Motor Pathways Flashcards
what are the CNS components that control movement?
basal ganglia, cortical motor areas, thalamus, brainstem, cerebellum
what do upper motor neurons do?
carry motor outputs from cerebrum/brainstem to LMN
what are lower motor neurons? what do they do?
cell bodies in brainstem or spinal cord
innervate muscles in the periphery
alpha motor neurons
large cell bodies
axons innervate skeletal muscle
gamma motor neurons
smaller axon fiber diameter
innervate muscle spindles to help control stretch reflexes
what will a lower motor neuron lesion cause?
muscle weakness and atrophy
fasciculations (twitching)
decreased tone
hyporeflexia
what will an upper motor neuron lesion cause?
muscle weakness, increased tone, hyperreflexia, abnormal reflexes or signs
how might acute UMN lesions present initially?
flaccid paralysis, decreased tone, hyporeflexia
motor pathways with cortical origins
lateral and ventral corticospinal, corticobulbar
motor pathways with brainstem origin
rubrospinal, vestibulospinal, tectospinal, reticulospinal
which tracts lie laterally in the spinal cord? what do they control?
lateral corticospinal, rubrospinal, corticobulbar*
appendicular muscles
which tracts lie medially in the spinal cord? what do they control?
ventral corticospinal, vestibulospinal, tectospinal, reticulospinal
axial/girdle postural muscles
why do medial pathways have a bilateral influence?
although they descend ipsilaterally, they synapse on interneurons in the intermediate zone as well as LMNs in the ventral horn
what movements occur due to the lateral corticospinal tract
rapid, dextrous movements at individual joints
where do most fibers originate in the lateral corticospinal tract?
precentral gyrus, primary motor cortex
what are other fiber origins for the lateral corticospinal tract?
premotor, supplementary motor, or parietal lobe
where are all the cell bodies of the lateral corticospinal tract?
cortical layer 5
lateral cortico spinal tract pathway
primary motor cortex
through posterior limb of internal capsule as corona radiata
middle 1/3 of crus cerebra
ventral pons
pyramids
axons cross in the pyramidal decussation
descend in lateral funiculus of spinal cord
synapse of LMN cell bodies in ventral horn
what movements occur due to the corticobulbar tract?
movement of facial, tongue, jaw, laryngeal, and pharyngeal muscles
where are cell bodies of the corticobulbar tract located?
lateral aspect of pre central gyrus
corticobulbar tract pathway
lateral aspect of pre central gyrus
genu of internal capsule
projections to facial motor nucleus, trigeminal motor nucleus, nucleus ambiguous, and hypoglossal nucleus
what happens if you lesion the corticobulbar tract?
paralysis of the contralateral lower face
what happens if you lesion the facial motor nucleus?
paralysis of the ipsilateral whole face
where is the trigeminal motor nucleus located?
mid-pons
bilateral projections
where is the nucleus ambiguus located?
rostral medulla
bilateral projections (pharyngeal/laryngeal muscles)
where is the hypoglossal nucleus located?
rostral dorsal medulla
most often bilateral projections
where is the spinal accessory nucleus located?
caudal medulla
non-symmetrical bilateral projections
rubrospinal tract function
exact function is unclear, likely influences flexors of upper limbs
rubrospinal tract pathway
cell bodies in red nucleus
axons decussate in midbrain immediately
dorsolateral aspect of pons and medulla
lateral funiculus of the spinal cords
ventral horn of cervical cord
what does flexor posturing indicate?
the corticospinal tract is damaged above the red nucleus
what does extensor posturing indicate?
brainstem damage below the red nucleus
key traits of posturing
occur in a comatose patient
only see a response in the upper limbs
move in the direction of painful stimuli
where does the ventral corticospinal tract project to?
only to cervical and upper thoracic spinal cord
what movements occur due to the ventral corticospinal tract?
control of bilateral axial and girdle muscles
ventral corticospinal tract pathway
axons originate in lateral cortical spinal tract and follow this pathway until pyramidal decussation
tract does NOT decussate, descends into ventral funiculus of cord
some axons cross in the spinal cord, synapse on LMN and interneurons
what is the vestibulospinal tract important for?
maintaining balance and posture
receives input from vestibular organs
where are cell bodies of the vestibulospinal tracts?
medial and lateral vestibular nuclei of medulla and pons
lateral vestibulospinal tract pathway
ipsilaterally in ventral funiculus of sc
synapse in ventral horns on LMNs and intermotor neurons
(posture and balance)
medial vestibulospinal tract pathway
descends bilaterally to superior cervical sc levels
(control head position related to eye position)
tectospinal tract pathway
originates in neurons in deep layers of superior colliculus, decussates immediately
projects to cervical spinal segments
what is the tectospinal tract important for?
partial control of neck, shoulder, and upper trunk muscles
roles in eye/head movement coordination
reticulospinal tract pathway
originate in pontine/medullary reticular formation
descend in ventral funiculus
ipsilateral tract with bilateral motor control
what is the reticulospinal tract important for?
influencing automatic movements like posture control and balance on uneven terrain
what are segmental interneurons?
short axon that distributes branches ipsilaterally within a single spinal segment
synapse on MN or other interneurons
segmental interneuron input
receives input from somatic sensory receptors for reflex control of movement
what are commissural interneurons?
axons distribute bilaterally for movement coordination of both sides of the body
what are propriospinal interneurons?
axons project for multiple spinal segments before synapsing on MNs
(upper-lower limb coordination)
where is the supplementary motor area located? what is its role?
medial surface of cerebral hemisphere
specific role unknown
where is the cingulate motor area located? what is its role?
medial surface, deep in cingulate sulcus
part of the limbic system
where is the premotor cortex located?
lateral hemisphere, ventral to primary motor cortex
what is the dorsal premotor cortex function?
helps control reaching
what is the ventral premotor cortex function?
helps control grasping
contains mirror neurons that activate when watching others perform an action
what occurs when there is damage to the premotor areas?
apraxia, motor planning disorders
loss of ability to produce learned purposeful movements
what is needed in order to produce movement?
decision to move (limbic and prefrontal)
visual info (posterior parietal cortex)
what is multiple sclerosis?
autoimmune inflammaotry disorder to the CNS myelin that affects UMNs
plaques of demyelination can appear and disappear on an MRI
what is Guillain-Barré syndrome?
immune-mediated demyelination of peripheral nerves
typically onsets 1 to 2 weeks following a viral or bacterial illness
Guillain-Barré presentation
ascending progressive weakness, areflexia, tingling paresthesia of hands and feet
what is Amyotrophic Lateral Sclerosis?
gradual degeneration of upper and lower motor neurons
