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.
Disuse can cause muscle wasting {atrophy}|.
Belgian Blue and Piedmontese cattle {double-muscled} have myostatin that binds but does not signal.
Low ATP and glycogen can cause inability to contract {muscle fatigue}| {fatigue, muscle}.
Perhaps, lactic acid accumulates while using muscles {oxygen debt}|. However, this idea is not correct.
Muscles have moving ends {insertion, muscle}.
Muscles can have sustained muscle contraction {tetanus, muscle}|.
Muscles always have slight contraction {tonus}|.
Nerve signals travel through muscles {latent period}, followed by contraction and then relaxation.
Muscle cells uptake glycogen and oxygen to recover from contraction {recovery time}.
After contraction, muscles are not responsive {refractory period, muscle}.
Body has muscles {musculature}|.
Muscles are across abdomen {midriff}|.
Muscles across abdomen can become weak and sag {paunch}.
muscles or tendons {sinew}|.
down abdomen middle {abdominal muscle}.
back {back muscle}.
upper-arm front {bicep}|.
seat {buttock}|.
lower-leg back {calf muscle}|.
over shoulder {deltoid}|.
seat {duff, muscle}.
face {facial muscle}.
lower arm {forearm muscle}.
lower-leg back {gastrocnemius}|.
over rear end {gluteus maximus}|.
upper-leg back {hamstring}|.
neck {neck muscle}.
over breast {pectoral}|.
tail muscle {prehensile}|.
between ribs {rib muscle}.
upper-leg front {thigh}|.
neck back {trapezius}|.
upper-arm back {tricep}|.
twist appendage {rotator}.
pull away from spine {abductor}.
pull toward spine {adductor}.
raise {elevator muscle}.
lower {depressor muscle}.
close {sphincter}|.
open {dilator}.
bend {flexor muscle}.
extend {extensor muscle}.
pull up and forward {pronator}.
pull down and backward {supinator}.
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Date Modified: 2022.0225