The heads of myosin molecules contact the actin filaments when a muscle is relaxed. The heads of myosin molecules contact the actin filaments when a muscle is relaxed. True False

The above statement is "false".

Explanation:

The following events take place during contraction-relaxation of a muscle:

•Action potential in T tubule activates voltage-sensitive receptors,which in turn trigger Ca ions release from terminal cisternae of sacroplasmic reticulum(SR) into cystol.

•Ca ions bind to troponin;troponin changes shape,removing the blocking action of tropomyosin;actin active sites is exposed.

•CONTRACTION; myosin heads alternatively attach to actin and detach,pulling the actin filaments toward the center of the sarcomere;using ATP in this process.

•removal of Ca ions by active transport into the SR after the action potential ends.

•RELAXATION occurs.Actin and myosin return back to its unbound state.

the answers are a and c

stimulus is a change in the environment that causes an organism to react. the response is the reaction to the stimulus. some examples of stimuli for zebras are drought, to many predators, and bad feeding grounds such as dead grass or plants. zebras respond to stimuli just like all other living organisms