Cranial Nerves (Lecture: Apr 23, 2010)

Front 1

Ciliary muscle

Back 1

Parasympathetic innervation by the Edinger-Westphal nucleus.

- Contraction = reduced tension on the lens, producing a more spherical shape for focusing on near objects. (accommodation)

Front 2

Sphincter muscles of the iris

Back 2

Parasympathetic innervation by Edinger-Westphal nucleus and fibers of CN III (medial rectus- eyes move inward when focusing on near).

Contract in response to light or near response.

Lesion of CN III = dilated pupil (mydriasis)

Front 3

Muller's muscle

Back 3

aka Tarsal

2' Elevator of the eyelid, innervated by sympathetic ANS.

Interruption of fibers will cause a mild ptosis as part of Horner's Sx.

Front 4

Levator Palpebrae Superioris

Back 4

Major elevator of the eyelid.

Lesions of CN III will cause major ptosis.

Front 5

CN III Palsy

Back 5

Severe ptosis of affected eye.

Eye will appear slightly down and out b/c lateral rectus and superior oblique are still working.

Front 6

Trochlear nucleus

Back 6

Innervates the superior oblique muscle. Lies contralateral to the innervated muscle and is the only CN to exit dorsally.

eg. The left trochlear nucleus sends a nerve exiting the brainstem posteriorly on the left, it completely crosses to the right, and shoots forward through the superior orbital fissure and innervates the right superior oblique.

Front 7

CN IV Palsy

Back 7

At rest the affected eye deviates upward.

**Differentiate from a skew deviation (supranuclear) b/c when the eye is tested individually, it shows weakness when trying to move down and in.

Front 8

Compensation for diplopia due to strabismus

Back 8

Pt will tilt away from the higher eye to reduce double vision. Tilting toward the higher eye will make it worse.

Front 9

CN VI Palsy

Back 9

When pt is attempting to look straight ahead, affected eye will be adducted b/c medial rectus is unopposed.

Front 10

Looking to the left. Pathway beginning w/ Rt FEF

Back 10

Rt Frontal eye field (FEF) -->
Projects down in the anterior limb of the internal capsule -->
Crosses @ the midbrain pontine junction-->
Innervates contralateral paramedian pontine reticular formation (PPRF) which contains burse neurons -->
innervates CN VI (2 neurons) -->

- Neuron #1 directly innervates ipsilateral LR (left)

- Neuron #2 is an excitatory interneuron that decussates and ascends in the contralateral MLF to synapse on MR nucleus of CN III --> CN III then innervates right MR

Front 11

Right MLF lesion

Back 11

INO- Internuclear Ophthalmoparesis.

Internuclear b/c between CN VI --> CN III

The MLF lesion is disrupting communication between Left CN VI nucleus and right CN III nucleus.

When trying to look left, the left abducts, but the right MR isn't functioning and the right eye doesn't adduct or is weakened.

Front 12

Pupillary light reflex

Back 12

Light input from the retina is directed from the optic nerves to the pretectal area

- Paired pretectal nuclei receive direct photic input from the retina along with input from the
contralateral pretectal nucleus via the posterior commissure

Paired pretectal nuclei output --> to both ipsi- & contralateral E-W nuclei

- Both E-W nuclei project parasympathetics to the ciliary ganglion along the CN III

- Post-ganglionic parasympathetics (short ciliary) project to --> sphincter muscle of the iris --> cause contraction and innervation of the ciliary muscle, allowing the lens to round and focus on near objects

**Good overall test for integrity of the midbrain

Front 13

Argyll-Robertson pupil

Back 13

Small bilateral pupils that constrict poorly to light, but may constrict with near stimulus.

Most commonly associated w/ CNS syphilis.

Can be unilateral.

Front 14

Near triad

Back 14

Reflex function to achieve near vision. Composed of:

1. Convergence of the eyes (co-contraction of both MR to align eyes w/ near object)

2. Rounding of the lens (Contraction of the ciliary muscle to relax tension on the lens, allowing it to round and increase optical power)

3. Constriction of the pupil (Improvement of vision through limiting entrance of stray light)

Front 15

Sympathetic input to the pupil

Back 15

Sympathetic neurons start in hypothalamus and descend through the brainstem and cervical spinal cord
• They synapse in the interomediolateral cell column, then exit the cord and ascend and travel in the sympathetic chain
• They synapse again in the superior cervical ganglion
Post-ganglionic sympathetic fibers then ascend
surrounding the internal carotid artery to the
level of the cavernous sinus
• Functions: innervate a pupillary dilator m. (radially oriented), innervate tarsal m. (Muller’s), & contributes sudomotor (sweating) control over ½ the face

Front 16

CN V

Back 16

sensory and motor
• Supplies the major sensory input over the face and external ear
– Sensation over the external ear and canal is also shared by
CN VII, IX & X
• Carries proprioceptive fibers from the joint capsule of the jaw, muscles of mastication, and teeth
• Carries motor fibers to the muscles of mastication and tensor tympani in middle ear, and tensor veli palatini.

