Flashcards in Cranial Nerves - HY Deck (117):
What is the only sensory system that has no precortical relay in the thalamus?
The olfactory nerve consists of what?
Unmyelinated axons of bipolar neurons that are located in the nasal mucosa --> the olfactory epithelium.
How does the olfactory nerve enter the cranial cavity?
Through the cribriform plate of the ethmoid bone.
What are the olfactory receptor cells?
1st order neurons that project to the mitral cells of the olfactory bulb.
What are the mitral cells?
The principal cells of the olfactory bulb --> They are excitatory and glutaminergic.
Where do the mitral cells project?
Through the olfactory tract and lateral olfactory stria to the primary olfactory cortex + amygdala.
What is the primary olfactory cortex?
Consists of the piriform cortex overlies the uncus.
What Brodmann's area is the primary olfactory cortex?
How most lesions of the olfactory nerve result?
From trauma (skull fracture) and often from olfactory groove meningiomas.
What may lesions that involve the parahippocampal uncus cause?
Olfactory hallucinations (uncinate fits (seizures) with deja vu).
What is the Foster Kennedy syndrome?
1. Ipsilateral anosmia
2. Ipsilateral optic atrophy
3. Contralateral papilledema
--> Usually caused by an anterior fossa meningioma.
What is the optic nerve?
A special somatic afferent (SSA) nerve that subserves vision and pupillary light reflexes.
How does the optic nerve enters the cranial cavity?
Through the optic canal of the sphenoid bone.
Is the optic nerve a true peripheral nerve?
No - it is a tract of the diencephalon.
Can a transected optic nerve regenerate?
What is the oculomotor nerve?
A general somatic efferent (GSE), general visceral efferent (GVE) nerve.
What are the actions of the oculomotor nerve?
1. Moves the eye
2. Constricts the pupil
What is the course of the oculomotor nerve?
It exits the brain stem from the interpeduncular fossa of the midbrain --> passes through the cavernous sinus --> enters the orbit through the superior orbital fissure.
Where does the GSE component of the oculomotor arise from?
From the oculomotor nucleus of the rostral midbrain.
What does the GSE component of the oculomotor innervate?
4 extraocular muscles + levator palpebrae muscle.
What does the GVE component of the oculomotor consist of?
Preganglionic PNS fibers.
What is the PNS nucleus of the oculomotor?
Edinger - Westphal nucleus - accessory nucleus of the oculomotor.
--> Projects preganglionic PNS fibers to the ciliary ganglion of the orbit through CN III.
What is the role of the ciliary ganglion?
Projects postganglionic PNS fibers to the sphincter pupillae (miosis) and the ciliary muscle (accomodation).
When do we see oculomotor paralysis?
With transtentorial herniation (tumor, subdural, or epidural hematoma).
What is the result of the denervation of the extraocular muscles innervated by oculomotor?
Causes the affected eye to look "down and out" as a result of the unopposed action of the lateral rectus and superior oblique muscles.
When does oculomotor palsy result in diplopia?
When the patient looks in the direction of the paretic muscle.
What happens in internal ophthalmoplegia of the oculomotor nerve?
Interruption of PNS innervation --> Results in a dilated, fixed pupil and paralysis of accomodation (cycloplegia).
What are the effects of a transtentorial herniation on oculomotor?
Compresses or stretches the oculomotor nerve:
--> Sphincter pupillae fibers are affected first --> resulting in a dilated, fixed pupil.
--> Somatic efferent fibers are affected later --> external strabismus (exotropia).
Can an aneurysm of the internal carotid or posterior communicating artery compress CN III?
Yes - within the cavernous sinus or interpeduncular cistern.
--> Usually affect the peripheral pupilloconstrictor fibers first.
Can diabetes mellitus affect the oculomotor nerve?
Yes - Diabetic oculomotor palsy.
--> Damages the central fibers and spares the sphincter pupillae fibers.
Where does the trochlear nerve arise from?
