NRS - Week 8 Notes - Fine Motor Development and Play & Upper Limb Function
Overview
Lecture focus: development of fine motor skills and play, with emphasis on the emergence of prehension (reaching, grasp, release).
Key aim: understand how play relates to fine motor development and categorize types of play and their developmental progression in early childhood.
Emphasis on play as an occupation and its importance for children’s development and therapy planning.
Practical implications for clinical practice and paediatric placement, including considerations for children with disabilities and the role of positioning and assistive technology in promoting reaching.
Foundational concepts include the links between sensory exploration, object interaction, and motor skill development, plus the social and cognitive dimensions of play.
Emergence of Prehension
Prehension comprises three components: reach, grasp, and release.
Reach: moving the hand from an initial location to a target.
Grip/grasp: shaping the hand around an object.
Release: letting go of the object, involving extensor movement patterns.
Reach and grasp are interrelated but emerge at different times in the first year.
Pre-reaching: stage preceding successful reach and grasp.
In utero: as early as , hand movements toward the mouth observed; CNS is immature, so intentionality debated.
From birth: hand-to-mouth movements persist, aligning with survival (self-feeding/soothing).
Evidence suggests some degree of intentionality in early hand movements.
Guiding mechanisms for pre-reaching: proprioception is likely more influential than vision at early stages due to limited neonatal vision.
Newborns may swipe at toys but may not yet grasp; initial attempts are observed.
Influences on Reaching
Head control and shoulder coactivation are critical for reaching stability.
Stable shoulder girdle provides a base for reaching; hands open and emerge in the field of view.
Stability in sitting; development from bilateral to unilateral reach; more degrees of freedom (DOF) as control improves.
Clinically, children with increased muscle tone or dystonia may have coactivation or shoulder girdle stability issues.
Interventions: positioning and assistive technology can improve reach by providing support.
The linkage between reaching development and play: curiosity drives development in infancy and beyond; lack of motivation may signal broader concerns.
Early environment: visual exploration, mouthing, and tactile experiences drive learning from birth to 12 months.
Mouthing of objects is developmentally appropriate and supports environmental exploration; choking hazards require careful object management.
Sensorimotor play in infancy: from birth
From : infants actively explore objects to create sounds/visual effects (sensorimotor toys like rattles, bright colors, lights).
From : manipulative play expands; cause-and-effect games become prominent (e.g., hammer toys, pop-ups, flashing lights).
Imitation emerges (e.g., peekaboo, waving) and combining objects (e.g., ring and stacker) to explore relations.
Grasp Development Timeline (Neonate to 12 Months)
Grasp reflex in neonates: fisted hand with a strong grasp reflex; elicited when the palm is stimulated.
Reduction of reflex by ; palmar grasp develops (fingers flex around object) from .
: radial palmar grasp with supination, enabling inspection and mouthing.
: radial digital grasp emerges; object held between fingers and thumb; supports finger feeding.
: proximal stability improves (shoulder girdle); wrist extends during grasp; new grasps appear (scissor grasp: thumb beside index finger at DIP level); index finger isolation begins (pointing).
: inferior pincer grasp develops (thumb moves toward the side of index finger tip).
: fine pincer grasp (thumb opposes index fingertip); need to monitor for choking hazards (tiny objects).
Release development follows a different trajectory:
Neonate: dorsum of hand/fingers producing opening reflex with dorsiflexion.
: transition to purposeful release.
: release onto a surface while supported (e.g., floor, high chair).
Object transfer between hands develops; exploration and manipulation of toys increases.
9\text to }10\text{ months}: casting (dropping objects from a high chair) emerges; aligns with object permanence (formerly believed objects vanish when out of sight).
By : graded release appears; enables precise play (e.g., stacking blocks with controlled releases) and enables posting activities.
Unilateral and bilateral hand use:
: bilateral manipulation dominates; objects held with two hands; visual inspection and hand-to-hand transfer observed.
: one hand holds an object while the other explores.
From onward: coordinated but asymmetric hand use in functional activities (e.g., scribbling, Play-Doh manipulation).
Later milestones:
By 5$ to $6\text{ years}: tripod grasp increasingly develops, supporting writing; some immaturities may be visible (e.g., thumb curling, DIP hyperextension).
LECTURE 2: UPPER LIMB FUNCTION
Role of the Upper Limb in Everyday Function
Upper limbs are involved in virtually all daily activities and functional tasks; nothing we do with hands is entirely separate from arm movement.
