I & III
Why does a fracture of the cribriform plate potentially lead to anosmia?
Because olfactory nerve fibers pass through the cribriform foramina and can be torn when the plate fractures.
What is the primary action of the superior oblique muscle?
Intorsion and depression of the eye in an adducted position.
Where is the nucleus of the abducent nerve located?
In the pons
Where is the nucleus of the hypoglossal nerve located
Medulla oblongata
Why does an oculomotor nerve palsy lead to ptosis?
Because the levator palpebrae superioris loses innervation
Where is nucleus of the trochlear nerve located?
In the midbrain at the level of the inferior colliculus
What are the nuclei of the accessory nerve and where they are located?
Nucleus ambiguus (medulla oblongata)
Spinal accessory nuclei (spinal cord, 6 upper segments)
CN XII innervates all tongue muscles except which one?
Palatoglossus (vagus nerve).
Why is the pupil often involved early in compressive lesions of CN III (e.g., aneurysm)?
The parasympathetic fibers run superficially on the nerve and are compressed first.
Describe the pathway the trochlear nerve takes
Motor neuron leaves from the posterior surface of the midbrain. Turns anteriorly and runs on the lateral wall of the cavernous sinus. Enters the orbit via the superior orbital fissure. Innervates the superior oblique muscle
Why does CN XI injury cause difficulty turning the head to the opposite side?
SCM rotates the head to the opposite side; loss of SCM weakens this movement.
What happens to the tongue on protrusion in unilateral CN XII damage?
It deviates toward the side of the lesion
A patient reports loss of smell after a car accident. They can still taste sweet and salty flavors but cannot perceive flavors of food. CT shows no skull base fracture. What is the most likely mechanism of CN I injury?
Shearing/stretching of olfactory fila due to sudden brain movement (coup–contrecoup), damaging the nerve without bone fracture.
After mild head trauma, a patient complains of double vision especially when reading. They tilt their head to the right. The left eye shows difficulty depressing when adducted. Which nerve is affected?
Left trochlear nerve palsy
Describe the pathway the accessory nerve takes along with its external and internal branches
Cranial root (from nucleus ambiguus) exits the brainstem through the retro-olivary groove. Spinal root (from spinal accessory nucleus) goes up, enters the cranium through foramen magnum, and fuses with the cranial root. Trunk of the accessory nerve goes through the jugular foramen and splits into an internal and an external branch. External -> sternocleidomastoid and trapezius & Internal -> levator veli palatini, palatoglossus, palatopharyngeus, musculus uvulae, lateral crico-arytenoid, vocalis, thyro-arytenoid
How could a carotid endarterectomy injure the hypoglossal nerve?
CN XII crosses near the carotid bifurcation, making it vulnerable during vascular surgery
A patient shows: eye deviated “down and out” ;
dilated pupil ; drooping eyelid. MRI reveals a posterior communicating artery aneurysm. Which fiber group explains the dilated pupil?
Damaged superficial parasympathetic fibers of CN III supplying the sphincter pupillae.
Why is vertical diplopia worse when a CN IV–lesioned patient walks downstairs?
The superior oblique normally depresses the adducted eye; without it, the eyes misalign during downward gaze → diplopia
A patient with suspected cavernous sinus thrombosis shows impaired eye abduction on the right. Other ocular movements are intact. Pupils normal. Which cranial nerve is isolated?
Right abducens nerve (CN VI)
A patient presents with slurred speech and difficulty articulating lingual consonants. On exam, the tongue shows muscle atrophy and fasciculations on the right. Where is the lesion?
Right hypoglossal nerve lower motor neuron lesion.