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Biopsych - Motor Systems / Control (Y1), Principles of each area - …

- - - - Reflexes - involuntary, rapid stereotyped (always the same) movement, originating from the spinal cord, peripheral nerves and muscles
        
        Knee jerk reaction, fight or flight from sympathetic nervous system
        
        Knee jerk - tap stimulates primary sensory receptors in the muscle, synapse with alpha motor neurons, stimulate muscles fibres, produces muscle contraction
        
        Skin -> afferent neuron (sensory) -> spinal cord -> efferent nerve -> muscle
        
        Proprioception and Kinesthesia - balance and position of muscles, movement and learning respectively (learning what movement sequences you need for an action)
        Deafferentation - destruction of afferent connections (towards neurons, or motor neurons) - loss of proprioception - have to look as you have lost the ability to sense position of limbs in space
        Afferent dysgraphia - problems in the use of feedback control graphomotor patterns
        
        Patient VB - visual problems preventing visual feedback due to neglect - losing double letters in words, adding letters in words with double letters (stroke experienced)
        
        Deafferentation prevented motor feedback
        
        Spelling errors involve omission or repetition of strokes and letters, impaired ability to utilize visual and motor feedback in controlling handwriting
        
        In normal subjects - omission / repetition errors can be induced by removing visual feedback (removing visual input) and tapping fingers in a 5-4-3-2-1-2-3-4-5 pattern to reduce kinesthetic feedback
      - Rhythmic / Central pattern generators e.g. walking, running and chewing:
        
        Combines voluntary and reflexive acts
        
        Intention and termination - voluntary
        
        Once initiated they are repetitive and reflexive
        
        Rhythmic activity in spinal interneuron
        -> Walking initiated when a steady input excites the two interneurons that control flexors or extensors - also involves pacemaker neurons
        -> Pacemaker neurons - continuous input from brain -> excitatory neurons allow flexor motor neuron, alongside the excitatory interneuron allowing extensor motor neuron action - stopped by inhibitory interneurons, allowing next set to fire allowing walking
        -> Activity alternates because they inhibit each other via interneurons
        -> There is cross inhibition to the opposite side of the body
      - Voluntary movements - most important to behaviour -
        
        writing, playing piano or football
        
        Purposeful and goal directed
        
        Learned (improve with practice)
        
        Complex actions
  - - - Learning changes the nature and locus of sensorimotor control
        
        During initial changes, each individual response is performed under conscious control, and after practice individual responses become organised into continuous integrated sequences of action that flow smoothly and are adjusted by sensory feedback without conscious regulation
        
        Continuous motor programs that transfer control to lower levels of the CNS that characterise most sensorimotor learning
- - - - Two dorsolateral motor pathways and two ventromedial motor pathways:
        
        Similar as both have two major tracts, one with axons descending directly to the spinal cord and another whose axons synapse on brain stem on neurons that descend
        
        Two major differences -
        
        Ventromedial tracts are much more diffuse - many of the axons innervate interneurons on both sides of the spinal grey matter and in several different segments, whereas the axons of the dorsolateral tracts terminate in the contralateral half of one spinal cord segment, sometimes directly on a motor neuron
        
        Motor neurons activated by the VM tracts project to proximal muscles of the upper body and limbs, whereas motor neurons activated by the DL tract project to distal muscles
        
        All 4 originate in the cerebral cortex, and so all are presumed to help with voluntary movement - different routes and destination does suggest different functions
        
        Lawrence and Kuypers (1968) - transected DL tract in monkeys and found they could move normally but their limbs were limp when sat - raking action
        -> When VM tract was transected, they had postural difficulties and could not walk or sit, and also had poor balance
        
        DL = control limbs
        
        VM = posture control and whole body movements, exerting limb control in these activities
- - - - Parkinson's disease - atrophy -
        
        slow movement
        
        difficulty initiating willed movement (akinesia)
        
        Increased muscle tone (rigidity)
        
        Tremors of hands, jaw, most prominent at rest
        
        Increased output of indirect pathway, decreased output of direct pathway
      - Huntington's disease -
        
        Hyperkinesia
        
        Chorea - spontaneous, uncontrollable and purposeless movement
        
        Loss of neurons in striatum decrease spatial inhibition of the direct pathway - caudate nucleus, putamen and globus pallidus
        
        Loss of inhibition over thalamus