16 Questions
What is the energy configuration of the myosin head when it is bound to ATP?
Low energy configuration
What is the result of calcium binding to troponin?
The actin binding site is opened
What is the role of SERCA1a in excitation-contraction coupling?
To pump calcium ions back into the sarcoplasmic reticulum
What is the outcome of the myosin head cleaving ATP into ADP + P?
The myosin head is in a high energy configuration
Which term correctly describes the overall process which transforms a nerve impulse into a muscle contraction?
Excitation-contraction coupling
What happens to ADP after the power stroke?
ADP detaches from the myosin head
What is the term for when the myosin head moves from a high energy state to a low energy state, causing actin to be pulled closer to the M-line?
Power stroke
What is the term for when the myosin heads bend towards the center of the sarcomere?
Micro-contraction
What is the primary function of RyRs in excitation-contraction coupling?
To release calcium ions from the sarcoplasmic reticulum
What is the role of DHPR in excitation-contraction coupling?
To sense voltage changes and trigger calcium release
What is the term for when myosin is still attached to actin?
Rigor state
What is the outcome of the action potential causing a conformational change in the DHPR?
The RyRs calcium channels open
What is the name of the theory that describes actin-myosin binding for muscle contractions?
Walk along theory
Which is the correct order of events, in regards to excitation-contraction coupling?
AP scatters across sarcolemma, AP travels through T-Tubule, DHPR conformational change, RyRs calcium release, Muscle contraction
What is the primary function of the sarcoplasmic reticulum?
To store calcium ions
Which is the correct order of events, in regards to the "walk along theory"?
Cross bridge, power stroke, micro-contraction, rigor state
Study Notes
Excitation-Contraction Coupling: General Info
- Excitation-contraction coupling transforms a nerve impulse into a muscle contraction.
- T-Tubules are associated with the sarcoplasmic reticulum, which stores calcium.
- The sarcoplasmic reticulum consists of terminal cisternae and longitudinal tubules surrounding myofibrils.
- DHPR (dihydropyridine receptors) are voltage-sensing proteins mechanically coupled to RyRs (ryanodine receptors).
- RyRs are calcium channels on the sarcoplasmic reticulum membrane.
- Muscle contraction continues as long as calcium ion concentration remains high.
- SERCA1a (sarcoplasmic reticulum calcium ATPase) is a calcium pump continuously active in the sarcoplasmic reticulum walls.
Excitation-Contraction Coupling: Steps
- Action potential travels from the motor end plate to the sarcolemma.
- The action potential depolarizes the T-Tubule and penetrates the cell.
- DHPR conformational change triggers RyRs calcium channels to open.
- Calcium rapidly diffuses out of the sarcoplasmic reticulum.
- Muscle contraction is initiated.
- SERCA1a removes calcium ions from the myofibrillar fluid after contraction.
Walk Along Theory (of muscle contractions): General Info
- Myosin head bound to ATP is in a low energy configuration.
- Myosin head cleaves ATP into ADP + P, forming a "cocked position" in a high energy configuration.
Walk Along Theory (of muscle contractions): Steps
- Myosin head binds to ATP, entering a low energy configuration.
- Myosin head cleaves ATP, cocking into a high energy configuration.
- Calcium binds to troponin, opening the actin binding site.
- Myosin head binds to actin, forming the cross bridge.
- Cross bridging triggers Myosin to release the phosphate group, leaving ADP attached.
- Power stroke occurs, moving myosin from high to low energy state, causing actin to pull closer to the M-line (micro-contraction).
- ADP detaches from myosin, leaving it in a rigor state.
- ATP binds to the myosin head group.
- Myosin detaches from actin.
Learn about the process of transforming nerve impulses into muscle contractions, including the role of T-tubules and sarcoplasmic reticulum in calcium storage.
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