Chapter 17 - Normal Reach, Grasp, & Manipulation PDF

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CHAPTER 17 – NORMAL REACH. GRASP, AND MANIPULATION I. INTRO a. Upper extremity function is the basis for fine motor skills important to ADLs b. Important role in gross motor skills i. Crawling, walking, the ability to recover balance, ability to protect the body from injury when balance recovery isn’t possible c. Interweaving of upper-extremity control with fine and gross motor skills i. Recovery of function is an important aspect of retraining motor skills and falls within OT/PT d. Contextual factors impact function i. Environmental factors  characteristics of an object to be lifted/carried e. 3 factors contribute to sensorimotor processing i. Constraints of the individual (age, experience with the task, presence/absence of pathology) ii. Type of task (to point, to grasp/manipulate, to grasp and throw) iii. Specific environmental constraints (properties of the object) f. Key elements of upper-extremity reach, grasp, and manipulation skills: i. Locating a target (“visual regard”)  requires the coordination of eye-head movements and is essential to guiding hand movements ii. Reaching  involves transportation of the arm and hand in space as well as postural support iii. Grasping  includes grip formation, grasp, and release iv. In-hand manipulation skills g. Systems theory of motor control  specific neural and musculoskeletal subsystems contribute to the control of the components of reach, grasp, and manipulation i. Musculoskeletal: 1. Joint ROM 2. Spinal flexibility 3. Muscle properties 4. Biomechanical relationships b/w linked body segments ii. Neural: 1. Motor processing a. Coordination of eye, head, trunk, and arm movements b. Coordination of both the transport and grasp phases of the reach 2. Sensory processes a. Coordination of visual, vestibular, and somatosensory systems 3. Internal representations important for the mapping of sensation to action 4. Higher-level processes essential for adaptive and anticipatory aspects of manipulatory functions h. Control of manipulation involves both reflexive and voluntary movements and both feedback and feedforward processing i. Voluntary movements obey specific psychophysical principles i. Motor programs have invariant features ii. Movements show a lengthening of reaction time with increasing information II. MOVEMENT CONTROL PRINCIPLES a. FEEDFORWARD VS. FEEDBACK CONTROL OF MOVEMENT i. Learn to improve reaching efficiency and accuracy with practice 1. ANTICIPATE the requirements of the task and obstacles that might perturb the arm movement trajectory 2. CORRECT for the effects of perturbations ii. Feedback control involves input from the sensory systems (visual, somatosensory) being compared to a reference signal that represents a desired state of the system (arm position)

iii. Difference between the sensory input and the reference signal (error signal) is used to update the output of the system (muscles controlling the arm aka “actuators”) 1. Goal may be to maintain the position of the arm while catching a ball a. Reference signal  indicate the muscle contraction required b. Sensory info from the somatosensory or visual systems  provide feedback on the current position of the arm c. Difference between the current and desired arm position would be used to activate arm muscles to maintain that position iv. Feedforward (anticipatory) control takes advantage of previous experience to predict the consequences of sensory info that is received 1. Occurs before feedback sensors are stimulated  reduced the reliance on feedback control 2. Ex) when catching a ball, we use visual info about the ball’s trajectory to anticipate where to move the hand to catch it a. Acts as a feedforward controller (continuously updated through info from prior experience) and the controller activates the muscles at the correct level to catch the ball b. After the ball hits the hand, feedback processes will be used to react to the perturbation of hand position by the ball v. Feedback and feedforward mechanisms contribute to the muscle activation patterns involved in catching a ball 1. Same processes underlie the accurate movement of the eye, head, and hand toward a target III. LOCATING A TARGET a. EYE-HEAD-TRUNK COORDINATION i. IOT reach for an object successfully, we 1st have to locate the object in space ii. Vision is used for object location and to guide the movements of the hand (for reach, grasp, and manipulation) 1. Object location involves movements of the eyes alone, when the target is in our central visual field, or the eyes and head, when the target is on our peripheral visual field iii. Sequence of movement when object to grasp is in the peripheral field of vision: 1. Eye movement onset a. Shortest latency b. Eyes reach target first (before the head) because they move quickly  focus on the target before the head stops moving c. Activation of neck muscles happens 20-40 msec prior to activation of eye muscles d. Since eyes have less inertia than the head, the eyes move first (even though the neural signal occurs in the neck muscles first 2. When head movement is needed to look at an object a. Amplitude of head movement is usually only about 60%-75% of the distance to the target 3. When arm movements requiring great accuracy ate performed, this behavior may be modified a. People trained to throw with great accuracy make combined eye and head movements that go most of the distance to the target 4. Reaching to objects located in the far visual field requires a combo of eye, head, and trunk movements a. Eye-head coordination isn’t controlled by a unitary mechanism, but rather emerges from an interaction of several different neural mechanisms

