1. Chapter 13 Spinal Control of Movement

2. Introduction Motor Programs –Motor system: Muscles and neurons that control muscles –Role: Generation of coordinated movements –Parts of motor control Spinal cord  coordinated muscle contraction Brain  motor programs in spinal cord

3. The Somatic & Autonomic Motor Systems Types of Muscles –Smooth: digestive tract, arteries, related structures –Striated: Cardiac (heart) –skeletal (bulk of body muscle mass)

4. Graded Control of Muscle Contraction by Alpha Motor Neurons –Varying firing rate of motor neurons –Recruit additional synergistic motor units Lower Motor Neurons

5. Tetanus – as painted by Sir Charles Bell in 1809.

6. Types of Motor Units –Red muscle fibers: Large number of mitochondria and enzymes, slow to contract, can sustain contraction –White muscle fibers: Few mitochondria, anaerobic metabolism, contract and fatigue rapidly –Fast motor units: Rapidly fatiguing white fibers –Slow motor units: Slowly fatiguing red fibers Lower Motor Neurons

7. Figure 9.7a

8. Muscle Contraction –Alpha motor neurons release ACh –ACh produces large EPSP in muscle fiber –EPSP evokes muscle action potential –Action potential triggers Ca 2+ release –Fiber contracts –Ca 2+ reuptake –Fiber relaxes Excitation-Contraction Coupling

9. The Molecular Basis of Muscle Contraction –Z lines: Division of myofibril into segments by disks –Thin filaments: Series of bristles –Thick filaments: Between and among thin filaments –Sliding-filament model: Binding of Ca 2+ to troponin causes myosin to bind to action Myosin heads pivot, cause filaments to slide Excitation-Contraction Coupling

10. Figure 9.3a–c

11. Figure 9.3c–e

12. Figure 9.3d

13. Figure 9.4

14. Figure 9.6

18. Figure 9.11

19. Figure 9.12

20. Sensory feedback from muscle spindles - stretch receptor Spinal Control of Motor Units

21. The Myotatic Reflex Spinal Control of Motor Units

22. Two Types of Muscle Fiber –Extrafusal fibers: Innervated by alpha motor neurons –Intrafusal fibers: Innervated by gamma motor neurons

23. Spinal Control of Motor Units Golgi Tendon Organs –Additional proprioceptive input - acts like strain gauge - monitors muscle tension

24. Spinal Control of Motor Units Golgi Tendon Organs –Spindles in parallel with fibers; Golgi tendon organs in series with fibers

25. Excitatory Input –Crossed-extensor reflex: Activation of extensor muscles and inhibition of flexors on opposite side Spinal Control of Motor Units

26. Afferent fiber Efferent fibers Extensor inhibited Flexor stimulated Right arm (site of stimulus) Left arm (site of reciprocal activation) Arm movements Interneurons Key: + Excitatory synapse – Inhibitory synapse Efferent fibers Flexor inhibited Extensor stimulated + – + – + + Flexes Extends

27. Information gleaned about nicotinic ACh receptors utilzed the electric organs of electric eels because of their high concentration of the Ach receptor. The Disease Myasthenia gravis is an autoimmune disease where the body's immune system has damaged receptors on your muscles causing long term weakness and eventual, premature death. Individual showing classic, early signs of Myasthenia gravis