Descending Motor Pathways & Motor Cortex

Front 1

What structures are considered higher motor structures?

Back 1

cortex, cerebellum, and basal ganglia

Front 2

What structures are considered lower motor control structures?

Back 2

Spinal cord & brainstem

Front 3

What are higher motor structures and what is their function?

Back 3

planning of voluntary actions

Front 4

What are lower motor structures and what is their function?

Back 4

Spinal Cord, Brainstem

Execution of movements, automatic movements

Front 5

What are some examples of automatic movements?

Back 5

Postural control, respiration, reflexes

Front 6

What are the 3 major descending motor pathways?

Back 6

Ventromedial brainstem pathway
Lateral brainstem pathway
Corticospinal pathway

Front 7

From what nuclei does the ventromedial brainstem pathway arise & what are the individual tracts called?

Back 7

Superior colliculus (midbrain) --> Tectospinal tract
Reticular formation (Pons/Medulla) --> Reticulospinal tract
Vestibular nuclei (Medulla) --> Vestibulospinal tract

Front 8

What muscles are targeted by the tracts of the ventromedial brainstem pathway?

Back 8

Axial (trunk) muscles

Especially activates the extensors

Front 9

From what nucleus does the lateral brainstem pathway arise and what is its tract called?

Back 9

Red nucleus --> Rubrospinal tract

Front 10

What muscles are targeted by the lateral brainstem pathway?

Back 10

Proximal and girdle muscles (upper limb)

Especially activates the flexors

Front 11

From where does the corticospinal pathway originate and what is its tract called?

Back 11

Cerebral cortex and corticospinal tract

Front 12

What runs along with the rostral corticospinal tract?

Back 12

Corticobulbar tract

Front 13

From where does the corticobulbar tract originate and what is its target?

Back 13

Cerebral cortex --> Cranial motor nuclei in the brainstem

Front 14

What functions are mediated by the tectospinal tract and superior colliculus?

Back 14

Coordination of eye and head movements

Front 15

What functions are mediated by the ventromedial pathway?

Back 15

Balance and posture

Front 16

The corticospinal and corticobulbar tracts are considered what types of tracts?

Back 16

Pyramidal tracts

Front 17

Which are the extrapyramidal tracts?

Back 17

Rubrospinal Tract (Lateral Brainstem Path)

Tectospinal, Vestibulospinal, Reticulospinal Tracts (Ventromedial Path)

Front 18

Which tracts do not decussate?

Back 18

Reticulospinal and Vestibulospinal Tracts

Front 19

What path does the corticospinal tract run from cerebral cortex to the spinal cord?

Back 19

Cerebral cortex --> Internal Capsule --> Cerebral peduncles --> Medullary Pyramids --> Decussate at the Spinomedullary Jxn --> Lateral funiculus of the spinal cord

Front 20

Where do corticobulbar fibers decussate?

Back 20

At the level of the cranial nerve nuclei that they innervate

Front 21

What functions are mediated by the corticospinal pathway?

Back 21

Voluntary movements, fine, precise, skilled actions

Front 22

What muscles do corticospinal fibers target?

Back 22

Widely distributed, overlapping the projections of the ventromedial and lateral brainstem pathways

*Also target the distal limbs (legs, hands)*

Front 23

Onto what neurons do corticospinal fibers terminate?

Back 23

Mostly interneurons in the intermediate, ventral gray

Fibers targeting distal muscles terminate *directly* on motor neurons (e.g. finger muscles)

Front 24

What is an upper motor neuron?

Back 24

A neuron whose axon descends in one of the descending pathways

Front 25

What is a lower motor neuron?

Back 25

A neuron that projects directly to a muscle (e.g. cranial nerve motor neuron)

alpha motor neuron

Front 26

How prevalent are individual tract lesions?

Back 26

Not prevalent - usually all are damaged; expect a compilation of signs to present

Front 27

Name the upper motor neuron signs (aka. long tract signs)

Back 27

Paresis without atrophy (unless from disuse)
Plegia
Groups of muscles affected
No fibrillations or fasciculations
Spasticity (after weeks)
Babinski sign
Clonus

*Clinical signs are contralateral to the lesion, unless lesion is bilateral*

Front 28

What is paresis?

Back 28

Weakness

Front 29

What is plegia?

Back 29

Paralysis

Front 30

How would you expect a patient to present if he/she has a limited cortical or corticospinal tract lesion?

Back 30

Individual movements of limbs and trunk preserved, but with diminished speed, agility, and power

Paresis and clumsiness of hand movements ("clumsy hand syndrome")

*Clinical signs are contralateral to the lesion, unless lesion is bilateral*

Front 31

What is spasticity?

Back 31

Hyperreflexia, hypertonia (especially in antigravity mm)

Front 32

When does spasticity occur?

Back 32

Only occurs with lesions in the CNS (*not seen in peripheral neuropathy*)

Manifests weeks after damage to long motor tracts

Front 33

Immediately after upper motor neuron damage, what clinical finding could confuse your diagnosis?

Back 33

Pt will present initially with hypotonia and hyporeflexia, which counters an expected presentation of spasticity

Front 34

What is clonus?

Back 34

rhythmic, repetitive, involuntary muscle contractions due to sudden stretching of the muscle

Indicative of upper motor neuron damage - CNS failing to inhibit contractions

Front 35

What does a positive Babinski sign indicate?

Back 35

Damage specifically to the corticospinal tract

Front 36

What other clinical test will reveal corticospinal tract damage?

