Reaching Grasp 1 Flashcards
What are the two types of grasps?
Precision grip
Power grip
What is an example of a precision grip?
grasping a pen or needle
What is the precision grip mediated by?
primary motor cortex
What specifically activates with a precision grip?
individual cortical motor neuron projections
What is an example of a power grip?
when holding a hammer or climbing a rope
What is the power grip mediated by?
both cortical and non cortical motor projections
What are visuomotor transformations mediated by?
PPC and premotor cortex
What happens when there is damage to the PPC and premotor cortex?
impaired preshaping of the hand during goal directed grasping
What are some key elements to reach, grasp, and manipulate tasks?
- locating target (visual regard)
- coordination of eye and hand
- reaching (translocation of arm and hand AND postural support)
- grasping including grip and release
- in hand manipulation of object
What is feedforward?
anticipation of the requirements of the task and resultant actions based upon previous experiences
What is feedback control?
need for response to errors in performance of the task
For feedforward, what happens with a new task?
visual information updates previous experiences
What happens after the visual information is updated during feedforward?
muscle activation
Once the task is complete, what happens to react to the perturbation?
feedback mechanisms
What is feedback control represented by?
the short latency reflex response following impact
What is the first step in reaching and grasping?
target location (head eye location)
When there is an object in peripheral vision sequence of events during reaching and grasping, what happens?
eye movement (shortest latency) head movement (EMG activity in neck is before eyes but inertia of head is large so our eyes move first) -eyes focus on object before head stops moving
When there is vision of the object needed, which moves more the head or eyes?
head moved 60-75% distance and eyes completed motion
When do you use full head and eye simultaneous movement?
when greater accuracy is needed
What are the 3 distinct conditions in the target location?
eye movement alone
control of eye movement and head movement
locate in far periphery, eye, head and trunk movement together
What does the parietal cortex do to your eyes and head when reaching and grasping?
it anticipates the amount of eye and head movement that is needed and updates the brain’s representation of the visual field based upon the anticipated movement
How do we know that through visual saccades, the eyes catch up to the brain’s updated image?
because parietal neurons begin to fire 80 msec prior to the visual saccade
How does the parietal neurons communicate with the premotor cortex and the frontal eye fields?
through corollary discharges
Where are neurons that drive saccadic movements and UE movement located?
adjacent to the UE primary motor cortex in the frontal eye fields (saccadic movements) and the pre motor cortex (UE movement)
Hand eye coordination: Hand movements are more accurate when accompanied by?
eye movements
There is an _____ gain and _____ latency of visual pursuit movements when the hand is following the target.
increased gain and decreased visual pursuit
The link between hand and eye movement is not through proprioceptive feedback (movement is too fast to rely on feedback), so what is the linkage between?
afferent copy or corollary discharge
With hand eye coordination, what does proprioceptive feedback assist in?
accuracy of visual and manual pursuit
When used to point at an object, the arm and hand is controlled as what?
a unit
when reaching to grasp, the hand and arm are controlled how?
hand is controlled independently of the rest of the arm
What are the details of velocity with grasp?
acceleration phase < deceleration phase
What are the details of velocity with point and hit object?
acceleration phase > deceleration phase
velocity of grasp and throw
longer acceleration phase
velocity of grasp and fit object into box
shorter acceleration phase than grasp and throw
What are the different tasks that a patient should be able to do?
reach and point reach and grasp reach, grasp, and throw reach, grasp, and manipulate reach, grasp, and place in box or remove from box
What is the illusion called when there is a small object surrounded by larger object and the same small object surrounded by another small object would look bigger?
Ebbinghaus illusion
What two visual pathways does the Ebbinghaus illusion separate well?
dorsal and ventral visual streams
what is the ventral visual stream?
site where you cognitively recognize the relative size of objects
Where is the ventral visual stream going?
it is a pathway to the temporal lobe
What does the dorsal visual stream control?
grip size. positioning hands properly to pick up an object
Where is the dorsal visual stream going?
to the posterior parietal cortex
Duration of reaching with visual feedback?
longer duration but greater accuracy
What helps mediate cortically blind but visual behaviors when talking about pointing and target position?
superior colliculus
What role does visual feedback have on grasp?
no difference in the kinematics of grasp with or without feedback
What can be noted when using visual feedback when grasping?
the thumb position in relation to the wrist is the key
