Motor Tracts Flashcards
Where do upper motor neurons arise and what do they synapse with?
arise and are contained within crebral cortex or brainstem
synapse with LMN or interneurons of the spinal cord
Where are the cell bodies of LMNs?
What do they innervate?
in spinal cord or brain stem
synapse w/ skeletal muscle fibers
What are the types of LMNs?
gamma motor: medium sized, myelinated –> intrafusal fibers in muscle
alpha motor: large bodies and large myelinated axons –> extrafusal skeletal muscle
What part of the internal capsule does the corticospinal tract pass through?
posterior limb
Where do fibers cross in the corticospinal tract?
in the pyramids in the lower medulla
90% decussate = lateral corticospinal tract
10% stay ipsi = not clinically significant
Where is volontary motor movement controlled?
primary motor cortex (area 4) in precentral gyrus
(R side usually controls left side of body and vice versa)
Where do fibers of the lateral corticospinal tract descend in the spinal cord?
lateral column
Where do fibers from the cortex controlling the legs and arms end up in the lateral corticospinal tract?
legs –> lateral
arms –> medial
(across from where they are in the cortex)
Where do UMNs from the lateral corticospinal tract synapse?
with LMNs in the ventral horn of the spinal cord
hemorrhage of what arteries could cause issues with the corticospinal tract?
Lenticulostriate and ant choroidal As –> internal capsule
posterior cerebral A –> crus cerebri of cerebral peduncles
paramedian branches of basilar A –> pyramids of medulla
anterior and posterior spinal As
What does the median corticospinal tract control?
postural and proximal movements
don’t cross medulla
only 10% of fibers - isn’t clinically significant
Where do UMNs of the corticobulbar tract arise?
where do they go?
ventral part of cortical area 4 –> to brainstem and cranial nerves
axons cross and control muscles on contralateral side
What part of the internal capsule does the corticobulbar tract pass through?
where does it go to get to the brainstem?
genu
to cerebral peduncles –> anterior pons –> pyramids
Where do the axons of the corticobulbar tract cross over?
pyramidal decussation
Where are the trigeminal nuclei and how do the UMN run to get there?
anterior pons
50/50 split to either side
Where are the facial nuclei and how do UMNs run to get there?
lower anterior pons
lower face muscles: controlled contralaterally
upper face muscles: controlled ipsilaterally
What CN nuclei are located in the medulla and how do UMNs of the corticobulbar tract run to get there?
hypoglossal nucleus (12)
nucleus ambiguus (9,10)
contralateral projections
Where is the spinal accessory nucleus and how do UMNs from the corticobulbar tract run to synapse there?
in anterior horn of cervical spine
ipsilateral projections
Where are LMNs located topographically in the spinal cord?
all in anterior horn
proximal neurons = medial
distal = lateral
flexors = posterior
extensiors = anterior
Where do indirect pathways synapse?
brain stem
basal ganglia
thalamus
reticular formation
cerebellum
What do medial LMNs receive input from? (5)
tectospinal tract
medial vestibulospinal
medial reticulospinal
medial corticospinal
lateral vestibulospinal
What do lateral LMNs receive input from?
rubrospinal
lateral reticulospinal
lateral corticospinal
What artery supplies both horns of the sinal cord?
anterior spinal a
Where does the lateral vestibulospinal tract run?
lateral vestibular nuclei to spinal cord –> ipsilateral LMNs
innervate postural muscles and limb extensors
(help you extend against gravity)
Where does the medial vestibulospinal tract run?
superior, medial, and lateral vestibular nuclei –> cervical and thoracic levels = neck and shoulder muscles
ipsilateral?
