ZIAHAIZ: microstructure of muscle. I Band: only thin bands of actin (contains no myosin)

3. Sacromere: segment of myofibril between 2 z lines. Contains ½ of 2 I bands and a central A band. • ZIAHAIZ: microstructure of muscle. • I Band: only thin bands of actin (contains no myosin) • Z Line: perpendicular to myofibril holds the actintogether. • A Band: thick myosin (appear dark under the microscope) • H Zone: within the A band this part ‘shrinks’ during contraction and ultimately disappears

4. Sliding filament

6. Nerve and Blood Supply • Normal activity of skeletal muscle is totally dependent on its nerve and blood supply • Each skeletal muscle fiber is controlled by a nerve ending • Contracting muscle fibers use huge amounts of energy which requires a continuous supply of oxygen and nutrients • In general, each muscle is served by an artery and one or more veins

8. Neuromuscular Junction: area of contraction between the terminal end of a motor neuron and the sarcolemma of a skeletal muscle.

9. Resting Membrane Potential (RMP) – difference in charge across the membrane

10. Action Potential- when nerve cell is stimulated, its RMP is changed . • stimulus

11. Fiber at rest: Ca2+ions, stored in sarcoplasmicreticulum • Stimulus- causes action potential, which increases the sarcoplasmic reticulum permeability to Ca2+ions

12. Skeletal Muscle Actions • origin – immovable end • insertion – movable end • prime mover (agonist) – primarily responsible for movement • synergists – assist prime mover • antagonist – resist prime mover’s action and cause movement in the opposite direction

14. Microscopic structure of muscle • Muscle Fiber – single cell of skeletal muscle tissue (can be very long .5m in thigh. • Sarcolemma – plasma membrane of the fiber. • Sarcoplasm – cytoplasm of the fiber • Sarcoplasmic reticulum – functions in the storage of calcium. Needed for muscle contraction.

15. Structure continued • Transverse Tubule – connects with the sarcolemma to help in the calcium transport mechanism of muscle contraction. • Myofibrils – small units of a single muscle fiber. • Thick filaments: composed of myosin • Thin filaments: actin, troponin, topomysin

16. The Motor Unit • Each muscle is served by at least one motor nerve which contains hundreds of motor neuron axons • As a nerve enters a muscle it branches into a number of axonal terminals, each of which forms a neuromuscular junction with a single nerve fiber • A motor neuron and all the muscle fibers it supplies is called a motor unit

17. The Motor Unit • When a motor neuron transmits an electrical impulse, all the muscle fibers that it innervates respond by contracting • The average number of muscle fibers per unit is 150, but it ranges from 4 to several hundred

18. The Motor Unit • Muscles that exert very fine control have small motor units (eyes, fingers) • Large muscles of locomotion and weight bearing have large motor units and as a consequence have less precise control

19. The Motor Unit • The muscle fibers in a unit are not clustered together but rather are spread throughout the entire muscle • Stimulation of a single unit causes a weak contraction of the entire muscle • This allows control of the intensity of the contraction

20. Smooth Muscles • Smooth muscle lacks the courser connective tissue seen in skeletal muscle • Small amounts of endomysium is found between smooth muscle fibers