Lecture 8a, Sensory Contributions to Closed-Loop Motor Control

Question 1

M1

Answer 1

short latency/loop reflex - monosynaptic stretch reflex (30-50 ms)
- early burst and simplest stretch reflex - alerts the system (simple loop) for example like patella tap knew reflex

Question 2

M2

Answer 2

long latency/loop reflex (50-80 ms) - sensitive to goals/context
- second is called smart reflex, connected to motor program level (much larger and has this restorative capacity)

Question 3

M3

Answer 3

voluntary response (> ~120 ms)
- feedback is processed through these stages of information processing at the executive, higher level

Question 4

1. Muscle Spindles

Answer 4

3 points to know: muscle spindles respond to the changes in length and rate of change in length in the muscle, they are located in the belly of the muscle and in response to stretch you attain these 1a afferent signals sent upstream to the spinal cord

• spindle-shaped receptors oriented in parallel with muscle fibres
• sensory/afferent neuron (la) sends information to spinal cord and can excite motor/efferent neurons to muscle fibres (to say something is happening)
• sensitive to changes in length, and rate of change in length of muscle fibre
• muscle spindles respond to stretch (cares about change in length and rate of change in length) and in response to the stretch the 1a afferent neurons are sent to the spinal cord to say something is happening

Question 5

Monosynaptic One Synapse

Answer 5

M1 is just a very simple reflex loop: when there a sense of stretch in the muscle than 1a afferent neuron will synapse with a motor neuron to basically counteract the stretch

Question 6

M2 response

Answer 6

• innervates an interneuron; receives some descending signals from higher levels
• M2 is more complicated where there is some descending response
• will get still M1 response but now there will be some other response added on depending on the goal of the system

Question 7

2. Golgi Tendon Organs

Answer 7

• located in junctions between muscle and tendons
• detect changes in muscle’s tension (force)
• turn off if there is too much force (safety mechanism) and will tell you it too much and now it is time to relax
• at the muscle level muscle spindles play a primary role but the GTOs are very important as well
• GTOs care about force or tension in the muscle
• serve to regulate the levels of forces produced in the attached muscle

Question 8

What are the afferents or receptors that are sensing information more at the movement level?

Answer 8

vestibular, cutaneous and joint afferents

Question 9

3. Vestibular apparatus in inner ear. Information about movements of the head and sense of balance

Answer 9

• important for balance (ears play primary role) and underpinning most of the actions that we perform that necessitate a degree of balance
• semicircular canals are sensitive to changes in the angular acceleration (movements of the head like pitching, rolling and yawing)
  ◦ essentially fluid in the
  ear that are sensitive to
  the angular accelerations
• there are also organs that are sensitive to change in linear acceleration (sudden change)
  ◦ the hairs in the otolith
  organs respond to the
  linear acceleration - give
  you a sense of
  movement (how fast
  and the direction)

Question 10

4. Cutaneous receptors

Answer 10

signal information pertaining to touch, pressure, temperature and pain
- these receptors are critical for haptic sense and the sense of touch

Question 11

5. Joint Receptors

Answer 11

embedded within joint capsules and respond to the limits of joint range and pressure
- respond to pressure and limit of the joint (safety mechanism) - do not want to hyperextend or hyperflex
- pressure applied at beginning and end where afferents care about that (and when thumb is in extremes of joint motion (hyperextension and hyperflexion)
- give information about the extreme positions of the joints