muscle contraction relaxation notes

Contraction Sequence!!!

1. After the NMJ is depolarized, and simultaneously to its repolarization, a WAVE of depolarization spreads equally across the surface of sarcolemma in all directions.

terminal cisternae

Terminal cisternae of sarcoplasmic reticulum

(the “blue” tubes)

Transverse tubules (the “purple” tubes)

Myofibril

Sarcolemma

2. The depolarization wave (“signal”) then follows the surface of the transverse tubules which brings the “signal” (depolarization wave) deep inside the muscle fiber and parallel to the terminal cisternae of the sarcoplasmic reticulum.

T-tubule opening

Another look at how the “signal” spreads. Zoom in on box

Depolarization wave spreads across the sarcolemma away from NMJ

Depolarization wave spreads across the sarcolemma away from NMJ

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3. After the “signal” has completely depolarized the sarcolemma, it enters the sarcoplasmic reticulum.

The sarcoplasmic reticulum does not have an “internal” environment and an “external” environment (like the sarcolemma), since it is contained completely within the muscle fiber.

4. The sarcoplasmic reticulum does contain Ca+2 ions (calcium ions) however, and when the depolarization wave hits the sarcoplasmic reticulum it releases the Ca+2 ions into the sarcoplasm. Thus, there is a continuation of moving charged particles!

