Body systems {muscle}| can have 600 muscles and be 40% of human body weight.
types
Muscles are skeletal, cardiac, or smooth muscles.
types: opposites
Muscles have opposing muscles: flexor-extensor, abductor-adductor, elevator-depressor, pronator-supinator, and sphincter-dilator.
parts
Muscles have a fixed end {origin, muscle}, middle {belly, muscle}, and moving end {insertion, muscle end}.
parts: fiber types
Skeletal muscles have two fiber types. Slow fibers do not fatigue, are slower and weaker, have calcineurin, and use fat for periodic or sustained movements. Fast fibers fatigue, are stronger and faster, have 2B myosin and/or ACTN3 protein, and use sugar for rapid movements.
contraction
Muscles can shorten by up to one-third. Nerve stimuli activate muscles.
metabolism: PPAR-delta protein
PPAR-delta proteins regulate fat-catabolism genes and increase metabolism. PPAR-delta proteins make muscles with more slow-twitch fibers.
metabolism: lactic acid
Muscles make lactic acid from glucose or glycogen. Uptake transporter molecules carry lactate into mitochondria. This mechanism becomes more efficient with more endurance exercise.
metabolism: dystrophion
Dystrophin protein transfers energy to prevent muscle-fiber damage. Duchenne muscular dystrophy has no dystrophin.
metabolism: satellite cells
In response to insulin-like growth factor I, satellite cells divide and provide new nuclei to muscle cells. Myostatin decreases satellite-cell division.
Biological Sciences>Zoology>Organ>Muscle
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Date Modified: 2022.0224