Importance extends beyond basic tasks (e.g., drinking from a cup, throwing a ball) to stability, orientation, and mobility as we walk or move through environments.
Upper limb function is a key component of recovery after nervous system injuries (e.g., stroke, MS) because it underpins many activities of daily living (ADLs) and occupational tasks.
Biomechanics of the upper limb informs therapeutic inputs and recovery sequencing by detailing how movement is controlled and executed.
Personal reflection: upper limb dexterity is often more challenging to replicate with prostheses than leg/different limb replacements; dexterity and fine control are highly task-specific and difficult to restore fully.
Environmental constraints shape how upper limbs are used (example: navigating through a tight tube in a TV show challenge). These constraints illustrate how task demands and environment alter arm use and required control.
Practical implication: rehabilitation should consider a broad range of daily tasks (food preparation, writing, work duties, driving, clothes handling) as well as sport and musculoskeletal activities.
Neural Control of Upper Limb Movement
Movement of the upper limb is governed by neural control that translates intent into muscular action; understanding this helps explain recovery patterns after neural damage.
Two broad control strategies:
Feedforward (anticipatory planning): relies on prior experience and expectations about what will happen; uses sensory knowledge and previous tasks to generate a motor command before sensory feedback is received.
Feedback (sensory-driven) control: uses ongoing sensory input to compare action with a reference goal and to correct errors in real time.
An example: catching a ball involves feedforward planning of hand trajectory and grip, and feedback from somatosensory receptors once contact occurs.
Sensory inputs involved include muscle spindles (proprioception), cutaneous mechanoreceptors in the skin of the palm, and other somatosensory signals; these contribute to planning, execution, and error correction.
The motor plan is formed in higher centres (premotor/frontal regions) and sent to the motor cortex for execution; feedback flows back to refine the plan via cerebellum and other structures.
Visual input is integrated with somatosensory information to locate targets and guide movement planning and execution.
Basic Components of Upper-Limb Movement
Target location (visual input): identify where to reach (e.g., lift button, cup, obstacle).
Transport/Reach: move the arm and hand through space toward the target while maintaining postural control (trunk and head alignment).
Grasp/Manipulation: shape the hand to match the object and perform the grasp; manipulation may be separate from reaching but is tightly linked.
Task execution: push, lift, grasp, or manipulate an object (e.g., cup, pen, button).
Environment and task type affect how reaching and grasping are executed (e.g., different tools, cup shapes, or handling objects under visually occluded conditions).
Distinction between hand function and arm function: proximal control (shoulder/elbow/trunk) is often driven by reticulospinal/rubrospinal pathways for reaching; fine motor hand control is more dependent on corticospinal pathways.
Despite separate neural pathways, reaching and grasping are highly coupled and often trained together in rehabilitation.
Target Localization and Movement Planning
Location of a target is centring within the visual field; this involve eye movements, head orientation, and trunk adjustments to align with the target.
The process is synchronised across body parts: eyes, head, trunk, and hand are coordinated rather than strictly sequential.
Visual, proprioceptive, and somatosensory inputs converge in cortical areas to plan movement:
Higher centres (premotor/frontal regions) plan the movement.
Motor cortex (M1) executes the movement via descending pathways.
Somatosensory cortex provides feedback about the current state (position, sensation).
Parietal cortex contributes to perception and localisation relevant to the task.
Descending pathways:
Corticospinal tract: cortex to spinal cord; crucial for precise, fine motor control of the hand.
Brainstem pathways (reticulospinal, rubrospinal): originate in brainstem nuclei and predominantly influence proximal arm control (shoulder/elbow) and posture.
The cerebellum modulates and refines motor commands via feedback to motor cortex and brainstem.
The planning-feedback loop: cerebellum sends updated plans to motor cortex via thalamus; brainstem and spinal circuits implement refined commands; feedback from movement informs further adjustments.
Kinematics and Task-Specific Movement
Kinematics = study of joint movement and angles as the body moves through space; task-dependent and task-specific.
Reaching vs. grasping have distinct kinematic profiles and proximal vs. distal control:
Reaching is largely controlled by proximal muscles (scapular-humeral rhythm, elbow flexion/extension, shoulder movements).
Grasping involves fine motor control of the fingers and hand shaping to match object geometry and grip type.
Velocity patterns during tasks:
Reaching and grasping typically show a bell-shaped velocity profile: velocity increases to a peak and then decelerates as the target is approached and grasped.
In pointing, velocity may rise rapidly with less deceleration near the target; in throwing, velocity is maximised through extension and released at the end of movement.