Back 36

Failure in rapid hand movement test

Front 37

What is decerebrate rigidity and what is its cause?

Back 37

Caused by midbrain lesions

Lower brainstem and spinal cord receive no input from forebrain and midbrain, leaving the vestibulospinal and reticulospinal tracts unregulated

Front 38

How does decerebrate rigidity present clinically?

Back 38

Person has a posture of exaggerated extension of all four limbs because axial extensors activated by vestibulospinal/reticulospinal tracts, proximal extensors activated by lesion to rubrospinal tract, and distal extensors activated by lesion to corticospinal tract

All four limbs extended

Front 39

What is decorticate rigidity and what is its cause?

Back 39

Caused by large scale lesions to the cerebral cortex

Lateral brainstem pathway left intact, providing a net flexor drive to the upper limbs

Front 40

What is the clinical presentation of decorticate rigidity?

Back 40

Arms can flex, legs cannot

Front 41

What is the clinical presentation of damage to all three descending pathways?

Back 41

Death :(

Front 42

What are some causes of decerebrate rigidity?

Back 42

syringobulbia - formation of a syrinx (cystic cavity) around the 4th ventricle

syringomyelia - formation of a syrinx around the central canal of the spinal cord

midbrain tumor

midbrain stroke (basilar)

Front 43

Explain the pathology of locked-in syndrome

Back 43

Caused by bilateral ventral pontine lesions (e.g. basilar infarct), resulting:

- bilateral transection of long descending cortical fibers (quadraplegia)
- damage to CN VI, VII, IX, X, XII (no horizontal eye mvmt, facial mvmt, speech)

Front 44

What functions are left intact in a person with locked-in syndrome?

Back 44

vertical eye movements and blinking (CN III)

Front 45

What functions are generated by the primary motor cortex?

Back 45

Skilled, voluntary, finely graded movement

Direction, speed, and amplitude of movement

Front 46

What is the function of supplementary motor cortex (area 6)?

Back 46

Motor planning

Front 47

From where does the motor cortex (areas 4, 6) receive inputs?

Back 47

VL Thalamus (basal ganglia, cerebellum)
Somatic Sensory Cortex
Parietal Association cortex
Brainstem & Basal Forebrain

Front 48

What is the function of the parietal association cortex?

Back 48

receive inputs from auditory somatosensory, higher visual, prefrontal cortical areas

Front 49

To where does the motor cortex send its outputs?

Back 49

Cortico-striatal projection to Basal ganglia
Cortico-ponto-cerebellar projection to Pons
Descending motor pathways (3)
VL Thalamus
Parietal Association cortex
Somatic Sensory cortex

Front 50

A patient comes into the ED presenting with bilateral leg weakness. What are potential causes of this presentation?

Back 50

Damage along the falx cerebri:
- Meningeal tumor on the medial surface of the cerebral hemispheres
- Infarct of an ACA branch

Spinal Cord Injury (more likely):
- Herniated disk

Front 51

Damage to what structure is the most likely cause for paresis of both arms and/or legs?

Back 51

Spinal cord

Front 52

Lesions to what area causes apraxias?

Back 52

Supplementary Motor Area (medial of area 6)

Pre-motor Area (lateral part of area 6)

Posterior Parietal Cortex

Front 53

What is an apraxia?

Back 53

*Loss of the ability to perform a pre-learned task,* even though:

The request or command is understood
Pt is willing to perform the task
The muscles needed to perform the task are intact
Pt does not have sensory loss

Front 54

A supranuclear lesion to CN VII nucleus cause will what clinical presentation?

Back 54

Will interrupt all the corticobulbar input to the muscles of the LOWER HALF of the face

Only the upper part of the face can still be voluntarily activated by the remaining ipsilateral corticobulbar projection

Front 55

A nuclear lesion to CN VII nucleus will cause what clinical presentation?

Back 55

Paresis or plegia of the entire face because nucleus cannot register stimulus from ipsilateral nor contralateral corticobulbar fibers

Front 56

An infranuclear lesion with respect to the CN VII nucleus will cause what clinical presentation?

Back 56

Paresis or plegia of the entire face because axons traveling to the face are damaged

Front 57

Which artery supplies the area of the motor cortex projecting to the face, arm, and hands?

Back 57

Middle cerebral artery (MCA)

Front 58

Which artery supplies the part of the motor cortex projecting to the foot and legs?

Back 58

Anterior cerebral artery (ACA)

Front 59

Which structures does the basilar artery and/or its branches supply?

Back 59

Cerebral peduncles, midbrain tegmentum, pons (pontine arteries), cerebellum (AICA)

Front 60

What is the blood supply for the medulla?

Back 60

Vertebrals and vertebro-basilar junction

Front 61

What is the blood supply for the spinal cord

Back 61

Anterior and posterior spinal arteries?

Front 62

From where do the anterior and posterior spinal arteries receive their blood supply?

Back 62

Primarily from vertebral arteries; also from various branches of the aorta

Front 63

From where does the internal capsule receive its blood supply?

Back 63

Middle cerebral artery

Front 64

From where do the basal ganglia receive their blood supply?

Back 64

Middle cerebral artery

Front 65

What is the peri-Rolandic cortex?

Back 65

Synonymous with the sensory-motor cortex; all of the cortical areas involved in motor control

Front 66

How can the cortex control its own sensory input?

Back 66

Via the corticospinal axons that originate in the parietal sensory cortex and project to sensory relay structures (dorsal horn/dorsal column nuclei)