Week 15 Prehension

Question 1

Prehension =

Answer 1

voluntary movement performed with little conscious effort

Question 2

What are the 2 seamless temporally integrated stages of prehension?

Answer 2

1. reach

2. grasp

Question 3

The reach stage of prehension =

Answer 3

transport hand to target so digits align with target
* produced primarily by proximal mm
• guided extrinsically by target

Question 4

The grasp stage of prehension =

Answer 4

pre-shapes digits; opens them to match target size
• produced primarily by distal mm of hand and fingers
•guided by intrinsic properties of target (size and shape)

Question 5

manipulation =

Answer 5

carrying out target’s intended use

Question 6

Grasps vary because of location, size and shape of an object. What are the 4 power grips?
What are the 4 precision grips?

Answer 6

Power = cylindrical, spherical, hook and lateral prehension

Precision = pinch (aka precison), key, (3-jaw_) chuck, and pulp pinch

Question 7

The hand is a complex mechanical structure of ______ bones activated by _________ extrinsic mm and __________ extrinsic mm.

Answer 7

27 bones
18 intrinsic
18 extrinsic

Question 8

How many DF does the kinematic model of hand consists of for each finger? the thumb? and the radio-ulnar joint? wrist?

Answer 8

each finger - 4
thumb - 4/5
plus 1 DF at the radio-ulnar joint
2 DF at the wrist = 23/24

Question 9

with so many DF, how is the hand controlled?

Answer 9

synergies

Question 10

What are the 2 hand synergies that account for 80% of movements alone or in combination?

Answer 10

1. PC2

2. PC1

Question 11

pc2 =

Answer 11

MCP flexion and adduction of fingers = L line

Question 12

pc1 =

Answer 12

finger aperture closure by flexion at PIPs of finger and thumb adduction and IR = R line

Question 13

When reach = transport there are 2 phases: acceleration- deceleration… How is prehension different from pointing/aiming task?

Answer 13

1. the person intends to use the object to achieve some type of goal
2. reach has acceleration & deceleration phases

Question 14

transport grip aperture =

Answer 14

preshaping and closure

Question 15

Describe grasping kinematics:

Answer 15

1. hand preshapes during movement to target (object)
2. max grip aperture (distance between thumb and index finger tip) occurs within 60-80% of movement completion
3. scaling of max grip aperture traces correlated to object size

Question 16

What factors affect grip aperture?

Answer 16

• faster reach-grasp movements –> maximum grip apertures
• grasp at normal speed vs grasp “as fast as possible” with dropping the object
  • larger maximum apertures were observed for the faster movements. thus, faster reach -
  •reach-grasp movements that start with an open grip aperture show a tendency of the hand grip to partially close before achieving its maximum aperture

Question 17

visual regard =

Answer 17

locating the target

Question 18

Why is vision very important in prehension?

Answer 18

• Enables corrections that occur just before grasp
• determines EN regulatory conditions in which the action will occur: distance/ location; size, orientation
• binocular vision aids grip size and force of grip
• person needs to look directly at object for grasp = point of gaze

Question 19

Two primary findings of EMG prehension (reach and grasp) research are:

Answer 19

1. neck mms fire first (20-40ms) before (increase inertia) eyes, and then arm
2. arm has triphasic mm program (agonists-antagonists for breaking and then agonist)

Question 20

When locating a target: visual regard, for reach, limb is directed to object by eyes. Further describe the reach -

Answer 20

Reach (at normal speed) is under closed loop control , visual info (feedback) is used constantly during reach and grasp
• preparation and initiation of movement - assess EN
•transports hand to object - central vision (peripheral vision provided movement feedback)
• grasp object - supplements tactile and proprioceptive feedback

Question 21

Prehension and vision: development from phase 1 to phase 2:

Answer 21

• Infants: @ 1 week can reach for and intercept moving object, but hand is wide open- with no grasp formation which develops ~10-22 weeks
• 4 months: prehension controlled proximally; poor contact with object
• 5 months: prehension controlled distally; contact orients hand to object
• 6 months: squeeze emerges (fingers close around object)
• 9 months: prehension controlled by thumb and 1 finger (pincer grip) ; hand oreints before contact. Pre-shapes for object size; poor adjusting grip force
• 13 months: fingers oppose action of thumb without hand being stabilized
• 18 months: child can release the object

Question 22

Major finding about prehension and child development:

