EXSS 380 Exam 2 Outline PDF

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Information Processing Information Processing  Sensory information from internal/external environments processed by CNS  CNS = a computer Information Processing Model  Temporal analysis of what happens to sensory information as it passes through CNS o CNS = ‘black box’ (unable to measure internal processes) o Reaction time (RT)  Stages of Information processing o Stimulus identification o Response selection o Response programming Information Processing  Evidence of information processing o Donder’s Subtractive Method  Simple Reaction time  Go/No-Go Reaction time (2 stimuli)  Choice Reaction Time (2 stimuli) Stages of Information Processing  Stimulus Identification o Stimulus detection o Pattern recognition  Response Selection Stage o Time to select appropriate response depends on: 1. # of stimulus-response alternatives  Hick’s Law (as # of response alternatives INCREASE, so does choice RT) o Exceptions to law—practice and experience 2. Stimulus-response compatibility  Response-Programming stage o Voluntary responses = complex in nature o Retrieved from ‘Motor Memory’ (feedforward) o Classical experiment by Henry & Rogers  Motor programming theory—3 separate tasks  Stimulus was the same  No response selection stage  Complexity of movement differed between tasks (more complex task = increase in RT) Memory 1. Short-term sensory store (STSS)  Somatosensory cortex  High capacity; brief duration 2. Short-term memory (‘working area’)  Buffer area for STSS & LTM  Implications for motor behavior o Response selection stage of info. processing  Limited capacity; short duration 3. Long-term memory  Stored “sensory memories”  Somatosensory Association Cortex  Long-term sensory info store (via: rehearsal/practice) Memory example: ‘Joint Position Sense’

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As retention interval (‘delay’) INCREASES, errors also increase o STSS = decay quickly

Sensory Contributions to Motor Control Motor control  Two systems for Neuromuscular control: o Closed loop (feedback) systems  Reflexes o Open loop (feedforward) systems  Sensory information essential for selection of appropriate activity BEFORE  Pre-programmed 

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Sensory info integrated by CNS into 3 types of info. critical to neuromuscular control 1. Proprioception: joint position, spatial orientation of body segments 2. Kinesthesia: joint motion 3. Force Sense: amount of force produced by muscle activation Multiple sources of sensory info to inform CNS of movement: 1. Vision  Provides most important sensory info. about external environment  Not essential for movement (accuracy great impaired without; postural instability)  Role in planning and executing movement o Target identification o Obstacle identification  Error detection 2. Tenomuscular receptors  Muscle Spindle  Sensitive to: muscle length (type II) & change in muscle length (type Ia)  Indirect indicator of: proprioception & kinesthesia  [Ia afferent] output distorted by tendon vibration  Golgi tendon organ  Sensitive to: muscle tension (indicates  muscle activation status)  Indirect indicator of: proprioception & kinesthesia o Limitations—multiple inputs for the SAME joint position 3.

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Articular receptors  Sensitive to: joint displacement; velocity; acceleration  Indirect indication of: proprioception & kinesthesia o Limitations---high frequency activity for limited joint RM (‘extremes’)  Sensitive to: joint loading  Limitations—different afferent activity at same joint angle (for differing levels of contraction) o ‘Frequency of firing’  some loading = lots of firing  no loading = much LESS firing Cutaneous receptors  Sensitive to: touch, pressure, pain, temperature  ‘Force sense’ (essential for precision control of grip force)  Contributes to proprioception & kinesthesia  Study: neoprene knee sleeve improved  proprioception, balance, gait biomechanics in knee OA patients

Ensemble coding (‘single stream’) o Tenomuscular/Articular/Cutaneous receptors provide input to  STSS (somatosensory cortex)

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Short-term memory = sensory integration (‘ensemble coding’)  Input from: STSS & LTM

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Proprioception & Kinesthesia in motor control o How is this info used to control movement? 1. Online (real-time) monitoring of long-duration movements 2. Goal-orientated feedback for rapid movements

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Long Duration Movements o Error analysis and correction require considerable time  Goal = to maintain a constant state/path (correctness) Short-duration (rapid) movements Reflexive neuromuscular control o Long-duration activities—certain level of conscious awareness for error detection & correction o Inherent reflex mechanisms---subconscious error detection & correction

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Reflexive Neuromuscular Control  Joint Perturbation o Change in position = error  EMG burst ~ 30 ms (after perturbation) = spinal stretch reflex  2nd burst ~ 50ms = medium-latency reflex  3rd burst ~70ms = long-latency reflex  Earliest VOLUNTARY response = after 150-200ms  Medium and Long-latency stretch reflexes o Polysnaptic o Longer duration (compared to ‘spinal-stretch reflex’) o Greater amplitude of EMG activity o Referred to as: “Functional Stretch Reflex” (b/c more info. processing)  Long-latency stretch reflex o Integrated w/ additional sensory info. to provide more effective response  Greater latency b/c of more info. processing  Situation-specific alteration of reflex responses o ‘H-reflex’ (electrical version of ‘spinal-stretch reflex’)  Better control of reflexes = better balance  Amplitude attenuated based on postural demands  Descending inhibition  Triggered Reactions o Latencies = 80-200ms o Bypass some stages of info. processing o Goal-orientated o ‘Wine-Glass Effect’  Detected slippage of object via vibrations in in cutaneous receptors  Latency = ~ 80ms  Unconscious recognition  Non-autogenic (stimulus and response does NOT occur in the same muscle)  Increase gripping (in fingers/hands); decrease elbow flexor activity Feedforward Motor Control  Movement initiation centers o Corollary discharge (efference copy) = ‘action plan’ prepare CNS for what is about to happen  Preparatory/Anticipatory Postural Adjustments (APAs, PPAs) o Postural muscles activated ~ 60ms BEFORE primary movers o Reaching tasks cause translation of total body COM The Dynamic Restraint System  Muscle activity enhances joint stability by:

