Motor Control Concepts and Motor Cortex

Sequencing movement
Feeds correct motor instructions in correct sequence to the primary motor cortex
Active during mental rehearsal of coordinated movements

Involuntary, rapid, stereotyped movements: Eye-blink, coughing, knee jerk reflex
Initiated by an eliciting stimulus

Complex actions: writing, speaking, playing piano, preparing food (many activities of daily life)
Purposeful, goal-oriented
Learnt and can be improved with practice
Voluntary movement is initiated at cerebral cortex level
To generate a desired movement or action a motor command is configured which involves the integration of sensory information, the selection of appropriate sets of muscles and joint activations, and the determination of the required forces needed.
- Planning: Formulating the strategy of action by specifying motor goals
- Programming: Procedure orientated; constructing the actual sub parts of the movement
- Execution: Getting the commands to the muscles by descending pathways and modulated by sensory feedback and higher subcortical centers

CPGs are neuronal circuits that produce rhythmic motor patterns in the absence of sensory or descending inputs that carry specific timing information.
E.g. Walking - involves alternating contraction/relaxation of flexors/extensors
CPGs are initiated by higher centers (i.e. brainstem) and modified by sensory input from PNS.

Adaptable networks of spinal interneurons that activate the lower motor neurons that innervate hip/knee flexors/extensors to give the pattern of alternate flexion and extension required for walking.
Activated when a conscious signal from the brain initiates walking.
Output is adapted to the task, the environment, and the stage of the walking cycle.
I.e. the exact position of the limb, the status of muscle contractions, and the relationship of the limb to the environment (somatosensory information)
Aids in walking. But, walking requires normal basal ganglia and cerebellar control, trunk control, arm swing, cortical control of dorsiflexion, and afferent information.

Motor control is defined as the ability to regulate or direct the mechanisms essential to movement (Shumway-Cook)

Comes from receptors in peripheral nervous system (Muscle spindles, Golgi tendon organs, Joint receptors, Touch/pressure receptors)
Provides information about weight bearing & about limb position before movement onset

Provides information about visual cues for movement and guidance during movement
e.g. Reaching for object - use vision to fixate on object, provide corrective adjustments to achieve contact with object

Input from inner ear receptors tells us about head position relative to gravity and during movement

How does the central nervous system organize the many individual muscles and joints into coordinated functional movements?
How is sensory information used to select and control movement?
Do our perceptions of ourselves, the tasks we perform, and the environment influence movement?

Organizational control that is top down.
Each successively higher level exerts control over the level below it, never bottom-up control.
For example, higher centres inhibit these lower reflex centres and reflexes controlled by lower levels of the neural hierarchy are present only when cortical centres are damaged.
Limitations:
- Cannot explain the dominance of reflex behavior in certain situations in normal adults.
- E.g. Withdrawal reflex after stepping on something sharp. This is an example of a reflex within the lowest level of the hierarchy dominating motor function. It is an example of bottom-up control.
- We must be cautious about assumptions that all low-level behaviors are primitive, immature, and non-adaptive, while all higher level (cortical) behaviors are mature, adaptive, and appropriate.

Whole body is a mechanical system, with mass, and subject to both external forces such as gravity and internal forces such as both inertial and movement-dependent forces
Degrees of freedom: Human beings have many degrees of freedom that need to be controlled (E.g. Joints) and therefore human movement has inherent variability that is critical to optimal function
DST sees variability not to be the result of error but necessary for optimal function
Optimal variability provides for flexible, adaptive strategies, allowing adjustments to environment
Too little variability can lead to injury
Too much variability leads to impaired movement performance
A small amount of variability indicates a highly stable behavior.
Limitations:
- Can presume the nervous system has a less important role, giving mathematical formulas and principles of body mechanics a more dominant role in describing motor control.
- Understanding the application and relevance of this type of analysis to clinical practice can be very difficult.

Suggests motor control evolved to cope with the environment
Suggests actions require perceptual information specific to a desired goal-directed action performed within a specific environment.
Theory has broadened our understanding of nervous system function from that of a sensory / motor system, reacting to environmental variables, to that of a perception/action system that actively explores the environment to satisfy its own goals.
Expanded our knowledge significantly with regard to the interaction of the us and the environment
Limitations:
- Gives less acknowledgement to the structure and function of the nervous system.