short and long loop Flashcards
Mastery
Measuring feedback control in the lab
order of the EMG
why is visual last
We can apply mechanical disturbances (i.e., torques) to measure how the nervous system uses sensory feedback to guide and control different motor actions
apply stretches to see how we react
perturbation-SLR-LLR-Voluntary
voluntary is last because it involves visual interpretation and takes a long time to process
Order of latency response
Short-latency response (SLR: 20-50 ms): spinal
proprioceptive feedback.
Long-latency response (LLR: 50-105 ms): spinal
and cortical proprioceptive feedback.
Voluntary response (VOL: 120+ ms): spinal and
cortical proprioceptive , and visual feedback
What is a SLR
what does it recruit
what affects it
A muscle’s response to stretch with a latency
of 25 to 50 milliseconds. Also called the ‘spinal
stretch reflex’ or ‘monosynaptic stretch
reflex’.
only recruits spinal circuits and has simple processing capabilities. IT ALL OCCURS IN THE SPINE
SLRs get larger with background muscle activity, more MU is recruited. Henneman size principle. Larger knee extension and more force produced
SLRs get larger with a higher rate and amount of muscle stretch, larger stretch, more action potentials fired, more activation of homonymous muscles
Long latency reflex
long loop, long latency, transcortical
what part of the brain, what do they recruit
Long-Latency Reflex (LLR):
latency of 50 to 105 milliseconds
In addition to the rapid, short-loop reflexes that engage the spinal cord, long latency reflexes involve a transcortical feedback loop that recruits structures in cerebral cortex
Recruit sensory and motor circuits in the brain and show flexible, goal-directed processing
Voluntary actions and LLRs recruit the same sensory and motor areas of the brain
LLR, when you have to stay in a certain area
With the exception of the largest target, the SLR is mostly driven by the rate and amount of motion caused by the perturbation
LLR and voluntary responses to the same mechanical perturbation are inversely proportional to the size of the target
when does LLR increase
the more you resist perturbation, the larger the increase of LLR. More EMG when you must resist
change the reflex based on the goal
Desired State
Motor Plan
Motor Command
expected state
error
error signal
closed loop or feedback control
Comparator
executive
Effector
Desired State: Goal of the task. In this example, maintain the arm in a fixed target
Motor Plan: Maintain the arm in the target
Motor Command: Activity in limb motor circuits (cortical or subcortical) to maintain the hand in the target
Expected state is the intended or planned movement (i.e., hand is in target).
Error is based on difference between ‘expected’ (hand in target) and ‘actual’ position of the hand (hand in target or not)
Error signal used to adjust ongoing movement
Closed-Loop or Feedback Control System: Movement
control mechanism that uses sensory feedback to detect errors and correct voluntary motor actions
Comparator: Compares the actual and expected state of the body (i.e., position and motion of the arm). An error is any difference between actual and expected hand position
Executive
(Feedback Controller) processes sensory information, selects and programs appropriate response
Effector
The Effector is the component of the peripheral motor system (i.e., leg, arm) that generates the desired motor response.
Summary of LLR and SLR
Summary:
1. SLRs allow rapid, stimulus dependent responses to a mechanical perturbation.
all in the spine, simple. not to comparator or S1.
- LLRs are slower, polysynaptic responses that enable rapid, task- dependent control of sensory feedback to support voluntary motor actions.
no visual stimuli
send out motor plan, sen back the actual state, comparator looks at error, send input back to ID, then selection, to response program, then to motor commands into the spine and move the limbs. Reevaluate
