Motor Control

Question 1

2What was Lund’s (1991) proposed pain adaption theory?

How was this theory limited?

Answer 1

Following a nociceptive stimulus, the group 3 & 4 afferent nociceptors trigger inhibition of the agonist muscle and excitation of the antagonist muscle resulting in decreased amplitude and velocity of movement & therefore reduced risk of further injury

The studies informing this theory were performed with animals with their cortex removed which meant there was no driving factor for them to continue movement after experiencing pain. This is seldom the case when humans experience pain.

Question 2

How did Hodges & Tucker’s (2012) pain adaptation model differ from Lund’s?

Answer 2

This new model (2012) focused on human studies for adaptation to pain. They found that there were changes to multiple levels of the nervous system rather than just at the muscle.

They also found that if there was a clear way for the nervous system to reduce stress while maintaining function (i.e. by using alternative muscles) than it would reduce stress where pain was experienced and this was more pronounced with greater degrees of freedom.

Question 3

What did Sohn (2000) and Farina (2004) find happened to motor unit discharge rate during pain?

How can there be the same force being produced with an altered discharge rate?

Answer 3

It was lower despite matching force production

There is an altered motor unit recruitment pattern between pain and no pain studies

Question 4

Tucker’s (2012) study found that there is an altered discharge rate and motor unit recruitment pattern in both participants who experienced pain and those who anticipated pain. What does this suggest?

Answer 4

There is likely involvement from higher centres contributing to these altered motor unit behaviour during pain

Question 5

What are the limitations to using surface EMG to assess changes in single motor unit discharge during an acute pain experiment?

Answer 5

Surface EMG is not sensitive to altered motor unit recruitment during pain as it only indicates the summation of all single motor unit activity.

This is why fine-wire EMG is necessary, it is able to discern between single motor unit activity and give an accurate reading of how many and which motor units are being recruited.

Question 6

There are many motor adaptations that are possible during acute pain. Describe the changes in single motor unit discharge that are observed during acute pain and if these changes are associated with a decrease in load within the painful part.

Answer 6

Single motor unit discharge may alter in rate and in recruitment pattern. These changes are only associated with a decrease in load if there is a clear alternative for the nervous system i.e. if the movement being performed can be compensated for by an alternate muscle or muscle group, then a decrease in stress in the painful muscle will be observed.

Question 7

What is the primary motor cortex (M1) responsible for? How many of our upper motor neurons originate here?

Answer 7

The initiation and execution of motor plans by developing a program of commands for lower motor neurons

~60% of UMN originate here

Question 8

What are the pre motor cortices responsible for?

Answer 8

The planning and selecting of complex movements as well as having a role in postural preparation prior to an event & processing visual information.

Question 9

What is the supplementary motor area responsible for?

Answer 9

It provides a plan that specifies the sequence and extent of muscle contractions needed to execute a movement

Question 10

What is the posterior parietal cortex responsible for?

Answer 10

It takes in sensory information and forms a conscious map of the body and it’s relationship with its surroundings

Question 11

What is transcranial magnetic stimulation (TMS) and what is it used for?

Answer 11

A device that can stimulate certain areas of the motor cortex and trigger a motor response. It allows researchers to pinpoint which areas of the motor cortex are responsible for which muscles in the body.

Question 12

How does transcranial magnetic stimulation (TMS) work?

Answer 12

It creates a magnetic field towards the motor cortex which creates an electrical current in the brain resulting in excitation of cortical motor neurons. This excitation travels from the cortex down the UMN to the spinal cord where it synapses on the LMN and innervates the appropriate skeletal muscle.

Question 13

What does MEP stand for?

Answer 13

Motor evoked potential

Question 14

What does it mean if the MEP amplitude increases between conditions?

Answer 14

If there is an increased corticospinal excitability at both the spinal and cortical level (i.e. by voluntarily contracting a muscle that is also being stimulated by transcranial magnetic stimulation) then there will be an observed increase in the MEP amplitude

Question 15

What is training induced motor plasticity?

Answer 15

TMS will evoke a particular movement (i.e. thumb extension). If a short training period is done (15-20 minutes) of a voluntary movement in the opposite direction (i.e. thumb flexion), TMS after this training period will evoke a response in the opposite direction (i.e. thumb flexion) for a short period of time. This is evidence of short term motor plasticity.

Question 16

What did Boudreau (2007) conclude about the effect pain had on learning a task?

What was the major limitation to this study?

Answer 16

Pain reduced the participants ability to learn a new motor task and therefore no motor plasticity was observed as there was no increase in cortico-motor excitability with training

It is unclear as to whether it was pain directly causing there to be no motor plasticity or if it was simply because the participants were unable to participate in training due to pain and therefore no motor plasticity was seen because no training was undertaken.