The contralateral trochlear nucleus of the caudal midbrain.
What is the course of the trochlear nerve?
It decussates beneath superior medullary velum of the midbrain and exits the brain stem on its dorsal surface, caudal to the inferior colliculus --> Encircles the midbrain within the subarachnoid space --> passes through the cavernous sinus - enters the orbit through the superior orbital fissure.
To what is the trochlear nerve particularly susceptible?
To head trauma because of its course.
In what does CN IV palsy result?
1. Extorsion of the eye + weakness of downward gaze.
2. Vertical diplopia --> increases looking down.
3. Head tilting --> to compensate for extorsion (may be misdiagnosed as idiopathic torticollis).
What is the trigeminal nerve?
A special visceral efferent (SVE) + general somatic afferent (GSA) nerve.
What are the 3 divisions of the trigeminal nerve?
Where is the SVE component of the trigeminal nerve found?
Arises from the motor nucleus of trigeminal that is found in the lateral midpontine tegmentum.
What does the motor nucleus of the trigeminal innervate?
The muscles of mastication:
3. Lateral + medial pterygoids
1. Tensor tympani
2. Veli palantini
3. Mylohyoid muscle
4. Anterior belly of the digastric muscle
What does the GSA component of the trigeminal nerve provide?
Sensory innervation to:
2. Mucous membranes of the nasal and oral cavities + frontal sinus
3. Hard palate
4. Deep structures of the head (proprioception from muscles and the temporomandibular joint).
--> Innervates the dura of the anterior and middle cranial fossae (supratentorial dura).
Lesions of the trigeminal nerve can result in what?
1. Loss of general sensation (hemianesthesia) from the face and mucous membranes of the oral and nasal cavities.
2. Loss of the corneal reflex (afferent limb).
3. Flaccid paralysis
4. Deviation of the jaw to the weak side --> unopposed action of the opposite lateral pterygoid muscle.
5. Paralysis of the tensor tympani muscle --> hypoacusis (partial deafness to low-pitched sounds).
6. Trigeminal neuralgia (tic douloureux) --> recurrent paroxysms of sharp, stabbing pain in one or more branches of the nerve.
What is the abducent nerve?
A pure GSE nerve that innervates the lateral rectus muscle, which abducts the eye.
Where does the abducent nerve arise from?
From the abducent nucleus that is found in the dorsomedial tegmentum of the caudal pons.
What is the course of the abducent nerve?
Exiting intraaxial fibers pass through the corticospinal tract --> lesion results in alternating abducent hemiparesis.
--> It passes through the pontine cistern and cavernous sinus --> enters the orbit through the superior orbital fissure.
What is the MC isolated palsy?
CN VI that results from the peripheral course of the nerve.
In what patients do we see abducent nerve palsy?
2. Subarachnoid hemorrhage
3. Late stage syphilis
Abducent nerve palsy results in what?
1. Convergent (medial) strabismus (esotropia) with inability to abduct the eye.
2. Horizontal diplopia with max separation of the double images when looking toward the paretic rectus muscle.
What is the facial nerve?
A GSA, GVA, GVE, SVA, SVE nerve.
What does the facial nerve mediate?
1. Facial movement
5. General sensation from the external ear
What nerve does the CN VII include?
The intermediate nerve which contains GSA, SVA, and GVE fibers.
What is the course of the facial nerve?
Exits the brain stem in the cerebellopontine angle --> Enters the internal auditory meatus and facial canal --> Exits the facial canal and skull through the stylomastoid foramen.
Discuss the GSA component of the facial nerve.
1. Cell bodies located in the geniculate ganglion.
2. Innervates the posterior surface of the external ear through the posterior auricular branch of CN VII --> Projects centrally to the spinal tract and nucleus of trigeminal nerve.
Discuss the GVA component of the facial nerve.
1. Has no clinical significance.
2. Cell bodies located in the geniculate ganglion.
3. Fibers innervate the soft palate and the adjacent pharyngeal wall.
Discuss the SVA component of the facial nerve.
