1. The Sliding Filament Theory

2. Troponin complex

3. The Sliding Filament Theory

4. REVIEW: The Contraction Cycle

5. Sliding Filament Theory article & Concept Map - As you read the article that tells you about the first experiments that led scientists closer to the present- day understanding of skeletal muscle, be looking for…

6. 5 Golden Rules of Skeletal Muscle Activity

7. Muscles & Body Movements Movement is attained due to a muscle moving an attached bone Muscles are attached to at least 2 points Origin Attachment to moveable bone Insertion Attachment to immovable bone

8. Isotonic Contractions Isotonic Contraction: Example: lifting dumbbells with arm Tension (effort) increases & muscle fibers shorten & lengthen Concentric contraction: Tension (effort) exceeds resistance (weight) & muscle shortens Eccentric contraction: Resistance exceeds tension (effort) & muscle lengthens (due to gravity)

9. Isometric Contractions Isometric Contraction: Example: pushing against a wall Tension (effort) never exceeds resistance (weight) Muscle does NOT change length

10. Muscle Relaxation Relaxation of muscle fibers Passive process Combo of elastic forces, opposing muscle contractions & gravity to elongate a contracted muscle Elastic force: some energy used to stretch tendons in contraction phase forces a recoil Opposing muscle contractions: muscles move in antagonistic pairs Gravity: pulls down muscle to extended position

11. Rigor mortis Within 3-4 hours after death Dying muscle cell membranes become more permeable to Ca+ ions Promotes myosin cross-bridge binding After death, circulation of nutrients ends Without ATP, Ca+ ions are not removed & cross- bridges cannot detach from actin sites so muscles become locked in place – “ stiff ” Rigor mortis disappears as muscle proteins break down several hours after death (48-60 hours)

12. Effect of Exercise on Muscles Exercise increases muscle size, strength & endurance Aerobic (endurance/ cardiovascular) exercise (biking, jogging) results in stronger, more flexible muscles with greater resistance to fatigue Makes body metabolism more efficient Improves digestion & coordination Resistance (isotonic & isometric) exercise (weight-lifting) increases muscle size & strength

13. Fast vs. Slow-Twitch Muscles Fast Twitch Fibers Most skeletal muscle fibers Contract in 0.01 sec or less after stimulation Large in diameter Contain densely-packed myofibrils Have large glycogen reserves & few mitochondria Produce powerful contractions Fatigue rapidly “white muscle fibers”

14. Fast vs. Slow-Twitch Muscles Slow Twitch Fibers ~Half the diameter of fast fibers Take 3x as long to contract after stimulation Specialized to continue contracting for extended periods Contain extensive network of capillaries & has higher oxygen supply Contain red pigment myoglobin Contain more mitochondria than fast fibers “red muscle fibers” Intermediate Fibers Contain properties of fast fibers & slow fibers

15. Tetanus Many toxins, drugs & diseases may interfere with events occurring at the neuromuscular junction Tetanus: infection of Nervous System from potentially deadly bacteria Clostridium tetani – Bacteria spreads & makes poison called tetanospasmin – Poison blocks nerve signals from spinal cord to skeletal muscles, causing severe muscle spasms – Prolonged muscle contractions, spasms & stiffness – Spasms can be so powerful that they tear the muscles or cause fractures of the spine