Lecture 1 Motor control Flashcards
Motor control
ability to regulate or direct the mechanisms essential to movement
the movement we produce is the result of 3 things
our capabilities – the individual
what we are trying to do – the task
where/how we are trying to do it – the context or environment
What’s the difference between voluntary and reflex movement?
Premotor area (PMA) and suppl. motor area (SMA) devise movement plan
What’s the difference between upper motor neurons (UMN)and lower motor neurons (LMNS)?
upper motor neurons are responsible for motor movement, whereas lower motor neurons prevent excessive muscle movement. Upper motor disorders usually cause spasticity; lower motor disorders usually cause flaccidity.
medial motor tracts
synapse with MNs that innervate postural and girdle muscles
lateral motor tracts
synapse with MNs that innervate muscles used for fractionated movement and innervate wrist and finger extensors
Information processing of human motor behavior occurs in stages
Stage 1 = stimulus identification
Stage 2 = response selection
Stage 3 = response programming
Stage 1 = stimulus identification
relevant stimuli about current body state, movement, and environment, are identified and selected – occurs via somatosensory, visual, and vestibularsystems
Stage 1 = stimulus identification cognitive processes
memory, attention, motivation, and emotional control, all play an integral role in ensuring the ease and accuracy of information processing during this stage
stimulus pattern complexity
complicated and novel patterns of stimuli prolong stimulus identification
Stage 2 = response selection
motor plan= an idea or plan for purposeful movement and is made up of component motor programs
ease and speed of response selection depends on
Number of possible responses – movement alternatives
Link or compatibility between the stimulus and response green light and crossing the street vs someone signaling you to cross on a red light
Stage 3 = response programming
neural control centers translate the idea for movement into muscular actions defined by a motor program
Motor program
an abstract representation that, when initiated, results in the production of a coordinated movement sequence
movement parameters are specified by the constraints of the
individual, the task, and the environment
Feedforward control
send signals in advance of movement
to prepare part of the system for incoming sensory feedback or a future motor command – anticipatory adjustments in postural activity
Feedback control
response-produced sensory information received during or after the movement
Used to monitor movement output for corrective action – reactive adjustments
what systems in the individual are responsible for controlling movement/motor control?
motor/action
sensory/perceptual
cognitive
Motor/Actions Systems
includes neuromuscular and biomechanical systems
degrees of freedom problem
Problem of choosing among equivalent solutions then coordinating the multiple joints
Sensory/Perceptual Systems
transformation of sensory impressions into psychologically meaningful information
Provide information about:
state of the body – e.g. location of body parts
state of the environment – features critical to regulation of mvmnt
Cognitive Systems
Inc attention, planning, problem solving, motivation, and emotional aspects of motor control needed for establishing intent or setting goals
Open movement tasks
require adapting movement strategies to constantly changing and unpredictable environments
requires a constant monitoring of sensory inputs, which are used to update, modify, and regulate motor output.
Closed movement tasks
performed in relatively fixed or predictable environments
less dependent on constant monitoring of sensory inputs related to environmental change
Discrete movements
have a recognizable beginning and end
Discrete examples
throwing and kicking a ball, a shot put, discus or javelin throw, or a somersault
continuous movements
have no distinct, identifiable bringing or end
continuous examples
swimming, jogging, skipping and walking.
closed movements
Performed in fixed or predictable environments
closed examples
doing dishes, squat, pushup
open movements
adapt movement strategies to a constantly changing and unpredictable environment
open examples
playing sports, running
Stability movements
performed in a nonmoving BOS
stability examples
sitting or standing
Mobility movements
moving BOS
mobility examples
walking or running
Environmental Constraints on Movement Control
CNS has to account for attributes of the environment when planning task-specific movements.
