Cross references: Human Neuroanatomy
"Muscles are predominantly powered by the oxidation of fats and carbohydrates, but anaerobic chemical reactions are also used, particularly by fast twitch fibers. These chemical reactions produce adenosine triphosphate (ATP) molecules which are used to power the movement of the myosin heads."
"Skeletal (voluntary) muscle is further divided into two broad types: slow twitch and fast twitch:
"Various exercises require a predominance of certain muscle fiber utilization over another. Aerobic exercise
involves long, low levels of exertion in which the muscles are used at
well below their maximal contraction strength for long periods of time
(the most classic example being the marathon).
Aerobic events, which rely primarily on the aerobic (with oxygen)
system, use a higher percentage of Type I (or slow-twitch) muscle
fibers, consume a mixture of fat, protein and carbohydrates for energy,
consume large amounts of oxygen and produce little lactic acid. Anaerobic exercise
involves short bursts of higher intensity contractions at a much
greater percentage of their maximum contraction strength. Examples of
anaerobic exercise include sprinting and weight lifting.
The anaerobic energy delivery system uses predominantly Type II or
fast-twitch muscle fibers, relies mainly on ATP or glucose for fuel,
consumes relatively little oxygen, protein and fat, produces large
amounts of lactic acid and can not be sustained for as long a period as
aerobic exercise. Many exercises are partially aerobic and partially
anaerobic; for example, soccer involves a combination of both.
- Type I, slow twitch, or "red" muscle, is dense with capillaries and is rich in mitochondria and myoglobin, giving the muscle tissue its characteristic red color. It can carry more oxygen and sustain aerobic activity using fats or carbohydrates as fuel. Slow twitch fibers contract for long periods of time but with little force.
- Type II, fast twitch muscle, has three major subtypes (IIa, IIx, and IIb) that vary in both contractile speed and force generated. Fast twitch fibers contract quickly and powerfully but fatigue very rapidly, sustaining only short, anaerobic
bursts of activity before muscle contraction becomes painful. They
contribute most to muscle strength and have greater potential for
increase in mass. Type IIb is anaerobic, glycolytic,
"white" muscle that is least dense in mitochondria and myoglobin. In
small animals (e.g., rodents) this is the major fast muscle type,
explaining the pale color of their flesh."
"Simplified schema of basic nervous system function. Signals are picked
up by sensory receptors and sent to the spinal cord and brain via the
afferent leg of the peripheral nervous system, whereupon processing
occurs that results in signals sent back to the spinal cord and then out
to motor neurons via the efferent leg."
UAMS Department of Neurobiology and Developmental Sciences - Muscle Tables (Goog)
This is a huge data base which contains far more information than I need. However, it does specify the innervation of every muscle. Unfortunately, at first glance, I don't see any differentiation between slow and fast twitch.
Muscle Groups According to Innervation (Goog)
As above, lots of info but no differentiation between slow and fast twitch. Perhaps both are innervated by the same nerve.