Motor Control Flashcards
Motor Control
Motor Development Milestones
0-3 months: Holding head up
4-5 months: Rolling over (both ways)
5-7 months: Rising up on hands
6-8 months: Crawling
6-8 months: Sitting without support
9-10 months: Standing with support
11-15 months: Walking
Definition of Motor Control
Encompasses neural, physical, and behavioral processes governing posture and movement.
Involves the ability to maintain and change posture and movement through neurologic and mechanical processes.
Studies how the central nervous system (CNS) regulates the musculoskeletal system and environment to achieve specific task goals.
Crucial Elements of Motor Control
Neural Circuit: Cortex, brainstem, cerebellum, and spinal cord processing inputs and outputs.
Motor Plan (Effector): Usually a limb, executing the output of the neural circuit.
Environment: Context where movement occurs, shaping the interplay between the neural circuit and motor plan.
Goal-Oriented Movements
Task Goal: Reaching for a coffee mug.
Control Policy: Mapping the task goal to motor commands.
Motor Command: Activating specific muscle groups to move the hand in a certain trajectory.
Sensory Information: Utilizing past movements to guide upcoming movement and online sensory feedback for ongoing movement.
Sensory Forward Model: Predicting sensory outcomes of a task.
Motor Control Development
Begins with control of self-generated movements.
Progresses to controlling movements relative to changing demands of tasks and environment.
Self-movement control arises from the development of neuromotor systems.
Movement emerges as the nervous and muscular systems mature.
Motor control directs which muscles to use, in what order, and how quickly to solve movement problems.
Example: An infant overcoming gravity, moving a larger head compared to a smaller body.
The task within the environment dictates the type of movement solution needed.
Motor Abilities and Motivation
Motor abilities change over time.
Motor solutions to a given problem may also change.
Individual's motivation to move can change, affecting the intricacy of the movement solution.
Motor Control Time Frame
Motor control happens in fractions of seconds.
Physiologic processes happen quickly for timely and efficient movement.
Neurologic dysfunction can cause:
Impaired timing: Movement is too slow to be functional.
Impaired sequencing: Muscle contraction occurs at the wrong time.
Role of Sensation in Motor Control
Sensation plays an important role.
Sensation cues reflexive movements.
Infant motor behavior is cued by sensation (reflexes, weightbearing).
Sensation provides feedback accuracy (e.g., hand placement, creeping, interacting with objects).
Sensory information is crucial when interacting with objects and the environment.
Sensory experience contributes to development of postural control and motor skill acquisition.
Movement generation can be described as a sensorimotor loop.
Optimal Neuromuscular Transmission
Requires a healthy:
Motor cortex
Brain stem motor nuclei
Descending CNS motor tracts
Motor units
Role of Feedback
Feedback is a crucial feature of motor control.
Defined as sensory or perceptual information received as a result of movement.
Used to detect errors in movement.
Sensory information (feedback) is transmitted in ascending pathways to higher centers.
Importance of Feedback and Error Signals
Feedback provides a means to understand the process of self-control.
Reflexes are initiated and controlled by sensory stimuli from the environment.
Motor behavior generated from feedback is initiated by an error signal produced within the individual.
Feedback provides a way for learning new motor skills.
Intrinsic feedback: Sensory source inside the body (proprioceptors) or outside the body (seeing the target was not hit).
Extrinsic feedback: Outside source providing feedback (therapist, coach, biofeedback, mirror, touch).
Types of Extrinsic Feedback
Knowledge-of-Performance Feedback: Informs the patient of the quality or efficiency of the movement pattern.
Given as the person is performing the task.
Examples: "Keep your balance over your feet," "Push down on your walker," "Put your foot farther forward."
Knowledge-of-Results Feedback: Informs the patient if the task is accomplished or how close the movement came to accomplishing the task.
Given at the end of the task.
Examples: “You came to standing without my help,” “You should not sit down without looking because you just sat on Mr. M.”
Both types of feedback give the learner information regarding error
External Feedback Presentation
Summary Feedback: Feedback is given after a set number of trials of the task.
Faded Feedback: Initially provides feedback after every trial, then decreases in frequency.
Delayed Feedback: Feedback is withheld for a short time after the task.
Faded feedback: Appears to be most effective for facilitating motor learning.
