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18 Cards in this Set
- Front
- Back
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Which neurons fire first: fast fatigable, fast fatigue-resistant, or slow? Why?
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Slow, because slow motor units have the smallest cell bodies which have the largest input resistance. Thus, it takes less synaptic input to reach threshold voltage
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When are fatigable motor neurons fired?
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Only when needed to achieve greater forces
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Why do large, fatigable neurons need more synaptic current to fire?
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Their input resistance is low because of large cell bodies and leaky channels
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What kind of position are joint afferent sensory receptors most sensitive to?
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Position at extreme joint angles
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Which receptors help one determine finger location?
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Tactile receptors in skin (Ruffini afferents)
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What are golgi tendon organs? What do they detect?
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Located in muscle tendon and detect TENSION
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How is the body able to have position sense even when the afferent position input is gone?
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Upper motor neurons provide sense of position thru corollary discharge
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What are the 3 main components of the muscle spindle organ?
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Intrafusal muscle fibers, Type Ia and II sensory fibers, and the Gamma motor neurons
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What are intrafusal muscle fibers? What do they detect?
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modified muscle fibers in the non-contractile region that detect fast, dynamic changes in muscle length (Nuclear bag) or static changes (Nuclear chain)
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What are type Ia sensory fibers and what do they detect?
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wrap around the center of all intrafusal fibers and detect VELOCITY change of muscle stretch and speed of movements. In turn, they innervate alpha-motors for reflexes
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What fibers are activated to regulate the static adn dynamic sensitivity of the muscle spindle?
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gamma motorneurons
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What prevents spindle activity from completely stpping during contraction (since there is no more stretching)?
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gamma motorneurons
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When is the golgi tendon organ fired?
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Usually in periods of high muscle tension and soemteimes during normal movement to monitor tension
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How does the golgi tendon organ work?
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Stretching of the GTO during contraction activates Ib sensory afferents.
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What are three mechanisms involved in the recovery of reflexes after a spinal cord/nerve injury?
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Sprouting of afferent terminals of spinal cord distal to the lesion, increased # post syn receptors, supersensitivity
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When a muscle is being stretched, how do gamma static and dynamic fibers fire in nuc bag and chain fibers?
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Gamma static fires for both bag and chain fibers but the dynamic fibers only fire with the nuclear bag.
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What is the main purpose of the gamma fibers and when they fire, what do they do?
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Insure muscle spindle fibers are not silenced during contrxn, when fire result in contrx of polar ends of muscle spindle
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How might one tx muscle spacisity by affecting muscle spindle?
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administer a GABA receptor agonist (baclofen) to decrease Ia aferent terminal... gives reduced reflex response
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