Na+Na+ Na+

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Ca+2

Ca+2

Ca+2

Ca+2

Ca+2

Ca+2

Na+Na+ Na+

Na+ Na+ Na+

K+ K+

K+K+

K+K+

K+ K+ K+ K+ K+ K+

K+K+

K+K+

K+K+

K+K+

K+K+

K+K+

K+K+

K+K+

K+K+

K+K+

K+K+

K+K+

K+K+

K+K+ K+

K+

K+K+

K+K+

K+K+

K+K+

K+K+

K+K+

Na+Na+ Na+

Na+Na+ Na+

Na+

Na+ Na+

Na+Na+ Na+

Na+Na+Na+

Na+ Na+ Na+

Na+Na+Na+

Na+Na+Na+

Na+

Na+ Na+

Na+Na+Na+

Na+Na+Na+

Na+

Na+ Na+ Na+

Na+ Na+

K+K+

K+K+

Na+ Na+ Na+Na+ Na+ Na+

Na+ Na+ Na+

Na+ Na+ Na+

Na+ Na+ Na+

Na+ Na+ Na+

Na+ Na+ Na+Na+ Na+ Na+

Na+ Na+ Na+

Na+ Na+ Na+

Na+ Na+ Na+

Na+ Na+ Na+

Na+ Na+ Na+

Na+Na+ Na+

Ca+2

Ca+2

Ca+2

Ca+2 Ca+2

Ca+2 Ca+2 Ca+2

Ca+2 Ca+2 Ca+2

Ca+2

Ca+2

Ca+2

Ca+2

Ca+2

Ca+2

Ca+2

Ca+2

Ca+2Ca+2Ca+2Ca+2

Ca+2

Ca+2Ca+2Ca+2

Ca+2Ca+2

Ca+2

Ca+2

Ca+2

Ca+2

Ca+2

Ca+2

Ca+2

Na+Na+ Na+

Na+ Na+ Na+

K+ K+

K+K+

K+K+

K+ K+ K+ K+ K+ K+

K+K+

K+K+

K+K+

K+K+

K+K+

K+K+

K+K+

K+K+

K+K+

K+K+

K+K+

K+K+

K+K+

K+K+ K+

K+

K+K+

K+K+

K+K+

K+K+

K+K+

K+K+

Na+Na+ Na+

Na+Na+ Na+

Na+

Na+ Na+

Na+Na+ Na+

Na+Na+Na+

Na+ Na+ Na+

Na+Na+Na+

Na+Na+Na+

Na+

Na+ Na+

Na+Na+Na+

Na+Na+Na+

Na+

Na+ Na+ Na+

Na+ Na+

K+K+

K+K+

Na+ Na+ Na+Na+ Na+ Na+

Na+ Na+ Na+

Na+ Na+ Na+

Na+ Na+ Na+

Na+ Na+ Na+

Na+ Na+ Na+Na+ Na+ Na+

Na+ Na+ Na+

Na+ Na+ Na+

Na+ Na+ Na+

Na+ Na+ Na+

Na+ Na+ Na+

Na+Na+ Na+

Ca+2

Ca+2

Ca+2

Ca+2 Ca+2

Ca+2 Ca+2 Ca+2

Ca+2 Ca+2 Ca+2

Ca+2

Ca+2

Ca+2

Ca+2

Ca+2

Ca+2

Ca+2

Ca+2

Ca+2Ca+2Ca+2Ca+2

Ca+2

Ca+2Ca+2Ca+2

Ca+2Ca+2

Ca+2

Ca+2

Ca+2

Ca+2

Ca+2

Ca+2

Ca+2

Na+Na+ Na+

Na+ Na+ Na+

K+ K+

K+K+

K+K+

K+ K+ K+ K+ K+ K+

K+K+

K+K+

K+K+

K+K+

K+K+

K+K+

K+K+

K+K+

K+K+

K+K+

K+K+

K+K+

K+K+

K+K+ K+

K+

K+K+

K+K+

K+K+

K+K+

K+K+

K+K+

Na+Na+ Na+

Na+Na+ Na+

Na+

Na+ Na+

Na+Na+ Na+

Na+Na+Na+

Na+ Na+ Na+

Na+Na+Na+

Na+Na+Na+

Na+

Na+ Na+

Na+Na+Na+

Na+Na+Na+

Na+

Na+ Na+ Na+

Na+ Na+

K+K+

K+K+

Na+ Na+ Na+Na+ Na+ Na+

Na+ Na+ Na+

Na+ Na+ Na+

Na+ Na+ Na+

Na+ Na+ Na+

Na+ Na+ Na+Na+ Na+ Na+

Na+ Na+ Na+

Na+ Na+ Na+

Na+ Na+ Na+

Na+ Na+ Na+

Na+ Na+ Na+

Na+Na+ Na+

Ca+2

Ca+2

Ca+2

Ca+2 Ca+2

Ca+2 Ca+2 Ca+2

Ca+2 Ca+2 Ca+2

Ca+2

Ca+2

Ca+2

Ca+2

Ca+2

Ca+2

Ca+2

Ca+2

Ca+2

Ca+2

Ca+2Ca+2

Ca+2

Ca+2Ca+2Ca+2

Ca+2Ca+2

Ca+2

Ca+2

Ca+2

Ca+2

Ca+2

Ca+2

Ca+2

Na+Na+ Na+

Na+ Na+ Na+

K+ K+

K+K+

K+K+

K+ K+ K+ K+ K+ K+

K+K+

K+K+

K+K+

K+K+

