Muscles and Muscle TissuePart C1

Prepared by Janice Meeking, W. Rose, and Jarvis Smith.

Figures from Marieb & Hoehn 8th ed.

Portions copyright Pearson Education

1

Actin

Cross bridge formation

Cocking of myosin head Power (working) stroke

Cross bridge detachment

24

3

ADP

Pi

ATP

ATP

ADP

ADP

Pi

Pi

Figure 9.12

Cross Bridge Cycle reminder

Skeletal Muscle Contraction

Muscle Metabolism: Energy for ContractionATP is the only direct source of energy for muscle

contraction

Available stores of ATP depleted in 4–6 seconds

ATP is regenerated by:

– Direct phosphorylation of ADP by creatine phosphate (CP)

– Anaerobic pathway (glycolysis)

– Aerobic respiration

Copyright © 2010 Pearson Education, Inc. Figure 9.19a

Coupled reaction of creatinephosphate (CP) and ADP

Energy source: CP

(a) Direct phosphorylation

Oxygen use: NoneProducts: 1 ATP per CP, creatineDuration of energy provision:15 seconds

Creatinekinase

ADPCP

Creatine ATP

Anaerobic Pathway (glycolysis)• Occurs when O2 delivery cannot keep up with O2

use• As contractile activity increases, O2 consumption

may increase above O2 delivery capability, so anaerobic metabolism begins

• Pyruvic acid lactic acid when not enough O2• Lactic acid (lactate)

• Makes muscle cells acidic, less efficient• Diffuses into bloodstream• Liver (with O2) can convert it back into pyruvic acid

Copyright © 2010 Pearson Education, Inc. Figure 9.19b

Energy source: glucose

Glycolysis and lactic acid formation

(b) Anaerobic pathway

Oxygen use: NoneProducts: 2 ATP per glucose, lactic acidDuration of energy provision:60 seconds, or slightly more

Glucose (fromglycogen breakdown ordelivered from blood)

Glycolysisin cytosol

Pyruvic acid

Releasedto blood

net gain

2

Lactic acid

O2

O2ATP

Aerobic Pathway • Produces 95% of ATP during rest and light to

moderate exercise• Occurs when O2 delivery can keep up with O2

use: • Krebs cycle

• Electron transport chain

• Fuels: stored glycogen, then glucose (blood), pyruvic acid from glycolysis, and free fatty acids and amino acids

Copyright © 2010 Pearson Education, Inc. Figure 9.19c

Energy source: glucose; pyruvic acid;free fatty acids from adipose tissue;amino acids from protein catabolism

(c) Aerobic pathway

Aerobic cellular respiration

Oxygen use: RequiredProducts: 32 ATP per glucose, CO2, H2ODuration of energy provision: Hours

Glucose (fromglycogen breakdown ordelivered from blood)

32

O2

O2

H2O

CO2

Pyruvic acidFattyacids

Aminoacids

Aerobic respirationin mitochondriaAerobic respirationin mitochondria

ATP

net gain perglucose

Short-duration exerciseProlonged-durationexercise

ATP stored inmuscles isused first.

ATP is formedfrom creatinePhosphateand ADP.

Glycogen stored in muscles is brokendown to glucose, which is oxidized togenerate ATP.

ATP is generated bybreakdown of severalnutrient energy fuels byaerobic pathway. Thispathway uses oxygenreleased from myoglobinor delivered in the bloodby hemoglobin. When itends, the oxygen deficit ispaid back.Figure 9.20

Anaerobic Aerobic

Muscle FatigueMuscle FatiguePhysiological fatigue: muscle doesn’t respond to nerve impulses• ATP deficit? Surprisingly, no. ATP drops very little.• Intracellular acidity, due to lactate? Maybe not, since pH hardly

drops.• Ionic imbalances interfere with E-C coupling: K+ accumulation in

T tubules• Pi may accumulate, inhibiting release of Pi from myosin• Disrupted storage & release of Ca due to SR damage (causes

slow-developing fatigue during submaximal exercise)

Central (“psychological”) fatigue: CNS doesn’t produce the neural commands

• Cause unclear. Maybe partly a response to elevated body pH due to lactate. “Central governor” theory (disputed): brain won’t let the body hurt itself.

