Motor Systems

Question 1

What is the general function of the Basal Ganglia wrt motor control?

Answer 1

suppresses unwanted movements and helps to initiate movements

Question 2

What is the general function of the Cerebellum wrt motor control?

Answer 2

critical for “motor error” – difference between intended and actual movements – helps correct those

Question 3

What is a lower motor neuron?

Answer 3

Neurons in the brainstem and spinal cord that directly innervate muscles.

Question 4

What is another name for a lower motor neuron?

Answer 4

An alpha motor neuron.

Question 5

What do gamma motor neurons do?

Answer 5

Innervate intrafusal muscle fibers which allows muscle spindles to detect stretch info when the muscle is contracted.

Question 6

Where are motor neurons located in the spinal cord and how are they organized?

Answer 6

Located in the ventral horn and organized in columns along the rostral-caudal axis.

Question 7

How are the trunk and limb muscles mapped onto the spinal cord?

Answer 7

Motor neurons (MNs) innervating the trunk are more medial while MNs innervating the limbs are more lateral in the spinal cord.

Question 8

Where are local circuit neurons located and what are their functions?

Answer 8

located within the spinal cord, are often inhibitory, and make up basic reflex circuits.

Question 9

What are group 1a afferent axons?

Answer 9

They are axons which detect changes in stretch in a muscle spindle

Question 10

What are group 2 afferent axons?

Answer 10

Axons which signal the state of stretch in a muscle spindle

Question 11

What is the typical pattern of muscle activation in a stretch reflex?

Answer 11

It activates one muscle/ muscle group of an antagonistic pair while inhibiting the other.

Question 12

How do GTOs compare with muscle spindles

Answer 12

Muscle spindles activate the contracting muscle while inhibiting its antagonist. GTOs inhibit the contracting muscle while activating its agonist

Question 13

What is a “central pattern generator”?

Answer 13

Complex circuitry of the lower motor system that can produce rhythmic movements without the upper motor system.

Question 14

What does a “central pattern generator” control?

Answer 14

Generally, timing and coordination of rhythmic movements.

Question 15

What is the common name for amyotrophic lateral sclerosis and describe the pathology.

Answer 15

Also known as ALS or Lou Gehrig’s disease. Degeneration of a motor neurons and of neurons in the motor cortex cause muscles to whither due to lack of use and leads to death.

Question 16

What is lower motor syndrome and what are the outcomes?

Answer 16

Damage to brainstem and spinal cord potentially resulting in paralysis or weakness of muscles, absence of reflexes, and atrophy of muscles.

Question 17

How to recover some function after spinal cord injury

Answer 17

Exercise and artificial muscle stimulation ASAP can help to recover some function.

Question 18

What do the lower motor neurons of the lateral and medial ventral horns control?

Answer 18

Medial ventral horn: Axial and proximal limb muscles
Lateral ventral horn: Distal limb muscles

Question 19

What do the upper motor neurons of the cerebral cortex and brainstem control and what are their functions?

Answer 19

Cortex UMNs innervate lateral ventral horn neurons and influence skilled limb movements
Brainstem UMNs innervate medial ventral horn neurons and influence posture and balance

Question 20

Where are the neurons that project down to the lower motor system?

Answer 20

Layer 5 neurons in primary motor cortex (M1)

Question 21

How do betz cells compare to pyramidal cells in size?

Answer 21

They are much larger

Question 22

Where do the corticobulbar and corticospinal tracts respectively terminate?

Answer 22

Corticobulbar – terminate in brainstem mostly bilaterally
Corticospinal – terminate in spinal cord

Question 23

Where does the pyramidal tracts originate?

Answer 23

From the corticobulbar tract that pass through the caudal medulla.

Question 24

What path/ neurons feed into and form the lateral corticospinal tract?

Answer 24

Axons passing through the medullary pyramid which form the “pyramidal” motor system

Question 25

What do the axons of the pyramidal path that don’t decussate do?

Answer 25

Form ventral corticospinal tract and terminate bilaterally.

Question 26

Do most corticospinal tract axons decussate or not?

Answer 26

Most decussate.

Question 27

What do the axons of the pyramidal path that don’t decussate do?

Answer 27

Form ventral corticospinal tract and terminate bilaterally.

Question 28

Alpha motor neurons for what regions are directly innervated by lateral corticospinal tract axons?

Answer 28

Alpha motor neurons controlling the forearm and hand.

Question 29

Where do most lateral corticospinal axons terminate and what are their functions?

Answer 29

Most terminate on local circuit neurons which have less fine control and more activation of rhythmic movements

Question 30

What are the parts of the corticospinal/corticobulbar pathways from somatosensory regions do?

Answer 30

Modulate proprioceptive signaling.

Question 31

How is the motor cortex organized?

Answer 31

Could be a map of different movements with the context of general body regions, or of ethologically (species specific) relevant kinds of behaviors.

Question 32

What does mirror neuron research suggest?

Answer 32

Mirror neuron research suggests that at least some neurons (especially outside M1) are really mapping the intention of performing action

Question 33

How do M1 neurons code for movement direction?

Answer 33

Individual neurons are tuned for certain directions and the pattern of activation is summed to generate a movement vector.

Question 34

Compare and contrast premotor and M1 cortex

Answer 34

Premotor: Receives more information from multisensory systems elsewhere in brain and from prefrontal systems involved in intention, motivation, and decision-making

M1: more direct control over movements

Question 35

What are the lateral portions of the premotor cortex responsible for?

Answer 35

Movement in response to external cues.

Question 36

What do ventrolateral premotor cortex mirror neurons do?

Answer 36

Fire in preparation for organism’s movement but ALSO when someone else makes the same action