Download Proprioception - School of Applied Physiology

Proprioception
• Sense of place and position
• Sensory afferents
– Muscle spindles
– Joint receptors
– Cutaneous afferents
• Other mechanisms
– Force feedback (Golgi tendon organ)
– Effort feedback (Renshaw/recurrent inhibition)
Muscle spindle
• Bundles of encapsulated,
specialized fibers
– “Intrafusal”
• Contractile polar regions
• Passive equatorial region
– Isolated from surrounding
structure
• Sensory afferents
Spindle Innervation
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Gamma motor innervation
Primary (Ia) annulospiral equatorial ending
Secondary (II) polar ending
Mechanical filtering
Spindle Response
• Primary ending adapts rapidly, velocity sensor
• Secondary ending adapts slowly, length sensor
• Directionally asymmetric
Spindle Response
• Depends on neuromuscular set
• Depends on L,V, A Muscle
stretch
Primary ending
Spindle response (Hz)
Spindle
response
Time
Increasing
Stretch velocity
Length
Increasing
Central drive
Houk JC, Rymer WZ, and Crago PE.
Dependence of dynamic response of
spindle receptors on muscle length
and velocity. Journal of
Neurophysiology 46: 143-166, 1981.
Stretch reflex circuitry
• Spindle afferent synapses
with homonymous
motorneuron
• Inhibits antagonist
motorneuron
• Length controller
– Postural mechanism
• Myotatic unit
Stretch Reflex
• Coordination with muscle mechanics
• Crossbridge mechanics provide short-range
stability
• Larger perturbations could be catastrophic
Reflex “compensation”
Reflexive muscle
“Short range” stiffness.
Crossbridge response
“Yield” Forcible
crossbridge detatchment
Areflexive muscle
Golgi Tendon Organ
• Interwoven collagen and neural fibrils
• Series connection between fiber & tendon
• Active force sensor
– Fibers pulls collagen
– Collagen deforms neuron
GTO Response
Twitch Response
Tetanic Response
Instantaneous
GTO frequency
Muscle
Force
Houk J and Henneman E. Responses of
Golgi tendon organs to active contractions
of the soleus muscle of the cat. Journal of
Neurophysiology 30: 466-481, 1967.
GTO Circuitry
• Di-/Tri-synaptic inhibition of homonymous MN
– Inhibitory interneuron
– Also modulated by 1a, cutaneous, joint, …
• Broad intermuscular distribution
• Force dependent inhibition
– Loss-of-force excitation
– Reflex compensation for fatigue
Renshaw interneurons
• Activated by recurrent collaterals of motor
axon
• Inhibit homonymous motor pool
• Drive dependent inhibition
Higher spinal organization
• Locomotion
• Sensory information may entrain CPG
• Positive feedback
Locomotor feedback
• Phase dependent
response (fictive
locomotion,
decerebrate)
• Excitation of
Extensors during
flexor phase initiates
extensor phase
• During extensor
phase, extends
extensor phase
• Broad, multimuscular
response