Oxygen DeficitDuring intense exercise, O2 demand > supply.

O2 deficit develops; deficit must be paid back later.

Extra O2 needed after exercise to

•Replenish O2 reserves (attached to myoglobin)

•Replenish glycogen stores

•Replenish ATP and CP reserves

•Convert lactic acid to pyruvic acid, glucose, glycogen

O2 needed afterward = difference between O2 that was actually used during exercise & what would been needed to do it aerobically.

Force of muscle contraction affected by:• Number of muscle fibers stimulated (recruitment)• Muscle cross-sectional area: hypertrophy of cells

increases strength• Frequency of stimulation: stimulation rate allows

time for more effective transfer of tension to noncontractile components

• Length of muscle (length-tension relation): a muscle contracts most strongly when its fibers are 80–120% of their normal resting length

Copyright © 2010 Pearson Education, Inc. Figure 9.21

Largenumber of

musclefibers

activated

Contractile force

Highfrequency ofstimulation

Largemusclefibers

Muscle andsarcomere

stretched to slightly over 100%of resting length

Sarcomeres greatly shortened

Sarcomeres atresting length

Sarcomeres excessivelystretched

170%

Optimal sarcomere operating length

(80%–120% of resting length)

100%70%

Observable in whole muscleCellular basis:•At short muscle length, force because thin filaments overlap each other•At long muscle length, force because # of potential crossbridges that can form

Figure 9.22

Length-tension relationship in skeletal muscle

Type of Muscle FibersClassified according to two characteristics:1. Speed of contraction: slow or fast, according to:

– Speed at which myosin ATPases split ATP• ATPases affected by pH1

2. Metabolic pathways for ATP synthesis:– Oxidative fibers—use mainly aerobic pathways– Glycolytic fibers—use mainly anaerobic

glycolysis

McArdle et al. Exercise Physiology. 4th ed1

Three types of muscle fibers:

• Slow oxidative fibers: low contraction speed and low force capability (small fibers, slow ATPases, high mitochondria, myoglobin and capillary)

• Fast oxidative fibers: intermediate contraction speed and force capability (intermediate fibers, ATPases, mitochondria, myoglobin and capillary)

• Fast glycolytic fibers: high contraction speed and force capability (large fibers, ATPases, mitochondria, myoglobin and capillary)

McArdle et al. Exercise Physiology. 4th ed

Aerobic (endurance) exercise leads to:

• muscle capillary density

• number of mitochondria

• myoglobin synthesis

• endurance, strength, fatigue resistance

• May convert fast glycolytic fibers into fast oxidative fibers

Effects of Exercise

Grete Waitz & Ingrid Chrisiansenmujeresriot.webcindario.com/Grete_Waitz.htm

Resistance exercise (typically anaerobic) leads to:

• Muscle hypertrophy (due mostly to cross sectional area of each fiber)

• mitochondria

• myofilaments

• glycogen stores

• connective tissue

Effects of Exercise

Arnold + exercise Arnold – exerciseconnect.in.com/arnold-schwarzenegger/photos-26045-368846.html

Copyright © 2010 Pearson Education, Inc.

Muscular Dystrophy

• Group of inherited muscle-destroying diseases

• Muscles enlarge due to fat and connective tissue deposits

• Muscle fibers atrophy

Copyright © 2010 Pearson Education, Inc.

Muscular Dystrophy

Duchenne muscular dystrophy (DMD):

• Most common and severe type

• Inherited, sex-linked, carried by females and expressed in males (1/3500) as lack of dystrophin

• Victims become clumsy and fall frequently; usually die of respiratory failure in their 20s

• No cure, but viral gene therapy or infusion of stem cells with correct dystrophin genes show promise