Neuroanatomy L7: Cortico-motor pathway and motor plasticity

Question 1

What is the function of the cerebral cortex, motor areas?

Answer 1

Planning and initiation of voluntary movement

Question 2

What is the function of the cerebellum?

Answer 2

• Sensory motor
• Basal ganglia integration & learning

Question 3

What is the function of the spinal cord/network?

Answer 3

Reflex (involuntary movement)

Question 4

What is the function of the brainstem?

Answer 4

Basic movement & posture

Question 5

What are the pyramidal and extrapyramidal pathways?

Answer 5

Begin in the brain stem, and received collaterals from the pyramidal tract to assist with modulation of posture etc.

Question 6

What are the pyramidal pathways also called?

Answer 6

Corticospinal tracts

Question 7

What is the corticospinal tract?

Answer 7

Direct pathway from the primary motor cortex to the spinal cord

Question 8

In corticospinal tracts, ________of the axons cross over (decussate) to the opposite side of the CNS in the medulla (referred to as pyramids). What is this tract called?

Answer 8

75-90% (the majority)

Lateral cortico-spinal tract or lateral pyramidal tract

Question 9

What is the function of the lateral cortico-spinal/pyramidal tract?

Answer 9

Essential for the fine movements of distal extremities (limbs)

Question 10

10-25% don’t cross over in the pyramidal decussation, but rather in the anterior white commisure at the level of synapse. What is this tract called?

Answer 10

Anterior corticospinal tract or anterior pyramidal tract

Question 11

What are the functions of the anterior corticospinal tract/anterior pyramidal tract?

Answer 11

• Innervate axial motor neurons
• Some innervate bilaterally (neat for bilateral tasks, walking etc)

Question 12

What is parallel processing?

Answer 12

Simultaneous transmission of the same general type of information along separate neural pathways (pyramidal and extrapyramidal tracts)

Question 13

If a pyramidal pathway was damaged, what happens to th extrapyramidal pathways?

Answer 13

The extrapyramidal system can partially compensate so that distal movements are not entirely lost (Function will be impaired but not lost in this scenario)

Question 14

What is the function of the primary motor cortex?

Answer 14

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

60% of upper motor neurons originate here.

Question 15

What is the function of the premotor cortices?

Answer 15

• Responsible for planning and selecting complex movements.
• Also has a role in postural preparation prior to an event and processing visual information.

Question 16

What is the function of supplementary motor area?

Answer 16

Provides a plan that specifies the sequence and extent of muscle contractions needed to execute a movement.

Question 17

What is the function of the posterior parietal cortex?

Answer 17

Takes in sensory information and forms a conscious map of the body and its relationship with its surroundings.

Question 18

What cortical areas are activated to flex the finger?

EXAM QUESTION

Answer 18

Primary motor cortex (M1)

very simple flexion of finger–> stimulate motor cortical (one descending output)

Question 19

What cortical areas are activated to write a letter with finger (complex sequence of movement)? EXAM QUESTION

Answer 19

M1, premotor and supplementary cortex

information coming from different areas needing to come together to create a sequence of tasks

Question 20

What cortical areas are activated to think about writing with the finger?

EXAM QUESTION

Answer 20

premotor and supplementary cortex, not M1

(no program of activity that is sent down to be executed)

Question 21

Why is the primary motor cortex not involved when thinking about writing with the finger?

Answer 21

The primary motor cortex is not involved, as there is not descending output to lower motor neurons during imagined tasks. The fact that the pre-motor and supplementary motor cortices are activated during imagined tasks has implications for mental practice of tasks.

Question 22

Where is the primary motor cortex located?

Answer 22

Located in the pre-central gyrus.

Question 23

In the somatotopic map of the primary motor cortex, there is a disproportionally____ (small/large) representation of parts requiring greater _____ control. Give an example.

Answer 23

large; precision

For example, a large portion of the primary motor cortex neurons are dedicated to the control of small muscles in the hand, due to the fine precision required to complete complex tasks involving the hand. The cortical mapping can be altered depending on training and use. Pianists and violinists often have increased cortical area dedicated to finger control due to the increased demand for complex movements.

Question 24

“Use-dependent plasticity of the motor-cortical map”. What does that mean?

Answer 24

areas can change which innervates muscle

Deprivation causes reduction of representation

Question 25

How does use-dependent plasticity of the motor-cortical map apply in the study of rats with denervation of the whiskers?

Answer 25

Area of brain that was once associated with whisker completely disappears - not receiving sensory input –> overtaken by other areas of brain

After dennervation of the neural supply to the whiskers, the cortical area that controlled the whiskers is taken over by other upper motor neurons that are still active.

Question 26

What is Functional Magnetic Resonance Imaging (fMRI) show?

Answer 26

detection of active brain areas

Question 27

How does Functional Magnetic Resonance Imaging (fMRI) work?

Answer 27

Determines regions of increase flow of oxygenated blood flow to “active” brain regions

Question 28

What are the 2 types of brain stimulation?

Answer 28

1. Intracortical stimulation
2. Transcranial Magnetic Stimulation

Question 29

How does the Transcranial Magnetic Stimulation work? Be specific. What motor neurons are stimulated?

Answer 29

Involves stimulation of cortical areas externally, in order to evoke a motor response.

Specific stimulation of upper motor neurons via an electric current.

Question 30

How is the excitability of the corticomotor pathway tested? Short term and long term.

Answer 30

short term: can change by voluntary contraction

long term: Strengthens with training (increased motor evoked potential (MEP) and movement)

Use dependent plasticity

Question 31

What is acceleration in terms of the excitability of the corticomotor pathway?