Feedback schedule depends on the patient and the task to be learned and practiced
Motor Learning Concepts
Initial Learning
Mass practice of motor program or functional skill is required.
Needs knowledge of both performance and results.
Initial reinforcement is immediate, showing high performance but lower retention.
Learning Shows
Reintroduction of corrections of impairments into the functional skill.
Practice progresses from mass to distributed as the patient begins to self-correct errors.
Widening the window of range within programming, the program can increase.
Design moves from block to random as program becomes more automatic.
Mental practice encourages internal repetition.
Learning Shows Motor Program
Practice schedule progresses from distributed to random.
Patient is self-motivated to run the correct procedure.
Patient internally corrects using inherent mechanisms and no longer needs the physical therapist assistant for reinforcement, except for social reasons.
Closed-Loop System
System control involving feedback, error detection, and error correction to maintain a system goal.
Applicable to maintaining constant states (posture, balance) and controlling slow, precise movements
Open-Loop System
System control where instructions for the effector system are determined in advance and run without feedback.
Rapid and skilled movement sequences or well-learned movements can be completed without sensory feedback.
Most movements involve elements of both closed- and open-loop control processes (hybrid control system).
Feedforward
Anticipated sensory consequences of movement that should occur if the movement is correct.
Sending signals in advance of movement readies sensorimotor systems and allows proactive adjustments in postural activity.
Theories of Motor Control
Reflex/Hierarchical Model
Early theories proposed by Sherrington and others in the 1800s.
Based on varying levels of the nervous system responsible for postural control and balance.
Focused on maturation of the developing brain and emergence of motor behaviors in infancy.
Nervous system maturation gauged by assessment of reflexes.
Reflex is the basic unit of movement in this model (pairing of sensory stimulus with motor response).
Reflexes are also referred to as primitive reflexes.
Primitive Reflexes
Occur early in infancy.
Can be simple (flexor withdrawal, palmar grasp) or complex.
Tonic Reflexes
Associated with the brain stem.
Produce changes in muscle tone and posture (e.g., tonic labyrinthine reflex, asymmetric tonic neck reflex).
Most infantile and tonic reflexes are integrated by 4 to 6 months.
Integration is the mechanism by which less mature responses are incorporated into voluntary movement.
Righting Reactions
Sensory information to orient the head in space and the body relative to the head and support surface.
Equilibrium Reactions
Complex postural responses to slow balance disturbances.
Continue into adulthood.
Involve the head and trunk.
Protective Reactions
Extremity movements in response to quick displacements of the center of gravity out of support base.
Serve as a backup system if righting or equilibrium reactions fail.
Development of Motor Control
Relationship of mobility and stability of body postures; acquisition of automatic postural responses.
Sequence:
Initial random movements (mobility).
Maintenance of a posture (stability).
Movement within a posture (controlled mobility).
Movement from one posture to another posture (skill).
Acquisition of each new posture involves development of control within that posture.
Stages of Motor Control
Stage One: Mobility
Movement is initiated.
Infant exhibits random movements within available range of motion (first 3 months).
Movements lack purpose and are often reflex-based.
Mobility is present before stability.
In adults, mobility refers to the availability of range of motion to assume a posture and sufficient motor unit activity to initiate movement.
Stage Two: Stability
Ability to maintain a steady position in a weight-bearing, antigravity posture.
Also called static postural control.
Divided into tonic holding and co-contraction.
Tonic Holding: Isometric movements of antigravity postural extensors at the end of the shortened range of movement; evident when the child maintains the pivot prone position (prone extension).
Co-contraction: Simultaneous static contraction of antagonistic muscles around a joint to provide stability in a midline position or in weight bearing; allows the developing infant to hold postures such as prone extension, prone on elbows and hands, all fours, and a semisquat.
Stage Three: Controlled Mobility
Mobility superimposed on previously developed postural stability by moving within a posture.
Occurs when limbs are weight bearing and the body moves, such as in weight shifting on all fours or in standing.
Also referred to as dynamic postural control.
Example: Reaching for a toy in prone, weightshifts.
Stage Four: Skill
Most mature type of movement, usually mastered after controlled mobility within a posture.
Mobility is superimposed on stability in non–weight bearing; proximal segments stabilize while distal segments are free for movement.
