Transcript Slide 1
Biology 463 - Neurobiology Topic 14 Spinal Control of Movement Lange 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 The Somatic & Autonomic Motor Systems Types of Muscles – Smooth: digestive tract, arteries, related structures – Striated: Cardiac (heart) – skeletal (bulk of body muscle mass) Lower Motor Neurons Graded Control of Muscle Contraction by Alpha Motor Neurons – Varying firing rate of motor neurons – Recruit additional synergistic motor units Tetanus – as painted by Sir Charles Bell in 1809. Lower Motor Neurons 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 Figure 9.7a Excitation-Contraction Coupling Muscle Contraction – Alpha motor neurons release ACh – ACh produces large EPSP in muscle fiber – EPSP evokes muscle action potential – Action potential triggers Ca2+ release – Fiber contracts – Ca2+ reuptake – Fiber relaxes Excitation-Contraction Coupling 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 Ca2+ to troponin causes myosin to bind to action • Myosin heads pivot, cause filaments to slide Figure 9.3a–c Figure 9.3c–e Figure 9.3d Figure 9.4 Figure 9.6 Figure 9.11 Figure 9.12 Spinal Control of Motor Units Sensory feedback from muscle spindles - stretch receptor Spinal Control of Motor Units The Myotatic Reflex Spinal Control of Motor Units Two Types of Muscle Fiber – Extrafusal fibers: Innervated by alpha motor neurons – Intrafusal fibers: Innervated by gamma motor neurons Spinal Control of Motor Units Golgi Tendon Organs – Additional proprioceptive input - acts like strain gauge monitors muscle tension Spinal Control of Motor Units Golgi Tendon Organs – Spindles in parallel with fibers; Golgi tendon organs in series with fibers Spinal Control of Motor Units Excitatory Input – Crossed-extensor reflex: Activation of extensor muscles and inhibition of flexors on opposite side Interneurons + + – Afferent fiber + + – Efferent fibers Efferent fibers Extensor inhibited Arm movements Flexor stimulated Key: + Excitatory synapse – Inhibitory synapse Right arm (site of stimulus) Left arm (site of reciprocal activation) Flexor inhibited Extensor stimulated 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 END.