Motor Systems

Question 1

What does the primary motor cortex control?

Answer 1

Controls execution of movement.

The “on” switch

Question 2

What does the supplementary motor area control?

Answer 2

1. Coordination and execution of sequences of movement.
2. Attainment of motor skills.
3. Executive control of movement (how the movement is executed)

Question 3

What does the premotor area control?

Answer 3

1. Coordinates selection of appropriate motor plans for voluntary movements.
   - lateral region = movements in response to external cues.
   - medial region = movements in response to internal cues.
2. Mirror motor neurons

Question 4

Where are mirror motor neurons located?

Answer 4

In the lateral premotor area.

• These neurons fire when watching someone else move.

Question 5

What tracts are located in the lateral motor systems?

Answer 5

1. Lateral corticospinal tract

2. Rubrospinal tract

Question 6

What tracts are located in the medial motor systems?

Answer 6

1. Anterior corticospinal tract
2. Reticulospinal tract
3. Tectospinal tract
4. Vestibulospinal tracts

Question 7

What does the lateral corticospinal tract control?

Answer 7

Movement of the extremities.

• Particularly important for rapid, dexterous movements at individual digits or joints.
• Modulatory control of myotactic reflex

Question 8

What is the internal capsule?

Answer 8

Major highway for ascending and descending pathways.

Question 9

What are the gray matter borders of the internal capsule?

Answer 9

Medial border = thalamus and caudate

Lateral border = globus pallidus and putamen

Question 10

What are the components of the anterior limb of the internal capsule?

Answer 10

Thalamic and brainstem fibers that project to prefrontal and parietal cortical regions.

• Also associated with different aspects of emotion, motivation, cognition processing, and decision - making.

Question 11

Where is the genu located in the internal capsule?

Answer 11

The middle portion between the anterior and posterior limbs.

Question 12

What are the components of the posterior limb of the internal capsule?

Answer 12

1. Descending motor fibers from frontal lobe going to brainstem and spinal cord.
2. Ascending somatosensory fibers from spinal cord.

Somatotopically organized

Question 13

Describe the somatotopic organization of the lateral corticospinal tract from lateral to medial in the subcortical regions.

Answer 13

Leg –> Trunk –> Arm –> Face (corticobulbar tract)

Question 14

What does the anterior corticospinal tract control?

Answer 14

Controls bilateral axial and girdle muscles.

Question 15

What percent of the corticospinal tract deccusates and what percent stays ipsilateral?

Answer 15

85% will deccusate and turn into the lateral corticospinal tract
15% remains ipsilateral to become anterior corticospinal tract

Question 16

What does the rubrospinal tract control?

Answer 16

Controls movement of the extremities:

• Modulation of flexor muscle tone.
• Inhibition of anti-gravity muscles (extensors)
• Modulation of reflex activity (flexor withdrawal reflex)

Question 17

What does the reticulospinal tract control?

Answer 17

Descending modulation from reticular formation that controls automatic posture and gait-related movements:

• Pontine reticular formation = inhibits limb flexors and excite extensors
• Medullary reticular formation = excite limb flexors and inhibit extensors.

Question 18

What does the tectospinal tract control?

Answer 18

Controls coordination of head and eye movements.

• Effect head movements to match eye movements.

Question 19

Where do multipolar alpha motor neurons exit the spinal cord?

Answer 19

Exit the spinal cord from the ventral horns, go through the ventral nerve root, and on to innervate target musculature.

Question 20

Can peripheral nerves only travel solo or can they be found in plexi as well?

Answer 20

Found in both!

Question 21

What is a myotome?

Answer 21

A group of muscles innervated by a single spinal nerve root.

Question 22

What is the neuromuscular junction?

What is it essential for?

Answer 22

A highly specialized synapse between a motor neuron and its target muscle fiber.

Essential for muscle contraction and prevention of muscle atrophy.

Question 23

What structures are found in the neuromuscular junction?

Answer 23

Synaptic bouton, synaptic cleft, and motor end plate.

Question 24

How many neuromuscular junctions are there for each muscle fiber?

Answer 24

Just 1

Question 25

What is the synaptic bouton?

Answer 25

Terminal axons of motor neurons.

Question 26

What is the motor end plate?

Answer 26

The area that falls under synaptic boutons.

It has unique junctional folds that hold ligand-gated acetylcholine receptors.

Question 27

Describe the steps of the neuromuscular synapse.

Answer 27

1. Action potential from presynaptic motor neuron triggers release of acetylcholine into synaptic cleft.
2. Binds to ACh receptors, which open to allow Na+ to flow into the muscle fiber.
   - -> Leads to ESPS, which leads to AP to travel down muscle fiber to facilitate muscle contraction.
3. ACh is broken down by acetylcholinesterase to end muscle contraction.

Question 28

Describe type 1a motor units.

Answer 28

• Slow motor units.
• Small muscles
• Sustained muscle contraction

Question 29

Describe type 2a motor units.

Answer 29

• Fast fatigue-resistant motor units.
• Intermediate in size
• Generate 2x force as slow, and better resistance to fatigue that fast-fatigable.

Question 30

Describe type 2b motor units.

Answer 30

• Fast fatigable motor units.
• Large muscles
• Brief, but forceful contractions

Question 31

Describe the size principal for motor units.

Answer 31

Weak synaptic stimulation recruits the smallest motor units.
As input increases, progressively larger motor units are activated, which leads to larger force being generated.

Question 32

What is the order that motor units are recruited?

Answer 32

Slow –> fast fatigue resistant –> fast fatigable