12.2 MSK and Neural Control

Question 1

What are the two parallel visual pathways involved in reaching?

Answer 1

The “what” (perception/identification) pathway and the “where” (localization/action) pathway.

Question 2

What is the primary function of the “what” pathway?

Answer 2

Identifying the object—its size, shape, texture—to guide hand shaping and required force.

Question 3

What is the primary function of the “where” pathway?

Answer 3

Determining the location of the object in space and guiding arm/trunk movements to reach it.

Question 4

Why must the “what” and “where” pathways work together?

Answer 4

You can’t grasp what you haven’t identified, and you can’t act on what you can’t locate.

Question 5

What role does sensory feedback play during movement execution?

Answer 5

Detecting and correcting errors in real time—especially in the final, precise part of the reach.

Question 6

What is feedforward control based on?

Answer 6

Predictions from previous experience that help plan movement before it begins.

Question 7

When does visual/proprioceptive feedback become critical during a reach?

Answer 7

During the latter part of the movement for fine adjustments.

Question 8

How long does it take to process sensory feedback?

Answer 8

About 100 milliseconds.

Question 9

What coordinate system does vision use?

Answer 9

Eye-centered coordinates.

Question 10

What coordinate system does audition use?

Answer 10

Head-centered coordinates.

Question 11

What coordinate system does somatosensation use?

Answer 11

Body-centered coordinates.

Question 12

Which reference frame does the CNS often use as the common planning frame?

Answer 12

Eye-centered coordinates due to vision’s reliability.

Question 13

What two parameters are essential for grasp planning?

Answer 13

Time-to-close-the-hand and minimum-jerk (smoothest trajectory).

Question 14

How do transport and grasp components interact?

Answer 14

They are continuously temporally matched—hand arrival must coincide with grip formation.

Question 15

What is the main function of visual feedback in reaching?

Answer 15

Ensuring final accuracy of hand placement.

Question 16

How does reaching across midline compare to reaching on the same side?

Answer 16

It is slower and less accurate.

Question 17

How should rehab progress regarding midline reaching?

Answer 17

Start with same-side reaching, then progress to cross-midline tasks.

Question 18

What does proactive visual/somatosensory control regulate at the start of movement?

Answer 18

Initial limb direction and intersegmental coordination.

Question 19

How does vision help pre-program grip force?

Answer 19

By using object size, shape, and weight information before contact.

Question 20

When is somatosensory input not required?

Answer 20

For simple, single, or non-repetitive movements.

Question 21

What happens without somatosensory feedback during repeated or multi-joint tasks?

Answer 21

Internal representations drift, leading to movement drift and poor coordination.

Question 22

Why do patients recovering from paralysis often feel limb heaviness?

Answer 22

The brain senses the intensity of motor commands even before movement—reflecting motor–sensory interaction.

Question 23

What do cutaneous receptors detect during object handling?

Answer 23

Early detection of slip.

Question 24

What two adjustments occur when slip is detected?

Answer 24

Increased finger muscle activity (grip force) and adjustments at elbow/shoulder to reduce hand acceleration.

Question 25

What scapular motion is required for effective arm movement?

Answer 25

Scapular rotation.

Question 26

What forearm motion is required for proper hand orientation?

Answer 26

Supination.

Question 27

What degrees of shoulder/elbow flexion are typically required for reaching?

Answer 27

Approximately 100–120° flexion.

Question 28

What wrist position supports functional grasp?

Answer 28

Slight extension beyond neutral.

Question 29

How do postural demands change between seated and standing reaching?

Answer 29

Standing requires greater trunk and leg activation to maintain stability.

Question 30

How does reducing postural demands (e.g., with supports) affect arm movement?

Answer 30

Movements become faster because less effort is spent stabilizing the body.

Question 31

Which neck muscles activate feedforward before rapid arm movements?

Answer 31

Sternocleidomastoid and cervical extensors.

Question 32

Why do neck muscles activate before arm movements?

Answer 32

To stabilize the head for accurate visual and vestibular processing.