Control system - peripheral 2

Question 1

receptors

Answer 1

• Muscle
• Tendon
• Joint
• Ligament
• Skin

Question 2

Muscle spindles

Answer 2

DETECT CHANGE IN MUSCLE LENGTH
Sensitive to length and velocity of lengthening
• Contractile element – intrafusal muscle fibres control sensitivity of muscle spindle
• Controlled by gamma-motoneurons
• Coactivated with alpha-motoneurons
• Important for perception of movement
• Stimulation of single afferent does not give conscious perception

Question 3

Golgi tendon organs

Answer 3

• Proprioceptive - changes in muscle tension
Inhibitory input to alpha-motoneurons
• Not just involved in strong forces
• Each attached to small group of muscle fibres – sensitive to small forces
• Important feedback

Question 4

Joint afferents

Answer 4

• Majority fire at end-range
• Some receptors fire over certain
ranges of motion
• Stimulation modifies muscle activity

Question 5

ligaments

Answer 5

ALSO HAVE SENSORY FUNCTION
mechanical properties > joint stabaility
sensory properties >The γ-muscle spindle system > Movement and position sense or control of muscle stiffness and coordination > joint stability

Question 6

ligament reflexes

Answer 6

Protective reflexes are too slow
↓
State of changeable (continuously regulated) muscle stiffness at thetime of displacement/ trauma

Question 7

Skin receptors

Answer 7

• Tactile receptors
• Important for perception of joint motion – stimulation can induce illusion of joint motion
• Relationship between firing of afferents and motor units in finger muscles
* rub on skin can stimulate muscle

Question 8

Loss of feedback

Answer 8

• Direct trauma to mechanoreceptors
• Subfailure trauma to ligaments or joint capsule – compromised sensitivity
• Abnormal feedback – Poor proprioception (almost all injuries have some form of proprioception loss)

Question 9

What are the consequences of impaired proprioception?

Answer 9

injurt > mechanoreceptors (corrupted transductor signals > controlls (corrupted command) > Incoordinated muscle activity which leads to corrupted feedback, Increased Trauma, load, Inflammation and pain

Question 10

Loss of feedback

Answer 10

– impaired proprioception
– Impaired control
– Potential factor in perpetuation of painand injury or recurrence
– Exercise must be specific to retrain control

Question 11

Effusion in facet joint

Answer 11

• Reduced response to disc stimulation

Question 12

Loss of sensory function of ligaments

• Summary

Answer 12

– Impaired contribution of mechanoreceptors to muscle control
– Exercise must be specific to retrain control

Question 13

Reflex inhibition

Answer 13

• Reduction in alpha motoneurone excitability in response to altered afferent input from injury
• Can occur in absence of pain
• Near-linear relationship between effusion volume and inhibition (Isles et al 1990)
• What receptor – Ruffini ending in joint capsule?

Question 14

Are all muscles affected equally?

Answer 14

*Pinching of the joint capsule leads to inhibition of knee extensors & facilitation of knee flexors
• Isolated wasting of the quadriceps with hamstring sparing in knee joint injuries
• Not uniform = greater change in slow muscles (i.e. more type I muscle fibres) leads to more functional implications

Question 15

Atrophy of paraspinal muscles is common in low back pain

Answer 15

• Chronic low back pain
– Atrophy of paraspinal muscles – ↓ cross-sectional area - L4/5
– Signs of denervation

• Acute low back pain
– ↓ cross-sectional area at level of pain, ipsilateral to symptoms

• Involves changes at multiple levels of the motor system: May be competitive

Question 16

Reflex inhibition

• Summary

Answer 16

– Appears to be anatomically specific
– Particularly affects muscles that are important for joint control (extensors and antigravity muscles)
– Likely to have functional implications
– Exercise – needs to be specific
* about precision and specificity

Question 17

Muscle spindles & pain

• Summary

Answer 17

– Diffuse reflex effects – Increased activity

– Exercise must be specific – retrain patterns

Question 18

Central Neuro-immune interactions Spinal cord

Answer 18

Repetitive loading leads tp Neuropeptides & inflammatory cytokines in spinal cord

Question 19

summary

Answer 19

• Peripheral elements of the control system are profoundly affected by pain, injury and pathology
• Requires specific attention in rehabilitation

Question 20

Prevention and rehabilitation

Answer 20

Muscles that are inhibited will not be retrained automatically
• Retraining very important after injury

Question 21

• Activation of inhibited muscles.

Answer 21

– EMS
– EMG biofeedback
– Voluntary activation of muscles involved
– Isometric strengthening programs + EMG biofeedback
– Ultrasound feedback

Question 22

Prevention and rehabilitation

• Facilitation techniques

Answer 22

–  Manual contact
–  Verbal commands
–  Stretch facilitation
–  Traction
–  Approximation
–  Gentle resistance

Question 23

Prevention and rehabilitation

• Train sensory function

Answer 23

–  Repositioning
•  Return to target position (neutral) 
–  Acuity
•  Joint motion 
•  Vibration
–  Function
• Balance boards, etc