Cranial Nerves Flashcards
,What are the 3 major cranial nerves serving special sense organ?
I- olfactor
II- Optic
VIII - Vestibulocochlear
They develop in part from epidermal neurogenic placodes
are not parts of other cranial sensory-motor nerve
What are the 4 somatic motor nerves that move the eye and tongue?
III - Oculomotor (exits from venral midbrain)
IV - Trochlear (exits dorsally and decussates)
VI - Abducens (emerges caudal to VII)
XII - Hypoglossal
- have no affiliated sensory ganglia, thus they have only efferent components
- sensory fibers in the peripheral parts of these nerves are “hitch-hikers” from nearby mixed nerves
- are more (XII, VI, III) or less (IV) comparable to ventral roots of spinal nerves
What are the 4 mixed branchial nerves that move and sense jaws, face, pharynx, and larynx?
V - trigeminal
VII - Facial
IX - Glossopharyngeal
X - Vagus
This nerve is the only special motor nerve that is cranial only in a roundabout way and innervates the sternocleidomastoid and trapezius muscle
XI - Spinal Accessory
What is the Otic Placode?
auditory and vestibular sensory haircells and ganglion cells
Involves Cranial nerve VIII
What is the Optic Placode?
Lens
Involces CN II
WHat is the olfactory placode?
Central Projecting sensory cells
This structure is located at the diencephalon wall. What is it and what does it contain?
This is the Optic Vesicle
contain sensory cells and ganglion cells
What does CN I (Olfactory Nerve) consist of?
consists of the central-projecting axons of bipolar olfactory sensory neurons (= olfactory receptor cells) situated in the olfactory epithelium.
The axons collect as fine bundles that traverse the olfactory foramina in the cribriform plate of the ethmoid bone to reach the olfactory bulbswhere they synapse on second order olfactory neurons.
This “Cranial Nerve” is actually a CNS tract, not peripheral nerve and covered by meningies. Located in the nasal cavity?
CN I (Olfactory)
It is covered with dura, arachnoids, and pia mater
Patient comes in reporting that he has difficulty smelling after doing some drugs. What is one possible diagnosis that can be considered?
Anosmia (loss of sense of smell)
This occurs when there is Damage to the olfactory sensory epithelium or disruption of the fibers at the cribiformplate
To exam the function of CN I you will expose the patient to test odorants
What is the path of the Optic nerve (CN II)
begin at the retina and extend to the optic chiasma, where approximately half of the optic fibers cross to the other side. The fibers continue as the optic tracts and most of them terminate by synapsing in the lateral geniculate nuclei of the thalamus.
What is different about the Optic nerve compared to some other cranial nerves?
The retina and optic nerves arise from the walls of the embryonic diencephalon. Accordingly, the optic nerves are brain tracts, not peripheral nerves.
Most of the axons that make up the optic nerve come from where? axons of retinal ganglion cells.
axons of retinal ganglion cells.
This nerve is actually made of two nerves. It enters the brain at the pontomedullary junction, just dorsal to the root of the VIIth nerve.
CN: VIII
(Vestibulocochlear Nerve)
The VIIIth nerve fibers pass peripherally to into the _____, accompanied by the VIIth nerve, via the __________.
Temporal bone
Internal Acoustic meatus
What does the cochlear nerve (portion of CN VIII) comprise of?
afferent axonal processes of cells in the spiral ganglion which innervate the auditory haircells of the spiral organ(Organ of Corti)
as well as,
efferent axons of central neurons located in the superior olivary/periolivarynuclei that form the olivocochlear bundle
The Vestibular nerve (part of CN VIII) comprises of?
afferentaxonal processes of cells in the vestibular ganglion (Scarpa’s)which innervate:
vestibular hair cells of the ampullae of the semicircular canals, sensing angular acceleration
vestibular hair cells of the maculae of the saccular and utricular otoliths, sensing linear acceleration
as well as,
efferent axons of central neurons located in two vestibular efferent nuclei
Where do the afferent fibers of the cochlear nerve project?
project to the lowest order brainstem auditory centers, the dorsal and ventral cochlear nuclei
The vestibular nerve afferent fibers project to where?
to the vestibular nuclei (superior, medial, lateral and descending) and to the vestibulocerebellum
The vestibular nuclei connect to what other structures besides the Vestibular nerve afferetn fibers?
connect with brainstem, spinal and cerebellar centers involved in postural and gaze control (among others)
MLF and Vestibulospinal tracts are what?
Major central vestibular pathways
They lead to extrocular and cervical motor nuclie controlling eye and head movements
How do you test Vestibular function?
Routine auditory test (done with a tuning fork)
or
asking the patient to walk a straight line
or
observing eye movements during introduction of cool or warm water into the external ear canal.
What is the Caloric Test?
Observing eye movement during introduction of cool/warm water.
induces alternating eye movements (Nystagmus) by generating convection in the endolymph of the horizontal semicircular canal. The caloric vestibulo-ocular reflex is especially useful in testing brainstem function in comatose patients.
