Chapter 3 Flashcards
three major subdivisions of the brainstem
1) medulla
2) pons
3) midbrain
cranial nerves
twelve; attached to ventral surface of brain
- most serve sensory and motor functions of head and neck region
- responsible for facial displays of emotion
four main functions of the cranial nerves
sensory, motor, special sensory/motor, parasympathic
cranial nerves at the medulla
cranial nerves 12, 11, 10, 9, and 5
medulla
the caudal medulla resembles the rostral spinal cord in structure and function and contains the same pathways and sensory and motor nuclei
cranial nerve I
olfactory
cranial nerve II
optic
cranial nerve III
oculomotor
cranial nerve IV
trochlear
cranial nerve V
trigeminal
cranial nerve VI
abducens
cranial nerve VII
facial
cranial nerve VIII
vestibulocochlear
cranial nerve IX
glossopharyngeal
cranial nerve X
vagus
cranial nerve XI
acessory
cranial nerve XII
hypoglossal
trigeminal nerve (cranial nerve V)
- very long nucleus divided into several parts that extends down as low as the lower medulla and goes up as high as the midbrain
- motor from motor nucleus of trigeminal to muscles of mastication
- sensory divided into three parts: pain and temperature, tactile, position sense
three parts of the trigeminal nerve (cranial nerve V)
mesencephalic trigeminal nucleus, pontine trigeminal nucleus, spinal trigeminal nucleus
sensory functions of the trigeminal nerve (cranial nerve V)
- pain and temperature: from face to caudal parts of nucleus of spinal tract (ST)
- tactile: two-point discimination to chief (main) sensory nucleus; touch-pressure to rostral part of nucleus of ST
- position sense: from jaw muscles to mesencephalic nucleus
three divisions (branches) of the trigeminal nerve carry the sensations from the face to the brain
- opthalmic (V1)
- maxillary (V2)
- mandibular (V3)
opthalmic (V1) branch of the trigeminal nerve
includes the cornea
maxillary (V2) branch of the trigeminal nerve
includes the nose, upper teeth, and roof of pharynx
mandibular (V3) branch of the trigeminal nerve
includes inside mouth, lower teeth, anterior two-thirds of tongue
muscles of mastication
responsible for mostly jaw movement; chewing
central pathways for the trigeminal nerve (carries sensory information)
- pain fibers from spinal nucleus travel close to fibers from the spinothalamic tract (STT)
- tactile and proprioception fibers from main sensory and mesencephalic nucleus travel close to fibers from medial lemniscus (ML)
- all then reach the thalamus
axons from medial lemniscus, trigeminal tracts, and spinothalamic tract all terminate in…
ventral posterior nuclei of thalamus (VPI for spinal; VPm for trigeminal)
- from the thalamus, axons ascned in posterior limb of internal capsule and terminate in somatosensory cortex
trigeminal motor nucleus
corticobulbar fibers descend from motor cortex through internal capsule, both crossed and uncrossed, and then synapse in the motor nucleus of V (corticobulbar tract)
- efferents of motor nucleus of trigeminal are to muscles of mastication
sensory deficits of trigeminal nerve
- loss of pain and temperature on the face (ipsilateral)
- loss of touch-pressure on the face (ipsilateral)
- loss of position sense (proprioception) in jaw (ipsilateral)
- loss of corneal reflex
tests for sensory deficits of trigeminal nerve
- pin pricks, vibration, light touch on various areas of the face
- moving jaws and asking for direction of movement
testing loss of corneal reflex due to deficit in trigeminal nerve
- touch the edge of the cornea with a wisp of cotton; bot eyes should close, i.e., blink
- if the left side of the trigeminal nerve is damaged, hen touching the left eye’s cornea will not cause a blink; patient will not feel the touch; however, when you touch the right eye, both eyes will blink normally
motor deficits of trigeminal nerve
ipsilateral signs of muscle paralysis in the jaw (the jaw deviates to the side of the lesion)
test for motor deficits of trigeminal nerve
- ask the patient to bite down hard (you should see the masseter [jaw] muscle contract)
- open the mouth and move the jaw to one side, then move the jaw back to the center against resistance
- lesions involving the motor nucleus or the motor root of the trigeminal nerve result in ipsilateral muscle paralysis, causing the jaw to deviate to the side of the lesion
hypoglossal nerve (cranial nerve 12)
strictly a motor nerve (no other components) that supplies muscles of the tongue
- corticobulbar fibers to the hypoglossal nucleus extend from the motor cortex to the hypoglossal nucleus in the medulla
- efferent fibers from the hypoglossal nucleus innervate the muscles of the tongue (each side controls half of the tongue muscles, i.e., the ipsilateral side)
lesions in the hypoglossal nucleus/nerve
result in ipsilateral paralysis and atrophy of the tongue
- signs: the tongue deviates to the side of the lesion when protruded
two divisions of the accessory nerve (cranial nerve 11)
cranial part, spinal part
cranial part of the accessory nerve (cranial nerve 11)
motor; arises from the nucleus ambiguus and functionally blends with the motor functions of cranial nerve 9 and cranial nerve 10 (larynx movement)