1. Cell bodies located in the geniculate ganglion.
2. Projects centrally to the solitary tract and nucleus.
3. Innervates the taste buds from the anterior 2/3 of the tongue.
How does the facial nerve innervate the taste buds?
1. Intermediate nerve
2. Chorda tympani
3. Lingual nerve
4. Central gustatory pathway
Where is the chorda tympani located?
In the tympanic cavity medial to the tympanic membrane and malleus.
What fibers does the chorda tympani contain?
SVA and GVE (PNS) fibers.
Of what nerve is the lingual nerve a branch?
Of CN V3.
Discuss the central gustatory pathway.
Taste fibers from CN VII, and CN IX, X project through the central tegmental tract to the VPM of the thalamus.
--> The VPM projects to the gustatory cortex of the parietal lobe (parietal operculum).
Discuss the GVE component of the CN VII.
A PNS component that innervates the lacrimal, submandibular and sublingual glands.
--> Contains PNS neurons that are located in the superior salivatory nucleus of the caudal pons.
Discuss the lacrimal part of the GVE component of CN VII.
Superior salivatory nucleus projects through the intermediate nerve and greater petrosal nerves to the pterygopalantine (sphenopalantine) ganglion --> the ganglion projects to the lacrimal gland of the orbit.
Discuss the submandibular pathway of the GVE component. Of the CN VII.
Superior salivatory nucleus projects through the intermediate nerve and chorda tympani to the submandibular ganglion --> the ganglion projects and innervates the submandibular and sublingual glands.
Discuss the course of the SVE component of the CN VII.
Arises from the facial nucleus --> loops around the abducent nucleus of the caudal pons --> exits the brainstem in the cerebellopontine angle --> enters the internal auditory meatus --> traverses the facial canal --> sends a branch to the stapedius muscle of the middle ear --> exits the skull through the stylomastoid foramen.
What muscles does the SVE component of the facial nerve innervate?
1. Muscles of facial expression.
3. Posterior belly of the digastric
4. Stapedius muscle
Lesions on CN VII may cause what?
1. Flaccid paralysis of the muscles of facial expression (upper + lower face).
2. Loss of corneal reflex (efferent limb) --> may lead to corneal ulceration.
3. Loss of taste (ageusia-gustatory anesthesia) from the anterior 2/3 of the tongue.
5. Bell's palsy
6. Crocodile tears syndrome (Lacrimation during eating).
7. Supranuclear (central) facial palsy
8. Möbius' syndrome
Lesion to what part of the facial nerve may result in ageusia-gustatory anesthesia?
From damage to the chorda tympani.
What lesion must happen to result in hyperacusis?
A result of stapedius paralysis.
How is Bell's palsy caused?
Peripheral facial paralysis --> caused by trauma or infection and involves the upper and lower face.
What is the mechanism of crocodile tears syndrome?
Result of aberrant regeneration of SVE fibers after trauma.
What is the effect of supranuclear (central) facial palsy?
Results in contralateral weakness of the lower face - SPARING of the upper face.
Where do we see bilateral facial nerve palsies?
What happens in Möbius syndrome?
Consists of congenital facial diplegia (CN VII) and convergent strabismus (CN VI).
What is the vestibulocochlear nerve?
An SSA nerve.
1. The vestibular nerve, which maintains equilibrium and balance.
2. The cochlear nerve, which mediates hearing.
What is the course of the CN VIII?
Exits the brainstem at the cerebellopontine angle and enters the internal auditory meatus --> confined to the temporal bone.
With what is the vestibular nerve associated?
1. Functionally with the cerebellum (floccunodular lobe).
2. Ocular motor nuclei.
What movements does the vestibular nerve regulate?
Compensatory eye movements.
Where are the 1st order sensory bipolar neurons of the vestibular nerve located?
In the vestibular ganglion in the fundus of the internal auditory meatus.
Where does the vestibular nerve project its peripheral processes?
