Upper-Extremity Function and CNS Control

Neural Contributions to Reach, Grasp, and Manipulation

• The course focuses on neural contributions to upper extremity (UE) function, specifically reach, grasp, and manipulation.
• The primary resource is Shumway-Cook and Woollacott's Motor Control, Chapter 17.
• Upper extremity function is fundamental to fine and gross motor skills.
• It plays a vital role in motor skill recovery and retraining.
• Contextual factors, including the environment and the individual, significantly impact upper extremity function.
• UE function is integrated into most self-care, work, and household activities.

International Classification of Function (ICF)

• ICF framework categorizes health conditions (disorders or diseases) in relation to body structures and functions, activities, and participation.
• Body structure and function include neuromusculoskeletal and movement-related functions, control of voluntary movements, visually directed movements, and eye-hand coordination.
• Activities encompass mobility, carrying, moving, and handling objects.
• Participation includes self-care tasks, domestic life activities, and real-world activities.

Sensorimotor Processing

• Sensorimotor processing for eye-head and hand coordination involves individual constraints, task type, and environmental constraints.
• The goal is to understand how the central nervous system (CNS) controls upper extremity (UE) movements.

What is going on in the Brain?

• Visual cortex, posterior parietal association area, somatosensory cortex, prefrontal area (dorsolateral frontal association), premotor cortex, primary motor cortex, basal ganglia, and cerebellum are crucial for sensory and motor processing.
• Spinal cord carries motor commands to motor neurons, activating hand and forearm muscles.
• Sensory receptors in fingers and hands send signals via spinal cord pathways (dorsal column/medial lemniscus) to the somatosensory cortex.
• Further analysis assesses the involvement of the limbic system in the process.

Hedmann's Model for Movement Observation Analysis

• The model analyzes movements, from initial conditions to outcomes, to understand movement execution.
• Factors like posture, ability to interact with the environment, stimulus identification, response selection, response programming, timing, amplitude, direction, smoothness, speed, stability, and termination are considered.
• Reaction time is crucial as it reflects CNS anticipatory processing time.

Motor Control Principles

• Feedforward and feedback control mechanisms are essential in motor control.
• Motor program theory explains open and closed-loop control concepts.
• Visual system and somatosensation are crucial for feedforward and feedback control respectively.

Feedforward versus Feedback Control of Movement

• Efficient reaching involves both feedback and feedforward processes.
• Feedforward (anticipatory) control utilizes prior experiences to predict sensory information consequences.
• Feedback control uses input from sensory systems to determine movement accuracy and correct errors by comparing the actual movement to a reference signal.

Role of Sensory Information in Anticipatory Control of Reach and Grasp

• Visual system is critical for locating targets and determining the characteristics of objects, influencing the initial direction of the reach.
• Visual cues are important for object and hand location.
• Somatosensory system helps determine initial position and coordination of limbs.

Role of Sensory Feedback to Reach and Grasp

• Visual feedback is important for accuracy in reaching but slower.
• Without feedback, movement is faster but less accurate.
• Visual feedback plays a lesser role in grasping compared to reaching.
• Continuous object manipulation relies significantly on visual feedback.

Motor System in Reach and Grasping: Execution of Movement

• The premotor and primary motor cortices receive inputs from the posterior parietal cortex to execute movement.
• The intentions/goals of movement, location-direction, joint formation characteristics, and grasp type are important factors.
• Evidence suggests the posterior parietal cortex encodes visual reference while the premotor cortex encodes body reference.

Two Separate Descending Pathways for Reach and Grasp

• Motor development of reaching and grasping is linked to maturation of the corticospinal tract.
• Individuals with corticospinal injury may show grasp and manipulation impairment but transport remains intact.
• Transport component involves shoulder and elbow pathways, potentially using midbrain and brainstem structures (reticulospinal and rubrospinal tracts).
• "Hand precision" component relies on wrist and hand pathways using corticospinal pathways.

