Motor Control & Movement Disorder

Question 1

Motor system is used for:

Answer 1

• Movement
• Posture & balance
• Communication

Question 2

Voluntary movements

Answer 2

Purposeful and goal directed.
Learned (improve with practice).
Complex actions.

Question 3

Reflexes

Answer 3

Involuntary, rapid and stereotyped.

Spinal cord, peripheral nerves and muscles.

Question 4

Rhythmic motor patters

Answer 4

Combines voluntary and reflexive actions.
Intention, initiation and termination.
Once initiated: repetitive and reflexive.

Question 5

3 principles: Hierarchical organisation

Answer 5

Low- execution- activation of motor neuron; adjustment of posture. (Brain stem & spinal cord).
Middle- tactic- sequence of muscle contractions arranged in space and time to smoothly and strategically achieve a goal. (Motor cortex, cerebellum).
High- strategy- goal of movement; best strategy to reach goal. (Association areas of neocortex, basal ganglia).

Question 6

3 principles: Sensory input guides motor control

Answer 6

Lowest level (execution): sensory feedback used to maintain posture, muscle length and tension before and after voluntary movements.
Middle level (tactics): tactical decisions are based on memory and sensory info from past experiences. 
Highest level (strategies): sensory info generated a mental image of the body and its relationship to the environment.

Question 7

G.O- man with too little feedback

Answer 7

Had trouble with intricate motor responses (eg. doing up buttons).
Inability to adjust motor output to unexpected external disturbances.
Inability to maintain a constant level of muscle contraction.

Question 8

3 principles: Learning changed the locuss of sensorimotor control

Answer 8

Conscious vs. automatic.
Many brain regions vs. fewer brain regions.

Most active brain regions during:

• newly learned sequences: cerebellum, DLPFC, PPC, PMC, MC1.
• well practiced sequences: MC1 & somatosensory cortex, supplementary motor area.

Question 9

PFC PPC: movement strategy

Answer 9

PPC/PFC to PMC to MC.
Posterior parietal cortex: generation of mental body image and external objects- Uses somatosensory and visual info.
Prefrontal cortex: evaluation of external world and initiation of voluntary reaction in anticipation of consequences of action- abstract thought, decision making.

Question 10

Movement disorders: neglect

Answer 10

Lesions to right hemisphere PPC causes abnormalities of body image ad spatial relations to environment.
Contralateral neglect.
Possible association with denial disorder: unawareness or denial or illness.
Line bisection task- attention biased to ipsilesional side.
Spatial neglect is associated with lesions to right IPL and ventral frontal cortex.

Question 11

Movement disorders: apraxia

Answer 11

Heliman & Rothi- “limb apraxia is an inability to correctly perform purposeful, skilled movements with forelimbs.”
Unable to: - carry out learned movements in response to verbal instruction.
- imitate movements.
- produce movements made using familiar tools.

Question 12

Limb kinetic apraxia

Answer 12

Loss of deftness including ability to make finely graded, precise but coordinated finger movements.
- Lesions to cortico-spinal system.

Question 13

Ideomotor apraxia (IMA)

Answer 13

Make most errors when asked to pantomime acts to verbal commands; performance may improve when tools are used.
- Lesions of corpus callosum, IPL and supplementary motor area (SMA).

Question 14

More apraxia

Answer 14

Conduction apraxia: more severely apraxic when imitating that pantomiming.
Ideation apraxia: inability to carry out series of acts or formulate an ideation plan- caused by frontal lobe dysfunction.
Conceptual apraxia: production errors and also make content and tool selection errors- TPJ is in integral to mediation of conceptual knowledge.

Question 15

Secondary motor cortex areas

Answer 15

At least 8 areas:

• Supplementary motor area (SMA) (3).
• Premotor cortex (PMC)
• Ventral (medial) premotor cortex.
• Dorsal (lateral) premotor cortex.
• Cingulate motor areas (3).

Input: mainly association cortices.
Output: mainly MC.

Question 16

Movement planning: ready, set, go paradigm

Answer 16

• Ready: PFC, PPC, brain centres that control attention & awareness.
• Set: SMA, PMA; movement strategies devised and held until executed.
• Go: MC, Basal ganglia.

Question 17

Mirror neurons: Rizolatti (monkeys)

Answer 17

Ventral PMC neurons & inferior parietal lobule neurons: active during the performance and observation of actions.
Mirror neurons: play a role in imitating movements.

