IPHY 3430 3-31-11
Skeletal Muscle Metabolism
Use of ATP
1. Provide power stroke of myosin
2. Binding causes detachment of cross bridge on
myosin and actin cross bridge binding site
3. Active transport of Ca++ into vesicles
4. Action potential of muscle membrane
Skeletal Muscle Metabolism
Temporal variation in supply of ATP as exercise
starts
1. Creatine phosphate
2. Aerobic ATP production
myoglobin donates O2
3. Glycolysis with lactic acid formation
Fatigue
Muscle fatigue
1) depletion of glycogen (more low intensity)
2) accumulation of lactic acid
3) conduction failure (K+ buildup)
4) Inhibition of cross-bridge cycling
Central fatigue
1) brain no longer adequately activates motor
neurons
Muscle Fiber Types
Slow oxidative Fast oxidative Fast glycolytic
myosinATPase low
contrct. speed slow
fatigue resist. high
oxidative phos.
activity
high
glycolytic activ. low
mitochondria
high
myoglobin
high
glycogen content low
blood supply
high
high
fast
intermed.
high
fast
Low
high
intermed
high
high
intermed.
high
low
high
low
low
High
low
Muscle fiber types of world-class athletes
Event
% slow twitch
long dist.
64.4
800 m
51.9
100 m
24.0
shotput
37.7
couch pot. 52.6
glycolytic oxidative
764
16.6
868
14.8
1287
12.9
1058
4.3
822
7.4
Other muscle fiber data
Animal
high oxidative
Quarter horse
7%
heavy hunter
31%
greyhound
mongrel
3%
31%
hummingbird
turkey
100%
1%
low oxidative
93%
69%
97%
69%
0
99%
Training Effects
Aerobic
 vascularity, FA oxidative capacity, mitochondria,
triglyceride storage,
 lactate dehydrogenase activity
Strength
 diameter of fast, glycolytic fibers, myosin and
actin, and in number of cells
5 mo weight training --> 11%  circumf., 28%  in
strength
5 mo immobiliz.-->  5% circumf., 35%  strength
Smooth Muscle differs from skeletal
actin, myosin and intermediate filaments that
serve as cytoskeleton
can be stretched very much and still contract
actin lacks troponin, has tropomyosin
myosin must be phosphorylated
arrangement of actin and myosin differs
slow contraction, can remain contracted for very
long periods of time
most cells myogenic, but also some can be
stimulated by PNS
Skeletal, cardiac and smooth
all use ATP
all have actin and myosin
Ca++ plays some role in contraction initiation
but...
Skeletal
innervation motor
contr. initiat. neurogenic
Ca++ source sarcopls. ret.
T tubules
yes
Cardiac
Smooth
PNS, SNS
myogenic
xtracell.
yes
PNS
both
xtracell.
no