What is a complication of the CN III?
This is the oculomotor nerve and it also has parasympathetic components - to smooth muscle of the eye
What are the Embryonic Origins of Striated Cranial Muscles Innervated by Somatomotor Cranial Nerves III, IV, VI and XII?
- Dorsal head mesoderm in front of the ear (pro-otic) produces the extraocular muscles, innervated by cranial nerves III, IV and VI
- Occipital somites 1-4 give rise to a migratory stream of myocytes that travel ventrally into the floor of the oral-pharyngeal region to produce the tongue muscles innervated by CN XII.
Which ganglion does CN III innervate?
parasympathetic ciliary ganglion.
Side note: Innervates most of the striated and smooth muscles of the eye, thus has both somatic and visceral (parasympathetic) motor fibers
The parasympathetic ciliary ganglion and the occular smooth muscles innervated by CN III are derived from what?
Neural crest
The CN III roots emerge from where?
emerge from the ventral midbrain, on either side of the posterior perforated substance, and between the mamillarybodies and the pontine fibers
Edinger-Westphal Nucleus* (GVE)
Preganglionic parasympathetic neurons in the Edinger-Westphal Nucleus innervate post-ganglionicneurons in the ciliary ganglion
Oculomotor Nucleus (GSE)
Motor neurons innervate:
4 striated muscles that move the eye
- superior rectus
- inferior rectus
- medial rectus
- inferior oblique
1 striated muscle that elevates the upper eyelid
-levator palpebrae superioris
Ciliary ganglion neurons innervate 2 smooth muscles in the eye?
- thepupillarysphincter musclewhich constricts the pupil (red)
- theciliary muscle which regulates the curvature of the lens (blue)
What are the characteristics signs of a unilateral c=occulomotor nerve palsy?
“down out syndrome”
Ptosis (drooping) of the upper eyelid, due to lack of action of the levatorpalpebrae superioris
Dilation of the pupil due to loss of sphincter pupillae function
Depressed and abducted resting eye position due to the IVthand VIthnerve eye muscles acting unopposed
CN IV (Trochlear) innervates only what?
ONLY the superior oblique muscle
(contains somatic motor fibers)
The trochlear nerve received that name because the superior oblique muscle passes through a pulley (L., trochlea) before inserting on the globe.
What is the direction of the Trochlear nerve roots?
roots exit dorsallyat the midbrain/hindbrain junction and cross to the opposite side (right to left, left to right)
Where is the trpchlear nuclei located?
trochlear nuclei are located near the midline beneath the most superior part of the fourth ventricle
(green arrow)
*look at picture*
What are the two main actions of the superior oblique muscle?
Depresses and medially rotate (in-tort) the eye
Trochlear Nerve palsy
Most notable effect of loss of SO muscle function due to trochlear nerve palsy is a persistent laterally rotated eye posiition (ex-torsion)
The laterally rotated eye position may be compensated for by tilting the head away from the direction of the non-functional SO mucle.
This nerve only innervates the lateri rectus muscle, which Abducts the eye
CN VI (Abducent nerve)
Contains only somatic sensory fibers
Where does the root of CN VI emerge from?
emerge near ventral midline at ponto-medullary junction
Loss of function of the abducens nerve leads to what?
It causes the eye to remain adducted during forward gaze (i.e. inability to abduct)
If this occurs bilaterally = crossed eye
What exactly has many oppourtunities to disrupt Cranial Nerve II, III, IV, and VI?
The Cavernous Sinus
Because of the close proximity of the pituitary and internal carotid to the optic chiasma and the nerves to extraocular muscles (III, IV, VI), visual and eye movement deficits are often involved in cases of pituitary tumors, internal carotid anurysmsor thrombosis in the cavernous sinus.
What is Cranial nerve XII
This is the hypoglossal nerver
Somatomotor innervation of the tongue muscles
This nuclei is located in the medulla oblangata, just below the ventricle
Hypoglossal motor nucleus
What is the direction of the Hypoglossal nerve?
The nerve exits the skull via the hypoglossal foramen, between the jugular foramen and the occipital condyle
The rootlets exit the brain over a long distance along the groove separating the pyramids and inferior olive. They are followed by the rootlets of C1
The motor fibers of C1 that travel with CN XII enter where together?
the ansacervicalis (blue)
Where they innervate the thyrohyoid (red) and geniohyoid (green) muscles
What are the muscle that are innervated by the hypoglossal nerve?
Genioglossus m.
Hyoglossus m.
Styloglossus m.
Chondroglossus m.
intrinsic tongue muscles
(but not the palatoglossus m., by CN X)
This test is used for?
Patient protrudes the tongue, press left and reight on the cheek against the tester’s finger pressure and make fast movements by saying “la la la”
To test the hypoglossal nerve
When is unilateral hypoglossal weakness more evident?
During tongue protrusion
the tongue deviates to the weak side
Branchiomotor cranial nerves include
V, VII, IX, X, XI
Mixed nerves each with one or more sensory ganglia