Front 17

Corneal reflex

Back 17

Stimulating corneal edge w/ cotton wisp --> produce ipsi- (direct) & contralateral (consensual) corneal reflex in intact trigeminal sensation
• unilateral lesion: reflex lost due to lack of afferent input from CN V
– Stimulate the nx side: still produce bilateral lid closure as this is mediated efferently by CN VII

**Good general test of pontine function.

Front 18

CN VII

Back 18

sensory and motor
• 3 nuclei
– motor nucleus of VII
• Innervates: muscles of facial expression, orbicularis oculi
• Sends fibers to the stapedius muscle in the middle ear
– Lesion = Hyperacusis
– Salivatory (superior) nucleus
• Innervate the lacrimal, submandibular, & sublingual glands
– nucleus solitarius
• Taste to anterior 2/3 of tongue

Front 19

Lesions of CN VII

Back 19

Upper (cortical) lesions:
Facial droop of the lower face contralateral to the lesion.

- b/c ventral motor nucleus innervating the upper face receives bilateral input, and dorsal mn (innervating lower face) only gets contralateral input.

Lower lesions involving the motor nucleus or root:
Bell's Palsy- flaccid paralysis of the upper & lower facial muscles (excluding muscles of mastication), inability to close the ipsilateral eyelid, wrinkle, forehead, show teeth or smile ipsilateral to the lesion. Also hyperacusis due to stapedius m. interruption.

Front 20

CN IX

Back 20

Glossopharyngeal:
Mixed sensory and motor

• 3 nuclei
– Nucleus Ambiguus
• Motor fibers innervate stylopharyngeus, raises and dilates pharynx, participates w/ CN X & XI for swallowing

– Salivatory (inferior) nucleus
• Supply the parotid gland for salivation

- Nucleus Solitarius
• Sensation, including pain, temp and touch from pharynx and posterior tongue
• Afferent limb of gag reflex
• ***Blood pressure info relayed from carotid sinus
• Taste sensation: posterior 1/3 of the tongue
– gustatory nucleus
• Pain sensation from external auditory meatus

Front 21

CN X

Back 21

Vagus
Mixed sensory & motor
• nucleus ambiguus
– Motor to pharynx & larynx

• dorsal efferent nucleus
– Motor to thoracic & abdominal viscera

• nucleus solitarius
– Sensory from viscera and pharynx, swallowing reflex
– Taste from epiglottis

• Pain sensation from external auditory meatus

Front 22

CN XI

Back 22

Accessory
Primarily motor nerve

• nucleus ambiguus
– Motor to pharynx and larynx

• dorsal efferent nucleus
– Motor to thoracic & abdominal viscera

• spinal gray
– Motor to SCM & trapezius muscles
– Turns head in opposite direction, shrugs shoulder

Front 23

CN XII

Back 23

Hypoglossal
Primarily a motor nerve
• The arrangement of muscles in the tongue allows for tongue protrusion when equal contraction occurs bilaterally

• Paralysis of the muscles on one side causes tongue to deviate to that same side when pt attempts to protrude it

Front 24

CN XII Lesions

Back 24

Since the nucleus and nerve supply the muscles ipsilaterally, a nucleus or nerve lesion will be followed by deviation of the tongue to the ipsilateral side
• A lower motor neuron lesion of CN XII will “lick” the lesion.

• Supranuclear derived tongue weakness, basically an UMN lesion, would be produced by a lesion in the opposite hemisphere of the brain or higher
in the brainstem, so the tongue would deviate away from the lesion.

Front 25

Palate and tongue movements

Back 25

Left palate pulls left, right palate pulls right.

Left tongue moves it to right, right tongue moves it to left.

Front 26

Possible cause of CN III palsy

Back 26

aneurysm of the PCA of the circle of Willis

Front 27

Possible cause of CN VI palsy

Back 27

increased intracranial pressure due to the long intracranial course the nerve takes over several bony prominences

Front 28

CN V testing

Back 28

Motor function:
judge jaw closure strength (palpate masseters and temporalis ) and symmetry of jaw opening.

Sensory function:
check all 3 divisions for fine touch (chief sensory nucleus) and pain (spinal tract and nucleus of CN V)

Front 29

CN VIII hearing testing

Back 29

Gross hearing test for threshold:
rub fingers together softly next to each ear

Determine asymmetry and neural vs conductive defect:
Weber and Rinne tests

Front 30

Gag reflex

Back 30

Mediated by CN IX and CN X

**Good test for integrity of the medulla

- For intubated patients, the cough reflex elicited by suctioning down the endotracheal tube can substitute.