Anatomy 230

Front 1

Step 1

Back 1

The motor nueron at the nueromuscular junction releases ACH to bind to the sarcolemma of the skeletal muscle fiber (cell) Signal the start of the contraction

Front 2

Step 2

Back 2

The signal is spread throughout the sarcolemma of skeletal muscle fiber (cell)

Front 3

Step 3

Back 3

The signal is spread down t-tubles to center of cell

Front 4

Step 4

Back 4

T-tubles spread signal to cell interior and pass signal to the sarcoplasmic reticulum, this causes the release of calcium ions from SR

Front 5

Step 5

Back 5

Calcium ions combine with the troponin-tropomyosin complex on actin exposing binding sites for myosin

Front 6

Step 6

Back 6

Myosin crossbridge heads (with ATP attached) do not attach to actin (This si the low affinity state)

Front 7

Step 7

Back 7

Myosin heads cause ATP to split (hydrolosis of ATP ->ADP+inorganic phosphate) causing mypsin crossbridge heads to swivel to ready position and attach to exposed binding sites on actin. Myosin is cocked (This is high affinity)

Front 8

Step 8

Back 8

Attachment of myosin and actin results in ATP+inorganic phosphate release, actin 'slides' past myosin (sarcomeres shorten/muscle cell shortens/Zlines pulled together)

Front 9

Step 9

Back 9

To release myosin-actin, another ATP molecule binds to myosin heads, resulting in the release of crossbridge attachment to actin (retunring to low affinity state)