1. Unit V: Movement Muscle Contraction - Part II Chapter 9 – pg 293-307

2. Review 1.What are the four stages of muscular activity? 2.Before a muscle fiber can contract, ATP must bind to: a.) a Z disc, b.) the myosin head, c.) sarcomere, d.) motor end plate 3.Before a muscle fiber can contract, Ca 2+ must bind to: a.) calsequestrin, b.) the myosin head, c.) tropomysin, d.) troponin, e.) G-actin 4.The __________ portion of the thin filament houses the active site to make muscles contract. 5.Whereas the ______________ is the portion of the thin filament that changes shape and allows the muscles to relax.

3. Neural Control Muscle Activity A skeletal muscle fiber contracts when stimulated by a motor neuron The action potential causes the release of ACh which leads to the production of an action potential in the sarcolemma. Release of calcium ions from the sarcoplasmic reticulum. Contraction cycle begins. The sarcomeres shorten, pulling the ends of the muscle fiber closer together. Skeletal muscle produces tension on the tendons at either end. Tension production Muscle fiber contraction leads to Thick-thin filament interaction triggers Calcium release Excitation

4. Muscle Twitch in Frogs Threshold = –Twitch: cycle of contraction and relaxation at threshold (lasting less than 1/10 second) Phases of a twitch contraction –latent period (2 msec delay) –contraction phase –relaxation phase Myogram

5. Contraction Strength of Twitches Intensity: Multiple motor unit summation (recruitment) –lift a glass of milk versus a whole gallon of milk Varies with: Muscle temperature Muscle pH Hydration Concentration of Ca + Stretch of muscle Intensity Frequency

6. Contraction Strength of Twitches Frequency: Higher frequency = stronger contractions –sustained fluttering contractions Maximum frequency stimulation (40-50 stimuli/second) –Tetanus Twitch Muscle twitches Stimuli (a) HighHighest-Tetanus Low Complete tetanus Fatigue

7. Tension in tendon Motor unit 1 Motor unit 2 Motor unit 3 Tension Time Asynchronous motor unit summation during a sustained contraction Contraction Strength

8. Decrease in the resting sarcomere length reduces tension. Optimal range = optimal tension Increase in sarcomere length, reduced tension When overlap equals zero, fibers cannot produce tension. Normal range Decreased length Increased sarcomere length Optimal resting length: 75 to 130% of the optimal length. With complete overlap, tension equals zero. Tension (% of maximum) Sarcomere Length vs. Tension

9. Isometric and Isotonic Contractions Isometric muscle contraction –prelude to muscle movement Isotonic muscle contraction –Concentric –Eccentric 6 kg Tendon 2 kg

10. Muscle Contraction Phases

11. Immediate Energy Needs Phosphagen system –myokinase –creatine kinase Short, intense exercise (100 m dash) Result is power enough for 1 minute brisk walk or 6 seconds of sprinting

12. Energy Needs Short-term Glycogen-lactic acid system – produces ATP for 30-40 seconds of maximum activity playing basketball or running around baseball diamonds Long-term Aerobic respiration –Produces 36 ATPs/glucose molecule Aerobic respiration using oxygen from myoglobin Glycogen–lactic acid System (anaerobic fermentation) Phosphagen system Duration of exercise 010 seconds40 seconds Aerobic respiration supported by cardiopulmonary function Repayment of oxygen debt Mode of ATP synthesis

13. Muscle Fatigue Progressive weakness from use –ATP synthesis declines –Na + and K + pumps slow –lactic acid inhibits enzyme function –accumulation of extracellular K+ –motor nerve fibers use up their ACh

14. Oxygen Debt Difference between resting rate of O 2 consumption and elevated rate following exercise. Purposes for extra oxygen –replace oxygen reserves –replenishing the phosphagen system –oxidizing lactic acid –serving the elevated metabolic rate

15. Slow- and Fast-Twitch Fibers Slow oxidative, slow-twitch fibers, red –adapted for aerobic respiration and resistant to fatigue –postural muscles of the back (100msec/twitch) Fast glycolytic, fast-twitch fibers, white –adapted for anaerobic fermentation –sarcoplasmic reticulum releases calcium quickly so contractions are quicker (7.5 msec/twitch) –extrinsic eye muscles, gastrocnemius and biceps brachii Proportions genetically determined

16. Cardiac Muscle Autorhythmic due to pacemaker cells aerobic respiration –resistant to fatigue –very vulnerable to interruptions in oxygen supply

17. Types of Smooth Muscle Functional categories: Multiunit smooth muscle –terminal nerve branches synapse on myocytes –large arteries, iris, arrector pili muscles –independent contraction Single-unit smooth muscle –blood vessel walls, digestive, respiratory, urinary, and reproductive tracts –coupled by gap junctions –large number of cells contract as a unit Synapses Autonomic nerve fibers (a) Multiunit smooth muscle Gap junctions Autonomic nerve fibers

18. Smooth Muscle Contraction Ca 2+ binds to calmodulin activates myosin light- chain kinase which activates myosin ATPase power stroke occurs Thin filaments pull on plasma membrane –shortens the entire cell in a twisting fashion

19. Repsonses to Stretch Ex. – esophagus distended by food brings on peristalsis Stress-relaxation response –Ex. - urinary bladder The process of peristalsis Food bolus Toward anus Longitudinal muscle Circular muscle Circular muscles contract behind bolus. Bolus of food arrives in digestive system. Longitudinal muscles ahead of bolus contract. Contraction in circular muscle layer forces bolus forward.