Characteristics of Muscle
Fibers: Type I and Type II fibers
Type I fibers:
- Smaller.
- Produce less force than type II fibers.
- Much more energy efficient.
- Less myosin ATPase
- Slow myosin molecules.
- Underdeveloped Sarcoplasmic Reticulum
Fewer Voltage
Dependent Gates - that means the SR has fewer doors for calcium to pass
through,
and therefore it
takes longer for calcium to hit a threshold level in the sarcoplasm.
- Troponin has a lower affinity for calcium.
- Innervated by slower alpha motor neurons.
The speed that an
alpha motor neuron can transmit a signal is determined by the thickness
of the
axon. The
thicker the axon, the faster the speed of transmission. So, slower
alpha motor neurons
have thinner
axons.
- Better capacity for energy production.
Larger
mitochondria, more mitochondria, and more blood vessels (important for
oxidative work).
- More geared towards oxidative work, although it also performs
nonoxidative work.
Type II fibers:
- Rapid response, due to a higher
concentration of myosin ATPase and fast myosin molecules.
- High force production.
- Fast rate of fatigue.
- Hypertrophy (increase in size / cross-sectional area) moreso
than Type I fibers.
- Several types. Type IIa and IIb are the types we know the
most about.
- Type IIa fibers may work both oxidatively and nonoxidatively.
- Type IIb may work only by nonoxidative metabolism.
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