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Transcript
NEUROMUSCULOSKELETAL SYSTEMS LECTURE 10 REFLEX PHYSIOLOGY Medical Science Dr R G Luckwill KNEE JERK REFLEX (Monosynaptic Reflex) Extensor muscle of knee (quadriceps femoris) Muscle spindle Patellar tendon Alpha motor neuron Figure 8.26 Page 285 Capsule Alpha motor neuron axon Gamma motor neuron axon Secondary (flower-spray) endings of afferent fibers Extrafusal (“ordinary”) muscle fibers Intrafusal (spindle) muscle fibers Contractile end portions of intrafusal fiber Noncontractile central portion of intrafusal fiber Primary (annulospiral) endings of afferent fibers Figure 8.24 Page 283 MUSCLE INNERVATION Extrafusal Ia II Annulospiral (primary) Flower Spray (secondary) α -motor Intrafusal γ-motor Firing Rate Spindle Ending Responses Secondary Stretch Primary Time KNEE JERK REFLEX (Monosynaptic Reflex) Extensor muscle of knee (quadriceps femoris) Muscle spindle (Primary endings) Ia Sensory neuron Single synapse Patellar tendon Alpha motor neuron Figure 8.26 Page 285 WITHDRAWL (FLEXION) REFLEX & ANTAGONIST INHIBITION REFLEX Thermal pain receptor in finger Afferent Pathway = Inhibitory interneuron = Excitatory interneuron = Synapse = Inhibits = Stimulates Ascending pathway to brain Stimulus Biceps (flexor) contracts Hand withdrawn Efferent pathway Triceps (extensor) relaxes Integrating center (spinal cord) Effector organs Response Figure 5.31 Page 174 WITHDRAWL & CROSSED EXTENSOR REFLEXES Afferent pathway Efferent pathway Efferent pathway Flexor muscle contracts Pain receptor in heel Extensor muscle relaxes Injured extremity (effector organ) Response Integrating center (spinal cord) Flexor muscle relaxes Extensor muscle contracts Opposite extremity (effector organ) Stimulus Response Figure 5.32 Page 175 Levels of Reflex Connections Figure 8.26 (1) Page 287 Extrafusal skeletal muscle fiber Spinal cord Intrafusal muscle spindle fiber Afferent input from sensory endings of muscle spindle fiber Alpha motor neuron output to regular skeletal-muscle fiber Stretch reflex pathway Gamma motor-neuron output to contractile end portions of spindle fiber Descending pathways coactivating alpha and gamma motor neurons Figure 8.25 (1) Page 284 α−γ COACTIVATION Relaxed muscle; spindle fiber sensitive to stretch of muscle Contracted muscle in hypothetical situation of no spindle coactivation; slackened spindle fiber not sensitive to stretch of muscle Contracted muscle in normal situation of spindle coactivation; contracted spindle fiber sensitive to stretch of muscle Figure 8.25 (2) Page 284 MUSCLE INNERVATION Extrafusal Ia II Annulospiral (primary) Flower Spray (secondary) α -motor Intrafusal γ-motor Servo-mechanism of Muscle Contraction 1. Descending command to γ-motoneuron 2. Ends of Intrafusal fibres contract 3. Spindle endings stretched & fire 4. AP volleys in Ia & II sensory fibres to Spinal cord 5. Reflex AP volley in α-motoneurons 6. Contraction of Extrafusal muscle fibres Synaptic inputs (presynaptic axon terminals) Dendrites Cell body of Motor Neuron Axon hillock Axon Myelin sheath Figure 4.15 Page 102 Motor Neuron Connections Swing Stance 100% Normal (Resting) Walking 0% Time Excitability of Gastrocnemius H-Reflex during Walking