How do people walk? Part II

"How do people walk?"

The biological answer.

(I will only discuss the muscle contraction part. I'm not a biologist, and there is a HUGE body of research on the biomechanics of walking; I couldn't do it justice.)

When you decide to pick up your foot and move it forward, the brain stimulates a neuron called an alpha motor neuron. This in turn sends a signal down its axon to stimulate the release of calcium (hey, that's from rocks!), which binds to troponin. This chemical reaction causes protiens on the actin (tropomyosin) to change their configuration slightly, exposing a site on the actin to which the myosin head binds.

So, now the muscle is in a configuration such that a thick filament is bound through the myosin heads to a thin filament. The thin filaments are more dynamic than the thick filaments and with the application of a little energy, the thin filament will be "walked" back toward the thick filament. The energy comes from hydrolysis of ATP, which basically transports chemical energy throughout the body.

All of this happens many, many times just to cause your muscles to contract a little bit. To walk, you do this (with many different muscles) over and over and over again.

So, here's a nice little animation of muscle contraction.