K+K+

K+K+

K+K+

K+K+

K+K+

K+K+

K+K+

K+K+

K+K+

K+K+ K+

K+

K+K+

K+K+

K+K+

K+K+

K+K+

K+K+

Na+Na+ Na+

Na+Na+ Na+

Na+

Na+ Na+

Na+Na+ Na+

Na+Na+Na+

Na+ Na+ Na+

Na+Na+Na+

Na+Na+Na+

Na+

Na+ Na+

Na+Na+Na+

Na+Na+Na+

Na+

Na+ Na+ Na+

Na+ Na+

K+K+

K+K+

Na+ Na+ Na+Na+ Na+ Na+

Na+ Na+ Na+

Na+ Na+ Na+

Na+ Na+ Na+

Na+ Na+ Na+

Na+ Na+ Na+Na+ Na+ Na+

Na+ Na+ Na+

Na+ Na+ Na+

Na+ Na+ Na+

Na+ Na+ Na+

Na+ Na+ Na+

Na+Na+ Na+

Ca+2

Ca+2

Ca+2

Ca+2 Ca+2

Ca+2 Ca+2 Ca+2

Ca+2 Ca+2 Ca+2

Ca+2

Ca+2

Ca+2

Ca+2

Ca+2

Ca+2

Ca+2

Ca+2

Ca+2Ca+2Ca+2

Ca+2

Ca+2

Ca+2Ca+2Ca+2

Ca+2Ca+2

Ca+2

Ca+2

Ca+2

Ca+2 Ca+2

Ca+2

Ca+2

Na+Na+ Na+

Na+ Na+ Na+

K+ K+

K+K+

K+K+

K+ K+ K+ K+ K+ K+

K+K+

K+K+

K+K+

K+K+

K+K+

K+K+

K+K+

K+K+

K+K+

K+K+

K+K+

K+K+

K+K+

K+K+ K+

K+

K+K+

K+K+

K+K+

K+K+

K+K+

K+K+

Na+Na+ Na+

Na+Na+ Na+

Na+

Na+ Na+

Na+Na+ Na+

Na+Na+Na+

Na+ Na+ Na+

Na+Na+Na+

Na+Na+Na+

Na+

Na+ Na+

Na+Na+Na+

Na+Na+Na+

Na+

Na+ Na+ Na+

Na+ Na+

K+K+

K+K+

Na+ Na+ Na+Na+ Na+ Na+

Na+ Na+ Na+

Na+ Na+ Na+

Na+ Na+ Na+

Na+ Na+ Na+

Na+ Na+ Na+Na+ Na+ Na+

Na+ Na+ Na+

Na+ Na+ Na+

Na+ Na+ Na+

Na+ Na+ Na+

Na+ Na+ Na+

Na+Na+ Na+

Ca+2

Ca+2

Ca+2

Ca+2 Ca+2

Ca+2 Ca+2 Ca+2

Ca+2 Ca+2 Ca+2

Ca+2

Ca+2

Ca+2Ca+2

Ca+2

Ca+2

Ca+2Ca+2

Ca+2Ca+2Ca+2Ca+2

Ca+2

Ca+2Ca+2Ca+2

Ca+2Ca+2

Ca+2

Ca+2

Ca+2

Ca+2

Ca+2Ca+2

Ca+2

Na+Na+ Na+

Na+ Na+ Na+

K+ K+

K+K+

K+K+

K+ K+ K+ K+ K+ K+

K+K+

K+K+

K+K+

K+K+

K+K+

K+K+

K+K+

K+K+

K+K+

K+K+

K+K+

K+K+

K+K+

K+K+ K+

K+

K+K+

K+K+

K+K+

K+K+

K+K+

K+K+

Na+Na+ Na+

Na+Na+ Na+

Na+

Na+ Na+

Na+Na+ Na+

Na+Na+Na+

Na+ Na+ Na+

Na+Na+Na+

Na+Na+Na+

Na+

Na+ Na+

Na+Na+Na+

Na+Na+Na+

Na+

Na+ Na+ Na+

Na+ Na+

K+K+

K+K+

Na+ Na+ Na+Na+ Na+ Na+

Na+ Na+ Na+

Na+ Na+ Na+

Na+ Na+ Na+

Na+ Na+ Na+

Na+ Na+ Na+Na+ Na+ Na+

Na+ Na+ Na+

Na+ Na+ Na+

Na+ Na+ Na+

Na+ Na+ Na+

Na+ Na+ Na+

Na+Na+ Na+

Ca+2

Ca+2

Ca+2

Ca+2 Ca+2

Ca+2 Ca+2 Ca+2

Ca+2

Ca+2 Ca+2

Ca+2

Ca+2

Ca+2Ca+2

Ca+2

Ca+2

Ca+2Ca+2

Ca+2Ca+2Ca+2Ca+2

Ca+2

Ca+2Ca+2Ca+2

Ca+2Ca+2

Ca+2

Ca+2

Ca+2

Ca+2

Ca+2Ca+2

Ca+2

Na+Na+ Na+

Na+ Na+ Na+

K+ K+

K+K+

K+K+

K+ K+ K+ K+ K+ K+

K+K+

K+K+

K+K+

K+K+

K+K+

K+K+

K+K+

K+K+

K+K+

K+K+

K+K+

K+K+

K+K+

K+K+ K+

K+

K+K+

K+K+

K+K+

K+K+

K+K+

K+K+

Na+Na+ Na+

Na+Na+ Na+

Na+

Na+ Na+

Na+Na+ Na+

Na+Na+Na+

Na+ Na+ Na+

Na+Na+Na+

Na+Na+Na+

Na+

