50 Overview of motor system

Question 1

What are saccades? What is its function?

Answer 1

Continuous jerky motion during focusing on one object.
Allow light from different parts of the object to focus on the fovea, so the brain can form a clear and comprehensive picture of the whole object.

Question 2

List the 5 main parts of the cerebral cortex involved in the motor system.

Answer 2

1. Primary motor area
2. Premotor area
3. Supplementary motor area
4. Cingulate area
5. Parietal Cortex

Question 3

Other than the cerebral cortex, which parts of the brain are included in the motor system?

Answer 3

1. Cerebellum
2. Spinal cord
3. Basal ganglia
4. Branstem

Question 4

List the stages of movement generation briefly.

Answer 4

1. Task goal >
2. Trajectories >
3. Joint angle >
4. Torque >
5. Muscle pattern >
6. Motion

Question 5

_______________ is the process between formulating a task foal and planning the trajectories.

Answer 5

Movement planning

Question 6

_______________ is the process between planning trajectories and computing the joint angle patterns.

Answer 6

Inverse kinematics

Question 7

What are the features of trajectories?

Answer 7

1. Straight line path
2. Bell-shaped velocity profile (speed of limb is highest in the middle of the motion)
3. Two-third power law: the greater the curvature, the slower the subject move (= the brain prefer straight line movements; curvature 2/3 positively related to angular speed of the limb)

Question 8

What does it mean by a hierarchical motor system? Why is it related to motor equivalence?

Answer 8

There are multiple components for generating muscle activation patterns that execute the planned trajectories;
Motor equivalence: similar trajectories can be produced by different body segments, meaning that there is abstract purposeful movement of the motor system

Question 9

What are the stages involved in inverse dynamics?

Answer 9

Computing joint angle patterns > computing joint torques and muscle activations

Question 10

State the stages of motor execution. (shorter)

Answer 10

Joint angle > Torque > Muscle patterns > Motion

Question 11

What are the 4 complexities of motor execution?

Answer 11

1. Complex inverse dynamics equations involving different degrees of freedom of limbs
2. Redundancy in musculature
3. Indeterminacy of muscle actions
4. Complexity of coordinating many muscles

Question 12

What does it mean by redundancy in musculature?

Answer 12

1. Multiple muscles with overlapping functions

2. Different muscle patterns compatible with each net joint torque pattern (same purposeful movement)

Question 13

What does it mean by indeterminacy of muscular actions?

Answer 13

Movement of the same set of muscles in the same way depends on the limb’s configuration and state.

1. Muscle length and activation: function of Muscle force
2. Joint angle: function of moment arm of muscle (the higher the moment arm, the better force of transmission)

Question 14

Both ________ and _________ systems are required for successful motor execution.

Answer 14

Motor; Sensory

Question 15

What are the 2 general strategies for motor execution and what are their differences?

Answer 15

1. Feedforward motor control
2. Feed-back motor control

Feedforward: centrally generated commands without regard to consequence
Feedback: motor commands specified by comparing desired state and actual state

Question 16

In _____________ motor control, no sensory component is needed and it contains a single velocity peak.

Answer 16

feedforward

Question 17

List the 2 advantages of feedforward motor control.

Answer 17

Advantages:

1. Fast generation
2. Precise commands can be shaped through learning

Question 18

In feedback control control, ______________ receives a copy of the descending motor pathway from ______________ motor control commands via _____________.

Answer 18

Spinocerebellum;
Cerebral cortex;
Ventral spinocerebellar tract

Question 19

What is the difference in terms of the peaks in feedforward and feedback control?

Answer 19

Feedforward: single peak
Feedback: contains secondary peaks from feedback adjustments

Question 20

List 3 disadvantages of feedforward motor control.

Answer 20

Disadvantages:

1. Movement error cannot be corrected (from imprecise motor planning/execution/ unexpected perturbations)
2. Requires good knowledge of the muscles and limbs
3. Needs not-too-noisy neural system

Question 21

List the advantage and disadvantages of feedback control compared to feedforward conrol.

Answer 21

Advantage:
- precise movement possible with feedback-driven correction

Disadvantages:
- Delayed arrival of sensory information can cause movement instability

Question 22

What are the differences of motor programs from reflexes?

Answer 22

1. Can be learned

2. Needs not to be triggered by specific sensory stimulation

Question 23

Motor programs are stored in motor system and it incorporates an _____________________ in which the movement is executed.

Answer 23

internal representation of the dynamical environment