Answer 31

movement of limb

Question 32

What is MEP in terms of the excitability of the corticomotor pathway?

Answer 32

motor evoked potential

Question 33

What is the effect of voluntary contraction on motor evoked potential?

Answer 33

Muscle contraction is associated with increased corticospinal excitability at spinal and cortical level

• Size of MEP is larger when already active- voluntary contraction
• Already motor neurons in the brain and spinal cord facilitated - ready to be activated/recruited

Question 34

Does training induced motor plasticity? What is the extent of the change?

Answer 34

Yes! –> change in direction (trained direction)- only lasted for 30 minutes (unless- continue to train)

Question 35

What is the effect of training on motor plasticity (direction)?

Answer 35

Altered direction of movement resulting from stimulation of the same cortical area after training.

Question 36

However, post 30 minutes of training, what is the effect on motor plasticity (direction)?

Answer 36

After training ceases, the movements evoked by that area of cortical motor neurons will gradually return to their original state.

This experiment demonstrated transient plasticity of upper motor neurons.

Question 37

Is the type of training important for motor plasticity to occur?

Answer 37

Yes

Question 38

What is type of training evokes and increases corticospinal excitability (i.e MEP amplitude)?

Answer 38

complex skill learning

Question 39

What is type of training does not have change to corticospinal excitability (i.e MEP amplitude)?

Answer 39

Strength training

Question 40

Does pain alter the ability to learn a new motor task? What are 2 effects?

Answer 40

Authors concluded that pain reduced ability to learn a new motor task (i.e. no increase cortico-motor excitability).

1. Decreased ability to perform task
2. Altered attention to task due to pain

Question 41

Wiith pain, ______ (able/unable) to match/produce force not doing task well

Answer 41

unable

Question 42

Does pain during training alters training induced motor plasticity when task performance is matched?

Answer 42

If pain is local to area being trained (participant is attending to the pain)= some motor cortical plasticity is present (some adaptions)

Question 43

Does the distraction of pain, rather than direct nociceptor stimulation near the trained area influences motor plasticity?

Answer 43

If attention is drawn away by pain (in other location) = no motor cortical plasticity

Question 44

Cortical map developed showing the neurons that fire to contract that muscle. The greater the action potential (shown in the image), the larger the role that upper motor neuron plays in initiating motor output. What does it look like?

Answer 44

Question 45

What is different in the TMS mapping of a normal person and a person with chronic lower pain? Why?

Answer 45

Posterior and lateral shift in trunk muscle representation.

Activation of the rectus abdominis

Question 46

Chronic low back pain is associated with altered _____ muscle coordination (delayed)

Answer 46

trunk

Question 47

What intervention can help to correct altered trunk muscle coordination (delayed) due to lower back pain?

Answer 47

Motor training 2x/day for 2 weeks

Question 48

What does MEP stand for?

EXAM QUESTION

Answer 48

Motor Evoked potential

Question 49

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

EXAM QUESTION

Answer 49

It means that corticospinal excitability has increased- which is associated with learning.

Question 50

How can we use the motor-cortical mapping to understand how the control of movement is altered in a musculoskeletal pain conditions?

Use either the Tsao or Schabrun paper as an example, to help you answer this question. Use the terms Transcranial Magnetic Brain Stimulation (TMS), motor evoked potential (MEP) and motor-cortical map within the response.

EXAM QUESTION

Answer 50

Low back pain is associated with altered trunk muscle coordination. This is also associated with motor cortical map changes in which the motor areas responsible for transverse abdominis shifting posterity and laterally.

TMS and MEP are devices used to draw motor-corticap map. Transcranial Magnetic Brain stimulation (TMS) uses magnetic current in the coils to generate an electrical impulse in the primary motor cortex of the brain which is somato-topically organized (specific area of the cortex responsible for a specific muscle— presence of motor cortical map) When TMS activates a region in the primary motor cortex containing the upper motor neuron, the signal travels down to the corticospinal tract and synapses at the alpha motor neuron which is a LMN to produce a movement. Motor evoked potential measures corticospinal excitability. Higher MEP is associated with motor learning which is driven by the plasticity in the motor cortical map.

Apart from training, MEP recording can also be increased when there’s already a voluntary contraction and if the TMS is applied to the area of the cortex responsible for the contraction of the muscle.

Study conducted by Tsao demonstrated that with motor training in people with chronic lower back pain, the altered trunk muscle coordination resolved. This was also associated with restoration of motor cortical map to the same area as the healthy controls.

Question 51

Describe how a motor cortical map is generated using TMS.

EXAM QUESTION

Answer 51

TMP- Activates area of the primary motor cortex (upper motor neurons) which sends an AP down to the A delta fibres in the spinal cord (LMN) to generate AP in the muscle to produce a movement.

MEP- electrical potential recorded from the Nervous system

TMP- generates input. MEP- measure of the output.

TMP is applied to the different areas of the brain- drawn out using a grid. MEP is measured with each stimulation. The area that produces the most amount of MEP after TMP is the cortical area responsible for the activation of that muscle.

Question 52

Can a motor cortical map change over time? Explain your answer with reference to either exercise, pain or denervation.

EXAM QUESTION

Answer 52

Yes. Motor cortical map can change over time.

For example, when a person is in pain, the altered biomechanics is associated with alteration in motor cortical map representation.

For example, in rats, when the whiskers has be de-innervated, then the areas of motor cortex previously responsible for whisker control has been shown to be taken over by adjacent motor areas such as the LL.

For example, after a period of training (of movement B, the area of the motor cortex previously responsible for movement A when activated using TMS, starts to produce movement B.