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BS4-2 Cranial Nerves Spiers

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alpha motor neurons function
muscle contractions for movement
gamma motor neurons function
muscle tone
M1
primary motor cortex - location of 1st UMNs
LMNs have cell bodies on ________ side to their skeletal musculature
ipsilateral
the pathway of change in MUSCLE STRETCH involuntary movement
(monosynaptic) muscle stretch --> muscle spindle fibers --> proprioceptive afferent impulse --> LMN (reflex)
the pathway of change in NOXIOUS CUTANEOUS STIMULUS
(polysynaptic) noxious stimulus (burn) --> interneuron* --> reflex to pull hand away
UMN have _______ effects on monosynaptic reflex arcs. This effects speed and intensity of knee jerk reflex.
inhibitory
Poliomyelitis
polio virus attacks LMNs in ventral horn, loss of LMNs leads to atrophy, paralysis, etc.
What are the 3 effects of an LMN lesion?
1) suppressed reflexes
2) muscle atrophy
3) ipsilateral flaccid paralysis
What is the effect of a UMN lesion?
hyperactive reflex - because brakes on MONOSYNAPTIC reflex arc are gone, there's an elevated muscle stretch reflex
The UMN cell body is _________ to LMN.
contralateral
The LMN is _______ to the innervated muscle
ipsilateral
voluntary contraction of skeletal muscle requires:
UMN + LMN
what's the difference between pyramidal tract vs. extrapyramidal motor system?
pyramidal = simple, involves corticospinal, corticonuclear, and corticoreticular fibers controlling movement
extrapyramidal = more complex, basal ganglia, red nucleus, cerebellum, etc control movements and planning of movements
what is the most important pathway for voluntary motor function?
pyramidal system
3 components of pyramidal
1) corticospinal
2) corticonuclear (bulbar)
3) corticoreticular
what's the pathway of all the pyramidal system generally?
telencephalon --> corona radiata --> posterior limb of internal capsule --> cerebral peduncles --> brainstem or spinal cord
What is M1?
precentral gyrus, Brodmann's area 4
What is the primary motor cortex in charge of?
upper motor neurons encoding for direction, force, and velocity of movement or skilled movements
What is the motor homunculus ?
distorted orderly map of skeletal muscles controlled by UMNs in CONTRALATERAL limbs and trunk
In the homunculus, UMNs that control cranial nerve innervated muscles are close to the ______ sulcus.
lateral
What's most heavily represented in the motor homunculus?
cranial nerve musculature and hand muscles
What's the breakdown of derivation of UMNs for complex movement?
30% from primary motor cortex
30% from premotor cortex
40% from parietal lobe
What's corona radiata?
bundles of descending motor axons
where does the corona radiata converge and start descending?
posterior limb of internal capsule
Lacunar stroke
- lesions resulting from interruption of penetrating arteries supplying deep structures
- common site = internal capsule
- ASSOCIATED WITH ELEVATED BP
Contralateral hemiplegia
- lacunar strokes lead to damage to corticospinal fibers which can cause loss of UMN control of certain areas of the body
- side effects: contralateral spastic hemiparesis
- note: although it's a UMN damaged, it's a small effect
Where are the cerebral peduncles?
brainstem (we continue the descent)
Corticonuclear fibers terminate in the ______ _____ ______ _____ providing the UMN innervation to LMNs in the _____ _____ _____
cranial nerve motor nuclei
cranial nerve nuclei
Which cranial nerves nuclei are we focusing on?
1) trigeminal motor nucleus
2) Facial motor nucleus
3) Nucleus ambiguous (pharynx, larynx, and palate)
4) Hypoglossal nucleus
5) Accessory nucleus
Which cranial nerve fibers innervated by corticonuclear fibers have bilateral innervation?
1) trigeminal motor nucleus
2) Nucleus ambiguous (pharynx, larynx, and palate)
3) Hypoglossal nucleus
Corticobulbar innervation is ______ to facial motor neurons that innervate EYES area.
bilateral
Corticobulbar innervation is exclusively _______ to facial motor neurons that innervate NOSTRILS and MOUTH.
Contralateral
summary: UMN innervation to LMNs in spinal nerves is _______
UMN innervation to LMN in cranial nerves is ______ except ______
contralateral
bilateral except muscles of nose and mouth (which are contralateral only)
What happens with a lesion of the facial nerve?
- bell's palsy
- complete paralysis of muscles of facial expression ipsilateral to lesioned nerve = EYES, NOSTRILS, AND MOUTH ARE AFFECTED
- can't wrinkle forehead, can't shut eye, can't flare nostrils, drooping mouth
What happens with a lesion of the corticobulbar fibers to facial motor nucleus?
- may result in only a lower face weakness
- drooping corner of mouth on side ipsilateral to the corticobulbar fiber
- they can wrinkle forehead, they can shut eyes, and can blink = EYES ARE NOT AFFECTED
What are 2 pathways of corticospinal fibers?
