Motor Pathways

Question 1

what are the CNS components that control movement?

Answer 1

basal ganglia, cortical motor areas, thalamus, brainstem, cerebellum

Question 2

what do upper motor neurons do?

Answer 2

carry motor outputs from cerebrum/brainstem to LMN

Question 3

what are lower motor neurons? what do they do?

Answer 3

cell bodies in brainstem or spinal cord
innervate muscles in the periphery

Question 4

alpha motor neurons

Answer 4

large cell bodies
axons innervate skeletal muscle

Question 5

gamma motor neurons

Answer 5

smaller axon fiber diameter
innervate muscle spindles to help control stretch reflexes

Question 6

what will a lower motor neuron lesion cause?

Answer 6

muscle weakness and atrophy
fasciculations (twitching)
decreased tone
hyporeflexia

Question 7

what will an upper motor neuron lesion cause?

Answer 7

muscle weakness, increased tone, hyperreflexia, abnormal reflexes or signs

Question 8

how might acute UMN lesions present initially?

Answer 8

flaccid paralysis, decreased tone, hyporeflexia

Question 9

motor pathways with cortical origins

Answer 9

lateral and ventral corticospinal, corticobulbar

Question 10

motor pathways with brainstem origin

Answer 10

rubrospinal, vestibulospinal, tectospinal, reticulospinal

Question 11

which tracts lie laterally in the spinal cord? what do they control?

Answer 11

lateral corticospinal, rubrospinal, corticobulbar*
appendicular muscles

Question 12

which tracts lie medially in the spinal cord? what do they control?

Answer 12

ventral corticospinal, vestibulospinal, tectospinal, reticulospinal
axial/girdle postural muscles

Question 13

why do medial pathways have a bilateral influence?

Answer 13

although they descend ipsilaterally, they synapse on interneurons in the intermediate zone as well as LMNs in the ventral horn

Question 14

what movements occur due to the lateral corticospinal tract

Answer 14

rapid, dextrous movements at individual joints

Question 15

where do most fibers originate in the lateral corticospinal tract?

Answer 15

precentral gyrus, primary motor cortex

Question 16

what are other fiber origins for the lateral corticospinal tract?

Answer 16

premotor, supplementary motor, or parietal lobe

Question 17

where are all the cell bodies of the lateral corticospinal tract?

Answer 17

cortical layer 5

Question 18

lateral cortico spinal tract pathway

Answer 18

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

Question 19

what movements occur due to the corticobulbar tract?

Answer 19

movement of facial, tongue, jaw, laryngeal, and pharyngeal muscles

Question 20

where are cell bodies of the corticobulbar tract located?

Answer 20

lateral aspect of pre central gyrus

Question 21

corticobulbar tract pathway

Answer 21

lateral aspect of pre central gyrus
genu of internal capsule
projections to facial motor nucleus, trigeminal motor nucleus, nucleus ambiguous, and hypoglossal nucleus

Question 22

what happens if you lesion the corticobulbar tract?

Answer 22

paralysis of the contralateral lower face

Question 23

what happens if you lesion the facial motor nucleus?

Answer 23

paralysis of the ipsilateral whole face

Question 24

where is the trigeminal motor nucleus located?

Answer 24

mid-pons
bilateral projections

Question 25

where is the nucleus ambiguus located?

Answer 25

rostral medulla bilateral projections (pharyngeal/laryngeal muscles)

Question 26

where is the hypoglossal nucleus located?

Answer 26

rostral dorsal medulla most often bilateral projections

Question 27

where is the spinal accessory nucleus located?

Answer 27

caudal medulla non-symmetrical bilateral projections

Question 28

rubrospinal tract function

Answer 28

exact function is unclear, likely influences flexors of upper limbs

Question 29

rubrospinal tract pathway

Answer 29

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

Question 30

what does flexor posturing indicate?

Answer 30

the corticospinal tract is damaged above the red nucleus

Question 31

what does extensor posturing indicate?

Answer 31

brainstem damage below the red nucleus

Question 32

key traits of posturing

Answer 32

occur in a comatose patient only see a response in the upper limbs move in the direction of painful stimuli

Question 33

where does the ventral corticospinal tract project to?

Answer 33

only to cervical and upper thoracic spinal cord

Question 34

what movements occur due to the ventral corticospinal tract?

Answer 34

control of bilateral axial and girdle muscles

Question 35

ventral corticospinal tract pathway

Answer 35

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

Question 36

what is the vestibulospinal tract important for?

Answer 36

maintaining balance and posture receives input from vestibular organs

Question 37

where are cell bodies of the vestibulospinal tracts?

Answer 37

medial and lateral vestibular nuclei of medulla and pons

Question 38

lateral vestibulospinal tract pathway

Answer 38

ipsilaterally in ventral funiculus of sc synapse in ventral horns on LMNs and intermotor neurons (posture and balance)

Question 39

medial vestibulospinal tract pathway

Answer 39

descends bilaterally to superior cervical sc levels (control head position related to eye position)

Question 40

tectospinal tract pathway

Answer 40

originates in neurons in deep layers of superior colliculus, decussates immediately projects to cervical spinal segments

Question 41

what is the tectospinal tract important for?

Answer 41

partial control of neck, shoulder, and upper trunk muscles roles in eye/head movement coordination

Question 42

reticulospinal tract pathway

Answer 42

originate in pontine/medullary reticular formation descend in ventral funiculus ipsilateral tract with bilateral motor control

Question 43

what is the reticulospinal tract important for?

Answer 43

influencing automatic movements like posture control and balance on uneven terrain

Question 44

what are segmental interneurons?

Answer 44

short axon that distributes branches ipsilaterally within a single spinal segment synapse on MN or other interneurons

Question 45

segmental interneuron input

Answer 45

receives input from somatic sensory receptors for reflex control of movement

Question 46

what are commissural interneurons?

Answer 46

axons distribute bilaterally for movement coordination of both sides of the body

Question 47

what are propriospinal interneurons?

Answer 47

axons project for multiple spinal segments before synapsing on MNs (upper-lower limb coordination)

Question 48

where is the supplementary motor area located? what is its role?

Answer 48

medial surface of cerebral hemisphere specific role unknown

Question 49

where is the cingulate motor area located? what is its role?

Answer 49

medial surface, deep in cingulate sulcus part of the limbic system

Question 50

where is the premotor cortex located?

Answer 50

lateral hemisphere, ventral to primary motor cortex

Question 51

what is the dorsal premotor cortex function?

Answer 51

helps control reaching

Question 52

what is the ventral premotor cortex function?

Answer 52

helps control grasping contains mirror neurons that activate when watching others perform an action

Question 53

what occurs when there is damage to the premotor areas?

Answer 53

apraxia, motor planning disorders loss of ability to produce learned purposeful movements

Question 54

what is needed in order to produce movement?

Answer 54

decision to move (limbic and prefrontal) visual info (posterior parietal cortex)

Question 55

what is multiple sclerosis?

Answer 55

autoimmune inflammaotry disorder to the CNS myelin that affects UMNs plaques of demyelination can appear and disappear on an MRI

Question 56

what is Guillain-Barré syndrome?

Answer 56

immune-mediated demyelination of peripheral nerves typically onsets 1 to 2 weeks following a viral or bacterial illness

Question 57

Guillain-Barré presentation

Answer 57

ascending progressive weakness, areflexia, tingling paresthesia of hands and feet

Question 58

what is Amyotrophic Lateral Sclerosis?

Answer 58

gradual degeneration of upper and lower motor neurons