When do muscles contract?
Monday, January 4th, 2010 at
10:47 am
Which is the best answer, sorry if this looks like homework im tryin to study for a test 
thnx in advance
which one:
a.actin and myosin slide over eachother
b.cross-bridges form between Z-discs and connect them
c.tendons pull on muscle fibers causing them to contract
d.bundles of muscles fibers push on two adjacent bones
(I think its c)
The answer is a – actin and myosin slide over each other.
In muscle cells, myosin actually pulls actin past itself. This occurs in layers, so you get groups of contractile units (called sarcomeres) all contracting at once. A bunch of these microscopic contractions causes one big muscle contraction.
b is not the answer because cross-bridges form between actin and myosin, not between Z-discs.
c is not the answer because tendons simply anchor muscle to bone. They do not contract. They are actually made of connective tissue, not muscle tissue.
d is not the answer because that really makes no sense. Muscle fibers never push – they always pull. Muscle groups are also oriented on the opposite sides of structures so that they can pull things back and forth (e.g. biceps and triceps flexing your arm and extending it). So yeah, no pushing, ever.
Hope that helps!