Answer:
Explanation:
This is because once a Voltage Gated Sodium Channels closes up after depolarization, they can not be reopened.The transmission of action potential is such a way that they are propagated one after the other in a forward direction, and never backwards. Thus once a sodium channel depolarizes,it closes up, to under go a shot rest.No matter the strength of the next stimulus it will not open. Then the channel ahead of it opens to depolarise to conduct action potential, this again after shut opening closes up for the channel ahead to open. This short period of rest when the sodium channels closes up is called refractive period. However after sometime of rest the rested sodium channels open, from the inactivated stage to conduct action potential.
C i think
let me know if i was right :)
Answer: The calcium ion binds to troponin, and this slides the tropomyosin rods away from the binding sites.
Explanation:
Contraction and relaxation of muscle cells brings about movements of the body. The contractile myofilament called sarcomeres are bounded at each end by a dense stripe called the Z - line, to which the myosin fibres are attached, and lying in the middle of the sarcomere are the actin filaments, overlapping with the myosin.
When action potential spreads from the nerve along the sarcolemma (muscle cell membrane), it penetrates deep into the muscle cell through the sarcoplasm (cytoplasm of muscle cell), and releases CALCIUM from the intracellular stores.CALCIUM triggers the binding of myosin to the actin filament next to it forming CROSS BRIDGES.
For this to occur, ACTIN BINDING SITE has to be made available. TROPOMYOSIN is a protein that winds around the chains of the actin filament and covers the myosin-binding sites to prevent actin from binding to myosin. The first step in the process of contraction is for calcium ions to bind to troponin so that tropomyosin can slide away from the binding sites on the actin strands.
