1. Chapter 6 The Muscular System

2. The Sliding Filament Theory

3. Contraction of a Skeletal Muscle oMuscle fiber contraction is “all or none” oWithin a skeletal muscle, not all fibers may be stimulated during the same interval oDifferent combinations of muscle fiber contractions may give differing responses oGraded responses – different degrees of skeletal muscle shortening

4. Types of Graded Responses oTwitch oSingle, brief contraction oNot a normal muscle function

5. Types of Graded Responses oTetanus (summing of contractions) oOne contraction is immediately followed by another oThe muscle does not completely return to a resting state oThe effects are added

6. Types of Graded Responses oUnfused (incomplete) tetanus oSome relaxation occurs between contractions oThe results are summed Figure 6.9a, b

7. Types of Graded Responses oFused (complete) tetanus oNo evidence of relaxation before the following contractions oThe result is a sustained muscle contraction Figure 6.9a, b

8. Types of Graded Responses Treppe’- when contractions in succession becomes stronger than the previous contraction. Treppe’- when contractions in succession becomes stronger than the previous contraction. This is why we do warm-ups. This is why we do warm-ups.

9. Types of Muscle Contractions Isometric contractions Tension in the muscles increases The muscle is unable to shorten Isotonic contractions Myofilaments are able to slide past each other during contractions The muscle shortens

10. Muscle Response to Strong Stimuli  Muscle force depends upon the number of fibers stimulated  More fibers contracting results in greater muscle tension  Muscles can continue to contract unless they run out of energy

11. Energy for Muscle Contraction Velocity- how fast a load is moved. Heavier loads make it slower; different types of fibers contract at different speeds. Velocity- how fast a load is moved. Heavier loads make it slower; different types of fibers contract at different speeds. Duration- how long the contractions will last; depends on the amount of load (resistance), and the type of fibers Duration- how long the contractions will last; depends on the amount of load (resistance), and the type of fibers

12. 3 muscle fiber Types Slow twitch fatigue resistant- (red muscle fibers) slow to fatigue, slower contractions; aerobic Slow twitch fatigue resistant- (red muscle fibers) slow to fatigue, slower contractions; aerobic Fast twitch fatiguable- (white muscle fibers) fast contractions, fatigue quickly; anaerobic Fast twitch fatiguable- (white muscle fibers) fast contractions, fatigue quickly; anaerobic Fast twitch fatigue resistant- fast twitch but slower than above. Middle of the road type fiber Fast twitch fatigue resistant- fast twitch but slower than above. Middle of the road type fiber Muscle fibers can adapt to the type of exercise. Muscle fibers can adapt to the type of exercise. Disuse atrophy- muscle fiber strength and size will deteriorate without use Disuse atrophy- muscle fiber strength and size will deteriorate without use

13. Energy for Muscle Contraction Initially, muscles used stored ATP for energy Bonds of ATP are broken to release energy Only 4-6 seconds worth of ATP is stored by muscles After this initial time, other pathways must be utilized to produce ATP

14. Energy for Muscle Contraction  Direct phosphorylation  Muscle cells contain creatine phosphate (CP)  CP is a high-energy molecule  After ATP is depleted, ADP is left  CP transfers energy to ADP, to regenerate ATP  CP supplies are exhausted in about 20 seconds

15. Energy for Muscle Contraction  Aerobic Respiration  Series of metabolic pathways that occur in the mitochondria  Glucose is broken down to carbon dioxide and water, releasing energy  This is a slower reaction that requires continuous oxygen

16. Energy for Muscle Contraction  Anaerobic glycolysis  Reaction that breaks down glucose without oxygen  Glucose is broken down to pyruvic acid to produce some ATP  Pyruvic acid is converted to lactic acid

17. Energy for Muscle Contraction  Anaerobic glycolysis (continued)  This reaction is not as efficient, but is fast  Huge amounts of glucose are needed  Lactic acid produces muscle fatigue

18. Muscle Fatigue and Oxygen Debt  When a muscle is fatigued, it is unable to contract  The common reason for muscle fatigue is oxygen debt  Oxygen must be “repaid” to tissue to remove oxygen debt  Oxygen is required to get rid of accumulated lactic acid  Increasing acidity (from lactic acid) and lack of ATP causes the muscle to contract less

19. Muscle Tone  Some fibers are contracted even in a relaxed muscle  Different fibers contract at different times to provide muscle tone  The process of stimulating various fibers is under involuntary control

20. Muscles and Body Movements  Movement is attained due to a muscle moving an attached bone

21. Smooth Muscle Muscle cells are much smaller than those of the skeletal systems. Muscle cells are much smaller than those of the skeletal systems. Sarcoplasmic reticulum- poor not as much connective tissue (less stress). Sarcoplasmic reticulum- poor not as much connective tissue (less stress). Nerve junctions- less precise Nerve junctions- less precise No sarcomeres- no repeating units No sarcomeres- no repeating units Alternating layers- have at least 2 layers, longitudinal and circular (so it can move, squish, and propel food etc.) Alternating layers- have at least 2 layers, longitudinal and circular (so it can move, squish, and propel food etc.)

22. Contraction of smooth muscles Stimulation- not always nerve stimulated, can also be chemically stimulated, allows for adaptation to body’s needs Stimulation- not always nerve stimulated, can also be chemically stimulated, allows for adaptation to body’s needs Synchronized- muscle not isolated into motor units, some may act as “pacemaker” (like in the heart) Synchronized- muscle not isolated into motor units, some may act as “pacemaker” (like in the heart) Longer contractions- than skeletal muscle also less energy needed Longer contractions- than skeletal muscle also less energy needed Stretch response- not as vigorous reaction (contraction) like in skeletal muscle. Why? Stretch response- not as vigorous reaction (contraction) like in skeletal muscle. Why? stretch allows organ to hold food, urine, etc. stretch allows organ to hold food, urine, etc.