Creeping and walking are considered skilled movements.
Skilled movements involve manipulation and exploration of the environment.
Development of Reactive Postural Control
Postural control develops in a cephalocaudal direction.
Shown by the ability to maintain the alignment of the body, alignment of body parts relative to each other and the external environment.
Sequence: righting reactions, protective reactions, and then equilibrium reactions.
Head righting reactions develop first, followed by trunk righting reactions.
Protective reactions of the extremities arise to safeguard balance in higher postures (e.g., sitting).
Balance is achieved in different positions relative to gravity (cephalocaudal direction).
Righting Reactions
Responsible for orienting the head in space and keeping the eyes and mouth horizontal.
Involve head-and-trunk movements to maintain or regain orientation or alignment.
Begin at birth; most evident between 4 and 6 months of age.
Vision cues an optical righting reaction, gravity cues the labyrinthine righting reaction, and touch of the support surface to the abdomen cues the body-on-the-head reaction.
Neck-on-body righting: the body follows the head movement.
Body-on-body righting reaction: upper or lower trunk is turned.
Neck-on-body righting or body-on-body righting can produce log rolling or segmental rolling (log rolling: immature righting response seen in the first 3 months of life).
Purpose is to maintain the correct orientation of the head and body in relation to the ground.
Protective Reactions
Extremity movements that occur in response to rapid displacement of the body by diagonal or horizontal forces.
Protective reactions of the upper extremities include propping on extended arms.
Equilibrium Reactions
Most advanced postural reactions, are the last to develop.
Allow the body as a whole to adapt to slow changes in the relationship of the center of mass with the base of support.
Incorporate learned head-and-trunk righting reactions.
Add extremity responses to flexion, extension, or lateral head-and-trunk movements to regain equilibrium.
Can occur if the body moves relative to the support surface or if the support surface moves.
Responses to lateral displacement of the center of mass toward the periphery of the base of support in standing:
Lateral head and trunk righting occurs away from the weight shift.
The arm and leg opposite the direction of the weight shift abduct.
Trunk rotation away from the weight shift may occur.
Motor Program Model of Motor Control
Developed to challenge the notion that all movements are generated through chaining or reflexes.
For efficient movement to occur in a timely manner, an internal representation of movement actions must be available to the mover.
Motor programs are associated with a set of muscle commands specified at the time of action production, which do not require sensory input.
Schmidt (1988) expanded motor program theory to include the notion of a generalized motor program or an abstract neural representation of an action, distributed among different systems.
Motor program may also refer to a specific neural circuit called a central pattern generator (CPG), which is capable of producing a motor pattern, such as walking; CPGs exist in the human spinal cord.
Systems Model of Motor Control
Currently used to describe the relationship of various brain and spinal centers working together to control posture and movement.
Neural control of posture and movement is distributed; areas of the nervous system that control posture or movement depend on the complexity of the task to be performed.
Nervous system has the ability to self-organize; several parts of the nervous system may be engaged in resolving movement problems.
Accounts for the flexibility and adaptability of motor behavior in a variety of environmental conditions.
Many systems interact to produce coordinated movement, not just the nervous system.
Cooperative actions of multiple systems allow for accommodation of movement to match the specific demands of the task and the environment:
Musculoskeletal system (body mass, inertia, and gravity).
Cognition (attention, memory, learning, judgment, and decision-making).
Perception (interpretation of sensation).
Characteristics of Systems Model
Body systems other than the nervous system are involved in the control of movement.
Musculoskeletal system: body is a mechanical system; muscles have viscoelastic properties.
Maturation occurs in all body systems involved in movement production: muscular, skeletal, nervous, cardiovascular, and pulmonary.
Contractile properties of muscle: may limit certain movements.
Muscular strength of the legs: if insufficient, ambulation may be delayed.
Muscle strength, posture, and perceptual abilities: exhibit developmental trajectories, which can affect the rate of motor development by affecting the process of motor control.
Systems Model of Motor Control - Feedback
Individual needs to know whether the movement has been successful.
Closed-loop model: sensory information is used as feedback to the nervous system to provide assistance with the next action; loop is formed from sensory information that is generated as part of the movement and is fed back to the brain; influences future motor actions; errors that can be corrected with practice are detected, and performance can be improved; example: playing a piano piece slowly while learning and receiving feedback.