Answer 22

If object is scaled to hand size, grasp is similar to adult pattern as early as age 6-7 years

Question 23

Kinematics: point vs reach to grasp -

Answer 23

control of UE movements changes depending on goal of task
•pointing-segments controlled as a unit
•reach to grasp-hand controlled independently of arm, with arm carrying out transport; hand carries out grasp and manipulation

Question 24

Kinematics: point vs reach to grasp - velocity profile and movement duration of reach vary, depending on task -

Answer 24

• reach the object: movement duration is > than pointing

* grasp an object: acceleration deceleration

Question 25

Describe the PERIPHERAL Neural subsystems contributing to R and G:

Answer 25

Peripheral tell what's happening around where you are in space and where your joints are relative to each other. • visual input is divided into 2 parallel paths • higher cortical centers make movement plan * basal ganglia plans forces to grasp • cerebellum refines movement • descending paths activate spinal cord neurons to mm

Question 26

What are the 2 visual paths for R and G?

Answer 26

1. dorsal stream | 2. ventral stream

Question 27

describe the dorsal stream?

Answer 27

- from visual to parietal cortex • provides action relevant info about all phases of reaching movement including object position, structure and orientation

Question 28

describe the ventral stream?

Answer 28

- from visual cortex to temporal lobe | • provides conscious visual perceptual experience

Question 29

In the posterior parietal cortex (PPC), BA5 = | BA7 =

Answer 29

BA5 = (posterior parietal lobe) integrates INTRAPERSONAL space ("body image") information; gets from BA2 BA7 = (posterior parietal lobe) cells respond to visual, auditory, and movement/tactile stimuli (from BA5) BA 7 = integrates intrapersonal information (BA5) with critical environmental cues to perceive EXTRAPERSONAL space

Question 30

Dorsal codes for:

Answer 30

reach WHERE for action

Question 31

ventral codes for:

Answer 31

grasp, WHAT, object stream

Question 32

Premotor cortex localizes position of object with respect to what?

Answer 32

with respect to our hand & specifies plan of action.

Question 33

Primary motor cortex (PMC) codes for what?

Answer 33

movement and force; sends motor commands to spinal cord

Question 34

PPC receives information from visual cortex and somatosensory cortex; localizes:

Answer 34

position of target with respect to the body

Question 35

Cutaneous input is essential for control of grpi forces: S1. What happens without it?

Answer 35

uncoordinated grip and uncoordinated forces

Question 36

With slippery objects, cutaneous receptors detect slip -->

Answer 36

activate motor activity to increase grip force in finger mm • patients wit sensory neuropathy may have difficulty with control of grip forces and have decreased ability to adapt grasp.

Question 37

(control of hand posture is seperate from regulation of contact force) Posture and force are not independent because hand must shaped properly so the correct set of fingers makes contact with the object. What have fMRI studies demonstrated?

Answer 37

Demonstrated that caudate and ant. putamen signal level of grip force prediction through: cortex, ventral thalalmus, cerebellum (efference copy/ corollary discharge/ reafference)

Question 38

(motor cortical control of movement) Reaching movement: what precedes activity in M1

