protein filaments is what makes meat such a
rich nutritional source of protein. An
electrical impulse from the nerve associated
with the muscle causes the protein filaments
to slide past each other, and then lock together
by means of cross-bridging, or forming bonds
with each other. The change in relative
position of the filaments shortens the muscle
cell as a whole, and the cross bridges maintain
the contraction by holding the filaments in
place.
Portable Energy: Fat Like any machine, the
muscle protein machine requires energy to
run. Almost as important to animals as their
propulsive machinery is an energy supply
compact enough that it doesn’t weigh them
down and impede their movement. It turns out
that fat packs twice as many calories into a
given weight as carbohydrates do. This is why
mobile animals store up energy almost
exclusively in fat, and unlike stationary