spinal part of the accessory nerve (cranial nerve 11)
arises from the accessory nucleus in the lower medulla, supplies two muscles in the neck: the trapezius and sternocleidomastoid
testing cranial nerve 11
- primarily focuses on the spinal part and its innervation of the shoulder muscles
- place your hands on the patient’s shoulders and press down as the patient elevates of shrugs their shoulders, then retracts them
- place your right palm on the lateral side of the patient’s left cheek; ask the patient to turn their head to the left, resisting the pressure you apply in the opposite direction
- accessory nucleus damage would be permanent
four functional components of the vagus nerve (cranial nerve 10)
motor, parasympathetic, sensory, taste
motor component of the vagus nerve (cranial nerve 10)
from the nucleus ambiguus (NA) to the muscles of the pharynx and larynx
- efferents from nucleus ambiguus (NA) that exit and travel along the fibers of cranial nerves 9 and 10 and cranial portion of cranial 11 are to: muscles of soft palate, pharynx, larynx
parasympathetic component of the vagus nerve (cranial nerve 10)
from the dorsal motor nucleus to the visceral organs in the thorax and abdomen
sensory component of the vagus nerve (cranial nerve 10)
from the palate, pharynx, and larynx, as well as a small area of the external ear
taste component of the vagus nerve (cranial nerve 10)
from the epiglottis and the posterior tongue
lesions in nucleus ambiguus
ipsilateral paralysis of pharyngeal and laryngeal muscles
- signs: hoarseness, difficulty swallowing (dysphagia), difficulties in articulation (dysarthria)
dysphagia
difficulty swallowing
dysarthria
difficulties in articulation
four functional components of glossopharyngeal nerve (cranial nerve 9)
motor, parasympathetic, sensory, taste
motor component of glossopharyngeal nerve (cranial nerve 9)
from the nucleus ambiguus to the muscles of the pharynx and larynx
parasympathetic component of glossopharyngeal nerve (cranial nerve 9)
from the inferior salivatory nucleus to the salivary (parotid) gland
sensory component of glossopharyngeal nerve (cranial nerve 9)
from the tonsillar area and upper pharynx; from the posterior one-third of the tongue
taste component of glossopharyngeal nerve (cranial nerve 9)
from the posterior one-third of the tongue to the nucleus of the solitary tract
testing of motor functions of cranial nerves 9 and 10
- hoarse voice
- difficulty swallowing
- check for palate or uvula displacement
- ask the patient to say “Ah” and observe for symmetrical soft palate movement
testing of sensory and motor functions of cranial nerves 9 and 10
test gag reflex
- touching one side of the pharyngeal wall in a normal individual elicits a bilateral response
testing of parasympathetic function of cranial nerve 10 (vagus)
assess vagal tone by measuring the ECG
testing of parasympathetic function of cranial nerve 9 (glossopharyngeal)
evaluate salivation from the parotid gland
testing of taste function of cranial nerves 9 and 10
test taste sensation on the posterior one-third of the tongue
medial medullary syndrome (anterior bulbar syndrome)
- causes: occlusion of the anterior spinal artery (ASA) or branches of the vertebral artery that supply the ASA
- structures involved: ML, pyramid, hypoglossal nucleus and nerve
- clinical signs: contralateral loss of position sense and discriminative touch with a positive Romberg sign; contralateral hemiparesis (upper motor neuron [UMN] type); ipsilateral paralysis of half of the tongue –> lower motor neuron (LMN) signs: paralysis, atrophy, and fibrillation; deviation of the tongue to the side of the lesion upon. protrusion
example of seeing pyramidal and hypoglossal deficits in a patient
- contralateral hempiparesis (UMN type) –> slight weakness in the left arm and leg; when both arms are outstretched, the left arm drifts downward and rotates inward (pronator drift)
- deviation of the tongue to the side of the lesion upon protrusion: over time, atrophy and fibrillation may become evident (i.e., LMN signs)
lateral medullary syndrome (Wallenberg’s syndrome)
- causes: occlusion of the posterior inferior cerebellar artery (PICA) (less frequently) or the vertebral artery (more frequently)
- structures involved: spinal nucleus of V and its tract, spinothalamic tract, nucleus ambiguus, descending autonomic fibers from the hyothalamus
- the lesion can be larger and include base of the interior cerebellar peduncle, vestibular nuclei
clinical signs of lateral medullary syndrome
- spinal nucleus of V/tract –> ipsilateral loss of pain and temperature sensation over the face
- spinothalamic tract –> contralateral loss of pain and temjperature sensation over the body
- nucleus ambiguus –> loss of gag reflex, dysphagia, hoarseness, and dysarthria
- descending autonomic fibers from the hypothalamus –> horner’s syndrome on the ipsilatera side: miosis (small pupil), pseudoptosis (slight drooping of the eyelid), anhidrosis (absence of sweating on the face), enophthalmos (slight retraction of the eyeball)
- base of the inferior cerebellar peduncle: ataxia, hypotonia, asynergia, nystagmus, dysmetria, tremor (intentional, as opposed to resting)
