Basic Concepts in the Control of Movement

Question 1

Motor control

Answer 1

ability to regulate or direct mechanisms essential to

movement.

Question 2

Motor learning/adaptation generally refers to the

Answer 2

neuronal changes that occur to allow an individual to accomplish a new motor task, to perform a task better, faster or more accurately than before usually
refers to motor adaptation.

Question 3

How are movements organised by the CNS to achieve

behavioural goals?

Answer 3

1. CNS predicts -> feedforward motor/postural command
2. Activates aMN’s in SC -> innervate muscles required to execute task
3. Resultant movement generates sensory feedback used to correct errors
4. Update plan

Question 4

Movement ability depends on

Answer 4

CNS development and experience

Question 5

Primary categories of movement

Answer 5

1. Reflex
2. Rhythmical
3. Voluntary

Question 6

What are the 2 basic types of motor activity?

Answer 6

Ballistic and guided by feedback

Question 7

Ballistic movement characteristics

Answer 7

• Forward model
• Open-loop
• Problems with accuracy but fast
• Useful for well-known tasks
• Updated through learning

Question 8

Guided by feedback characteristics

Answer 8

• Feedback model
• Closed-loop
• Accurate but problems with delay
• Useful for novel tasks
• Enables learning

Question 9

General model by which tasks are carried out

Answer 9

Idea, Plan, Execution, Appraisal

Question 10

3 types of control

Answer 10

Feedforward, feedback, biomechanical control (modulation of limb compliance)

Question 11

Forward model vs feedback system

Answer 11

1. Timing of sensory feedback: at least 50ms to get to sensorimotor areas of the brain and back to the
   spinal cord and muscle to adjust output.
2. Forward model/ feedforward command can initiate action on the basis of prediction.

Question 12

What are 2 basic models of motor control?

Answer 12

‘Servo’model i.e. feedback + Optimal feedback control

Question 13

How are motor tasks organised?

Answer 13

Movements occur on a continuum of automatic to voluntary

Question 14

2 main functions of muscles:

Answer 14

1. Generate power -> recruitment of motor units

2. Sensory information -> receptors that modulate muscle activation

Question 15

Proprioceptor

Answer 15

Any type of receptor which gives information about body position or movement e.g. primary muscle spindles, GTO

Question 16

Where are muscle spindles in relation to muscle fibres?

Answer 16

Muscle spindles (proprioceptors): intrafusal muscle fibres
attached at the end of extrafusal muscle fibres that envelop it and lie in parallel with the muscle fibres

Question 17

What type of muscle fibres make up the intrafusal portion of the muscle spindle?

Answer 17

Dynamic (bag) and static nuclear bag -> signals phasic and tonic aspects of muscle stretch

Question 18

Muscle spindle primary afferents are called ____ and arise from ____

Answer 18

Type 1a (large diameter) , arise from all intrafusal fibre types

Question 19

Muscle spindle secondary afferents are ____ and arise from ____

Answer 19

Type 2 ( medium diameter), from static fibres

Question 20

Muscle spindle sensitivity

Answer 20

controlled by the gamma (γ) efferent system

Question 21

Position of joints is determined by

Answer 21

Muscle length

Question 22

What is the role of the stretch reflexes in the control of

movement?

Answer 22

Feedback mechanism: responds and makes adjustments to small changes in length at the spinal cord level during contractions against loads, for unexpected disturbance and for stabilisation during postural activity, by reflexive corrections (Aniss et al 1990) and transmits signals about length and rate of change in length to supraspinal areas

Question 23

Why is the stretch reflex important (4 points)?

Answer 23

1. Muscle spindle is the sensory receptor for the reflex
2. Stretch reflex can be modulated by descending pathways & other inputs
3. Circuitry results in innervation of agonist & antagonist muscles
4. Useful to study the excitability of the α MN

Question 24

What are golgi tendon organs?

Answer 24

Proprioceptors: encapsulated receptors which lie at the junction between muscle fibres and tendons (musculo-tendinous junction): lie in series in the muscle that are sensitive to changes in muscle tension

Question 25

What are the components of GTO’s?

Answer 25

Have Ib afferent fibres onto one group of Ib interneurones that are inhibitory to agonist muscles (at least disynaptic) and others which are excitatory to antagonistic muscles (disynaptic or trisynaptic).

Question 26

How does the net firing rate of GTO’s relate to whole muscle force?

Answer 26

Closely

Question 27

How do GTO’s compare to muscle spindles?

Answer 27

Difference: muscle spindles do not have a mechanism to modulate their sensitivity
Similarity: Like muscle spindles they are mechanoreceptors and respond to stretch/tension which results in opening of their ion channels and generation of action potentials.

Question 28

What happens to 1b during locomotion?

Answer 28

Ib activity is depressed due to modification by descending

signals to allow excitation i.e. activity of GTO is task dependent

Question 29

What is the final output neurone?

Answer 29

Alpha m.n.