Transcript Muscle Tissue C1

Muscles and Muscle Tissue
Part C1
Prepared by Janice Meeking, W. Rose, and Jarvis Smith.
Figures from Marieb & Hoehn 8th ed.
Portions copyright Pearson Education
Skeletal Muscle Contraction
Cross
Bridge
Cycle
reminder
Actin
ADP
Pi
1
Cross bridge formation
ADP
ADP
Pi
Pi
4
2
Cocking of myosin head
Power (working) stroke
ATP
ATP
3
Cross bridge detachment
Figure 9.12
Muscle Metabolism: Energy for Contraction
ATP 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
(a)
Direct phosphorylation
Coupled reaction of creatine
phosphate (CP) and ADP
Energy source: CP
CP
ADP
Creatine
kinase
Creatine
ATP
Oxygen use: None
Products: 1 ATP per CP, creatine
Duration of energy provision:
15 seconds
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Figure 9.19a
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
(b)
Anaerobic pathway
Glycolysis and lactic acid formation
Energy source: glucose
Glucose (from
glycogen breakdown or
delivered from blood)
Glycolysis
in cytosol
2
O2
ATP
Pyruvic acid
net gain
O2
Released
to blood
Lactic acid
Oxygen use: None
Products: 2 ATP per glucose, lactic acid
Duration of energy provision:
60 seconds, or slightly more
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Figure 9.19b
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
(c)
Aerobic pathway
Aerobic cellular respiration
Energy source: glucose; pyruvic acid;
free fatty acids from adipose tissue;
amino acids from protein catabolism
Glucose (from
glycogen breakdown or
delivered from blood)
O2
Pyruvic acid
Fatty
acids
O2
Aerobic
respiration
Aerobic respiration
in mitochondria
mitochondria
Amino
acids
32
CO2
H2O
ATP
net gain per
glucose
Oxygen use: Required
Products: 32 ATP per glucose, CO2, H2O
Duration of energy provision: Hours
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Figure 9.19c
Anaerobic
Short-duration exercise
ATP stored in
muscles is
used first.
Figure 9.20
ATP is formed
from creatine
Phosphate
and ADP.
Glycogen stored in muscles is broken
down to glucose, which is oxidized to
generate ATP.
Aerobic
Prolonged-duration
exercise
ATP is generated by
breakdown of several
nutrient energy fuels by
aerobic pathway. This
pathway uses oxygen
released from myoglobin
or delivered in the blood
by hemoglobin. When it
ends, the oxygen deficit is
paid back.
Muscle
Fatigue
Muscle
Fatigue
Physiological 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 Deficit
During 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
Large
number of
muscle
fibers
activated
Large
muscle
fibers
High
frequency of
stimulation
Muscle and
sarcomere
stretched to
slightly over 100%
of resting length
Contractile force
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Figure 9.21
Length-tension relationship in skeletal muscle
Observable in whole muscle
Cellular basis:
• At short muscle length, force  because thin filaments overlap each other
• At long muscle length, force  because # of potential crossbridges that can
form 
70%
Sarcomeres
greatly shortened
100%
Sarcomeres at
resting length
170%
Sarcomeres excessively
stretched
Optimal sarcomere
operating length
(80%–120% of
resting length)
Figure 9.22
Type of Muscle Fibers
Classified 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
Effects of Exercise
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
Grete Waitz & Ingrid Chrisiansen
mujeresriot.webcindario.com/Grete_Waitz.htm
Effects of Exercise
Resistance exercise (typically
anaerobic) leads to:
• Muscle hypertrophy (due
mostly to  cross sectional
area of each fiber)
•  mitochondria
•  myofilaments
•  glycogen stores
•  connective tissue
Arnold + exercise
Arnold – exercise
connect.in.com/arnold-schwarzenegger/photos-26045-368846.html
Muscular Dystrophy
• Group of inherited muscle-destroying
diseases
• Muscles enlarge due to fat and connective
tissue deposits
• Muscle fibers atrophy
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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
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