Question

the ion necessary for cross - bridging is: iron. sodium. potassium. calcium. question 2 1 pts three phases of the twitch contraction are the latent period, contraction phase, and relaxation phase. latent period, contraction phase, and stimulation phase. latent period, stimulation phase, and excitement phase. stimulation phase, contraction phase, and relaxation phase. question 3 1 p physiological muscle fatigue may be caused by: a relative lack of atp. high levels of lactate. failure of the sodium - potassium pumps. all of the above.

Explanation:

• For the first question, calcium ions bind to troponin, which causes a conformational change allowing cross - bridging in muscle contraction.
• For the second question, a twitch contraction has a latent period (time between stimulus and start of contraction), a contraction phase (muscle shortens), and a relaxation phase (muscle returns to resting length).
• For the third question, a lack of ATP reduces energy for muscle contraction, high lactate levels can lower pH and affect muscle function, and failure of sodium - potassium pumps can disrupt ion gradients and muscle function.

Answer:

• Question 1: calcium.
• Question 2: latent period, contraction phase, and relaxation phase.
• Question 3: all of the above.