscles innervated by III, IV, VI come from dorsal head mesoderm in front of the ear (otic vesicle)
- parasympathetic ciliary ganglion and ocular smooth muscles innervated by III come from neural crest cells
- tongue muscles innervated by XII come from occipital somites 1-4
CN III
-innervates most of the striated and smooth muscles of the eye, thus has both somatic and visceral (parasympathetic) motor fibers
-Oculomotor nucleus (GSE) axons innervate: These move the eye: superior rectus inferior rectus medial rectus inferior oblique elevates the upper eyelid: levator palpebrae superioris
-Edinger-Westphal Nucleus (GVE; parasympathetic) axons innervate ciliary ganglion whose axons innervate:
pupillary sphincter muscle: constricts the pupil
ciliary muscle: regulates the curvature of the lens