Pages 187-195. Muscle fiber contraction is “all or none” ◦ There is no “in-between” contraction Not all fibers may be stimulated at one time Different.

Pages 187-195

Muscle fiber contraction is “all or none”◦ There is no “in-between” contraction

Not all fibers may be stimulated at one time

Different combinations of muscle fiber contractions may give differing responses◦ Graded responses= different degrees of

skeletal muscle shortening

© 2015 Pearson Education, Inc.

Graded responses can be produced by changing:◦ The frequency of muscle stimulation◦ The number of muscle cells being stimulated

(and therefore, recruited) at one time

more fibers= greater muscle tension◦ Muscles can contract until they run out of energy

© 2015 Pearson Education, Inc.

Adenosine Triphosphate (ATP)◦ Immediate source◦ Stored in muscle fibers in small amounts that are

quickly used up After this initial time, other pathways must be

utilized to produce ATP

© 2015 Pearson Education, Inc.

1. Direct phosphorylation of ADP ◦ by creatine phosphate

2. Aerobic (cellular) respiration (most ATP)

3. Anaerobic (cellular) respiration◦ glycolysis and lactic acid formation

© 2015 Pearson Education, Inc.

Muscle cells store CP, a high-energy molecule◦ After ATP is depleted, ADP remains

◦ CP transfers a phosphate group to ADP to regenerate ATP

◦ CP supplies are used up in less than 15 seconds (About 1 ATP is created per CP molecule)

*creatine phosphate is also known as phosphocreatine

© 2015 Pearson Education, Inc.

Figure 6.10a Methods of regenerating ATP during muscle activity.

(a) Direct phosphorylation

CP

CP ADP

ATPCreatine

Coupled reaction of creatinephosphate (CP) and ADP

Energy source:

Oxygen use:Products:

None 1 ATP per CP,creatine

15 secondsDuration of energy provision:

– breaks down glucose without oxygen– broken down to pyruvic acid, then to lactic acid– produces about 2 ATP very quickly

– Lactic acid accumulates in the muscles and produces fatigue

– After exercise, the oxygen deficit is repaid by rapid, deep breathing

© 2015 Pearson Education, Inc.

Figure 6.10b Methods of regenerating ATP during muscle activity.

glucoseEnergy source:

Glycolysis and lactic acidformation

(b) Anaerobic pathway

ATP2

O2

O2

Oxygen use:Products:

Duration of energy provision:

None 2 ATP per glucose,lactic acid

40 seconds, or slightly more

net gain

Releasedto blood

Glucose (fromglycogen breakdown ordelivered from blood)

Pyruvic acid

Lactic acid

Glycolysisin cytosol

Glucose is broken down to CO2 and H2O

◦ Creates about 32 ATP per glucose molecule◦ occurs in the mitochondria◦ slower reaction, requires continuous oxygen◦ Provides hours of sustained energy

© 2015 Pearson Education, Inc.

See page 194 for this side-by-side comparison of pathways

Comparison of pathways

Image source:http://www.udel.edu/chem/C465/senior/fall00/Performance1/phosphocreatine.htm.html

• Isotonic contractions– Myofilaments slide past each other during

contractions– The muscle shortens, and movement occurs– Example: bending the knee; rotating the arm

• Isometric contractions– Tension in the muscles increases– The muscle doesn’t shorten or produce

movement– Example: pushing against a wall with bent

elbows

© 2015 Pearson Education, Inc.

Increase in muscle:◦ Size ◦ Strength◦ Endurance ◦ Aerobic (endurance) exercise=

stronger more flexible muscles greater resistance to fatigue

◦ Resistance, or isometric, exercise like weight lifting increases muscle size and strength

© 2015 Pearson Education, Inc.