Open-loop model: movement is cued either by a central structure, such as a motor program, or by sensory information from the periphery; movement is performed without feedback; example: baseball pitcher throws a pitch, the movement is too quick to allow feedback; errors are detected after the fact.
Components of the Postural Control System
Posture and movement are considered systems that represent the interaction of other biologic and mechanical systems and movement components.
Posture: Readiness to move, an ability not only to react to threats to balance but also to anticipate postural needs to support a motor plan.
Motor plan or program: A plan to move, usually stored in memory.
Seven components identified as part of a postural control system: limits of stability, sensory organization, eye-head stabilization, the musculoskeletal system, motor coordination, predictive central set, and environmental adaptation
Postural control: complex and ongoing process
Limits of Stability
Boundaries of the base of support (BOS) of any given posture; if the center of mass (COM) is within the base of support, the person is stable.
Central nervous system senses the body’s limits of stability via various sensory cues.
Keeping the body’s COM within the BOS is part of balance.
Center of pressure (COP) motion: Point of application of the ground reaction force; COP under each foot in standing.
Cone of stability: In standing; the area in which the person can move within the limits of stability or base of support.
Sensory Organization
Visual, vestibular, and somatosensory systems provide the body with information about movement and cue postural responses.
Sensory input is needed for the development of postural control.
Vision is very important for the development of head control.
Vision is the dominant sensory system for the first 3 years of life; infants rely on vision for postural control in the acquisition of head control and walking.
Somatosensation
Combined input from touch and proprioception.
Used by adults as the primary source for making a postural response.
When there is a sensory conflict, the vestibular system acts as a tiebreaker in making the postural response decision.
Eye-Head Stabilization
Eyes and labyrinths: two of the most influential sensory receptors for posture and balance in the head; provide ongoing sensory input about the movement of the surroundings and head; provide orientation of the head in space.
Eyes: must maintain a stable visual image even when the head is moving; be able to move with the head as the body moves.
Labyrinths: relay information about head movement.
Musculoskeletal System
Mechanically linked structure that supports posture and provides a postural response.
Viscoelastic properties of muscles, joints, tendons, and ligaments can act as constraints to posture and movement.
Flexibility of body segments, such as the neck, thorax, pelvis, hip, knee, and ankle, contributes to attaining and maintaining a posture or making a postural response.
Normal muscle tone is needed to sustain a posture and to support normal movement.
Muscle Tone
Defined as the resting tension in the muscle and the stiffness in the muscle as it resists being lengthened.
Determined by assessing the resistance felt during passive movement of a limb.
Viscoelastic properties of muscle, the spindles, Golgi tendon organs, and descending motor tracts regulate muscle tone.
Motor Coordination
Ability to coordinate muscle activation in a sequence that preserves posture.
Examples: use of muscle synergies in postural reactions and sway strategies in standing.
Strength and muscle tone - prerequisites for movement against gravity and motor coordination
Predictive Central Set
Component of postural control that can best be described as postural readiness.
Sensation and cognition: used as anticipatory cues before movement as a means of establishing a state of postural readiness.
Mature motor control: characterized by the ability of the body, through the postural set, to anticipate what movement is to come.
Environmental Adaptation
Posture and movement adapt to the environment in which the movement takes place.
Adaptive postural control assists in making changes to movement performance in response to internal or external needs.
Nashner’s Model of Postural Control in Standing
Describes three common sway strategies seen in quiet steady-state standing: the ankle strategy, the hip strategy, and the stepping strategy.
Adult in a quiet standing sways at the ankles; strategy depends on having a solid surface in contact with the feet and intact visual, vestibular, and somatosensory systems; sway backward, the anterior tibialis fires to bring the person forward; sway forward, the gastrocnemius fires.
Hip strategy is activated when the base of support is narrow; muscles around the hip are activated to maintain balance before the muscles at the ankles.
Stepping if the speed and strength of the balance disturbance are sufficient, the individual may take a step to prevent loss of balance or a fall.
Issues Related to Motor Control
Question of where the control of movement resides (top-down or distributed control).
Reflex/hierarchical model: the cortex is the controller of movement.