Mirror neurons= possible neural basis of social cognition (knowledge of others’ mental processes).
Likely to be found in humans: indirect evidence from fMRI studies.

Question 18

Nicolesis & Chapin (2002)- owl monkey Belle

Answer 18

Learned to move joystick with right hand in direction of light.
100 microelectrodes recorded extracellular activity in MC.
Pattern of activity moved robot arm.
Implication: paralysed patients can move limbs through power of thought.

Question 19

Descending pathways

Answer 19

Primary MC to
Spinal cortex to
Muscles

Question 20

Lateral descending pathways (initiation of voluntary movement of of distal musculature)

Answer 20

1) Corticalspinal tract: - 2/3 of tract: MC areas - to spinal cord.
- 1/3 tract: somatosensory info from periphery to brain.
- pyramidal tract.

2) Rubrospinal tract: - MC areas - to red nucleus - to spinal cord.
- extrapyramidal tract.
- this tract decussates after it synapses with red nucleus.

Lesion studies: - Lesion of 1 = paralysis & recovery; weakness of distal flexors, can’t move fingers independently; posture unaffected.
- Lesion of 1 + 2 = paralysis without recovery.

Question 21

Ventromedial descending pathways (control and maintenance of posture and certain reflex movements)

Answer 21

1) Vestibulospinal tracts and tectospinal tracts: - keep head balanced on shoulders and body.
- turns head in response to sensory stimuli.
- keep eyes stable when body moves (only VST).
- orientation response (only TST, superior colliculus).

2) Pontine and medullary reticulospinal tracts: - stabilises posture by resting the effects of gravity (PRT).
- liberation of antigravity muscles from reflex control (MRT).

Question 22

Functional role of Basal Ganglia (movement initiation & movement planning)

Answer 22

BG release automatic sequences of action (motor learning): once a sequence of movements has been triggered the BG could be responsible for remainder of the action.
Response/movement selection and deselection: selection of motor program and keeping it ‘off-line’ until appropriate signal.
Learning and cognition: eg. reward based learning, task set shifting).

Question 23

Motor cortico-basal ganglia loop

Answer 23

• Produces excitatory and inhibitory output to motor and prefrontal areas of the cerebral cortex.
• These loops act like a well oiled ‘opposing circuit’ machine.
• Their function is motor selection and inhibition of actions (Mink).

Question 24

Movement disorder: Parkinson’s disease

Answer 24

James Parkinson, 1817.
Prevalence & incidence of PD: most common movement disorder (1-2% over 65 years); second most common neurodegenerative disorder after Alzheimers.

Motor symptoms: tremor, rigidity, akinesia.
Cognitive/emotional symptoms: dementia, executive functions, attention & learning, apathy/impulsivity (emotional).

Question 25

PD: basal ganglia function

Answer 25

Caused by decreased dopamine input to basal ganglia that have connections to many cortical areas.

Question 26

PD therapy: medication

Answer 26

Medication: L-DOPA (dopamine can’t pass the blood-brain barrier); dopamine agonists.
Side effects after several years: on/off periods (motor fluctuations); Dyskinesia’s.
Alternative therapies: deep brain stimulation- only subset of patients suitable.

Question 27

Functional role of cerebellum: control of fine motor coordination
(+ balance & muscle tone, timing etc)

Answer 27

Motor skill learning: establishment of new motor programs that enable to execute a sequence of action as a whole and automatically.

(Sensori)motor skill learning: - initial stage= each individual response performed under conscious control.
- after practise= individual responses- continuous sequences of action adjusted by sensory feedback without conscious regulation; transfer from higher level to lower levels of motor system.

Negative feedback: compare actual position with intended, if different make corrections.
Feed-forward solutions: sensory events control movement in advance; prediction; re-evaluation after complete.

Question 28

Anatomy of cerebellum

Answer 28

10% of the brains mass.
50% of all neurons of the brain.
2 hemispheres connect by vermis.
Each hemisphere controls ipsilateral movements (opposite from cerebral hemispheres).

Question 29

Movement disorder: damage to cerebellum

Answer 29

Similar symptoms to a drunk person- ataxic gait.
Dysynergia- decomposition of multi joint movement.
Dysmetric- miscalculation of movement distance.
Ataxia- uncoordinated and inaccurate movements.
Intention tremor.