Clinical Correlates
extradural (epidural) hematoma
Name the cranial nerve that innervates the hypoglossus m
CN XII
Name the function of the ophthalmic branch of CN V
somatic afferent to superior/rostral face and scalp
This purely motor n. supplies the mm of the tongue, and damage to it causes the tongue to deviate towards the side of the lesion when protruded
hypoglossal n (CN XII)
This "H-shaped" junction on the side of the skull is where the frontal, parietal, sphenoid, and temporal bones meet. The middle meningeal a. lies deep to this structure
pterion
A pt presenting with "thunderclap headache" following the rupture of an a. on the brain's surface likely has this type of headache
subarachnoid hemorrhage
Name the action of the genioglossus m
Protrude the tongue
Name the CN that does taste to posterior 1/3 of tongue and visceral afferents to carotid body and carotid sinus
CN IX or glossopharyngeal
The cranial n. is unique because it originates from the spinal cord (C1-C5) and enters the skull through the foramen magnum
Spinal accessory n. (CN XI)
This layer of the scalp is considered the "danger zone" because it allows for the easy spread of infection or blood across the calvaria
loose areolar tissue
A pt with a unilateral lesion of the vagus n (CN X) will exhibit this characteristic sign when asked to say "ahhh". Describe why this sign occurs, and the neuroanatomy behind it
the levator veli palatini (CN X) normally elevates the soft palate; in a lesion, the m on the affected side is paralyzed
Name two functions of the paranasal sinuses
Decrease the weight of the head, humidify and heat inhaled air, increase resonance of speech, acts as a crumple zone to protect vital structures in the event of facial trauma
List the special visceral efferent function of CN x
mm of soft palate, pharynx, larynx, and esophagus
This n. is actually an extension of the brain's white matter and its dysfunction is tested using visual field exams
optic n (CN II)
This bone forms the "floor" of the orbit and is the most common bone to fracture in a "blowout" injury
maxilla
Why does a pt with an internal carotid a. aneurysm in the cavernous sinus specifically lose the ability to abduct the eye before other movements are affected
CN VI (abducens) travels directly through the center of the cavernous sinus next to the ICA, making it the most vulnerable to an expanding aneurysm
CN VII via chorda tympani to anterior 2/3, CN IX to posterior 1/3
List the 3 places CN V exits the cranium and which branch exits from each
V1 exits superior orbital fissure, V2 exits foramen rotundum, V3 exits foramen ovale
Explain the mechanical cause of "medial strabismus" following a lesion of which n
A CN VI lesion paralyzes the lateral rectus, leaving the medial rectus (innervated by CN III) unopposed
Explain the hemodynamic mechanism that allows a superficial skin infection in the "danger triangle" of the face to spread retrogradely into the cavernous sinus, potentially causing meninigitis
caused by the lack of the valves and presence of direct venous communications
Explain why an infection originating in the "danger triangle" of the face can result in complete ophthalmoplegia (inability to move the eye)
Infection spreads via the opthalmic vv to the cavernous sinus, causing thrombosis that compresses CN III, IV, and VI
Describe what happens if there is a right sided lesion to CN XII
A right side hypoglossal n lesion would lead to right sided tongue (genioglossus) weakness and atrophy, causing the tongue to deviate towards the side of the lesion
List the 5 major functions of CN VII
Taste to anterior 2/3 of tongue (SVA), parasympathetic to salivary glands (VE), parasympathetics to lacrimal gland, nasal cavity, and palate (VE), sensory to posterior ear (SA), motor to mm of facial expression, stylohyoid, posterior digastric, and stapedius mm (SVE)
In a complete CN III palsy, why is the pupil "fixed and dilated" while the eye is positioned "down and out"
the "down and out" position is caused by the unopposed action of the superior oblique (CN IV) and lateral rectus (CN VI), while the dilation results from the loss of parasympathetic fibers that normally constrict the pupil
A pt with a venous thrombosis presents an initial loss of lateral eye movement, and impaired facial sensation over the forehead and cheek remains during the late stages. Why is this occurring and where is the thrombosis occuring
cavernous sinus thrombosis and impingement of CN VI, V1 & V2