Muscle fiber
18
Muscle fiber Motor neuron Nucleus
description
Muscle fiber. Motor neuron. Nucleus. Sarcoplasmic reticulum (SR). Sarcolemma. Myofibrils. SR Cistern. T-tubule. Action potential reaches synaptic terminal of motor neuron. New AP generated at motor end-plate and propogated down T-tubules. Myofibrils (relaxed). Sarcomere. - PowerPoint PPT Presentation
Transcript of Muscle fiber
Muscle fiber Motor neuron
Nucleus
Sarcolemma MyofibrilsSarcoplasmic reticulum (SR)
T-tubule
SR Cistern
Action potential reaches synaptic terminal of motor neuron
New AP generated at motor end-plate and propogated down T-tubules
Myofibrils (relaxed) Sarcomere
(Sarcolemma and other structures not shown)
Myofibrils (contracted) Sarcomere
Sarcomere (relaxed)
Actin(thin filaments)
Myosin(thick filaments)
Sarcomere (contracted)
Actin(thin filaments)
Myosin(thick filaments)
Actin(thin filament)
Myosin(thick filaments)
Myosinheads
Actin Myosin head
ADP and phosphate
Protein complex
Note that ATP is hydrolyzed at this point, but still attached to myosin head.
Calcium ion
Myosin-binding sites (exposed)
Protein complex
ADP and phosphate
Actin Myosin head
ADP and phosphate
Actin Myosin head
Pi
ADP
1. Release of Pi initiates the power stroke. 2. At the end of the power stroke, ADP is released. 3. A new ATP is required for myosin to release its hold on actin.
Actin Myosin head
ATP
ATP binds to the myosin head, causing it to detach from actin.
Actin Myosin head
ADP and phosphate
When the ATP is broken down to ADP and phosphate, the myosin head extends.
Actin Myosin heads
The sequence repeats as long as calcium ions are present. The combined work of many myosin heads causes the actin filaments to slide past the myosin filaments.
Actin Myosin headsProtein complex
When the action potentials stop, calcium ions are pumped back into the ER, the myosin-binding sites on actin are again blocked, and the muscle relaxes.
ActinMyosinCalcium
Sarcomere
(Ca+2 in green)
