Cranial Nerves, Brain Stem Reflexes, and Brain Stem Disorders Flashcards
What is CN I?
Olfactory nerve
Most common causes of impaired smell?
Mucosal swelling and inflammation during sinusitis or a URI
Causes of permanent loss of smell?
Head trauma (olfactory nerve branches sheared or torn where they pass through the bony cribriform plate)
Tumor near the olfactory lobe at the skull base (eg, meningioma)
What is CN II?
Optic nerve
What is CN III?
Oculomotor nerve
What is CN IV?
Trochlear nerve
What is CN VI?
Abducens nerve
Function of the superior oblique?
Depresses and abducts the eye
Function of the inferior oblique?
Elevates and abducts the eye
Function of the superior rectus?
Elevates and adducts the eye
Function of the inferior rectus?
Depresses and adducts the eye
Function of the lateral rectus?
Abducts the eye
Function of the medial rectus?
Adducts the eye
Which muscles may be weak if elevation of the eye appears incomplete?
Superior rectus or inferior oblique (or both)
Which muscles may be weak if depression of the eye appears incomplete?
Superior oblique or inferior rectus (or both)
Presentation of complete oculomotor nerve lesion?
Complete ptosis (levator palpebrae superioris muscle paralysis)
Unopposed LR muscle action -> “down and out”
Pupil of the involved eye is large and unreactive to light directly or consensually (parasympathetic innervation of the pupil is impaired
What is unique about the trochlear nerve?
It is the only cranial nerve which exits the brain stem dorsally and decussates to innervate the contralateral superior oblique muscle
Presentation of a trochlear nerve lesion?
Impaired downward gaze when involved eye is adducted
Presentation of an abducens nerve lesion?
Impaired abduction of the affected eyeball due to ipsilateral LR muscle weakness
Define binocular diplopia.
Most common type of diplopia, resolves if the patient coveres either ey
Causes of binocular diplopia?
Lesions of CN III, IV, or VI, or their related EOMs; lesions involving the brain stem or cerebellar connections
Define monocular diplopia.
Relatively rare, occurs when looking with one eye alone
Causes of monocular diplopia?
May occur from a problem in the optical system of an eye, such as a dislocated lens or detached retina, or may be related to a psychiatric disorder
Define nystagmus.
Repetitive, oscillatory, jerky eye movements