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Proprioception

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”

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Proprioception

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  1. 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)

  2. Muscle spindle • Bundles of encapsulated, specialized fibers • “Intrafusal” • Contractile polar regions • Passive equatorial region • Isolated from surrounding structure • Sensory afferents

  3. Spindle Innervation • Gamma motor innervation • Primary (Ia) annulospiral equatorial ending • Secondary (II) polar ending • Mechanical filtering

  4. Spindle Response • Primary ending adapts rapidly, velocity sensor • Secondary ending adapts slowly, length sensor • Directionally asymmetric

  5. Spindle Response • Depends on neuromuscular set • Depends on L,V, A Muscle stretch Primary ending Spindle response Increasing Central drive Time Spindle response (Hz) 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. Increasing Stretch velocity Length

  6. Stretch reflex circuitry • Spindle afferent synapses with homonymous motorneuron • Inhibits antagonist motorneuron • Length controller • Postural mechanism • Myotatic unit

  7. Stretch Reflex • Coordination with muscle mechanics • Crossbridge mechanics provide short-range stability • Larger perturbations could be catastrophic Reflex “compensation” Reflexive muscle Areflexive muscle “Short range” stiffness. Crossbridge response “Yield” Forcible crossbridge detatchment

  8. Golgi Tendon Organ • Interwoven collagen and neural fibrils • Series connection between fiber & tendon • Active force sensor • Fibers pulls collagen • Collagen deforms neuron

  9. Instantaneous GTO frequency Muscle Force GTO Response Tetanic Response Twitch Response 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.

  10. 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

  11. Renshaw interneurons • Activated by recurrent collaterals of motor axon • Inhibit homonymous motor pool • Drive dependent inhibition

  12. Higher spinal organization • Locomotion • Sensory information may entrain CPG • Positive feedback

  13. 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

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