Anatomy - Motor Tracts Flashcards
where are upper motor neurons located and where do their axons travel
- what do they synapse with
located in cerebral cortex or brain stem
- axons travel in descending tracts
- synapse with lower motor neurons and/or interneurons of the spinal cord
what tracts involve upper motor neurons
corticospinal tract
corticobulbar tract (corticonuclear)
where are the cell bodies of lower motor neurons and where do they synapse
cell bodies in spinal cord or brain stem
- synapse with skeletal muscle fibers
compare alpha and gamma motor neurons
alpha: large cell bodies, large myelinated axons, project to extrafusal skeletal muscle
gamma: medium sized, myelinated, project to intrafusal fibers of muscle spindle
what type neurons are peripheral and cranial nerves
lower motor neurons
describe the pathway of the lateral corticospinal tract
cell bodies arise in cortex –> descend through posterior limb of internal capsule –> cerebral peduncles –> anterior pons –> pyramids –> fibers cross in lower medulla –> descends in lateral column of spinal cord –> synapses with lower motor neurons in spinal cord
what does the medial corticospinal tract (of the corticospinal tract) encompass
postural muscles (10% of fibers)
- neck, shoulder, and trunk muscles
what does the lateral corticospinal tract (of the corticospinal tract) encompass
limb muscles, fractionation (90% of fibers)
what is the source of most of the neurons in the corticospinal tract
primary motor cortex
in what way (contralaterally/ipsilaterally) does the primary motor cortex control the body
contralaterally
(right side motor strip controls left side of body)
compare lateral and medial corticospinal tracts
the medial (anterior) corticospinal tract remains ipsilateral throughout its tract
- lateral tract becomes contralateral in the pyramids before descending into spinal cord
arterial supply to trunk/leg region of cortex
arterial supply to hand region of cortex
anterior cerebral a.
middle cerebral a.
blood supply to internal capsule
lenticulostriate arteries (posterior limb)
anterior choroidal artery
what artery supplies the midbrain where the corticospinal tract passes
posterior cerebral a.
what artery supplies the pons where the corticospinal tract passes through
paramedian branches of basilar a.
what artery supplies the medulla where the corticospinal tract passes through
sulcal branches of anterior spinal a.
arterial supply of corticospinal tract in the spinal cord
posterior and anterior spinal arteries
where do the axons of the corticobulbar tract arise from
ventral part of cortical area 4
(primary motor complex) (precentral gyrus)
describe the path of the corticobulbar tract
ventral part of cortical area 4 –> genu of internal capsule –> cerebral peduncles –> anterior pons –> pyramids –> stops in brainstem at specific motor nucleus
how do the axons of the corticobulbar tract travel
they cross to control the muscles on the contralateral side (except for CN 11 which stays ipsilateral and travels with median corticospinal tract)
how do the neurons of the corticobulbar tract affect the trigeminal nucleus in the pons
fibers split bilaterally to influence motor trigeminal nuclei
how do the neurons of the corticobulbar tract affect the facial nucleus in the pons
the facial motor nucleus that supplies the forehead is influenced bilaterally by the neurons of the corticobulbar tract
- the contralateral lower side of the face is controlled contralaterally
how do the neurons of the corticobulbar tract affect the nucleus ambiguus (CN 9 and 10) in the medulla
it influences nucleus ambiguus bilaterally but the actual muscle influence seems to be controlled contralaterally
how do the neurons of the corticobulbar tract affect the spinal accessory nucleus in the spinal cord
ipsilaterally
how do the neurons of the corticobulbar tract affect the hypoglossal nucleus
contralaterally
where are lower motor neurons found
ventral horns
in the ventral horn, where are the lower motor neurons for axial muscles, limb muscles, extensor muscles, and flexor muscles