Question 17

How did Ingham (2011) address the limitations seen in Boudreau’s study (2007)?

Answer 17

It was found that direct pain did not affect motor plasticity as long as the training occurred as planned. However pain at a site away from the muscle in question distracted the patient enough that training did not evoke motor plasticity suggesting the importance of concentration during the training period.

Question 18

What did Tsao (2008) find when looking at motor-cortical maps of the trunk muscles of both healthy people and people with lower back pain? What does this mean?

Answer 18

There was a posterior-lateral shift in trunk muscle representation

People with chronic lower back pain is associated with altered trunk muscle coordination

Question 19

What did Tsao & Hodges (2007/2008) find happened to the response of the transverse abdominal muscles in people with chronic lower back pain?

Answer 19

There was a delay in muscle activation compared with healthy individuals

Question 20

How can we use motor-cortical mapping to understand how the control of movement is altered in musculoskeletal pain conditions? Use either the Tsao or Schabrun paper as an example.

Use the terms transcranial magnetic brain stimulation, motor evoked potential and motor-cortical map within the response.

Answer 20

Motor-cortical mapping can provide insight into muscle coordination and activation in those with musculoskeletal pain conditions.

Tsao did this by comparing people who experience chronic lower back pain and with controls who did not. Tsao used transcranial magnetic brain stimulation and used the motor evoked potentials to map which areas of the brain corresponded to the deep multifidus and the longissimus erector spinal muscles. What was found was that in the people who had chronic lower back pain, the mapping of these muscles moved in a posterior direction compared to the controls and also that there was overlapping of the muscle groups in the cortex.

These results suggest that there is a loss of discrete control of the deep multifidus and longissimus erector spinal muscles in patients who experience chronic lower back pain and that motor rehabilitation addressing differentiation of these muscles may be of benefit to these patients.

Question 21

Describe how a motor cortical map is generated using TMS

Answer 21

Transcranial magnetic stimulation produces motor evoked potentials in the muscles of that specific cortical area. By mapping these based on which muscles are being targeted and where on the cortex the stimulation is being applied, we are able to see where on the cortex specific muscles are being targeted from.

Question 22

Can a motor cortical map change over time?

Answer 22

Yes

Studies by Tsao, Galea & Hodges (2009) have suggested that specific training of a muscle (with intent and concentration) is able change a cortical map over time and that this can have positive affects on motor performance. For example, when someone experiences lower back pain, their motor-cortical map may shift posteriorly in comparison to normal. When specific motor training is undertaken, this map can move back into its normal position on the cortex and can result in improved motor performance.

Question 23

What are some examples of constant and occasional external forces we need to adapt to when maintaining posture?

Answer 23

Constant= gravity
Occasional= ground reaction forces, being pushed, catching/hitting a ball

Question 24

What are some examples of rhythmic and occasional internal forces we need to adapt to when maintaining posture?

Answer 24

Rhythmic= Breathing, gait

Occasional coughing, laughing, preparing to catch a ball

Question 25

What 3 sensory inputs are important in postural control?

Answer 25

Visual, vestibular, somatosensory

Question 26

Why do we see an increase of postural sway with age?

Answer 26

There are changes in sensory information and motor ability with ageing

Question 27

Changes in centre of pressure (COP) is associated with what kind of injuries?

Answer 27

Both retrospective and prospective falls in the elderly population

Question 28

What are the 4 motor outputs in the postural system?

Answer 28

Voluntary
Anticipatory
Automatic
Reflex

Question 29

Describe voluntary motor output in the postural control system

What spinal pathways are involved?

Answer 29

Purposeful activities that are cortically driven, are self-generated or are in response to an external stimulus and occur ~200+ ms from initiation of signal in the cortex

Output via the corticospinal and corticobulbar tracts

Question 30

Describe anticipatory motor output in the postural control system

Answer 30

Activation of postural muscles before voluntary movement begins in anticipation of the destabilising forces caused by the coming movement

Also cortically driven and can be memory-based/learnt movements which can adapt with repetition or change of conditions (i.e. during pain)

Question 31

Describe automatic motor output in the postural control system

Answer 31

‘First line’ response to external stimuli controlled by the spinal cord and cortex. Takes 90 to 100ms to kick in. These responses are highly generalised and adaptable to conditions

Question 32

Describe reflex motor output in the postural control system

Answer 32

This kind of response comes directly from the spinal cord (no cortex involvement) making it the simplest neural circuit in the postural control system. It controls local muscle contraction only and is highly stereotypical.

Triggered by external stimuli and occurs ~35 to 40ms after stimulus

Question 33

Is centre of pressure variation greater in the antero-posterior direction or the medio-lateral direction?

Answer 33

antero-posterior direction