Where are vestibular nuclei located?
pons
Where does the medial/pontine reticulospinal tract run?
pontine reticular formation –> SC –> ipsilateral LMNs
to posteral muscles and limb extensors
Where does the rubrospinal tract run?
red nucleus of midbrain –> SC –> contralateral LMNs
to upper limb flexors
Where does the lateral reticulospinal tract run?
medullary reticular formation –> spinal cord –> mainly ipsi, some contra
facilitates flexor motor neurons and inhibits extensors
Where doew the tectospinal tract run?
superior colliculus of midbrain –> upper spinal cord –> ipsi LMNs
to neck muscles –> visual reflexes to turn head to where eyes and ears are
What do you see in LMN lesions?
flaccid paralysis
wasting or atrophy
hyporeflexia or areflexia
hypotonia
denervation hypersensitivity = fasiculations (neuron is dying)
What do you see in UMN lesions?
loss of distal extremity strength and dexterity
babinski sign
hypertonia - spasticity and rigidity
hyperreflexia - clonus
spasticity
pronator drift
What is rigidity due to?
basal ganglia disease
not rate or force dependent
What side do LMN lesions cause clinical signs?
same side of lesion!
Where do you see clinical signs of UMN lesions?
if lesion is above lower medulla –> contralateral side
if lesion is in SC –> ipsilateral side
What levels do you see clinical signs of spinal cord lesions?
UMN signs below level of lesion
LMN signs at level of lesion
What is decorticate posture?
due to lesion above level of red nucleus
thumb tucked under fingers in fist
pronated forarm
flexed arms
extended legs, foot inversion
What is decerebrate posture?
due to lesion below red nucleus, but above reticulospinal and vestibulospinal nuclei
arms extended, pronated
lower extremity extended
What do you see in complete transection of SC?
all sensation lost 1-2 levels below lesion
bladder and bowel control lost
spinal shock
UMN signs below lesion
LMN signs at level of lesion
What do you see in hemisection of the spinal cord?
pain and temp from contralateral side of body lost
complete loss of pain 2-3 levels below
discriminative touch and proprioception on ipsilateral side
LMN signs at level on ipsi
UMN signs below on ipsi
*Brown-sequard syndrome
What do you see in syringomyelia?
pain and temp first affected bc of anterior white commissure –> cape pattern
If ventral horns affected –> LMN signs
If CST affected –> UMN signs
What syndrome is syringomyelia associated with?
Chiari I
What things are damaged in Anterior cord syndrome?
lateral corticospinal tract –> UMN ipsi, below level
Anterior horn damage –> LMN ipsi, at level
Lateral spinothalamic tract –> contralateral pain and temp lost
What things are damaged in central cord syndrome?
*usually due to cervical hyperextension
- Ant white commissure affected first –> bilateral pain and temp lost
- Ant horn affected –> LMN loss at level
- lateral corticopsinal tract –> UMN loss at level
What things are damaged in medial medullary syndrome?
Pyramid
medial leminiscus –> contra prop, vibration sense
CN 12 nucleus –> tongue deviates toward lesion
Hemorrhage of what A can cause medial medullary syndrome?
anterior spinal a
What things are damaged in lateral medullary syndrome?
ALS –> contra loss of pain and temp
Spinal trigeminal nucleus and tract –> ipsi loss of pain and temp to face
Nucleus Ambiguus –> 9 and 10 CN loss
Inferior cerebellar peduncle –> ataxia
Hemorrhage of what A can cause lateral medullary syndrome?
PICA
What is central sevel palsy?
lesion of the corticobulbar tract involving 7th CN
If superior to facial motor nucleus:
Ms of the upper face are controlled by fibers from both hemispheres –> can still wrinkle forehead
Ms of lower face controlled by contralateral hemisphere –> drooping ms at corner of mouth on contra side
What occurs in Weber syndrome?
lesion of midbrain
CN III damage –> ipsilateral motor damage (down and out, dilated pupil)
contra UMN sx
Central 7 sx (contra lower face droop)
uvula dev to same side of lesion (10)
tongue dev to opposite side (12)
ipsi SCM and Trap paralysis (11)
Occlusion of what arteries can cause Weber syndrome?
posterior cerebral A
branches of basilar A
What is Amyotrophic Lateral Sclerosis?
ALS
destroys only somatic motor neurons = UMNs and spinal cord LMNs
paresis, myoplastic hyperstiffness, difficulty breathing, swallowing, and speaking
What is polyneuropathy?
damage of nerves: involvement of sensory, motor and autonomic Ns
Progresses distal to proximal = stocking/glove pattern
(diabetic neuropathy)
