Hard

Question 1

Describe the steps in the excitation-contraction coupling process.

Answer 1

1. ACh released and binds to receptors on the sarcolemma.
2. Action potential travels along the T-tubules.
3. Sarcoplasmic reticulum releases calcium ions.
4. Calcium binds to troponin, exposing active sites on actin.
5. Contraction begins.

Question 2

What happens to the sarcolemma and T-tubules during muscle relaxation?

Answer 2

They repolarize, and voltage-gated calcium channels close.

Question 3

What does the myosin head do after the power stroke?

Answer 3

It detaches, re-energizes (reactivates), and reattaches to actin.

Question 4

Why is ATP required for both muscle contraction and relaxation?

Answer 4

It powers the myosin heads for contraction and helps detach them for relaxation.

Question 5

How does the sarcoplasmic reticulum regulate calcium availability?

Answer 5

It releases calcium ions during contraction and reabsorbs them during relaxation.

Question 6

Explain the importance of troponin in muscle contraction.

Answer 6

Troponin binds calcium, shifting tropomyosin to expose active sites, enabling myosin-actin interaction.