6. Motor System

Question 1

Posture and balance monitored by

Answer 1

Proprioceptive pathways
Vestibular labyrinths
Visual input

Question 2

Posture and balance maintained by

Answer 2

Postural adjustments mediated by descending pathways

Question 3

What are your antigravity muscles?

Answer 3

Flexors in the upper extremities

Extensors in the lower extremities

Question 4

Hierarchy of Motor Control

Answer 4

Lower motor neurons
–Innervate skeletal muscle

Interneurons (Local circuit neurons)
–Integrate sensory and descending input
–Mediate reflexes

Upper motor neurons
–Regulate activity of local circuit neurons and lower motor neurons

Basal Ganglia and Cerebellum
–Regulate activity of upper motor neurons

Question 5

In medial ventral horn (where LMNs innervate axial muscles): Local circuit neuron axons extend over ______ segments and terminate_____.

Answer 5

Many

Bilaterally

Question 6

Local circuit neuron axons extend over ______ segments and terminate______.

Answer 6

Few

ipsilaterally

Question 7

Descending pathways with fiber in anterior funiculus terminate

Answer 7

Over several segments and terminate bilaterally

Question 8

Cell bodies of LMN are found in

Answer 8

Cranial nerve nuclei of brainstem or ventral horn of spinal cord

Question 9

Lower motor neurons axons innervates

Answer 9

Skeletal muscles

Question 10

Upper motor neurons cell bodies are located

Answer 10

Motor cortex

• corticospinal tract
• corticobulbar tract

or brainstem centers

• Vestibular nuclei – vestibulospinal tracts
• Reticular formation – reticulospinal tract
• Superior colliculus – colliculospinal tract

Question 11

Upper motor neurons axons terminate on

Answer 11

Lower motor neurons or interneurons

Question 12

UMN in motor cortex project________
terminate_________
Descend in _______
regulate_______

Answer 12

• Project contralaterally
• Terminate in lateral ventral horn
• Descend in lateral funiculus
• Regulate LMNs innervating distal limb muscles essential for skilled movements

Question 13

UMNs in brainstem:
Terminate in _______
Descend in _______
Regulate ______

Answer 13

• Descend in anterior funiculus
• Terminate in medial ventral horn
• Regulate LMNs innervating axial and proximal limb muscles essential for control of posture and balance

Question 14

Primary Motor Cortex initiates what type of movements

Answer 14

Contralateral movements

Question 15

Course of corticospinal tract

Answer 15

1. Origin in sensorimotor cortex
2. Internal capsule
3. Crus cerebri of midbrain
4. Fiber bundles in base of pons
5. Pyramid of medulla
6. Lateral corticospinal tract:
   • crosses midline in caudal medulla via pyramidal decussation
   • located in lateral funiculus of spinal cord

Question 16

Corticobulbar fibers tract course is from

Answer 16

1. Originate in head neck and face and travel with corticospinal tract to brainstem and exit at various brainstem level

They are motor nuclei of cranial nerve

Question 17

Descending pathways from brainstem function

Answer 17

To control posture and balance

Question 18

Lateral vestibulosoinal tract function is

Answer 18

Excitatory to antigravity muscles

Question 19

Upper motor neuron syndrome 1 symptoms

Answer 19

Initial period (several days - few weeks) of spinal shock: flaccidity (hypotonia) in limbs

Followed by:

1. Spasticity = hypertonia and hyperreflexia in extremities
2. Clonus = oscillating muscle contraction/relaxation in response to passive stretch
3. Decreased superficial reflexes (hyporeflexia): corneal, superficial abdominal and cremasteric reflexes***
4. Babinski sign (positive or upgoing)