Excitation-contraction coupling: (started by an _____ _____ along the _____ _____ of a _____)
Releases into the _____ to start _____-_____ _____.
Excitation-contraction coupling: (started by an Action potential along the plasma membrane of a myofibre)
Releases into the cytoplasm to start cross-bridge cycling.
Transverse tubule or T-tubule
_____ that carry the _____ _____ from the outside (_____ _____) of the muscle cell to the calcium stores (_____ _____ in the _____ _____ ).
This allows the signal to get close to the _____ _____ so it can _____ the _____.
T-tubule membrane has _____-_____ _____ _____ (_____) that are connected to _____ _____ on the _____ _____.
When an action potential travels down the _____ DHPR activates the _____ _____ to release _____ to _____ to all of the _____ _____.
Transverse tubule or T-tubule
Pathways that carry the action potential from the outside (plasma membrane) of the muscle cell to the calcium stores (lateral sacs in the sarcoplasmic reticulum ).
This allows the signal to get close to the sarcoplasmic reticulum so it can release the calcium.
T-tubule membrane has voltage-sensitive Dihydropyridine receptors (DHPR) that are connected to ryanodine receptors on the sarcoplasmic reticulum.
When an action potential travels down the T-tubule, DHPR activates the ryanodine receptor to release calcium to diffuse to all of the troponin sites.
Calcium Release from the Sarcoplasmic Reticulum:
At rest, the calcium level in the muscle _____ is very _____
When an _____ _____ occurs, calcium is quickly released from the _____ _____ into the _____.
The sarcoplasmic reticulum is like the _____ _____; it _____ around each _____.
At the ends of the sarcoplasmic reticulum are _____ _____, which _____ _____.
A _____ + _____ _____ _____ = a triad (essential for _____–_____ _____).
Calcium Release from the Sarcoplasmic Reticulum:
At rest, the calcium level in the muscle cytoplasm is very low
When an action potential occurs, calcium is quickly released from the sarcoplasmic reticulum (SR) into the cytoplasm.
The sarcoplasmic reticulum is like the endoplasmic reticulum; it wraps around each myofibril.
At the ends of the sarcoplasmic reticulum are lateral sacs, which store calcium.
A T-tubule + 2 lateral sacs = a triad (essential for excitation–contraction coupling).
Steps of Muscle Contraction
_____ _____ travels down the _____, opening _____ _____ in the _____ _____
_____ floods into the _____ and binds to _____ _____ _____, changing its _____,
The _____-_____ complex “pulls” _____ off the _____-binding site of _____,
_____ binds to _____ = _____-_____ cycle = muscle _____.
_____ is pumped back into the _____ _____ by _____ (_____ _____ _____ _____ _____). _____ blocks the _____ again, which _____ the muscle.
Steps of Muscle Contraction
Action potential travels down the T-tubule, opening calcium channels in the sarcoplasmic reticulum
Calcium floods into the cytoplasm and binds to troponin subunit C, changing its shape,
The calcium-troponin complex “pulls” tropomyosin off the myosin-binding site of actin,
Myosin binds to actin = cross-bridge cycle = muscle contracts.
Calcium is pumped back into the sarcoplasmic reticulum by SERCA (Sarco Endoplasmic Reticulum Calcium ATPase). Tropomyosin blocks the sites again, which relaxes the muscle.
The Role of ATP:
Myosin heads break down _____ into _____ + _____, which _____ the head.
When calcium moves the _____ to reveal the _____ _____ _____, the myosin head _____ and releases _____ + _____, causing a _____ _____.
This restarts as _____ attaches to the _____, unattaching the _____, and _____ the _____ to _____ the head.
If there is no fresh _____, then actin and myosin remain _____. (_____ _____)
The Role of ATP:
Myosin heads break down ATP into ADP + Pi, which cocks the head.
When calcium moves the tropomyosin to reveal the actin binding site, the myosin head attaches and releases ADP + Pi, causing a power stroke.
This restarts as ATP attaches to the head, unattaching the actin, and hydrolyzes the ATP to recock the head.
If there is no fresh ATP, then actin and myosin remain attached. (Rigor Mortis)
