spinal.reflexes - SPINAL REFLEXES Medical Neuroscience Dr....

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SPINAL REFLEXES Medical Neuroscience Dr. Kristine S. Vogel, C&SB
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MYOTATIC REFLEX ARC (aka DEEP TENDON REFLEX) * muscle stretch reflex, i.e. stimulus is stretching of muscle spindle * components = Group Ia receptor (muscle spindle)/afferent + α -motor neurons to homonymous muscle * monosynaptic * Group Ia receptors sensitive to rate (velocity) of muscle stretch * maintains dynamic (phasic) muscle tone
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GROUP II REFLEX ARC * stimulus is the stretching of a muscle spindle * components = Group II receptor (muscle spindle)/afferent + excitatory interneuron + α -motor neurons to homonymous muscle * Group II receptors sensitive to changes in muscle length * maintains static (tonic) muscle tone * neurological testing example: resistance to dorsiflexion of foot
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Examples of Myotatic Reflexes Tested in the Neurological Exam CNS Level Muscles Tested CN V Muscles of mastication C5,C6 Biceps, brachioradialis C7,C8 Triceps C8 Finger flexors L2,L3,L4 Quadriceps femoris S1 Gastrocnemius-soleus Grading of Myotatic Reflexes Grade Rating Significance 0 absent Usually pathologic 1 just elicitable Normal 2 easily elicitable Normal 3b r i s k N o r m
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MYOTATIC REFLEXES COMMONLY TESTED for UPPER EXTREMITY A. Biceps B. Triceps
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MYOTATIC REFLEXES COMMONLY TESTED for LOWER EXTREMITY C. Quadriceps femoris * patellar tendon * “knee jerk” D. Gastrocnemius * Achilles tendon * “ankle jerk”
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As α -motor neuron firing begins to shorten a muscle, the muscle spindles also become shorter. Group Ia and II excitatory input to the
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This note was uploaded on 03/19/2008 for the course BIO 337 taught by Professor Mihailoff during the Fall '07 term at University of Texas at Austin.

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spinal.reflexes - SPINAL REFLEXES Medical Neuroscience Dr....

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