- vestibular nuclei: vertigo/vomiting, ataxia, nystagmus/nausea
nuclei
area where neuronal tracts of similar function come together to synapse
two major regions of the pons
tegmentum, basis pontis
tegmentum of the pons
dorsally located, containing cranial nerve nuclei and sensory tracts
basis pontis of the pons
ventrally located, containing descending pathways, pontine nuclei, and motor tracts
cranial nerves that arise in the pons
trigeminal (5), abducens (6), facial (7), vestibulocochlear (8) (lies at the medulla/pons border)
two sensory components of vestibulocochlear nerve (cranial nerve 8)
audition (hearing) through the cochlear part of the nerve; vestibular (balance) through the vestibular component of the nerve
auditory pathways of the vestibulocochlear nerve (cranial nerve 8)
- one cranial nerve mediates hearing: the cochlear component of VIII
- cochlear nerve projects to cochlear nuclei in brainstem (near vestibular nuclei)
- from cochlear nuclei: multi-synaptic, both crossed and uncrossed pathways, to the auditory cortex of the brain
- clinical significance of this arrangement: loss of hearing can only result fro damage to the ear or the cochlear nerve itself; any damage within the brain itself does not lead to hearing loss (can cause disturbances however) because of the bilateral representation
vestibular pathways of the vestibulocochlear nerve (cranial nerve 8)
- from labyrinth of inner ear to vestibular component of cranial nerve 8 to vestibular nuclei
- from the vestibular nuclei, there are three central pathways
- functions: keep eyes stable and on target even when the body is moving (i.e., maintain oculovestibular balance)
three central pathways from the vestibular nuclei
- to cerebellum
- to spinal cord
- to medial longitudinal fasciculus (MLF): this connects the cranial nerves that control eye movement to spinal tracts supplying muscles in the neck
vestibular labyrinth
- three semicircular canals
- responsible for head movement
clinical testing of cranial nerve 8
- usually testing is for auditory nerve (hearing)
- vestibular test is done only when patient complains of dizziness
- usually, a vibrating fork is used and the patient is asked whether they can hear it, differentiate intensities (loudness), identify the source of the sound, etc.
cerebellopontine angle tumor (acoustic neuroma)
- originates in Schwann cells of the sheath surrounding cranial nerve 8 in the internal auditory canal
- characterized by: tinnitus, hearing loss (gradual), loss of corneal reflex due to compression of cranial nerve 5 roots in the area and compression of the nucleus of spinal tract which is underneath, cerebellar signs
signs of vestibular disorders
(VAN) –> vertigo/vomit, ataxia, nausea/nystagmus
vertigo
illusory sensation of motion
ataxia
ipsilateral postural disequilibrium; inability to stand upright without support; tendency to fall towards the side of the lesion; incoordination (drunk looking)
nystagmus
ipsilateral oscillatory involuntary eye movements, i.e., induced when attempting to gaze in the direction towards the side of the lesion
four functional components of facial nerve (cranial nerve 7)
taste, parasympathetic, sensory, motor
taste component of facial nerve (cranial nerve 7)
from anterior to two-thirds of tongue to nucleus of solitary tract
parasympathetic component of facial nerve (cranial nerve 7)
from salivatory and lacrimal nuclei to salivary and lacrimal glands
sensory component of facial nerve (cranial nerve 7)
from small area behind the ear— non-significant
motor component of facial nerve (cranial nerve 7)
from facial motor nucleus to muscles of facial expression
- corticobulbar fibers go: to the upper face (both crossed and uncrossed); to the lower face (only crossed)
three cranial nerves mediate taste
facial nerve (cranial nerve 7), glossopharyngeal nerve (cranial nerve 9), vagus nerve (cranial nerve 10)
taste loss is usually associated with…
a lesion in one of the nerves mediating taste
- because of the multi-synaptic and diffuse central pathways for taste and the poor localization of taste in the cortex, brainstem and cortical lesions are not usually associated with taste loss
- disturbances in taste functions are of minor significance to the patient
lesions involving the supranuclear nucleus (facial nerve; cranial nerve 7)
cause contralateral muscle weakess, affecting only the lower face (central facial palsy)
why do lesions involving the supranuclear nucleus (facial nerve; cranial nerve 7) only affect the lower face
because corticobulbar fibers cross for the lower face but there are uncrossed fibers (and also crossed) for the upper face
lesions involving the facial nucleus or nerve (cranial nerve 7)
- ipsilateral paralysis of facial muscles (peripheral palsy): both upper and lower facial muscles are affected
- lesion outside the CNS can present as Bell’s palsy
difference between motor functions of the trigeminal nerve (cranial nerve 5) and the facial nerve (cranial nerve 7)
- trigeminal –> only to muscles of mastication (chewing)
- facial –> only to muscles of facial expression (e.g., for smiling, frowning, etc.)