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a. Increasing joint compression and congruency b. Eccentric energy absorption c. Heightening muscle stiffness Reflexive neuromuscular control o Joint motion and perturbations EXCITE  tenomuscular & articular receptors  Reflexive muscle activation (resist perturbation/joint loading)- Ligament-stress induced reflex  Spinal-stretch reflex; medium-latency reflex; long-latency reflex Ligament as sensory organs o Golgi endings: detect mechanical stress (tension placed on ligament) o Ligament-stress-elicited reflex The Muscle Spindle o Excitation  produces a series of 3 stretch reflexes (spinal-stretch reflex, medium-latency reflex, long-latency reflex) Reactive neuromuscular control o Responses from: tenomuscular & articular receptors o ATT (anterior); Hamstrings on (posterior load) Limitations of Reactive Neuromuscular control 1. 1st peroneal activity = ~ 45ms AFTER perturbation onset 2. 54 ms + EMD = 1st sign of eversion (noted at 176 ms)  Lateral ankle ligaments-stressed @ 40 degrees of inversion: (occurs ~ 107ms) Feedforward neuromuscular control essential for dynamic stability o Eccentric energy absorption o Heightened muscle stiffness (greater resistance to muscle lengthening and joint perturbation) o Heightened muscle spindle sensitivity Feedforward neuromuscular control o Preparatory/anticipatory muscle activity

Muscle Stiffness & Joint Stability  Muscle activity heightens muscle stiffness  Stiffness = change in Force/ change in length Feedforward Neuromuscular Control  Prepatory/anticipatory muscle activity essential for dynamic joint stability Functional Stability Paradigm  Mechanical stability (arthokinematics; passive structures)  Functional stability (dependent on neuromuscular control; muscles) ****Functional instability can exist w/ mechanical stability

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Central Contributions to Motor Control Voluntary Motor Commands  Open-loop processes  Voluntary movements involve: complex interactions in musculoskeletal system o ‘Triphasic agonist/antagonist activity’ (e.g. rapid elbow extension)  Direct involvement of ‘higher’ brain centers & feedback = UNLIKELY o Degrees of freedom Problem  Numerous parameters involved in limb movements  Large % of ‘RAM’ taken up to process incoming sensory info & produce appropriate response  Similar responses with deafferentation (monkey with cut dorsal roots  still shows triphasic agonist/antagonist activity; suggests that sensory information is not processed in real-time)  Feedback plays role in refinement and adjustment only Agonist-antagonist timing Problem  Central delay associated w/ perception of sensory info Motor Program o Specifies degrees of freedom to act as ‘single unit’ o Controlled by ‘higher’ brain structures Evidence for motor programs o Feedback processes = too slow to impact rapid movements o Complex movements possible w/ deafferentation o Voluntary movements are PREPROGRAMMED  ‘Point of no return’ (Henry & Harrison)  carousal example  increased in complexity of movements, increase in RT (Henry & Rogers study) Potential problems w/ motor programs 1. Storage problem 2. Novelty problem o

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Generalized Motor Programs  Generalized motor programs (‘adaptable’) o Motor programs responsible for a ‘class of actions’  Grasping o When object properties are known:  Appropriate grip force & lifting force o Changes in output w/ Changes in object parameters  Invariant Features vs. Parameters o Invariant Features  Order of events (‘Tri-phasic pattern’)  Relative Force  Ratio of muscle forces (2:1)  Phasing (relative temporal organization—proportional) o Parameters (‘expression’ of a motor program)  Overall duration  Faster movement—‘compresses’ movement time (proportionally)  Overall force  Proportional changes in muscle forces  Muscle selection  Ex. Handwriting  Bilateral transfer

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Voluntary Motor Commands  Influence of sensory input on Motor programs  Execution of motor programs integrated w/ sensory input  3 sources of sensory info. crucial to control of voluntary movement: i. Visual input ii. Somatosensory iii. Vestibular apparatus (postural control)  Prior to movement—  Determination of appriopriate parameters  Sensory cues about initial state of motor system  Functional tuning  What is the appropriate overall force? o Gravity: max. effect down (when segment is horizontal) o Biarticulate muscle (e.g. ‘biceps’ & ‘triceps)  Although movement is the same, the muscle has to produce differing amounts of force in order to overcome gravity and passive tension  During movement—  Monitoring and adjustments (long duration)  Feedback NOT necessarily used (unless errors occur)  leads to reflexive corrections  Following movement—  Assessment of previous movement  Leads to: MOTOR LEARNING  Role of cerebellum

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Locomotion Locomotion = motor activity involving translation of total body COM  ‘Rhythmicity’ Locomotion  Central Pattern Generator (CPG) o Rhythmic motor activity (in ABSENSE of sensory info.) o CPGs identified for numerous rhythmic motor systems o CPG for gait/locomotion = spinal level o Evidence on CPGs— 1. Spinal preparations (cats) 2. Electrical stimulation of spinal cord produces stepping (cats) 

Descending control of CPGs  Initiation & Speed control

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