It projects its peripheral processes to the hair cells of the cristae of the semicircular ducts and the hair cells of the utricle and saccule.
Where does the vestibular nerve project its central processes?
To the four vestibular nuclei of the brain stem + floccunodular lobe of the cerebellum.
True or false? The vestibular nerve conducts efferent fibers to the hair cells from the brain stem.
What do lesions of the vestibular nerve result in?
Where are the 1st order sensory bipolar neurons of the cochlear nerve located?
In the spiral (cochlear) ganglion of the madiolus of the cochlea, within the temporal bone.
Where do the peripheral processes of the cochlear nerve project?
To the hair cells of the organ of Corti.
Where do the central processes of the cochlear nerve project?
To the dorsal and ventral cochlear nuclei of the brain stem.
True or false? The cochlear nerve conducts efferent fibers to the hair cells from the brain stem.
What are the clinical problems of the cochlear nerve?
1. Destructive lesions result in hearing loss (sensorineural deafness).
2. Irritative lesions can cause tinnitus (ear ringing).
3. Acoustic neuroma (Schwannoma) --> deafness.
What is the glossopharyngeal nerve?
A GSA, GVA, SVA, SVE, and GVE nerve.
What is primarily the glossopharyngeal nerve?
A sensory nerve.
What does CN IX mediate, along with X, XI, and XII?
What inputs does the CN IX mediate?
1. Input from the carotid sinus - baroreceptors.
2. Input from the carotid body - chemoreceptors that monitor the CO2 and O2 concentration of the blood.
What is the course of the IX nerve?
Exits medulla from the postolivary sulcus with CN X, and XI --> exits the skull through jugular foramen with X, and XI.
Discuss the GSA component of CN IX.
1. Innervates part of the external ear + external auditory meatus through the auricular branch of the vagus nerve.
2. Cell bodies in the superior ganglion.
3. Projects its central processes to the spinal tract and nucleus of trigeminal nerve.
Discuss the GVA component of CN IX?
1. Innervates structures that are derived from the endoderm.
2. Mucous membranes of the posterior 1/3 of the tongue, tonsil, upper pharynx, tympanic cavity, and the auditory tube.
3. Innervates carotid sinus (baroreceptors) and carotid body (chemoreceptors) through the sinus nerve.
4. Cell bodies in the inferior petrosal ganglion.
5. Projects its central processes to the solitary tract and nucleus.
Discuss the SVE component of the glossopharyngeal nerve.
1. Innervates only the stylopharyngeus muscle.
2. Arises only from the nucleus ambiguus of the lateral medulla.
Discuss the GVE component of the CN IX.
1. PNS component that innervates the parotid gland.
2. Preganglionic PNS neurons are located in the inferior salivary nucleus of the medulla.
3. Project through the tympanic and lesser petrosal nerves to the otic ganglion.
4. Post ganglionic fibers from the otic ganglion project to the parotid gland through the auriculotemporal nerve (CN V3).
Lesions of the CN IX can cause what?
1. Loss of the gag (pharyngeal) reflex.
2. Hypersensitive carotid sinus reflex (syncope).
3. Loss of general sensation in the pharynx, tonsils, fauces, and back of the tongue.
4. Loss of taste from the posterior 1/3 of the tongue.
5. Glossopharyngeal neuralgia --> severe stabbing pain in the root of the tongue.
What is the vagal nerve?
A GSA, GVA, SVA, SVE, GVE nerve.
What is the role of the vagus nerve?
1. Mediates phonation, shallowing (along with IX, XI, XII).
2. Elevation of the palate, taste, and cutaneous sensation from the ear.
3. Innervation of the viscera of neck, thorax, and abdomen.
What is the anatomy of the vagus?
Exits the medulla from the postolivary sulcus --> exits the skull through the jugular foramen with CN IX and CN XI.
Discuss the GSA component of the vagus nerve.