Cortex can initiate movement but it is not the only neural structure that can (e.g., basal ganglia, the cerebellum, and the spinal cord).
Systems view of movement: no one location of control exists; movement emerges from the combined need of the mover, the task, and the environment.
Movement control improves because of maturation of both the nervous system and the musculoskeletal systems.
Degrees of Freedom
Mechanical definition: number of planes of motion possible at a single joint.
Degrees of freedom of a system: all of the independent movement elements of a control system and the number of ways each element can act.
CNS minimizes degrees of freedom or number of independent movement elements that are used.
First hold joints stiffly through muscle co-contraction, then as we learn, decrease co-contraction and allow the joint to move freely.
Increase in joint stiffness used to minimize degrees of freedom at the early stages of skill acquisition may not hold true for all types of tasks
Age-Related Changes in Postural and Motor Control
Variability in postural control is seen during infancy.
Ability to adapt one’s posture makes exploration of the surrounding environment easier.
Balance Strategies in Sitting
Control of the trunk develops segmentally in a top-down manner between 3 and 9 months.
Anticipatory control of sitting increases from 2 to 11 years of age, but is still variable and incomplete when compared with adults
Strategies in Standing
Postural control matures between 10 and 12 years.
Young children tend to quickly make fast corrections to try and maintain standing balance.
.* Older adults have been found to use a stiffening response of co- contracting muscles around the ankles joints rather than switching to using other sensory cues when vision is eliminatedThe model of motor control that best explains changes in posture and movement seen across the lifespan depends on the age and experience of the mover, the physical demands of the task to be carried out, and the environment in which the task is to be performed.
Motor Learning
The process that brings about a permanent change in motor performance as a result of practice or experience.
The study of how individuals acquire, modify, and retain motor memories so they can be used, reused, and modified during functional activities.
*Skill takes time to master; teens and adults refine their skills, becoming more efficient • Adults learn to perform tasks related to an occupation efficiently Olde adults modify motor skill performance to accommodate changestime frame of motor learning falls between the milliseconds in motor control and the years in motor development.
Motor learning will continue as long as the environment asks for change and the CNS retains control.
Theories of Motor Learning
Adam’s Theory of Motor Learning
Based on closed-loop control.
Sensory feedback from ongoing movement is compared with stored memory of the intended movement (perceptual trace) to provide the CNS with a reference of correctness and error detection.
Movements are performed by comparing an ongoing movement with an internal reference of correctness (perceptual trace).
Does not easily explain open-loop control and learning without sensory feedback(deafferentation studies)
Schema Theory
Proposed by Schmidt
Schema: a rule, concept, or relationship formed based on experience
Concerns movements without feedback
Motor program reflects general rules to complete movement; can be applied to tile, grass, and hills.
Motor program is composed of the schema, or abstract memory, of rules related to skilled actions.
Stages of Motor Learning
Fitts and Posner Model
Cognitive Stage (Acquisition of a Motor Skill)
Learner consciously considers task goal and environmental features. Cognitive mapping allows assessment of abilities, task demands, and initial movement strategy. Performance is inconsistent with large gains.Associative Stage (Refinement)
Learner practices and refines patterns with spatial and temporal organization with less dependence on visual feedback while proprioceptive feedback rises.Autonomous Stage (Refinement)
Spatial and temporal components become organized as movements become automatic and error-free movements concentrate on other aspects
Model considers the learner’s ability to master multiple degrees of freedom
In the novice stage, the learner reduces the degrees of freedom; fix the joints.
When advanced learner allows more joints to participate in the task, Coordination is improved with agonists and antagonists working together.
In the expert stage, all degrees of freedom necessary to perform a task in an efficient, coordinated manner are released with speed.
Effects of Practice
*Practice environment should replicate actual
*Massed versus Distributed mass is greater time. Distributed rest is longer
*Random versus Blocked practice(Random many tasks in random order. Blocked-tasks are in block-same a number of times.)
Mixed practice sessions are useful Random/blocked practices are helpful
*Constant one variation of a movement Varible-learner practices verious skills during practice/learning.Whole vs Part task
Whole vs part
Whole: can be preformed whole
Part: part of the motion, best discrete parts
Whole vs part task
Learning Whole-motor is worked on a