1. Muscles n Skeletal muscle organization and how it contracts

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 Sarcomere: repeating unit of muscle tissue, composed of…. n Z lines~ sarcomere border this gives “striated” appearance in muscle

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) but their length stays the same

4. Actin-myosin interaction n 1- Myosin head breaks down ATP to ADP and inorganic phosphate (Pi); termed the “high energy configuration” with ADP and phosphate attaching to the head. (GRABBING ON) n 2- Myosin head binds to actin; termed a “cross bridge” n 3- Releasing ADP and (Pi), myosin relaxes sliding actin; “low energy configuration” (PULLS THE ACTINS FROM BOTH SIDES TO BE CLOSER) n 4- Binding of new ATP releases myosin head (LET GO) n 5- This ATP is broken down (See #1)

5. Muscle contraction regulation, I n Relaxation: tropomyosin protein blocks myosin binding sites on actin n Contraction: calcium is released from ER of muscle cell due to action potential from neurons. It binds to troponin complex; tropomyosin changes shape, exposing myosin binding sites. MAKES SLIDING FILAMENT POSSIBLE

6. Muscle contraction regulation, II n Calcium (Ca+)~ Must be present n Sarcoplasmic reticulum~ a specialized endoplasmic reticulum (ER) in muscle that stores and releases Ca. n Stimulated by action potential in a motor neuron n Ca+ then binds to troponin allowing this to go forward