testing cranial nerves Flashcards
what is the brainstem?
adjoins the brain to the spinal cord
continuous with spinal cord caudally
how many parts are there to the brainstem? what are they?
3:
1 - midbrain (most superior)
2 - pons
3 - medulla (most caudal - continuous with the spinal cord)
what is the role of the brainstem?
regulation of cardio-respiratory functions and maintaining consciousness
what runs through the brainstem?
ascending and descending fibres between the brain and rest of body
what is the brainstem the major location for?
majority of cranial nerve nuclei
what is nuclei?
collections of cell bodies of nerve fibres that make up the whole cranial nerve
how do you test for olfactory nerve (CN I)?
test 1 nostril at a time
smelling salts
how do you test for optic nerve (CN II)?
test 1 eye at a time
visual tets and pupils
how are optic nerves usually seen?
directly with fundoscopy (see the optic disc)
what is different about olfactory and optic nerve?
paired anterior extensions of the forebrain rather than ‘true’ cranial nerves
arise from forebrain
what is optic nerve part of?
the visual pathway
describe the visual pathway
retina of the eyes –> optic nerve –> optic chiasm (mixing of fibres) –> optic tract –> (passes through thalamus) –> optic projection fibres –> visual cortex
how do you test for oculomotor nerve (CN III)?
inspection of eyelid and pupils
eye movements
pupillary light reflexes
what is the course of oculomotor nerve?
runs through cavernous sinus after leaving midbrain, exits the cavernous sinus to enter the superior orbital fissure
what is the cavernous sinus?
full of venous plexus (interconnected veins), created by dura (periosteal and meningeal) - the 2 dura layers split creating the space called cavernous sinus
which structure runs through the cavernous sinus?
internal carotid artery
clinical: how can infection spread to the cavernous sinus? leading to?
spread from the face, into cavernous sinus (thrombosis), blocking cavernous sinus, leading to pressure increase and compressing the oculomotor nerve (3rd nerve palsy)
which lesions tend to involve the pupil? which do not?
compressive lesions involves pupil
vascular lesions spare pupil
how do you test for trochlear nerve? (CN IV)
eye movements
what is the route taken by the trochlear nerve (CN IV)?
longest intracranial route of all CNs
only CN to arise from DORSAL aspect of brainstem
through superior orbital fissure into the orbit
passes through the cavernous sinus
which 2 nerves arise from midbrain?
oculomotor
trochlear
how do you test for trigeminal nerve?
sensation to face (sensory)
motor: muscles of mastication
where do the 3 branches of the trigeminal nerve synapse before branching off?
trigeminal ganglion
which of the 3 branches of the trigeminal nerve are most superior (forehead)?
opthalmic (forehead) > maxillary (zygomatic bone - cheeks) > mandibular (most inferior - chin)
how do you test for abducens nerve (CN VI)?
eye movements
what is the route taken by the abducens nerve?
pons –> cavernous sinus –> superior orbital fissure –> orbit –> lateral rectus muscle
how come abducens nerve is easily stretched? (CN VI)
nerve can be easily stretched in raised ICP due to its running under the surface of the pons upwards towards cavernous sinus
how do you test for motor function of facial nerve (CN VII)?
muscles of facial expression
how do you test for special sensory of facial nerve (CN VII)?
anterior 2/3 tongue (taste)
what are the autonomic parasympathetic innervation of the facial nerve?
lacrimal and salivary glands
how do you test for vestibulocochlear nerve? (CN VIII)
hearing
Rinne’s and Weber’s test
what is the route taken by vestibulocochlear nerve (CN VIII)?
through internal acoustic meatus
through same hole as ear - petrous part of temporal bone
what is an acoustic neuroma also known as?
schwannoma
where do acoustic neuroma commonly occur?
in the cerebellopontine angle
what does an acoustic neuroma in the cerebellopontine angle lead to?
compromising cranial nerves V, VII, VIII
what are the 4 cranial nerves arising from pons?
trigeminal (V)
abducens (VI)
facial (VII)
vestibulocochlear (VIII)
how do you test for the glossopharyngeal nerve?
gag reflex (sensory limb)
taste not often formally tested
tested in conjunction with CN X
course of glossopharyngeal nerve?
medulla oblongata –> jugular foramen
function of carotid branch of glossopharyngeal nerve (IX)?
carries sensory (afferent signal) from carotid body (chemoreceptors - blood oxygen and CO2 levels) to cardiorespiratory centres in brain medulla
testing for vagus nerve (CN X)?
noting speech
swallow
cough
gag reflex (efferent limb)
route of vagus nerve (CN X)?
brainstem medulla –> jugular foramen
where does left recurrent laryngeal nerve travel under?
arch of aorta
where does right recurrent laryngeal nerve travel under?
right subclavian artery
how do you test for spinal accessory nerve (CN XI)?
shrug shoulders
turn head against resistance
route of spinal accessory nerve (CN XI)?
through jugular foramen
how do you test for hypoglossal nerve (XII)?
inspection and movement of the tongue
route of hypoglossal nerve (CN XII)?
medulla –> hypoglossal canal –> supply muscles of tongue
where does CN XII run?
runs medial to angle of mandible; crosses internal and external carotid arteries in neck
which are the 4 nerves from the medulla?
glossopharyngeal
vagus
accessory
hypoglossal
what are the 4 sections of cranial nerve origins on the brain and nerves in each section?
brain - I, II
midbrain - III, IV
pons - V, VI, VII, VIII
medulla - IX, X, XI, XII