parts of environment CNS has to account for when planning movements:
regulatory and non regulatory features
regulatory features
shape movement or determine the movement
size, shape, weight of object s
type of surface to be walked on
non regulatory features
may affect performance, but movement does not have to conform to these
background noise, distractions, lighting level
Reflex Theory
Believed complex behavior could be explained by the combined action of individual reflexes chained together
Structure of a reflex: receptor, conductor, effector
limitations in reflex theory
does not explain spontaneous and voluntary movements
does not a explain and predict movement that occurs in the absence of a sensory stimulus
does not explain fast movements
fails to explain how a single stimulus can result in different responses depending on context and descending commands
does not explain the ability to produce novel movements
Reflex Theory
Clinical Implications
if reflexes are the basis for functional movement, testing reflexes should allow therapists to predict function
pts’ movement behaviors will be interpreted in terms of presence or absence of controlling reflexes
treatment will be basically aimed at enhancing or reducing effect of reflexes during motor tasks/movement
Hierarchical Theory
Nervous system is organized as a hierarchy - control is from top down; each successively higher level exerts control over level below it
Hierarchical Theory
Limitations
cannot explain dominance of reflex behavior in certain situations in normal adults
Can’t assume all bottom up control is bad or maladaptive and all top down control is good and adaptive
Hierarchical Theory
Clinical Implications
used to explain disordered motor control in patients with neurologic disorders
many of the traditional therapeutic techniques have been built on the hierarchical model of motor control
Motor Programming Theories
Have begun to see the CNS as more of an active system and less of a reactive system
can remove the stimulus or afferent input and still have a patterned motor response – not a reflex
motor program from
not reflexes that drive movements but central pattern generators (CPGs) – motor programs in the spinal cord that are modified or modulated by input from the brain and sensory inputs
motor program to
a more abstract idea of a central motor program – hierarchically organized motor programs at higher levels of the CNS that store rules for generating movements
Motor Programming Theories
Limitations
a single central motor program doesn’t explain all types of movements
doesn’t account for fact that CNS has to account for musculoskeletal and environmental variables when controlling movements
System Theories
saw the whole body as a mechanical system, with mass, and subject to external forces such as gravity and internal forces such as both inertial and movement-dependent forces
the interaction between external forces and variations in the initial conditions implies
the same central command could result in very different movements and -
different commands could result in the same movement
System theory example
the central command to flex an elbow results in different movements depending on initial conditions – does the movement start with the elbow bent or straight, the muscle fatigued or not etc
Systems Theory
hypothesized
that hierarchical control exists to simplify the control of the body’s multiple degrees of freedom
Systems theory hierarchy
higher levels of the nervous system activate lower levels
lower levels activate synergies, or groups of muscles that are constrained to act together as a unit
when the demands of a task increase, the control signal to the synergy increases, leading to parallel increases in the activation in all muscles in the synergy.
Principle of abundance
synergies not used by nervous system to eliminate redundant degrees of freedom, but to ensure flexible and stable performance of motor tasks
total activation of a muscle depends on
both the simultaneous activation of multiple synergies containing that muscle and the relative contribution of that muscle within each of these synergies
Modern expanded version of system theory = dynamic systems theory
when a system of individual parts comes together, its elements behave collectively in an ordered way
Nonlinear system
output is not proportional to its input
nonlinear behavior
transforms into a new configuration when a single parameter of that behavior is gradually altered and reaches a critical value
variability
is considered to be the consequence of errors in motor performance, assumption is that as performance improves during skill acquisition, error—and consequently variability—decreases
Optimal variability provides for
flexible, adaptive strategies, allowing adjustment to environmental change
too little variability can lead to
injury - repetitive strain problems
too much variability leads to
impaired movement performance, as occurs in persons with ataxia
a small amount of variability indicates
highly stable behavior
Attractor states
highly stable, preferred patterns of movement – used to accomplish common activities - preferred walking speed
Systems Theory
limitations
Have to be careful not to presume the nervous system is less important in determining movement behavior
Can be difficult to apply this mathematical, mechanistic model to clinical practice
Ecological Theory
the ecological approach to motor control suggests that motor control evolved so that animals could cope with the environment around them, moving in it effectively in order to find food, run away from predators, build shelter, and even play
Ecological Theory
Limitations
Research emphasis shifted from nervous system to organism/environment interface
Ecological Theory
Clinical Implications
individual is viewed as an active explorer of environment - allows the individual to develop multiple ways to accomplish a task
adaptability is important not only in the way we organize movements to accomplish a task but also in the way we use perception
