10 Reflexes & SC

10 Reflexes - Reflexes Spinal Cord SCI 1 Sensory organs of the muscle a Muscle spindle b Golgi tendon organ 1 Reflexes a Myotatic stretch reflex b

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Unformatted text preview: Reflexes, Spinal Cord, SCI 1. Sensory organs of the muscle a . Muscle spindle b. Golgi tendon organ 1. Reflexes a . Myotatic stretch reflex b. Inverse myotatic stretch reflex c. Cutaneous reflex 1. Disorders of the SC a . Herniated disc b. Spinal tumor c. Syringomelia 1. SCI • Muscle spindle: muscle receptor which provides info on length and rate of change in muscle Intrafusal muscle fibers Specialized muscle fibers inside the spindle Nuclear bag: Nuclear chain: Extrafusal fibers Afferents: Ia (large diameter): wrap around central region of each fiber; register quick and tonic stretch of the spindle II (smaller diameter): wrap or end mainly around nuclear chain fibers; register tonic stretch Sensory portion of the intrafusal muscle fiber is sensitive to tension Lengthening of the extrafusal muscle fiber causes lengthening of the intrafusal fibers; initiates the action potential of the afferent fibers When a muscle is passively stretched (static), both the Ia and II axons fires Velocity of change in muscle length is signaled only by the Ia afferents When muscle length is shortened, the spindle is slack (firing ceases) • So, what if the muscle is shortened? Does the spindle go slack? • Efferents: – Gamma: innervate intrafusal fibers • ONLY the contractile portion Muscle shortened: Ia fibers silent; spindle is “off the air,” no info is sent providing info about muscle length Muscle lengthened; afferents fire Gamma motor neuron activates and contracts polar ends • Innervate contractile elements at the poles of the muscle spindles, which causes the central region of the muscle spindle to stretch • Activation of the gamma motor neuron prevents the muscle spindle from slackening during shortening of the extrafusal fibers – this maintains the tension of the intrafusal fibers of the muscle spindle. • Because of this, the sensory fibers fire continuously in response to muscle shortening (as well as lengthening) • Information from the muscle spindles is transmitted to the spinal cord where it is • Used for reflex actions • Sent to the somatic sensory cortex...
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This note was uploaded on 09/02/2010 for the course OT 441 taught by Professor Stein during the Summer '10 term at USC.

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10 Reflexes - Reflexes Spinal Cord SCI 1 Sensory organs of the muscle a Muscle spindle b Golgi tendon organ 1 Reflexes a Myotatic stretch reflex b

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