If you're seeing this message, it means we're having trouble loading external resources on our website.

If you're behind a web filter, please make sure that the domains *.kastatic.org and *.kasandbox.org are unblocked.

Main content

Unit: Advanced muscular-skeletal system physiology

Muscles never sleep (literally). If you have ever taken a breath, you have benefited from the work of the diaphragm, which contracts to create an area of low pressure within your thoracic cavity, allowing air in. How exactly are some weightlifters able to support 717 lbs without breaking anything more than a little sweat? Fun fact: the largest muscle in your body is the gluteus maximus (that’s your butt) while the smallest skeletal muscle is the stapedius (it stabilizes the smallest bone, the stapes, which is in your middle ear).

About this unit

Learn how our muscles work from the cellular level to executing a kick or a dance move. Discover how our brain tells muscle to contract, and how that helps us respond to changes in temperature or even a lion chasing us