1)Action Potential in Motor Axon 2) End Plate Potential at Neuromuscular Junction

1. Muscle Excitation-Contraction • 1)Action Potential in Motor Axon • 2) End Plate Potential at Neuromuscular Junction • 3) Action Potential in Muscle Fiber. • 4) The AP induces, after a small latency, a twitch in the muscle fiber • Twitch - transient all-or-none contraction

3. 1. spindle stretch activates sensory neuron. 2. sensory neuron synapses on ventral cord motor neurons and interneurons 3. increase in motor neuron activity innervates same and synergistic muscles. 4. inhibits motor neurons that innervate antagonistic muscles

4. Stretch reflex

5. Types of motor neurons • a motor neurons- innervate the extrafusal muscle fibers that generate the forces needed for movement and posture. • g motor neurons- innervate muscle spindles in intrafusal muscle fibers. These fibers regulate the sensory input from spindles by setting the muscle fibers to an appropriate length.

6. g motor Neuron Activity Affects Reponses of Muscle Spindles Gamma neurons regulate excitation of spindles so they can activate the muscle indirectly through the stretch reflex.

7. Golgi tendon organ • Encapsulated afferent nerve endings located at the junction of the muscle and tendon. • Fire when muscle contracts and are less sensitive (not completely insensitive) to passive stretch of the muscle. • axons from Golgi tendon organs inhibit neurons in the spinal cord that synapse with the a motor neurons that innervate the same muscle. • Helps prevent fatigue • Protects muscle from large forces • Maintains steady level of muscle force

8. Golgi Tendon Organs

9. Comparison of the Function of Muscle Spindles and Golgi Tendon Organs

10. Comparison of the Function of Muscle Spindles and Golgi Tendon Organs

11. Negative Feedback Regulation of Muscle Tension By Golgi Tendon Organs Negative feedback by Golgi tendon organs When muscle contracts, feedback inhibits additional contractions – prevents damage and fatigue.

12. Flexion reflex • Reflexes that compensate posture when one withdraws from pain. • involves several synaptic links • excitation of nociceptor leads to ipsilateral and contralateral responses. • flexion reflex. Stimulation of cutaneous receptors in the foot leads to activation of spinal cord local circuits that withdrawal stimulated (pained) side and extend other side to provide compensatory support.

13. Spinal Cord Circuitry Responsible for the Flexion Reflex