Samples of Muscle Tissue

Striated - 400 X  (skeletal muscle) 211.05 Kb

Striated - 1000 X (skeletal) 204.17 Kb

Smooth - 1000 X (viscera of body) 240.31 Kb

Cardiac - 400 X (heart muscle) 232.82 Kb

Cardiac - 1000 X (heart muscle 208.08 K

   Striated Muscle has three major variations based on contractile characteristics.  All forms require excitation from a neuron at the motor end plate.  The fibers can be quite long with multiple nuclei maintaining these potentially elongate cells.  Powerful muscle with fast contraction speed is not particularly aerobic; contractile units that show up as striations are substituted for mitochondria.  Commonly called "white fibers", they depend on cellular energy stores rather than the ongoing manufacture of contractile energy sources The high use of ATP quickly tires this muscle form but rapid, forceful, motion is gained.
    Slower contracting forms with lots of oxygen storing pigments are important in many ways calling for extended delivery of force.  Commonly called "Red Fibers" after the pigment myoglobin, rich blood supplies, and mitochondria present in these cells.  Finally, an intermediate form - the fast oxidative fibers, are intermediate between the two extremes.  This form responds well to training.

    Smooth Muscle is small and tapered on the ends.  Often found in thin layers surrounding hollow, tubular, viscera.  These have the ability to contract slowly and for extended periods of time, and over a very wide range of cell lengths.  Some forms are self-exciting and can spread excitation from cell to cell in a direct fashion.  Other forms require neural stimulation to contract.

    Cardiac Muscle is a specialized form of striated muscle.  The cells are very small and divided.  Excitation can spread from cell to cell and any cell can potentially become self-exciting, if left alone long enough.  Cells have a very large proportion of their volume devoted to mitochondria.  This makes the contractions weaker than comparable amounts of skeletal muscle, but far more aerobic.  In fact, cardiac cells can be up to 24% mitochondria whereas the skeletal muscle cells - even aerobic ones - are typically no more than 4% by volume.