Muscle Contraction and Locomotion

Free Response

How would muscle contractions be affected if ATP was completely depleted in a muscle fiber?


Because ATP is required for myosin to release from actin, muscles would remain rigidly contracted until more ATP was available for the myosin cross-bridge release. This is why dead vertebrates undergo rigor mortis.

What factors contribute to the amount of tension produced in an individual muscle fiber?


The cross-sectional area, the length of the muscle fiber at rest, and the frequency of neural stimulation.

What effect will low blood calcium have on neurons? What effect will low blood calcium have on skeletal muscles?


Neurons will not be able to release neurotransmitter without calcium. Skeletal muscles have calcium stored and don’t need any from the outside.

Skeletal muscles can only produce a mechanical force as they are contracted, but a leg flexes and extends while walking. How can muscles perform this task?


Muscles are able to drive locomotion (and other tasks involving opposing motions) because they are paired. When walking, the hamstring muscle contracts first, causing the leg to flex around the knee joint. The quadriceps muscle then contracts (while the hamstring relaxes and extends) to straighten the leg as the foot returns to the ground.