Na+ Na+

Na+Na+Na+

Na+Na+Na+

Na+

Na+ Na+ Na+

Na+ Na+

K+K+

K+K+

Na+ Na+ Na+Na+ Na+ Na+

Na+ Na+ Na+

Na+ Na+ Na+

Na+ Na+ Na+

Na+ Na+ Na+

Na+ Na+ Na+Na+ Na+ Na+

Na+ Na+ Na+

Na+ Na+ Na+

Na+ Na+ Na+

Na+ Na+ Na+

Na+ Na+ Na+

Na+Na+ Na+

Ca+2

Ca+2

Ca+2

Ca+2 Ca+2

Ca+2

Ca+2 Ca+2

Ca+2 Ca+2

Ca+2

Ca+2

Ca+2

Ca+2Ca+2

Ca+2

Ca+2Ca+2Ca+2

Ca+2Ca+2Ca+2Ca+2

Ca+2

Ca+2Ca+2Ca+2

Ca+2Ca+2

Ca+2

Ca+2

Ca+2

Ca+2

Ca+2Ca+2

Ca+2

Na+Na+ Na+

Na+ Na+ Na+

K+ K+

K+K+

K+K+

K+ K+ K+ K+ K+ K+

K+K+

K+K+

K+K+

K+K+

K+K+

K+K+

K+K+

K+K+

K+K+

K+K+

K+K+

K+K+

K+K+

K+K+ K+

K+

K+K+

K+K+

K+K+

K+K+

K+K+

K+K+

Na+Na+ Na+

Na+Na+ Na+

Na+

Na+ Na+

Na+Na+ Na+

Na+Na+Na+

Na+ Na+ Na+

Na+Na+Na+

Na+Na+Na+

Na+

Na+ Na+

Na+Na+Na+

Na+Na+Na+

Na+

Na+ Na+ Na+

Na+ Na+

K+K+

K+K+

Na+ Na+ Na+Na+ Na+ Na+

Na+ Na+ Na+

Na+ Na+ Na+

Na+ Na+ Na+

Na+ Na+ Na+

Na+ Na+ Na+Na+ Na+ Na+

Na+ Na+ Na+

Na+ Na+ Na+

Na+ Na+ Na+

Na+ Na+ Na+

Na+ Na+ Na+

Na+Na+ Na+

Ca+2

Ca+2

Ca+2

Ca+2

Ca+2

Ca+2 Ca+2

Ca+2

Ca+2 Ca+2Ca+2

Ca+2

Ca+2

Ca+2Ca+2

Ca+2

Ca+2Ca+2Ca+2

Ca+2Ca+2Ca+2Ca+2

Ca+2

Ca+2Ca+2

Ca+2

Ca+2Ca+2

Ca+2

Ca+2

Ca+2

Ca+2

Ca+2

Ca+2

Ca+2

Na+Na+ Na+

Na+ Na+ Na+

K+ K+

K+K+

K+K+

K+ K+ K+ K+ K+ K+

K+K+

K+K+

K+K+

K+K+

K+K+

K+K+

K+K+

K+K+

K+K+

K+K+

K+K+

K+K+

K+K+

K+K+ K+

K+

K+K+

K+K+

K+K+

K+K+

K+K+

K+K+

Na+Na+ Na+

Na+Na+ Na+

Na+

Na+ Na+

Na+Na+ Na+

Na+Na+Na+

Na+ Na+ Na+

Na+Na+Na+

Na+Na+Na+

Na+

Na+ Na+

Na+Na+Na+

Na+Na+Na+

Na+

Na+ Na+ Na+

Na+ Na+

K+K+

K+K+

Na+ Na+ Na+Na+ Na+ Na+

Na+ Na+ Na+

Na+ Na+ Na+

Na+ Na+ Na+

Na+ Na+ Na+

Na+ Na+ Na+Na+ Na+ Na+

Na+ Na+ Na+

Na+ Na+ Na+

Na+ Na+ Na+

Na+ Na+ Na+

Na+ Na+ Na+

Na+Na+ Na+

Ca+2

Ca+2

Ca+2

Ca+2 Ca+2

Ca+2 Ca+2 Ca+2

Ca+2 Ca+2Ca+2

Ca+2

Ca+2

Ca+2Ca+2

Ca+2

Ca+2Ca+2Ca+2

Ca+2Ca+2Ca+2Ca+2

Ca+2

Ca+2Ca+2

Ca+2

Ca+2Ca+2

Ca+2

Ca+2

Ca+2

Ca+2

Ca+2

Ca+2

Ca+2

5. Chemical cross bridges form between actin and myosin within the sarcomeres whenever Ca+2 ions are released into the sarcoplasm.

6. These cross bridges “jump” or “ratchet” down the myosin thus sliding the actin over the myosin.

7. This causes the sarcomere to shorten, thus the muscle is contracted.

Muscle Contraction• The final result is that calcium from the sarcoplasmic

reticulum rushes into the sarcoplasm.

• This leads to a change in the myosin, so the actin filaments slide past myosin