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
What are the characteristic signs of a unilateral oculomotor nerve palsy?
- ptosis
- dilation of the pupil
- depressed and abducted resting eye due to unopposed IV and VI muscles
CN IV
- only innervates superior oblique muscle which depress and medially rotates the eye
- contains only somatic motor fibers (GSE)
- IVth nerve roots exit dorsally at the midbrain/hindbrain junction and decussate (cross to the opposite side); thus neurons of the left trochlear nucleus innervate the right superior oblique muscle and vice versa
What are the symptoms of a loss of function of CN IV?
- loss of superior oblique muscle function is persistent with laterally rotated eye position (ex-torsion)
- laterally rotated eye position may be compensated by tilting the head away from the direction of the non-functional SO muscle
CN VI
- only innervates the lateral rectus muscle which abducts the eye
- contains only GSE fibers
- VIth nerve roots emerge near the ventral midline at the pontomedullary junction
What are the symptoms of a loss of function of CN VI?
- adducted eye during forward gaze
- inability to abduct the eye during attempted lateral gaze
- bilateral abducens palsy is “crossed eyes”
Which sinus presents many opportunities to disrupt CN II, III, IV, VI?
cavernous sinus
-because of the close proximity of the pituitary and internal carotid to the optic chiasma and the nerves to the extraocular muscles (III, IV, VI), visual and eye movement deficits are often involved in cases of pituitary tumors, internal carotid aneurysms or thrombosis in the cavernous sinus
CN XII
-innervates: genioglossus m. hyoglossus m. styloglossus m. chondroglossus m. intrinsic tongue muscles
- hypoglossal motor nucleus located medially in the medulla oblongata just below the 4th ventricle
- XIIth nerve roots exit the brain over a long distance along the groove separating the pyramids and the inferior olive
- nerve exits the skull via the hypoglossal foramen which is between the jugular foramen and the occipital condyle
- they are followed immediately by C1
-some motor fibers C1 travel with CN XII to enter the ansa cervicalis which innervate the thyrohyoid and geniohyoid muscles
How does one test the hypoglossal nerve?
- ask the patient to protrude the tongue, press left and right on the cheek against the tester’s finger pressure
- unilateral hypoglossal weakness is evident during tongue protrusion where the tongue deviates to the weak side
What is branchiomotor (SVE)?
motor fibers to striated muscles formed in the pharyngeal arches
What is the embryonic origin of the branchiomotor muscles? What nerve correspond to what pharyngeal arches?
1st pharyngeal arch muscles innervated by mandibular division of the trigeminal nerve:
- muscles of mastication
- anterior digastric and 2 tensors
2nd pharyngeal arch muscles innervated by facial nerve:
- muscles of facial expression
- posterior digastric and stylohyoid muscles
3rd and 4th pharyngeal arch muscles innervated by IX and X nerve:
- stylopharyngeus
- levator palati
- pharyngeal constrictors
CN V
branchial nerve related to the mouth, first arch, and orbit
has three divisions: ophthalmic (V1): passes through superior orbital fissure
maxillary (V2): passes through the foramen rotundum into the pterygopalatine fossa
mandibular (V3): passes through the foramen ovale into the infratemporal fossa; is sensory and motor
- trigeminal ganglion is plastered onto the floor of the middle cranial fossa by dura
- Vth roots exit lateral surface of pons by passing passing through the middle cerebellar peduncle
- motor root is largely separate and joins mandibular division
What is the facial cutaneous and muscle innervation?
facial cutaneous innervation: CN V
Facial muscles innervation: CN VII
Sensory CN V fibers convey info about touch and pain/temp from the skin of the face, cranial meninges, linings, and contents of major cranial cavities through what nuclei?
- Principle of Trigeminal Sensory Nucleus in rostral pons serving touch
- Nucleus of the Trigeminal Spinal Tract in caudal pons and medulla serving temperature and pain
Mesencephalic Trigeminal Nucleus: in caudal midbrain and rostral pons serving proprioception from muscles of mastication and teeth
How is CN V tested?
jaw jerk reflex involving V motor neurons V mesencephalic neurons tested by a gentle tap which activates proprioceptors in the jaw muscles
corneal reflex involving sensory fibers V1, relay neurons in the main V sensory nucleus, and facial nerve motoneurons innervating the orbicularis oculi tested by gentle touch to the cornea
What is a complication of the trigeminal nerve?
- although the trigeminal nerve has no visceral motor components, that is, no preganglionic nucleus or fibers, most of the postganglionic parasympathetic fibers in the head travel along branches of the Trigeminal nerve
- hitchhiking parasympathetic pathways
CN VII
chorda tympani is a branch of the facial nerve that originates from the taste buds in the front of the tongue, runs through the middle ear, and carries taste messages to the brain
parotid plexus branches to muscles of facial expression
branchial nerve related to 1st pharyngeal pouch and hyoid arch
- VIIth nerve roots emerge at pontomedullary junction
- comprises a larger motor root and a smaller nervus intermedius which carries sensory and visceromotor fibers
- enters temporal bone at internal acoustic meatus
- has SVE from VII motor nucleus for muscles of facial expression, stylohyoid, posterior digastric, and stapedius
- has GVE from superior salivatory nucleus
- SVA to Nucleus of Solitary Tract serving a major gustatory (taste) component innervating taste buds on palate and anterior 2/3 of tongue
- GSA to Nucleus of Trigeminal Spinal Tract conveying touch and pain
What are the 3 major branches of the facial nerve arising in the temporal bone?
greater petrosal nerve
-goes to the pterygopalatine ganglion to go to the lacrimal gland and small mucous glands of palate and nasopharynx (parasympathetic)
facial nerve
-mainly motor to muscles of facial expression, stylohyoid, and posterior digastric
chorda tympani
-goes to submandibular ganglion which goes to submandibular and sublingual glands
How do you test CN VII?
ask the patient to do sweet, sour, salty, and funny faces
Why is the jugular foramen an important landmark?