Musculoskeletal Contributions

• The neural and musculoskeletal systems interact. Movement range of motion, strength, muscle tone impacts the command from the nervous system.
• Compensatory strategies may be necessary, like adjusting reaching when elbow extension range is limited or adjusting for weak elbow extensors.
• Scapular control plays a critical role during reaching and grasping tasks, differentiating between arm movement and arm stabilization.

Postural Support of Reaching and Grasping

• The postural system upholds upright posture and alignment of postural segments during arm movement.
• Anticipatory and reactive postural adjustments are crucial during reach and grasp actions.

Motor Control Elements

• Goal-directed commands affect postural support, reach, and grasp.
• Posture is influenced by medial activation of medial spinal tracts.
• Reach is influenced by rubriospinal and reticulospinal tracts.
• Grasp is influenced by corticospinal tracts.

Grasping Patterns

• Grasping involves power grip (using finger and thumb pads directed towards the palm for force transmission) and precision grip (using fingers and thumb for force transmission).
• Different grasping patterns include hook, spherical, and cylindrical grips.

Anticipatory Control of Grasp and Lift

• Grip formation happens during transport, anticipating grasping.
• Hands adapt to objects' size, shape, and intended use.
• Finger movements are timed relative to the transport.
• The nervous system anticipates grip needs for different weights and surfaces during lifting.
• The cerebellum plays a key role in predicting forces to maintain grasp, providing feedback loops for error correction, and storing force prediction information.

Coordination of Reach and Grasp

• Reach and grasp movements are kinematically coupled (simultaneous).
• Invariant features of reaching and grasping include movement time, and hand opening timing.
• Motor programs contain the rules stored in the CNS for reach, direction, distance, speed and grasp type which may vary based on the initial start parameters.

Reaction Time

• Reaction time (RT) is used to quantify sensorimotor processing before a movement.
• It measures the time between a stimulus and the beginning of a response.
• Reaction time increases with more choices available.

Simple versus Choice Reaction Time

• Simple reaction time involves a single stimulus-response pair.
• Choice reaction time involves several possible stimulus-response options.
• Choice reaction time takes longer than simple reaction time.

Fitt's Law of Movement

• Fitt's Law describes the relationship between movement time, distance, and accuracy demands.
• Movement time increases with increasing distance and accuracy requirements.
• Visual processing constraints are key to this relationship.

Theories of Reaching Control

• Distance programming theories suggest the CNS activates a set of agonist muscles to propel the limb, guided by perceived distance, often with reliance on initial visual perception.
• Impulse-driven control involves initiating the motion, followed by feedback correction.
• Location programming theories compare limb muscles to springs; the CNS programs muscles' stiffness based on targeted locations, with agonist-antagonist muscle interactions influencing the movement's final location and final extent of motion.

Interference between Reaching and Cognitive Tasks

• Dual task paradigms demonstrate that performing a cognitive task while coordinating a reach can affect reaction time, with an increase in reaction time suggestive of interference in movement planning.

Prefrontal Cortex and Limbic System Influence

• The prefrontal cortex plays a role in perceiving and initiating movements, stopping an action, and analyzing behaviors in context of goal-directed movement.
• The limbic system contributes to motivation, explicit memory learning, and emotional drive.

Conceptual Mapping of Neural Control of Reach and Grasp

• A conceptual map helps to visualize the various neural elements involved in reach and grasp, mapping visual processing (location, identification, planning), motor processing (motor plan selection), sensory processing (feedback related to grasp/movement), and consideration of the roles of frontal, parietal, and limbic systems.

Extrapolate Reaching and Grasping Research

• Research in reaching and grasping can be used to understand other upper extremity tasks such as picking up a spoon and eating, and overhead throwing.

This quiz explores the significance of upper-extremity function in daily activities, motor control retraining, and cognitive processing in relation to the central nervous system (CNS). Answer questions about the roles of different brain pathways, visual feedback, and contextual factors impacting upper-extremity function. Dive into the intricacies of upper-extremity control and its implications for clinical practice.