Answer 38

PMA precedes activity in M1, mm activation and finger movement

Question 39

PMA = M1 = EMG = Finger =

Answer 39

``` PMA = plan M1 = do EMG = activation Finger = fingers GO ```

Question 40

Anterior interparietal sulcus (AIP) or parietal cortex and premotor cortex are involved in:

Answer 40

visual motor transformation | • sensory coordinates related to object - motor objects

Question 41

(motor systems) Descending pathways -

Answer 41

Reach: arm movement ransports hand to target, moves together while hadn pre-shping of fingers for grasp occurs (• children with pyramidal lesions show problems with grasp, transport may be normal. Suggests that midbrain pathways (rubrospinal reticulospinal) may control more proximal mm involved in reaching), corticospinal required for fine control of grasp

Question 42

(motor systems) Precision vs power grip:

Answer 42

neurons in M1 fire only during execution of precise movement, but not power grip. Indicates connections to intrinsic hand mm rather than with forearm mm.

Question 43

Postural support of reaching:

Answer 43

*  control of body's position in space for stability and orientation * reach has shown key brain structure for learning of anticipatory postural adjustments during bimanual task is the cerebellum *  postural requirements are task dependent. Requirements in supported sitting are

Question 44

Slippage, what causes? What provides better grip?

Answer 44

• Slippage is related to cutaneous sensation. • evolution of normal and tangential forces with finger pad contact on glass • --> increase grip forces • "stick" decreases with increase in tangential forces ** finger prints improve grasp

Question 45

(adaptation of grip forces) Aging -->

Answer 45

decrease manual dexterity with larger grip forces

Question 46

What happens with loss of sensation?

Answer 46

larger grip forces, no matter the weight or texture of the material

Question 47

Application of the prosthetic hand:

Answer 47

* five fingered prosthetic hand consisting of digits driven by DC motors * force sensors resistors (FSR) placed at finger tip of and potentiometers attached at proximal and middle joints. Information from FSR can detect level of normal force exerted and also slippage between fingers and object

Question 48

What type of control is prehension under? Give examples of feedforward (open loop):

Answer 48

* anticipate requirements of task and obstacles that might perturb arm trajectory and correct for effects of perturbation * anticipatory control takes advantage of previous experience to predict consequences - occurs before sensory receptors are stimulated and reduces reliance of feedback

Question 49

What type of control is prehension under? Give examples of feedback (closed loop):

Answer 49

• feedback from vision and proprioception needed at end of movement to ensure hitting target accurately

Question 50

Motor program: invariant characteristics -

Answer 50

* path of the wrist during arm movement is unaffected by movement speed or by load (wts in hand). * these support joint angle coordinates at end-points * NS can directly control joints and produce straight line movement by varying onset times for joint movements with all joints stopping simultaneously

Question 51

Motor programming: distance vs location -

Answer 51

• Both strategies probably used, depending on task and context • Distnace theories: when making arm move to target, people visually perceive the distance (to target). activate mm to propel arm proper distance... turn off Aag mm and activate Antag mm to brake movement • Schmidt's impulse variability model • RELEVANCE to PT and retraining: important to practice fast movement of varying amplitudes so pt learns to program forces appropriate for quick, accurate movement. Location program: NS program balance of tensions/ stiffness of AG and Antag mm sets. Every location in space corresponds to a stiffness relationship between opposing mm (subjects blindfolded fingers anesthetize with cuff. Beforehand training to move fingers to specific position in space. Given perturbations, with loss of finger sensation, very little difference between perturbed and unperturbed movements.

Question 52

Schmit's impulse variability model:

Answer 52

make a fast mvmt (high velocity) over a fixed distance. - size of error increased in proportion to amonut of force; "make a fast but accurate mvmt" large forces caused increased force variability. Resulting in decreases accuracy.

Question 53

Dynamical systems: How does NS plan movement?

Answer 53

• NS possess a central representation of the movement that is in the form of a 'motor image' • believed that propriocepetion was important to final movement achievement • suggested that high number of DF for complex movements allow organization of actions in terms of synergies or groups of mm and joints acting together as a unit (ex. point of 2 targets (1 close & large, 1 far and small - Hands move simultaneously, even if pointing is different)

Question 54

Systems theory =

Answer 54

predicts specific neural and musculoskeletal subsystem contribute to control for each, grasp and manipulation (musculoskeletal = ROM, flexibility, mm properties, biomechanical relationships of linked segments) (neural = motor processes - coordination of eye, hand and trunk, and arm , sensory processes - coordination of visual, vestibular and somatosensory, internal representation for mapping sensation to action, higher level processes for adaptation and anticipatory aspects of manipulation, manipulation - voluntary and reflexive aspects_feedforward and feedback)

Question 55

What do we observe in patients?

Answer 55

* visual processing is more complex when a person reaches across their body * reaching a target on opposite side is slower and less accurate then movements to target on same side as arm *  so, when you examine a patient, consider where you have the target and for your intervention, you may want to begin ipsilateral reaching prior to progressing to contralateral reaching.

Question 56

Age and prehension; young =

Answer 56

*  infant can intercept moving objects; able to predict where an object will be which is anticipatory *  at 7 weeks: thumb opposition *  children open hands wider * children > variability * grip formation not mature til ~ 7 year

Question 57

age and prehension; elderly =

Answer 57

* 30% decrease in speed of reach * more time in target deceleration phase * accuracy is about the same for drawing tasks, just slower * increase 20-40% in time to do fine manipulations skills by age 70. * most decrements are reversible with practice

Question 58

What are the key elements of prehension & manipulation?

Answer 58

* locate target = visual regard (requires coordination of head-eye movements) * reaching = arm transport plus postural support * grasping (grip formation and release) * In-hand manipulation skills