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the liver, where it is metabolized to CO2 and water. Without dystrophin there is no structural link between
the muscle fibers and the extracellular matrix. Calcium
penetrates the plasma membrane (sarcolemma)
of the muscle cells and damages them, eventually
destroying the muscle cells (fibers). The Sliding Filament Theory (page 59)
1. Anatomy and Physiology 2. 3. (a) Myosin: Has a moveable head that provides a
power stroke when activated.
(b) Actin: Two protein molecules twisted in a double
helix shape that form the thin filament of a
(c) Calcium ions: Bind to the blocking molecules,
causing them to move and expose the myosin
(d) Troponin-tropomyosin: Bind to actin molecule in
a way that prevents myosin head from forming a
(e) ATP: Supplies energy for flexing of the myosin
head (power stroke).
(a) By changing the frequency of stimulation, so
that fibers receive impulses at a greater rate
(b) By changing the number and size of motor units
recruited (a few motor units = a small contraction,
maximum number of motor units = maximum
(a) Calcium ions and ATP.
(b) Calcium ions are released from a store in the
sarcoplasmic reticulum when an action potential
arrives. ATP is present in the muscle fiber and is
hydrolyzed by ATPase enzymes on the myosin. Muscle Tone and Posture (page 63)
1. (a) Muscle tone is the continuous and passive partial
contraction of muscles giving a firm appearance.
(b) At any one time, a few fibers in a muscle are
always contracting involuntarily (different fibers at
different times). 2. (a) The muscle spindle organ monitors the
degree of stretch (contraction) in a muscle and
provides information to bring about adjustment of
(b) Intrafusal fibers parallel to extrafusal fibers:
When the muscle relaxes, it lengthens and the
muscle spindle is stretched. The stretching results
in a reflex adjustment of contraction (usually to
Sensory neurons in non-contractile region:
When non-contractile portion is stretched (it
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This document was uploaded on 01/28/2014.
- Winter '13