Motor Control and Movement Disorder Flashcards
Voluntary Movements
Purposeful and goal-directed
Learned
Complex actions
Reflexive Movements
Involuntary/rapid/stereotyped
Caused by spinal cord, peripheral nerves and muscles
Rhythmic Motor Patterns
Combination of voluntary and reflexive movements
Intention/initiation: voluntary
Once initiated become repetitive and reflexive
3 Principles of Motor Control: 1. Hierachical Organisation
High: strategy: goal of movement: neo cortex and basal ganglia
Middle: tactic: muscle contractions arranged to achieve a goal: motor cortex and cerebellum
Low: execution: activation of motor neurons and adjustment of posture: brain stem and spinal cord
3 Principles of Motor Control: 2. Sensory Input Guides Motor Control
Strategies: sensory info generates mental image of body and relationship to environment
Tactics: decisions based on memory of sensory into from past experiences
Execution: maintains posture, muscle length and tension around voluntary movement
3 Principles of Motor Control: 3. Learning Changes the Locus of Sensorimotor Control
Conscious vs. automatic
After practice, lower levels perform learned tasks with little higher involvement
Fewer brain areas used for well learned tasks than new tasks
Brain Areas Involved in Highest Level Motor Movements
Strategy
Posterior parietal cortex (PPC) and prefrontal cortex (PFC) send signals to…
Area 6 (premotor cortex) and then,,,
Area 4 (primary motor cortex, MC)
Posterior Parietal Cortex in Movement Control
Generates a mental body image of the body and surrounding environment
Somatosensory, proprioceptive and visual info
Prefrontal Cortex in Movement Control
Evaluates external world and initiates voluntary reaction in anticipation of consequences
Decision making
Neglect and RH
Lesions to RH posterior parietal cortex (PPC) causes abnormalities of body image and spatial relations
Contralateral Neglect
Deficit in attention paid to one side of the visual field
Apraxia
Inability to…
Carry out learned movements when verbally instructed
Imitate movements
Ready, Set, Go! Paradigm
Ready: PFC, PPC, brain centres control attention and awareness
Set: supplementary motor area (SMA), primary motor area (PMA), movements strategies devised and held until executed
Go: primary motor cortex (MC), basal ganglia
Mirror Neurons (Rizzolati et al, 2001)
Suggested that mirror neurons play a role in imitating behaviour
Indirect evidence from fMRI show that they’re likely found in humans
MC Inputs and Outputs
Inputs: cortical areas and thalamus
Outputs: spinal cord, brain stem
Stimulation of MC Neurons
Brief stimulation - brief body movements Prolonged stimulation (e.g. 0.5 secs) - complex species typical movements towards target position
Lateral Descending Pathways
Initiate voluntary movement of distal musculature
Corticospinal Tract
2/3- MC areas to spinal cord
1/3- somatosensory info from periphery to brain
Rubrospinal Tract
Smaller tract
MC areas to red nucleus to spinal cord
Tract crosses after it synapses with the red nucleus
Lesion Studies on Tracts
Lawrence & Kuypers (1968)
Animal studies
Lesion of 1: paralysis and recovery
Lesion of 1 and 2: paralysis without recovery
Ventromedial Descending Pathways
Controls and maintains posture and certain reflex movements
Vestibulospinal Tracts and Tectospinal Tracts
Keep head balanced
Turn head in response to stimuli
VST: keep eyes stable when body moves
TST: orientation response
Pontine and Medullary Reticulospinal Tract
PRT: stabilise posture, resists gravity
MRT: liberation of antigravity muscles from reflex control
Basal Ganglia in Motor Control
Movement initiation and planning
Sequence of movement triggered by MC and BG
BG can be responsible for remainder of action e.g. practised skills
Selects motor program and keeps it offline until signal
Basal Ganglia Loop
Cerebral cortex
Through a few more areas then signals reach thalamus and midbrain
Signals from thalamus to motor and prefrontal areas of cerebral cortex
Loops produce excitatory and inhibitiry output to final areas of the loop
Mink (1996) function is motor selection and inhibition of actions
Rigidity in PD
Muscle tone increases providing constant resistance to passive movement of joints
Resting Tremor in PD
Most common symptom, usually asymmetric
Caused by decreased dopamine input into BG which has connections to many cortical areas
Medication for PD
L-DOPA - stops dopamine passing blood-brain barrier
Deep brain stimulation (DBS) - surgical procedure treating disabling symptoms
Motor Control Loops: Cerebellum
Motor skill learning and establishing new motor programs
Fine motor coordination/balance and muscle tone/ timing
Motor Skill Learning Stages
Initial stage: individual response performed under conscious control
After practice: responses become continuous sequences of action w/o conscious regulation
Transfer from higher to lower levels of motor system
Feedback/Feed-Forward Solutions in Cerebellum
Negative feedback and the adjustment of them leads to feed-forward solutions
Due to re-evalution, predictions
2 Hemispheres of the Cerebellum
2 hemispheres connected by the vermis
Each hemisphere controls ipslateral movements
Damage of the Cerebellum
Similar symptoms of alcohol abuse
Left cerebellar tumour: steady on right leg but not right leg, swayed right in standing position
Cerebellar Patients
Ataxia - uncoordinated/inaccurate movements
Intention tremor - tremor at endpoint of deliberate movements
Problems clapping hands, speaking, writing, typing etc - problems motor learning
