Thyrotoxic myopathy (TM) is a neuromuscular disorder caused by overproduction of the thyroid hormone thyroxine. One of the main symptoms of TM is muscle fatigue. [Figure 6.1] outlines the effects of overproduction of thyroxine on striated muscle.

1. (a)(i)The concentration of thyroxine in the blood usually fluctuates around a set point. Name the mechanism that keeps the concentration of thyroxine in the blood close to its set point.[1]
2. (a)(ii)Name the part of the striated muscle fibre that releases Ca2+.[1]
3. (a)(iii)Describe the role of Ca2+, troponin and tropomyosin in the contraction of striated muscle.[4]
4. (a)(iv)Cyclic AMP (cAMP) is also involved in the response of liver cells to glucagon. Describe the role of cAMP in the response of liver cells to glucagon.[2]
5. (b)An increase in the concentration of thyroxine in the blood can lead to a condition called insulin resistance (IR). IR decreases the sensitivity to insulin of target cells, such as muscle and liver cells. Suggest how decreased sensitivity to insulin affects target cells.[3]

This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.