clinical testing of facial nerve (cranial nerve 7)
- only the motor function is routinely tested during clinical evaluation
- inspect for facial droop or asymmetry
- test muscles of facial expression: ask the patient to look up and wrinkle their forehead; examine for loss of wrinkling, assess muscle strength by applying downward pressure on each side
- ask the patient to shut their eyes tightly: compare both sides
- ask the patient to grin: compare the nasolabial folds
- have the patient frown, show their teeth, and puff out their cheeks
abducens nerve (cranial nerve 6)
- strictly motor
- to one muscle of the eye –> lateral rectus
- originates in the abducens nucleus in the pons and travels to the lateral rectus muscle
lateral rectus muscle of the eye
responsible for abducting the eye; moves the eye outward, away from the midline of the body
clinical significance of abducens nerve (cranial nerve 6)
- if abducens nerve is lesioned, medial strabismus is present
- only the affected eye does not abduct
- when asked to gaze right, the right eye does not abduct (medial rectus unopposed); results in crossed eyes (medial strabismus)
objectives in the midbrain
- sensory pathways travel in the back
- motor pathways travel in the front
cranial nerves that arise in the midbrain
oculomotor (cranial nerve 3), trochlear (cranial nerve 4)
cranial nerves that arise in the medulla
glossopharyngeal (9), vagus (10), accessory (11), hypoglossal (12)
continuation of sensory pathways in the midbrain
- medial lemniscus (ML)
- spinothalamic tract
- both pathways move laterally but remain dorsal relative to the motor pathways, which are ventral)
motor pathways in the midbrain
corticospinal fibers (in the cerebral peduncles or crus cerebri)
substantia nigra of the midbrain
- part of the basal ganglia
- associated with dopamine production and implicated in Parkinson’s disease
cranial nerve structures of the midbrain
- trochlear nucleus and nerve (cranial nerve 4): at the level of the inferior colliculus
- oculomotor nucleus and nerve (cranial nerve 3): at the level of the superior colliculus
trochlear nerve (cranial nerve 4)
- controls movement of the superior oblique muscle
- function: when the eye is turned medially, the superior oblique acts to depress the eye; when the eye is turned laterally, the superior oblique acts to intort the eye
- origin: trochlear nucleus located in midbrain
- course/termination: exits the brainstem and travels to the anterior court; there, it joins the oculomotor nerve and enters the orbit to innervate the superior oblique muscle
clinical significance of trochlear nucleus (cranial nerve 4) lesions
- nucleus supplies contralateral superior oblique muscle
- lesions cause paresis in contralateral superior oblique muscle
- causes diplopia (double vision) when looking down the stairs
- intorts the eye (turns towards the nose), especially when the eye is looking out (i.e., abducted)
cranial nerve 4 (trochlear) (or superior oblique) palsy
- diplopia
- complain of diplopia especially when walking downstairs or reading (requiring eye intorsion)
- tilt head away from the side of the lesion (to compensate for the alignment of both eyes and help relieve the diplopia)
two components of the oculomotor nerve (cranial nerve 3)
- motor
- autonomic (parasympathetic)
motor component of the oculomotor nerve (cranial nerve 3)
- innervated levator palpebrae superioris (the eyelid)
- all ocular muscles except two: lateral rectus (abducens nerve, cranial nerve 6), superior oblique (trochlear nerve, cranial nerve 4)
- supplies these ocular muscles: medial, superior, and inferior rectus; inferior oblique
autonomic component of the oculomotor nerve (cranial nerve 3)
- Edinger-Westphal nucleus located rostral and medial to the motor nucleus of oculomotor nerve (cranial nerve 3)
- provides preganglionic parasympathetic innervation to the ciliary ganglion, which sends postganglionic fibers to constrict the pupil and contract the ciliary muscle (the latter acts to thicken the lens for accommodation)
- pupil constricts when light is shined into it
oculomotor nerve (cranial nerve 3) palsy
- lesions of the Edinger-Westphal nucleus or oculomotor nerve (cranial nerve 3)
- ipsilateral lateral (external) strabismus— eye is down and out
- ipsilateral ptosis— if eyelid is retracted –> diplopia
- ipsilateral mydriasis (dilated pupil)
- loss of direct and consensual pupillary light reflexes in the ipsilateral eye