1. Innervates infratentorial dura, external ear, external auditory meatus, and tympanic membrane.
2. Cell bodies in the superior (jugular) ganglion.
3. Projects its central processes to the spinal tract and nucleus of the trigeminal nerve.
Discuss the GVA component of the vagus.
1. Innervates the mucous membranes of the pharynx, larynx, esophagus, trachea, and thoracic and abdominal viscera (to the left colic flexure).
2. Cell bodies in the inferior (nodose) ganglion.
3. Projects its central processes to the solitary tract and nucleus.
Discuss the SVA component of the vagus.
1. Innervates taste buds in the epiglottic region.
2. Cell bodies in the inferior (nodose) ganglion.
3. Projects its central processes to the solitary tract and nucleus.
Discuss the SVE component of the vagus.
1. Innervates the pharyngeal (brachial) arch muscles of the larynx and pharynx, the striated muscle of the upper esophagus, the muscle of the uvula, and the levator veli palatini and palatoglossus muscles.
2. Receives SVE input from the cranial division of the spinal accessory nerve XI.
3. Arises from the nucleus ambiguus in the lateral medulla.
4. SVE component provides the efferent limb of the gag reflex.
Discuss the GVE component of the vagus.
1. Innervates viscera of the neck and the thoracic (heart) and abdominal cavities as far as the left colic flexure.
2. Preganglionic PNS neurons located in the dorsal motor nucleus of the medulla project to the terminal (intramural) ganglia of the visceral organs.
Lesions of the vagus can cause what?
1. Ipsilateral paralysis of the soft palate, pharynx, and larynx that leads to dysphonia (hoarseness), dyspnea, dysarthria, and dysphagia.
2. Loss of the gag (Palatal) reflex.
3. Anesthesia of the pharynx and larynx.
4. Aortic aneurysms and tumors --> compress the nerve.
5. Complete laryngeal paralysis --> rapidly fatal if it is bilateral (asphyxia).
6. PNS (vegetative) disturbances --> including bradycardia (irritative lesions, tachycardia (destructive lesion), and dilation of the stomach.
What 2 important reflexes are related to the vagus?
1. Oculocardiac reflex --> pressure on the eye slows the heart rate - (afferent limb) of CN V-1 and efferent limb of X.
2. Carotid sinus reflex --> pressure on the carotid sinus slows the heart - efferent limb of X.
What is the spinal accessory nerve?
An SVE nerve.
What does the XI nerve mediate?
Head and shoulder movement and innervates the laryngeal muscles.
What are the 2 divisions of the XI nerve?
1. Cranial division
2. Spinal division
What is the anatomy of the cranial division of the XI nerve?
Arises from the nucleus ambiguus of the medulla --> exits from the postolivary sulcus and joins the vagal nerve --> exits through the jugular foramen with IX and X.
What does the cranial division of the XI nerve innervate?
The intrinsic muscles of the larynx through the inferior (recurrent) laryngeal nerve, with the EXCEPTION of cricothyroid muscle.
What is the anatomy of the spinal division of the XI nerve?
1. Arises from the ventral horn of cervical segments C1 through C6.
2. Spinal roots exit the spinal cord laterally between the ventral and dorsal spinal roots.
3. Ascend through the foramen magnum.
4. Exit the skull through the jugular foramen.
What does the spinal division of the accessory nerve innervate?
1. Sternocleidomastoid muscle
2. Trapezius muscle
Lesions of the XI nerve can cause what?
1. Paralysis of the sternocleidomastoid --> difficulty turning the head to the contralateral side.
2. Paralysis of the trapezius muscle --> shoulder droop and inability to shrug the shoulder.
3. Paralysis and anesthesia of the larynx --> cranial root is involved.
What does the hypoglossal nerve mediate?
What is the anatomy of the XII nerve?
1. Arises from the hypoglossal nucleus of the medulla.
2. Exits the medulla in the preolivary sulcus.
3. Exits the skull through the hypoglossal canal.
What does the hypoglossal nerve innervate?
Extrinsic and intrinsic muscles of the tongue.