1) fibers --> cross in pyramids --> go down lateral funiculus --> form LATERAL corticospinal tract --> LMN
2) fibers --> descend ipsilaterally --> anterior funiculus --> LATERAL corticospinal tract --> LMN
What's the difference between corticospinal fibers terminating on LMNs either directly or indirectly?
indirectly occurs through interneurons.

direct innervation --> distal muscles --> FINE PRECISION MOVEMENTS
UMN lesion produces:
- paresis
- spasticity
- hyperreflexia (no brake on reflex)
- altered cutaneous reflexes
- disuse atrophy
LMN lesion produces:
- suppressed reflexes
- muscle atrophy
- ipsilateral flaccid paralysis
- spontaneous fascicultation (twitch)
Can either LMN or UMN lesions recover?
UMN can recover function over time using adjacent non-lesioned UMNs
The extrapyramidal system uses the cerebral cortex alongside the cerebellum and what 4 subcortical motor centers to carry out movement?
1) basal ganglia (telencephalon = caudate and putamen, diencephalon = globus pallidus)
2) motor areas of thalamus (subthalamic nucleus)
3) Tectum of midbrain (roof)
4) red nucleus, substantia nigra, reticular formation, vesticular nuclei, and olive in brainstem
How do feedback loops affect extrapyramidal system
movements --> feedback loops --> cerebral cortex --> influence cerebellum and basal ganglia --> upper motor neurons
What are 2 goals of cerebellum?
- regulates movements by comparing intended performance to actual performance
- reduces errors in movements
Is cerebellum contralateral to UMNs?
yes, cerebellum is contralateral to UMN is which is contralateral to LMN
thus cerebellum is ipsilateral to the LMN is affects
What are 2 goals of basal ganglia?
- initation of movement
- cognitive and limbic functions (emotion expression)
What is the stiatum?
large dorsal component, caudate nucleus and putamen
the basal ganglia influence UMNs in ________ cerebral cortex and brainstem.
IPSILATERAL
summary of contralateral vs. ipsilateral in cerebellum and basal ganglia
cerebellum influences contralateral UMNs
basal ganglia influences ipsilateral UMNs
What is lentiform nucleus?
globus pallidus + putamen
globus pallidus receives inputs from
striatum
What is the result of basal ganglia lesions?
tremors at rest
What is the result of cerebellum lesions?
tremors when you try to move
Function of substantia nigra and red nucleus?
like basal ganglia, they exercise motor control
Functions of direct and indirect motor pathways?
direct = excite motor cortex and initiate movement
indirect = inhibit motor cortex and surpress unwanted movement
Direct motor pathway is enhanced by what?
dopamin
loss of dopamine leads to...
Parkinson's disease and overactive indirect pathway
Lesions of direct pathway lead to..
- underactive motor cortex
- hypokinetic distrubances
- parkinson's disease signs and symptoms
- problems with initiating movements, tremors in fingers, rigidity of upper limbs, expressionless face
Indirect motor pathway is enhanced by what?
ACh
loss of GABA ACh leads to...
Huntington's Disease (chorea)
Lesions of indirect pathway lead to...
- overactive motor cortex
- hyperkinetic disturbances
- pronounced involuntary movements
- chorea (purposeless, quick jerks)
- athetosis (slow, involuntary movements in hands)
What's the function of vermis and adjacent paravermal regions of cerebellum?
they regulate ONGOING execution of movement, proximal limb and trunk coordination
What's the function of lateral hemispheres of cerebellum?
motor planning in extremities
What's the function of intermediate hemispheres of cerebellum?
distal limb coordination
pathway of cerebellar cortex
climbing and mossy fibers are inputs that influence --> purkinje fibers --> cerebellar cortex --> influence deep cerebellar nuclei outputs
Function of climbing fibers?
detect errors in movement and report them
Function of mossy fibers?
update cerebellum about ongoing movement or motor plan and report them
Lesion to cerebellum leads to...
- tremor with VOLUNTARY movements
- finger to nose test is shaky
- leads to DYSMETRIA (inability to stop movement at proper place)
lesions to cerebellum affect contralateral or ipsilateral LMNs?
IPSILATERAL! remember??
Summary pathway
deep cerebellar nuclei axons --> exit superior cerebellar perduncle --> cross the midbrain --> thalamic motor nuclei --> influence UMN in cortex --> influence corticospinal and corticobulbar UMNs --> axons cross or dont
function of extrapyramidal tract
red nucleus and reticular formation --> muscle tone, body posture, and reflex sensitivity
function of reticulospinal tract
pons --> cervical musculature (movements of head)
function of tectospinal tract
inputs from eyes and ears --> tectum nuclei --> rapid orientation of head in response