Reach to Grasp Flashcards
4 Key Elements for UE skill
- Locating the object
- Reaching (postural control + moving arm in space)
- Grasping (grip formation, stable grasp)
- Manipulation skills
Locating a target
- Eyes, Head and Trunk Movement
- Cenetral Eye = eye movement
- Peripheral Object Location
– Neck muscles activate, then eyes move first and focus before head stops - Amplitude of head movement
– Head will only turn 60-75% as an efficiency think, eyes will do the rest of the look.
– The bigger the accuracy requirement the more they will zone in on central vision.
How do we control the eye when locating a target?
- Maintain stable vision via corollary discharge (efference copy) to parietal areas
- Anticipatory signal is intended eye movement so vision remains stable as eye moves.
Send information to cerebellum for anticipatory control and feedback; same concept happens but with eye movement. Signal saying eyes will look right sends info to the parietal to help with stabilizing movement.
EX: Stroke in parietal; issues with stabilization to to issues with information processing.
Reaching and Grasping Curves
- Bell shape curver profile.
- Acceleration to deceleration phase.
- Prior experience and site is the preplanned phase and then the down slope is the adjustments to grab target.
- Deceleration plays a large role with reach to grasp.
Describe this in relation to reaching and grasping - motor processes
- Triphasic muscle burst for reaching (and other ballistic motions)
- Accel, decel, fine-tune (homing in)
- Acceleration is pre-planned based on experience
- Lower values are honing in on the target.
Pathway for grasp
Primary motor cortex to corticospinal tract―fine control of grasp
Pathway for reaching
Midbrain/brainstem pathway (rubrospinal tract) ―prime movers and postural control for reach
What do we need to consider with rehab and reach to grasp?
- Seperatr structures but processed in parallel and tightly coordinated
- Grasp formation must happen before reaching target.
- Ex: Cerebral A stroke lots of grasping issues, need to tie in both grasping and reaching into rehabilitation.
Reaching and grasping involves ____ joint coordination
Multi
Reaching and grasping - postural control
- Requires anticipatory postural adjustments for timing and adaptation
- Uses the cerebllum for this!
Other mechanics of the reach are considered in planning of movement - reach and grasp
- Distance to reach
- Weight to be lifted
- Inertial resistance provided by position and intrinsic stiffness of limb (think muscle tone)
- Think of functionality of movements (reaching straight arm vs bent arm)
Temporal coordination of arm and hand - reach and grasp
- Transport of hand must be coordinated with grasp (2 different pathways)
- Use vision to plane how wide to make hand.
- At 75-80% of reach, grasp is ready to go.
- Hand must be adapted to the shape, size and use of the object before making contact
Anticipatory control of Grasp
- Grip forms during transportation phase of reach
- Pre-grasp hand shaping is based on:
– Intrinsic properties of object (size, shape, texture)
– Extrinsic (contextual) properties of object (location, orientation, subsequent task)
Grasp Types - Power vs Precision Grips
- Power grasp=force directed from pads of fingers toward palm – transmit force
- Precision = forces directed from pad to pad – manipulate; Pad of finger to the thumb. Percision, most overlap of sensory information as possible.
Cerebellar contributions to grasp/manipulation
- Organizes predictive and adaptive responses via corollary discharge (efference copy)
Reaching and Grasping - Sensory Contributions
Vision:
* Important for final accuracy
* Needed for complex or repetitive movements
* Important for pre-programming based on experience
* Dorsal visual Stream primarily involved in grasp formation
* Premotor cortex has neurons that drive both eye movement as well as arm/neck movements
Somatosensory
* Muscle spindles are important for position sense – both arm and finger
What are the 4 phases of grasp/lift (manipulation)
- Finger contact (based on experience and vision)
- Generation of grip and load force
- Object movement
- Termination (decrease load and grip force)
Grip Force
- Horizontal
- Compressive
Load Force
- Vertical
- Sheer
Predictive control requires what 3 things?
Experience, cerbellum and vision
What is reactive control important for? What does this?
- Important for fine manipulation
- Cutaneous afferents (Temp, heaviness, etc) essential to position sense and to control grip force
Bimanual Coordination
focus on function and overflow concept; two hand coordination
Limb Specialization
limb is just better a certain things for things with trajectory in space and the other for stabilization. Ex: Go to write stabilize paper with left and writes with right.
Dynamic Dominance
Specialized limbs for trajectory and stabilization; body is efficient. We can use both hands.
How does limb specilization and dynamic dominance apply to rehab?
Rehab with RC stuff, right handed but left shoulder injury. Work on more stabilization with the left rather than trajectory which is what the right hand is used for.
Reach to grasp development
Infant
* Pre-reaching behaviors (fidgety reflex-based control)
Some visually triggered actions with head movement
2 months
* Increasing neck control to facilitate visually guided head movement
4 months
* Trunk control beginning, control mapping distally in arm for reaching
5 months
* Visually guided reaching emerges, hand shaping based on object size and orientation emerges = onset of successful reaching
9 months
* Pincer grasp develops (~timing of further development of CST)
Lifespan change in children
- Up to 4-6 year olds dependent on feed-forward control (lots of spills!!) – slow processing inhibits use of feedback
- 7-8 years starting to use feedback control (mostly vision)
- 9-11 years use both feedforward and feedback control, and starting to integrate vision/somatosensory information
Lifespan changes in Older Adults
- Slowed reaching (especially with complex tasks)
- Higher grip forces (compensation strategy), more variable, and longer time to attain final grip force
- Slowing of central processing