medial: axial muscles
lateral: limb muscles
posterior: flexor muscles
anterior: extensor muscles
what are the medial upper motor neuron tracts (4)
tectospinal
medial reticulospinal
lateral vestibulospinal
medial vestibulospinal
what are the lateral upper motor neuron tracts (2)
rubrospinal
lateral reticulospinal
describe the path of the lateral vestibulospinal tract
starts in superior/lateral vestibular nuclei in the pons –> stays ipsilateral to the spinal cord –> innervates lower motor neurons –> postural muscles and limb extensors (in relation to gravity)
**goes to all spinal cord levels**
describe the path of the medial vestibulospinal tract
starts in inferior vestibular nucleus in medulla –> descends bilaterally –> cervical and thoracic levels to innervate neck and shoulder muscle movement in relation to gravity
(don’t see this tract below T2/T3)
describe the path of the medial (pontine) reticulospinal tract
starts in pontine reticular formation in pons –> travels ipsilaterally to lower motor neurons in spinal cord–> innervates postural muscles and limb extensors (not in relation to gravity)
describe the path of the lateral (medullary) reticulospinal tract
starts in medullary reticular formation in medulla –> stays mainly ipsilateral with some contralateral projections down the spinal cord –> facilitates flexor motor neurons and inhibits extensor motor neurons
describe the path of the rubrospinal tract
starts in red nucleus of midbrain –> crosses to contralateral side –> travels down to spinal cord –> innervates upper limb flexors
describe the path of the tectospinal tract
superior colliculus in midbrain –> upper spinal cord –> neck muscles (turning head to where eyes want to go)
general function of corticospinal tract
fine motor control of hand
motor neuron recruitment to increase force
inhibition of postural reflexes
general function of corticobulbar tract
control of muscles of face, chewing, speech, and swallowing
general function of rubrospinal tract
facilitation of upper limb flexors
general function of lateral vestibulospinal tract
facilitation of extension against gravity
general function of medial vestibulospinal tract
coordination of head movements
general function of pontine reticulospinal tract
facilitation of postural reflexes
general function of medullary reticulospinal tract
inhibition of spinal segmental reflexes
general function of tectospinal tract
coordination of head with eye movements
sx of lower motor neuron lesion
flaccid paralysis
wasting or atrophy
hyporeflexia or areflexia
hypotonia
denervation hypersensitivity causing fasiculations
what is upper motor neuron syndrome
a combination of the loss of the corticospinal tract and its collaterals sent to the indirect pathways
sx of upper motor neuron lesion
loss of distal extremity strength (CST)
babinski’s (CST)
hypertonia
spasticity (clasp-knife phenomemon) - (CST or CBT)
rigidity
hyperreflexia
what is the clasp knife phenomenon
spacsticity caused by loss of inhibitory commands from UMN
(muscle first resists, then relaxes)
if a UMN lesion occurs above the lower medulla, where will the clinical signs be
contralateral
if a UMN lesion occurs in the spinal cord, where will the clinical signs be?
ipsilateral
compare spinal cord lesions between UMN and LMN
UMN signs will be below the level of the lesion
LMN signs will be at the level of the lesion
what causes decorticate posture
UMN lesion above the level of the red nucleus
- the rubrospinal tract will be intact (why you have flexion in UE) and reticulospinal and vestibulospinal (extension in LE)
if you have damage to the corticospinal tract and lower motor neurons, which clinical sign will predominate?
lower motor neuron
(it’s the final common pathway for motor)
pt comes in with thumb tucked under flexed fingers in fisted position, pronation of forearm, flexion at elbow, lower extremity in extension with foot inversion
- what sign is this?
decorticate rigidity
pt comes in with upper extremity in pronation and exntesion and lower extremity in extension
- what sign is this?
