Question

Action potentials are usually propagated in only one direction along an axon because

• A. nodes of Ranvier only conduct in one direction
• B. brief refractory period prevents a depolarization from occurring in the direction from which the impulse came
• C. axon hillock has a higher membrane potential than the tips of the telodendria
• D. both sodium and potassium voltage-sensitive gates open in one direction

Answer 1

Answer: (B)

brief refractory period prevents a depolarization from occurring in the direction from which the impulse came

• When ATP binds to myosin, it separates from the actin of the myofibril, which causes a contraction.
  
• The muscle contraction cycle is triggered by calcium ions binding to the protein complex troponin, exposing the active-binding sites on the actin.
• ATP then binds to myosin, moving the myosin to its high-energy state, releasing the myosin head from the actin active site.
• Muscle cannot always respond to the stimulus due to fatigue and production of lactic acid this period is called refractory period.

So, the correct option is 'brief refractory period prevents a depolarization from occurring in the direction from which the impulse came'.