For a cup grasp, acceleration is followed by controlled deceleration to avoid knocking the cup over.
The “car at traffic lights” analogy for velocity control: acceleration to a peak followed by controlled braking to settle at the target.
Implications for rehabilitation: tasks should train proximal stability and control first, then refine distal hand function (grasp and manipulation), with attention to movement velocity and deceleration at the endpoint.
Grasp Types: Precision vs Power Grips
Precision grips (finer control, small objects):
Pincer grip: index finger and thumb; pads meet for small objects (e.g., pin, small screw).
Pulp-to-pulp grip: fingers press against each other (e.g., placing a coin in a slot).
Lumbrical grip: fingers held together with thumb providing stabilisation; often used for manipulating thin objects.
Power grips (whole-hand grip for larger objects):
Spherical grip: holding a ball; all fingers wrap around a rounded object.
Hook grip: holding a handle or bag; fingers flexed with thumb not fully enclosing the object.
Cylindrical grip: gripping a cylindrical object like a mug, bottle, or tool; all fingers wrap around the surface with control through the palm and fingers.
The grasp type adapts during transport and as the hand shapes to the object; orientation and rotation of the hand (supination/pronation) occur as part of the reaching and grasping process (e.g., turning a key in a door lock).
Visual input supports shaping during reach; some tasks can be done without visual guidance (e.g., well-practised key turns) but most require visual feedback to adapt hand shape to object geometry.
Object size and surface properties influence grip strategy and hand opening during transport; larger objects require greater hand opening and sometimes different grip types.
Time coupling: maximum hand opening (preparation) occurs around ~75% of the transport phase for many tasks, indicating a synchronisation between reaching and grasping.
Neuroanatomical distinction: proximal control (reaching) is more influenced by brainstem pathways; distal control (grasp) relies more on corticospinal pathways for fine finger movements.
Rehabilitation implication: train both grip types and ensure hand shaping adapts to object geometry; integrate grasp with reaching to improve functional performance.
Grip-Lift Synergy and Force Coordination
When picking up objects, the brain coordinates grip force and lift/load force to prevent slips and ensure stable manipulation.
Initial grip is established before lift begins: Fgrip starts before Fload, ensuring the object is held before any lifting occurs.
Grip-load force ratio: a key measure of how well grip force matches the impending load, preventing slip while maintaining efficient force use:
Define:
The relationship between grip and load evolves as the object is lifted and moved; as the load decreases (object lowered), grip force is reduced in tandem. In typical successful performance, grip is on first and released last.
People with poor function may show abnormal grip-load patterns (e.g., grip force dropping below load force at critical moments, leading to slips).
Sensory feedback (cutaneous and proprioceptive) guides adjustments in grip during manipulation; if an object slips, the motor system can adjust grip and continue the lift.
Example study setup: force transducers measure grip force and load force as participants lift objects of varying weights; data show grip force precedes load force and scales with observed weight changes.
Practical takeaway: effective grasp-and-lift requires precise integration of anticipatory grip force (based on prior experience) and reactive adjustments from sensory feedback.
Sensory Feedback, Motor Planning, and Homunculi
Sensory inputs critical for planning and online control include:
Proprioception: information about body and joint position.
Cutaneous (skin) receptors in the palm and fingers: detect texture, temperature, slip, and contact.
Mechanoreceptors: provide force and pressure information.
Visual input complements somatosensory input, especially for object localisation and shaping of the hand to match object geometry.
The motor and sensory cortices are organised in homunculi:
Motor homunculus (precentral gyrus): representation of body parts with large emphasis on the hand and face due to fine motor control.
Sensory homunculus (postcentral gyrus): large representation for hand and face due to dense sensory feedback.
Brain regions involved:
Premotor cortex: movement planning and sequencing.
Primary motor cortex (M1): execution of motor commands.
Parietal cortex: perception and localisation relevant to manipulation tasks.
Cerebellum: real-time refinement and error correction; maintains smooth and accurate movements via feedback to cortex and brainstem.
Thalamus: relays sensory information and motor signals between cortex and subcortical structures.
The feedback loop: sensory feedback (proprioception, touch) updates motor plans via cerebellum and cortex to optimise subsequent movements; errors lead to adjusted plans in real time.
Without sensation, feedback-driven corrections are impaired, increasing reliance on vision and prior experience; this degrades manipulation accuracy, especially for novel tasks.