i. One neural mechanism that subserves the ability to locate objects in the near periphery  requires primarily eye movements ii. Second mechanism to locate objects in the further periphery  controls combined eye-head movements iii. Third mechanism to locate objects in the far periphery  controls the movements of the eye, head, and trunk together b. INTERACTIONS BETWEEN EYE MOVEMENTS AND HAND MOVEMENTS i. Eye and hand movements both interact with and influence each other 1. When accompanied by eye movements, hand movements are more accurate 2. During smooth pursuit eye movements, there is an increase in gain if the hand is also following the target 3. In deafferented subjects, there is an increase in gain and reduction in latency for smooth pursuit when the hand was used to follow the target a. Suggests that the efference copy or corollary discharge about limb movement that helps the smooth pursuit system (rather than proprioceptive feedback from the hand movement) 4. Proprioceptive signals from the eye muscles do contribute to our ability to localize targets in extrapersonal space IV. REACH AND GRASP a. Control of arm movements changes depending on the goal of the task i. When the arm is used to point at an object  all arm segments are controlled as a unit ii. When the arm is used to reach and grasp an object  hand appears to be controlled independently of the other arm segments 1. Arm carries out movements related to transport 2. Hand carries out movements related to grasping the object b. Reaching for an object can be divided into 2 subcomponents – controlled by separate areas of the brain i. Reach component ii. Grasp component c. KINEMATICS OF REACH AND GRASP i. Velocity profiles and movement durations of reach vary depending on the goal of the task 1. Movement duration of reach is longer when a subject is asked to grasp an object than when a subject is asked to point and hit a target 2. Acceleration phase of reaching movement is shorter than deceleration phase when preparing to grasp an object 3. If the subject is asked to hit a target with the index finger, the acceleration phase is longer than deceleration + subject hits the target at a high velocity ii. Subject grasping an object and then fitting it in a small box vs. throwing the object 1. Movement times were shorter for grasp and throw vs. grasp and fit 2. Acceleration phase of the movement was longer for grasp and throw vs. grasp and fit iii. Task constraints and goals affect the reaching phase of movement 1. Reaching movements need to be practiced within a variety of tasks V. NEURAL CONTROL OF REACH AND GRASP a. Many systems are critical to the control of reach and grasp i. Primary motor cortex ii. Premotor cortex iii. Areas of the posterior parietal lobe iv. Cerebellum 1. feedback and feedforward control of reach and grasp skills

b. SENSORY SYSTEMS i. Sensory inputs come in from the periphery to tell you what’s happening around you/where you are in space/where your joints are relative to each other  CREATE A MAP OF YOUR BODY IN SPACE ii. Visual input goes through 2 parallel pathways involved in goal-directed reaching 1. What is being reached for (perception and object recognition) a. Perceptual pathway goes from visual cortex to temporal cortex 2. Where the object is in extrapersonal space (localization) and the action systems involved in object manipulation a. Localization and action pathways go from visual cortex to parietal lobe iii. Higher centers in the cortex take this info and make a plan to act on it in relation to the goal 1. Make a specific plan 2. Plan is sent to the motor cortex 3. Muscle groups are specified 4. Plan is also sent to the cerebellum and basal ganglia (to modify and refine movement) iv. Cerebellum sends and update of the movement output plan to the motor cortex and brainstem v. Descending pathways from the motor cortex and brainstem activate spinal cord networks; spinal motor neurons activate the muscles, and then you reach 1. Spinal reflex pathways compensate for extra weight that you didn’t expect and activate more motor neurons 2. Sensory consequences of reach will be evaluated, and the cerebellum will update the movement vi. Sensory info plays many roles during the control of reaching 1. Correct errors during execution of the movement itself, ensuring accuracy during the final portions of movement 2. Used to proactively (feedforward) in helping to make the movement plan vii. VISUAL PATHWAYS RELATED TO VISUAL REGARD, REACH, AND GRASP 1....