As atp binds to the myosin head at the beginning of a muscle contraction cycle, the myosin head immediately a. detaches from actin. b. initiates binding with actin. c. tightens its bond to actin. d. swivels.

i dunno but  i think its b

the answer that best describes the relative refractory period in the neuron is the resting membrane potential is restored, but concentrations of sodium and potassium are not restored to their original state.

the refractory period is the time during which another stimulus given to the neuron will not lead to a second potential. thus, because na+ channels are inactivated during this time, additional depolarizing stimuli do not lead to new action potentials.  

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