Reaching and Grasp part 2 Flashcards
Compared to reaching on the same side, reaching across midline is what?
slower and less accurate
What happens to reaching when there is a loss of somatosensory input?
there are problems reaching immediately after loss of sensation
When there is a loss of somatosensory input, what will occur over time with reaching?
gradually skills might return but only for simple reaching movements that are well learned
new or complex movements are impaired
Is somatosensory input important for grip?
yes, it is essential
What happens with grip when there is a loss of cutaneous sensation?
it prevents control of slip of objects
What compensates when there is a loss of somatosensory input (loss of grip)?
There is typically an increase in force of muscles of grasp to compensate for the lack of “slip” information
How long do people typically maintain the increased muscle force for compensation of grip?
It often decreased over a 20-30 second period
Neurons in somatosensory cortex that are slow and fast adapting both respond to what?
slipping objects
What corticies are involved in reaching and grasp?
posterior parietal cortex and premotor cortex
Which cortex involves initiating the concept of reaching and grasp?
supplementary motor cortex
What area provides the motivation to accomplish the act?
anterior cingulate gyrus
What does the posterior parietal cortex do for grasp?
it provides numerous descriptions of objects for manipulation and multiple strategies to grasp objects
What does the premotor cortex do for reaching and grasp?
it helps choose the best strategy for reaching and grasp
How many motor pathways are involved in reaching and grasp? (child development evidence)
two
in an infant, when does reaching occur?
1 week
in an infant, when does grip appear?
after 10 weeks
What neurons are active in precision grip and inactive in power grip?
Motor cortex (cortical) neurons
What is the role of the cerebellum during reaching and grasp?
(more active during reaching and grasp rather than just gripping an object)
It also seems to play a role in anticipatory postural adjustments for reaching tasks (particularly untrained people)
What requires more postural support than reaching when sitting?
reaching when standing
How can postural demands effect reaching tasks?
it can effect the speed and accuracy
What could decrease postural demands and make movements more accurate and faster?
if there is external support of the trunk
What happens in the reaching hand as it is transported toward the object?
the hand opens up to maximum grasp size
How much of the movement time does hand opening occur?
75-80% of movement time no matter how fast or slow the movement is
After the hand opens up during transportation of the hand to the object, what happens?
The size of the grasp decreases to match object size
What distance is the largest during the last phase of reaching and grasping? why?
thumb and index finger distance
to decrease the size at contact
How does a perturbation of the reach affect grasp?
if reach (transport phase) is perturbed, grasp is affected with a brief interruption of the grip aperture formation
What happens if grasp is perturbed ?
the transport phase will also be disrupted
Are timing of the reach and the grasp correlated?
yes, there is a functional link of the timing of the two processes
Since reaching and grasping are highly correlated, how could we plan therapy?
we could work on retraining each component separately and then both components need to be retrained together
What are the two hypotheses in targeting distances?
Joint angle hypothesis
Distance point hypothesis
What is the joint angle hypothesis?
select proper joint angle to reach the object
what is the distance point hypothesis?
select a point in space to reach
What two types of feedback are used in reaching tasks?
visual
proprioceptive
What is visual feedback in reaching tasks?
point in space
what is proprioceptive feedback in reaching tasks?
joint angle
What is the distance programming theory?
- individual perceives a distance to target
- programs the activation of muscles at level & pattern to propel hand/arm that distance
What is the location programming theory?
-nervous system programs the relative activation of antagonistic muscles to move limb to a certain position in 3D space
Which movements are accomplished by the distance theory?
slow movements
What movements are accomplished by the distance and location programming theory?
ballistic movements