Descending Pathways and Neuroanatomy
Corticospinal tract (pyramidal tract): cortex
Decussates (crosses) at the medullary pyramids in the brainstem; contralateral control predominates for limb movements.
Brainstem-descending pathways:
Reticulospinal tract: originates in the brainstem reticular formation; influences proximal arm control and posture.
Rubrospinal tract: originates in the red nucleus; contributes to distal limb control, with more emphasis on coordination in some species and tasks.
These pathways provide parallel routes for descending control, with cortical pathways primarily handling fine, dexterous hand movements and brainstem pathways contributing to proximal control and postural stability.
The cerebellum is a key modulator of movement, receiving input about planned and actual movement and providing updated commands via thalamus and cortex to refine motor output.
Musculoskeletal Considerations in Upper-Limb Rehab
Rehabilitation must account for the entire kinetic chain from trunk and shoulder through scapulohumeral rhythm to the hand:
Trunk and head control can influence arm trajectory and reaching efficiency.
Scapular motion and rhythm are essential for effective shoulder function.
Glenohumeral joint mobility (shoulder) and elbow flexion/extension contribute to reaching capacity.
Biomechanical advantages in wrist and hand positioning are critical for optimal grasp:
Wrist extension provides a biomechanical advantage for shaping the hand into a functional grip and improves access to objects during reaching.
A comfortable, appropriate wrist position facilitates finger extension and opening needed for grasping objects like cups.
Typical recovery patterns after stroke: proximal segments (trunk, shoulder) tend to recover faster than distal hand function; hand opening and grip strength require more targeted rehabilitation.
Tone (spasticity) and muscle properties affect the ability to reach and grasp; managing tone is important to allow wrist extension and finger opening.
The role of therapy includes preventing compensations that limit restoration of normal movement, ensuring proper scapulothoracic and glenohumeral coordination, and progressively challenging coordination, timing, and force control.
Practical Implications for Clinicians and Students
Therapeutic focus should integrate reaching, grasping, and manipulation together, with attention to both proximal and distal components.
Training should include tasks that require anticipatory planning (feedforward) and on-going feedback adjustments (sensory feedback).
Vision and somatosensation are both critical; when one modality is impaired, compensate with the other and with task-specific practice.
Programing rehab to reflect real-world tasks (button pressing, cup handling, object transfer, lifting different weights) enhances functional outcomes.
Clinicians should appreciate the role of environment and task constraints in shaping arm use; practice in varied contexts improves generalisation.
Interdisciplinary collaboration is important: physiotherapists (proximal mobility, gait and posture), occupational therapists (manual dexterity and fine motor tasks), and other rehab professionals should work together to maximise recovery.
Ethical and practical considerations: recognising patient preferences (e.g., in amputee discussions) and balancing goals with realistic expectations regarding dexterity and prosthetic limitations. Safety, comfort, and patient-led goal setting are essential.
Key Takeaways
Upper limb function is essential for almost all activities and is a primary target in rehab after neural injuries.
Movement is governed by feedforward planning and continuous feedback; the brain integrates vision, proprioception, and somatosensation to plan, execute, and refine movements.
Distinct pathways control proximal vs. distal arm functions, with corticospinal tracts mainly mediating fine hand control and brainstem pathways supporting proximal control and posture.
Reaching and grasping are tightly coupled processes that rely on anticipatory shaping, proper grip type selection, and velocity control to achieve accurate, stable object interaction.
Grasp types include precision grips (pincer, pulp-to-pulp, lumbrical) and power grips (spherical, hook, cylindrical); hand shaping adapts during transport for efficient manipulation.
Grip-load coordination (grip force vs. load force) is critical to prevent slips and to manage object manipulation; this coordination is based on prior experience and sensory feedback.
Rehabilitation should target both proximal stability and distal dexterity, integrate tasks with real-world relevance, and consider sensory and visual contributions to motor control.
Understanding the neuroanatomy (corticospinal vs. brainstem pathways, cerebellar feedback) helps explain recovery patterns and informs therapy design.
Equations and Notation
Grip-load synergy (example measure):
Elbow flexion range referenced:
Planes of movement and decussation notes (conceptual): corticospinal tract decussates at the medullary pyramids (pyramidal decussation) in the brainstem; parallel descending pathways originate in brainstem for proximal control and in cortex for distal control.
Note: Many statements about velocity profiles and timing are described qualitatively as bell-shaped velocity curves or progressive acceleration/deceleration patterns rather than simple closed-form equations; these are represented here conceptually and can be modelled with task-specific kinematic data in practice.