Movement control

Question 1

What is postural control and how is it maintained

Answer 1

Postural control refers to the ability to maintain and regain an appropriate body orientation to complete a task. Regulates the relationship of our whole body and body segments to other segments, the task/internal forces and the environment/external forces.

Therefore can be seen as the ability to maintain postural stability (center of mass) within BOS.

• Externally generated perturbations
• Internally generated perturbation (breathing, GAIT, coughing)

We learn through exposure to int/ext forces

Posture maintained through combination of active (muscles) and passive structures (connective tissue)

Question 2

Sensory input for postural control

Answer 2

Sensory input

• Visual (self or environment)
• Vestibular (head orientation and movement)
• Somatosensory (pressure, movement, surface changes)

CNS will select and weigh inputs based on availability, accuracy (night then less visual) and task

Question 3

What is ataxia

Answer 3

Ataxia comes from a lack of proprioceptive information. Patient uses vison to monitor movements to compensate.

Question 4

Elderly changes to postural control

Answer 4

In elderly the decondition of muscle/connective tissue reduces ability to make postural responses.

Question 5

Maintenance of COM in BOS and oscillations

Answer 5

COM is just ant to S1

COP = center of pressure. Single point on a surface through which the force passes

Normal posture has small AP and ML oscillations due to small changes in muscle activation and connective tissue compliance. Greater amplitude in AP direction.

This postural sway increases with age.

Association with COP increases and occurrence of falls

Question 6

What are the 4 key motor outputs in postural control

Answer 6

Voluntary, Anticipatory, Autonomic, Reflex

Question 7

Voluntary motor output to postural control

Answer 7

Cortically driven, infinite variety, corticospinal and corticobulbar output

Question 8

Anticipatory motor output to postural control

Answer 8

• Activation of postural muscle before voluntary movement (feed forward)
• Cortically driven (part of movement plan), memory based/learnt movements, can adapt with repetition and change in circumstance (anticipation of pain)
• Reticulospinal

Question 9

Autonomic motor output to postural control

Answer 9

• Brain stem and cortex, triggered by external stimuli. First line of defence against perturbation
• Highly adaptable
• Tectospinal and vestibulospinal
• Ankle strat - slow/low amplitude perturbation with large contact surface, muscle recruited distal to prox, head in phase with hips (swing at ankle)
• Hip strat - fast/large amp perturbation, unstable surface or narrow, rapid trunk adjustment. Muscle recruit proximal to distal, hip out of phase with head (lower center of gravity)
• Step strat - prevent falls, large perturbation that are fast, all other strats fails. Alters BOS using many muscles

Question 10

Reflex motor output to postural control

Answer 10

Simplest neural circuit. Involves sensory receptor and its afferent axon and group of MUs. Modified direct at spinal cord. Local responses only, highly stereotypical

Question 11

Factors that can effect EMG singles

Answer 11

position of electrodes, type of electrodes, cross talk, depth of muscle, enviro noise, skin prep, contraction type (concentric has greater amplitude as can use passive forces as much)

Question 12

What is the optimal location and orientation of surface electrodes

Answer 12

Within the boundaries of the muscle and parallel to the muscle fibres. Helps to reduce the risk of cross talk

Question 13

How is TMS used to create a motor cortical map

Answer 13

TMS is used to provide stimulation to a specific region of the motor cortex, this will produce a response in muscles that are specific to that region of the cortex.
Electrodes are placed onto relevant muscle for that specific region of the cortex and their EMG activity is recorded.
This can determine which areas of the cortex provide the greatest EMG potential for specific muscles therefore allowing for the creation of a cortical map which shows what regions of the brain give EMG responses for specific muscles.
Researchers are looking for peal EMG response for specific muscles to determine the region most involved in muscle stimulation.

Question 14

MEP with contraction

Answer 14

Motor evoked potential (MEP) from TMS will increased when there is already contraction

Question 15

Why are bipolar electrodes used

Answer 15

Use bipolar electrode because it increases size of recording zone and should help to reduce noise from other electrical signals

Question 16

How does discharge rate different in long and short isometrics holds

Answer 16

• Note the long hold vs short hold isometric MU discharge rate (force is the same) both active and passive structures
  
  • Available cross bridges
  • More passive tension in long hold (titin)

Question 17

What is needed for motor plasticity

Answer 17

• Cortico-motor pathways is strengthened with voluntary contraction and training
• Increased MEP and movement amplitude for the same stimuli (Increased APs from same strength TMS pulse) or altered movement direction/amplitude (depends on what has been trained)
• The type of training is important in determining if corticomotor excitability will change. Complex skill training has greatest effect and causes increased MEP amplitude at rest and during contraction.

Question 18

How does pain effect motor plasticity

Answer 18

• Motor plasticity is possible with pain if attention is maintained to the task
  
  • If pain is elsewhere in the body then focusing on that may alter the ability for motor plasticity

Question 19

Brain regions involved in movement and planning

Answer 19

Primary motor cortex - initiation of motor plans

Premotor cortices - planning and selecting complex movement

Supplementary motor area - supplies a plan that specific the sequence and extent of muscle contractions needed to execute movement

Posterior parietal cortex - takes in sensory info and forms a conscious map of the body in relation to its surroundings

Question 20

Findings for low back pain in regards to cortical motor maping

Answer 20

People with low back pain tend to keep using back muscle on bending for longer before using passive structures (PLL, ligamentum flavum) compared to those with low back pain

Question 21

Short and long term motor adaptation to pain

Answer 21

Motor adaptations may have short term benefit such as avoiding pain or protecting a painful spot. They may also contribute to long term changes in motor patter and persistence or reoccurrence of pain (altered activation patterns)

Question 22

What occurs in motor adaptations to pain

Answer 22

• Not a simple generalised inhibition during pain
• Redistribution not a decrease
• SEMG not sensitive to this change

Motor unit discharge rate is lower during forced matched contractions with pain.

Force is able to be maintained due to the recruitment of new motor units. There is a difference from no pain not just extra units, some are only present in no pain.

During this adaptation there is minimal change in surface EMG.

Question 23

What drives altered MU discharge during pain

Answer 23

During a single joint task stress is not systematically altered within the painful muscle. However, if there is a clear alternative (double leg) then there is unloading in the painful part therefore decrease in stress.

• Redistribution of activity within and between muscles during acute pain and anticipation of pain
• Does not necessarily resolve after pain has stopped
• Redistribution not observed using SEMG
• Associated with absolute change in force and stress (not all in same way)
• Systematic decrease in stress/force when a clear option to compensate is available