CN IX, X, XI, and the internal jugular vein all traverse there
if these nerves are compressed here dysphonia could results
CN IX
- branchial nerve related to 2nd pharyngeal pouch and 3rd arch
- its nerve roots emerge at rostral medulla dorsal to inferior olive and in line with adjacent vagus roots
- enters jugular foramen with Xth and XIth nerves
- gives off tympanic nerve into the temporal bone which then emerges from the bone as the lesser petrosal nerve
exits jugular foramen at the base of the skull
What are the functional components of CN IX?
- branchiomotor to 3rd arch muscle from Nucleus Ambiguus (SVE)
- secretomotor control of parotid gland by parasympathetic (GVE) from Inferior Salivatory Nucleus to Otic ganglion via lesser petrosal nerve
- Afferent fibers conveying taste from posterior 1/3 of tongue (SVA) and sensory from carotid body and sinus (GVA) to Nucleus of Solitary Tract
- Afferent fibers conveying touch and pain from middle ear, tonsils, back of soft palate, and posterior 1/3 of tongue and pharynx projecting to Nucleus of V spinal Tract (GSA)
CN X
- motor fibers to 4th-6th arch muscles from Nucleus Ambiguus (SVE)
- preganglionic parasympathetic efferent fibers to all visceral structures from neck to upper hindgut from Dorsal Vagal Motor Nucleus (GVE)
- afferent projections to superior (jugular) and inferior (nodose) ganglia serving as major sensory inputs from cervical, thoracic and abdominal viscera from Nucleus of Solitary Tract (GVA) and touch and pain from ear canal, auricle, and meninges from Nucleus of Solitary Tract (GSA)
- mediates parasympathetic regulation of the heart, lungs, and all derivatives of the embryonic foregut and hindgut as well as the kidneys
- visceromotor fibers (GVE) from the Dorsal Motor Nucleus of the Vagus target parasympathetic ganglia in the heart, lungs, kidneys, and abdominal viscera
- afferent fibers (GVA) from the Vagal Sensory ganglia (Especially the inferior) bring information back to the brain from all of the organs that receive vagal efferents
- Vagal visceral sensory fibers (GVA) terminate in the Nucleus of Solitary Tract in the medulla
How do you test Cranial Nerves IX and X?
Problems with Nerves IX and X are most evident as difficulty in:
- Swallowing
- Phonation
Painful neuralgia can arise from IX-X innervated regions of the posterior tongue, pharynx, ear canal, and external ear
The gag reflex (IX), palatal elevation and vocal cord position during phonation can be readily tested by gently touching the pharyngeal wall.
CN XI
- provides motor innervation to SCM and trapezius
- has no permanent sensory ganglia
- motor nucleus is in the cervical spinal cord from C1-C6
- Roots exit laterally, they are neither ventral nor dorsal and its roots continue directly caudal vagal motor roots
- lesions of XI lead to deficits in contralateral head turns (SCM) and weakness in shoulder elevation and rotation
- XI axons form an ascending bundle within the dural sac, enter the skull through the foramen magnum and join with the caudal vagal fibers to leave the skull via the jugular foramen
Cranial nerve efferent Nuclei
GSE: III, IV, VI, XII motor nuclei
GVE: Edinger-Westphal, Superior and Inferior Salivatory, Dorsal Vagus Nuclei
SVE: V, VII, IX, X motor nuclei
Cranial nerve afferent Nuclei
G-SVA: nucleus of Solitary Tract
GSA: Mesencephalic, Principal and Spinal Tract Trigeminal Nuclei
SSA: Cochlear and Vestibular Nuclei
What cranial nerves have parasympathetic pathways?
III (oculomotor)
- brainstem nuclei (CNS/preganglionic nuclei): Edinger-Westphal Nucleus
- postganglionic nuclei: Ciliary Ganglion
- Efferent Target: sphincter pupillae/ciliaris mm.
VII (facial)
- brainstem nuclei (CNS/preganglionic nuclei): Superior Salivatory Nucleus
- postganglionic nuclei: Pterygopalatine Ganglion; Submandibular Ganglion
- Efferent Target: lacrimal, submandibular, and sublingual glands
IX (Glossopharyngeal)
- brainstem nuclei (CNS/preganglionic nuclei): Inferior Salivatory Nucleus
- postganglionic nuclei: Otic Ganglion
- Efferent Target: parotid gland
X (Vagus)
- brainstem nuclei (CNS/preganglionic nuclei): Dorsal Vagus Motor Nucleus
- postganglionic nuclei: numerous small PS ganglia throughout cervical, thoracic, and abdominal viscera
- Efferent Target: smooth muscle and glands in: larynx, esophagus, lungs, heart, foregut and midgut, abdominal viscera
Fibers conveying taste sensation project to what nuclei?
Nucleus of Solitary Tract
CN XI has roots in which horn?
lateral horns NOT ventral or dorsal horn
