One interaction between the nervous system and the skeletal system involves the calcium stored in the bones. The nervous system requires calcium for the proper transmission of nerve impulses. In which other way do the skeletal and nervous systems interact?

A. Red blood cells are produced in bone marrow.

B. The brain controls the contraction of muscles.

C. Bones protect the brain and spinal cord from injury.

D. The brain helps mount a defense against foreign bodies.