Motor Control & Movement Disorder Flashcards
Motor system is used for:
- Movement
- Posture & balance
- Communication
Voluntary movements
Purposeful and goal directed.
Learned (improve with practice).
Complex actions.
Reflexes
Involuntary, rapid and stereotyped.
Spinal cord, peripheral nerves and muscles.
Rhythmic motor patters
Combines voluntary and reflexive actions.
Intention, initiation and termination.
Once initiated: repetitive and reflexive.
3 principles: Hierarchical organisation
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).
3 principles: Sensory input guides motor control
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.
G.O- man with too little feedback
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.
3 principles: Learning changed the locuss of sensorimotor control
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.
PFC PPC: movement strategy
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.
Movement disorders: neglect
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.
Movement disorders: apraxia
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.
Limb kinetic apraxia
Loss of deftness including ability to make finely graded, precise but coordinated finger movements.
- Lesions to cortico-spinal system.
Ideomotor apraxia (IMA)
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).
More apraxia
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.
Secondary motor cortex areas
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.
Movement planning: ready, set, go paradigm
- Ready: PFC, PPC, brain centres that control attention & awareness.
- Set: SMA, PMA; movement strategies devised and held until executed.
- Go: MC, Basal ganglia.
Mirror neurons: Rizolatti (monkeys)
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.
Nicolesis & Chapin (2002)- owl monkey Belle
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.
Descending pathways
Primary MC to
Spinal cortex to
Muscles
Lateral descending pathways (initiation of voluntary movement of of distal musculature)
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.
Ventromedial descending pathways (control and maintenance of posture and certain reflex movements)
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).
Functional role of Basal Ganglia (movement initiation & movement planning)
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).
Motor cortico-basal ganglia loop
- 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).
Movement disorder: Parkinson’s disease
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).
PD: basal ganglia function
Caused by decreased dopamine input to basal ganglia that have connections to many cortical areas.
PD therapy: medication
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.
Functional role of cerebellum: control of fine motor coordination
(+ balance & muscle tone, timing etc)
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.
Anatomy of cerebellum
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).
Movement disorder: damage to cerebellum
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.
