Cranial Nerves and Nuclei Flashcards
Where are the nuclei of each cranial nerve located and what is the exception?
The same rostral-caudal level as the nerve entry/exit point
Except the trigeminal nerve
Where does the optic nerve carry visual information to?
The superior colliculi and the pretectal area
What are the two functional components of CN III?
Somatic motor - extraocular muscles
Visceral motor - pupillary constrictor and ciliary muscles
Where is the oculomotor nucleus?
Medial tegmentum in the rostral midbrain at the level of the superior colliculi
What is the Edinger-Westphal nucleus and where is it located?
Preganglionic parasympthetic cell bodies for CN III
Located dorsally to the oculomotor nucleus
What is the pathway of the pupillary light reflex?
Retinal ganglion cell axons from both eyes carry information (via CN II) to the pretectal area on each side
The pretectal area projects bilaterally to the Edinger-Westphal nucleus with the contralateral projection traveling through the posterior commisure
Motor output is conveyed by the EW nucleus to the ciliary ganglion
What is the result of a unilateral deficit in the motor output of the pupillary light reflex?
An eye with impaired pupillary constriction in response to light stimulation of either eye
Describe the pupillary light reflex in horner’s syndrome.
Both direct and consensual pupillary constriction can be observed in response to light stimulation
The affected eye will have reduced and slowed dilation when the light is removed
Describe the pupillary light reflex with a unilateral afferent defect.
The affected eye will be unable to detect of conduct light sensation
Will cause loss of direct and consensual response when the affected eye is stimulated
When unaffected eye is stimulated, both direct and consensual responses will occur
What is benign essential anisocoria?
Pupils which have unequal diameters under all lighting conditions and no dilation lag when going from light to dark
Present in approximately 20% of the population
What is the result of a complete unilateral lesion of CN III?
Diplopia - loss of extraocular muscle tone
Ptosis - paralysis of levator palpebrae superior
Dilated pupil
What are false localizing signs?
Neurological signs that reflect dysfunction distant from the expected locus of injury
E.g. uncal herniation can cause a CN III nerve sign even though the site of hemorrhage is distant from CN III
Where are the trochlear nuclei?
Midbrain tegmentum, near the midline and just ventral to the periqueductal grey
More caudal, at the level of the inferior colliculi
What is the result of a lesion to the trochlear nerve?
Diplopia due to elevation and extortion of the affected eye
Patient may compensate by tucking chin and tilting head
What are the two functional components of the trigeminal nerve?
Somatic Sensory
Branchial Motor
Where is the chief sensory nucleus (V) and what kind of input does it receive?
The lateral pons, at the level that the trigeminal nerve fibers enter
Receives input from sensory fibers carrying discriminative touch, pressure, and vibration
(analogous to the medial lemniscus pathway
Where is the spinal trigeminal nucleus (V) and what kind of input does it receive?
Lateral, extends from the mid pons to the upper cervical spinal cord
Crude touch, pain, temperature
How is the face represented in the spinal trigeminal nucleus?
“Onion skin” -like pattern with concentric rings centered on the mouth
The mouth is represented most rostrally, and areas furthest from the mouth most caudally in the nucleus
Where is the mesencephalic trigeminal nucleus located and what kind of input does it receive?
Laterally, extends from mid-pons into the midbrain where it is located along the lateral edge of the periaqueductal grey
Propioception
