Flashcards in Chapter 11: Muscular System Deck (123)
blocks the active sites of G actin & prevents myosin from binding when muscles are relaxed
small calcium binding protein on each tropomyosin molecule
myosin & actin
tropomyosin & troponin
what happens when calcium is released into the sacroplasm?
Ca binds to troponin which then changes shape and moves tropomyosin from the active site of actin
Z disc to Z disc
functional contractile of muscle fiber
Which myofilament is free floating?
myosin, it is not anchored like actin
dark; overlapping of thick and thin filaments
middle of A band (thick filaments ONLY)= bare zone
middle of H band
light; crosses over 2 sacromeres
provides anchorage for thin filaments and elastic filaments
what myofilaments do muscle fibers contain? (3)
thin, thick, and elastic
which band shortens during contraction
Why do muscle cells shorten?
because their individual sarcomeres shorten (Z disc pulled closer together)
a skeletal muscle never contracts unless stimulated by ______? what happens if this is severed?
a nerve; muscle is paralyzed
somatic motor neurons
nerve cells whose cell bodies are in the brainstem & spinal cord that serve skeletal muscles
what portion of somatic motor fibers lead to the skeletal muscle?
1 nerve fibers= ______ muscle fiber
what does an effective contraction require?
the contraction of several motor units (one nerve fiber + muscle fibers) at once
average motor unit?
200 muscle fibers for each motor unit
small motor units are used for what?
fine degree of control
ex. eye & hand muscles
large motor units are used for what?
more strength than control
point where a nerve fiber meets its target cell
when target cell is a muscle fiber
swollen end of nerve fiber
tiny gap between synaptic knob & muscle sarcolemma
What is the purpose of Schwann cells?
to isolate & insulate all of the NMJ from surrounding tissue fluid
synaptic vesicles undergo ______ releasing ACh into ______
exocytosis; synaptic cleft