1. Lecture #21 Date ____ n Chapter 49 ~ Sensory and Motor Mechanisms

2. Vertebrate Skeletal Muscle n Contract/relax: antagonistic pairs w/skeleton n Muscles: bundle of…. n Muscle fibers: single cell w/ many nuclei consisting of…. n Myofibrils: longitudinal bundles composed of…. n Myofilaments: Thin~ 2 strands of actin protein and a regulatory protein Thick~ myosin protein n Sarcomere: repeating unit of muscle tissue, composed of…. n Z lines~ sarcomere border n I band~ only actin protein n A band~ actin & myosin protein overlap n H zone~ central sarcomere; only myosin

3. Sliding-filament model n Theory of muscle contraction n Sarcomere length reduced n Z line length becomes shorter n Actin and myosin slide past each other (overlap increases)

4. Actin-myosin interaction n 1- Myosin head hydrolyzes ATP to ADP and inorganic phosphate (Pi); termed the “high energy configuration” n 2- Myosin head binds to actin; termed a “cross bridge” n 3- Releasing ADP and (Pi), myosin relaxes sliding actin; “low energy configuration” n 4- Binding of new ATP releases myosin head n Creatine phosphate~ supplier of phosphate to ADP

5. Muscle contraction regulation, I n Relaxation: tropomyosin blocks myosin binding sites on actin n Contraction: calcium binds to toponin complex; tropomyosin changes shape, exposing myosin binding sites

6. Muscle contraction regulation, II n Calcium (Ca+)~ concentration regulated by the…. n Sarcoplasmic reticulum~ a specialized endoplasmic reticulum n Stimulated by action potential in a motor neuron n T (transverse) tubules~ travel channels in plasma membrane for action potential n Ca+ then binds to troponin

7. Muscle contraction