decerebrate rigidity
what causes decerebrate posture
lesion below red nucleus but above the reticulospinal and vestibulospinal nuclei
- with lesion below red nucleus you lose the rubrospinal tract, so you lose ability to flex upper limb (UE will be in extension)
- reticulospinal and vestibulospinal nuclei will be in tact (allows extension of limbs)
if lesion occurs all along precentral gyrus, what tracts will it affect and where will the sx be
CST and CBT
- contralateral side (including bottom half of face)
sx of complete transection of the spinal cord
all sensation lost 1 or 2 levels below lesion
bladder and bowel control lost
spinal shock
UMN signs below the lesion
LMN signs at the lesion
sx of hemisection of spinal cord (below medulla)
contralateral loss of pain and temperature
ipsilateral loss of discriminative touch and conscious proprioception
LMN signs on ipsilateral side at level of lesion
UMN signs on ipsilateral side below level of lesion
what is Brown Sequard’s syndrome
the sx of a hemisection spinal cord
- contralateral loss of pain and temp
- ipsilateraly loss of disciminative touch and conscious proprioception
- ipsilateral LMN signs at level of lesion
- ipsilateral UMN signs below level of lesion
what causes syringomyelia and what are its signs
formation of cysts within spinal cord in the central canal
- shawl/cape pattern of pain and temp loss (from anterior white commissure being affected first)
- atrophy/weakness of hand
(if ventral horn is affected –> LMN signs)
(if lateral corticospinal tract is affected –> UMN signs)
what is anterior cord syndrome and what usually causes it
compression/damage to anterior part of spinal cord
causes: spinal cord infarction, intervertebral disc herniation, radiation myelopathy, occlusion of anterior spinal a.
sx of anterior cord syndrome
- ipsilateral UMN signs below level of lesion (from hitting lateral CST)
- contralateral loss of pain and temp (from hitting lateral spinothalamic tract)
- ipsilateral LMN signs (from hitting ventral horn)
(posterior columns intact and functional)
what mechanism of injury usually causes central cord syndrome
cervical hyperextension
what structures are hit in medial medullary syndrome
(“Dejerine Syndrome”)
pyramids
medial leminiscus
CN XII nucleus
what are the sx of medial medullary syndrome (Dejerine Syndrome)
contralateral UMN signs (from hitting pyramids)
contralateral loss of proprioception (from hitting ML)
ipsilateral deviation of tongue towards lesion (from hitting hypoglossal nucleus)
injury to what artery would cause medial medullary syndrome
anterior spinal a.
what structures are hit in lateral medullary syndrome
(“Wallenberg’s Syndrome”)
anterolateral system (ALS tract)
spinal trigeminal nucleus and tract
nucleus ambiguus
vestibular nuclei
what are the symptoms of lateral medullary syndrome
contralateral loss of pain and temp to body (from hitting ALS)
ipsilateral loss of pain and temp to face (from hitting trigeminal nucleus and tract)
hoarseness, difficulty swalloing, uvula deviation away, uneven elevation of pallate (from hitting nucleus ambiguus)
nystagmus, vertigo, ataxia (from hitting vestibular nuclei)
injury to what artery would cause lateral medullary syndrome
PICA
what causes central 7 palsy and what are the sx
lesion of corticobulbar tract involving CN 7
- contralateral drooping of lower face
- weak wrinkling of forehead bilaterally
compare Bell’s and Central 7 palsy
Bell’s: ipsilateral flaccid paralysis of upper and lower face
central 7: contralateral dropping of lower face, weak wrinkling of forehead bilaterally
what is Weber’s syndrome
lesion in the cerebral peduncle of the midbrain affecting CST, CBT, and neurons from CN III nucleus
in the midbrain, if red nucleus is visible what other two structures should be at that level
superior colliculus
CN III
if you are at the level of the inferior colliculus in the midbrain, what cranial nerve should also be at that level
CN IV
sx of Weber’s syndrome
contralateral UMN sx (from hitting CST)
central 7 symptoms (from hitting CBT)
uvula deviates contralateral to lesion, tongue deviates ipsilateral (from hitting CBT)
down and out eyes (from hitting nerves leaving nucleus of CN III)
sx of ALS
paresis (muscle weakness)
myoplastic hyperstiffness
hyperreflexia
babinski’s sign
atrophy
fasciculations
fibrillations
how does amyotrophic lateral sclerosis (ALS) work
destroys somatic motor neurons
(UMNs and brainstem and spinal cord LMNs)
what causes polyneuropathy
damage to sensory, motor, and autonomic neurons
if pt presents with “stocking/glove” presentation, what disease process is this and how does it work
polyneuropathy
- dying-back of imparied axonal transport
- demyelizaiton may also contribute
