HSES 375 Exam 2 Excitation-Contraction Coupling

Role of Ca++/EC-Coupling Steps

1. AP propagates on muscle fiber

2. AP travels down t-tubule

3. AP opens Ca++ channels in sarcoplasmic reticulum (SR), which increases conductance for calcium

4. Ca++ release from SR

5. Ca++ pump into SR

6. Ca++ binding to troponin

7. cross-bridge cycle

Role of Ca++ regulation in the process of muscle contraction

At rest, troponin/tropomyosin inhibit S1 binding to actin. When Ca++ is released from the SR and bind to Tn-C, disinhibition occurs. Conformational change occurs in proteins which exposes binding sites in actin. S1 binds to actin, and initiate the cross-bridge cycle

Explain the t-tubule in EC-coupling. Describe how the dihydropyridine and ryanodine receptor proteins link the action potential on the t-tubule to Ca++ release from the SR.

When there is an action potential that propagated down the muscle fiber it continues to the t-tubules. Once the dihydropyridine receptors on the t-tubules sense an AP they activate the ryanodine receptors which open Ca++ channels to release Ca++ into the cytoplasm

What is the function of the sarcoplasmic reticulum in the process of muscle contraction?

SERCA: sarco/endoplasmic reticulum Ca++-ATPase pump; stores and releases calcium

Explain how the information in an action potential on the sarcolemma is translated to muscle force production at the level of the myofibrils.

An action potential is propagated on a muscle fiber, the AP continues to propagate until it reaches a t-tubule where dihydropyridine receptors sense the voltage and transmit the information to the ryanodine receptors. When the ryanodine receptors are stimulated calcium channels open leading to an increase in the conductance for calcium. This results in the flow of Ca++ down the concentration gradient from the sarcoplasmic reticulum to the sarcoplasm. As the calcium moves into the muscle spindle it binds to troponin which moves it out of the way of the active binding sites on actin. Once the binding site is open the S1 unit on the thick chain myosin head can bind to the thin chain actin, producing a cross bridge formation and a power stroke.

Diagram the cross bridge cycle, including the role of ATP in the process.

1. ATP binds to S1, releasing S1 from actin

2. ATP hydrolysis -→ ADP + Pi + energy

3. When Ca++ is bound to troponin, S1 binds to actin and undergoes “powerstroke”- filament slides

4. Pi is released

Discuss how MRIs can be used to examine muscle activation and muscle characteristics?

They measure “relaxation rate” at which the elements return to original alignment, and muscle activity

Discuss how PET scans can be used to examine muscle activation and muscle characteristics?

Measures metabolic activity

Discuss how ultrasounds can be used to examine muscle activation and muscle characteristics?

Examine the frequency and amplitude of the reflected sound waves to create image. Quantifies muscle thickness, muscle CSA, fascicle orientation (pennation angle)