muscle spindle and gto Flashcards
(18 cards)
What are muscle spindles?
“Proprioceptive receptors within muscles that detect changes in length and rate of stretch. Composed of intrafusal fibers (nuclear chain/bag) with Ia/II afferents.”
What are Golgi tendon organs (GTOs)?
“Proprioceptive receptors at muscle-tendon junctions that detect muscle tension (force). Innervated by Ib afferents.”
Compare spindle vs. GTO function:
“Spindles: Monitor LENGTH/STRETCH (Ia/II). GTOs: Monitor TENSION/FORCE (Ib). Spindles excite homonymous muscle; GTOs inhibit it.”
What is the structure of muscle spindles?
“1. Intrafusal fibers (nuclear chain: static; nuclear bag: dynamic). 2. Sensory endings: Ia (velocity+length)
How do GTOs work?
“Muscle contraction → Tendon stretch → Ib afferents fire → Inhibitory interneurons → Relaxation (autogenic inhibition).”
What is the role of gamma (γ) motor neurons?
“Innervate INTRAFUSAL fibers to: 1. Maintain spindle sensitivity during muscle shortening. 2. Enable α-γ coactivation for smooth movement.”
How does γ activity affect muscle tone?
“↑γ drive → ↑spindle sensitivity → ↑Ia firing → ↑α motor neuron activity → ↑muscle tone (e.g.
Clinical: Hyperreflexia?
“UMN lesion → Loss of γ inhibition → ↑spindle sensitivity → Exaggerated DTRs (e.g.
Clinical: Clasp-knife rigidity?
“GTO override: Initial resistance (spindles) → Sudden release (GTO inhibition) - seen in UMN lesions.”
Climber with poor balance: Which structure is faulty?
“Muscle spindles (Ia afferents). Poor stretch detection → clumsiness.”
Parkinson’s rigidity: Role of γ neurons?
“↑γ drive → overactive spindles → constant Ia firing → hypertonia.”
Weightlifter drops barbell: Which reflex acted?
“GTO reflex (Ib inhibition) to prevent tendon damage.”
Stroke patient with hyperreflexia: Why?
“UMN lesion → ↑γ activity → exaggerated spindle responses.”
Clasp-knife phenomenon: Mechanism?
“Initial spasticity (spindles) → sudden GTO-mediated inhibition (Ib).”
How does LMN lesion cause flaccidity?
“α motor neuron damage → no extrafusal contraction → muscle limp/paralyzed.”
Why are reflexes absent in LMN lesions?
“No α output to extrafusals → areflexia.”
What happens to muscle spindles in LMN lesions?
“γ neurons often damaged → spindles slack → no Ia feedback.”
LMN vs. UMN flaccidity?
“LMN: Flaccid IMMEDIATELY (α dead). UMN: Flaccid only initially (spinal shock).”
