來自 其他
磅數 967.5磅
發文 389
註冊 2003/10/15
量級 重量級
★★★★
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鈣在肌肉收縮中當中界人的角色
(很多化學名詞)
http://health.howstuffworks.com/muscle4.htm
How Muscles Work
by Craig C. Freudenrich, Ph.D.
Triggering Contraction
The contractions of all muscles are triggered by electrical impulses, whether transmitted by nerve cells, created internally (as with a pacemaker) or applied externally (as with an electrical-shock stimulus). The electrical signal sets off a series of events that lead to crossbridge cycling between myosin and actin, which generates force. The series of events is slightly different between skeletal, smooth and cardiac muscle. Let's describe the events in skeletal muscle first.
The coupling process leading from electrical signal (excitation) to contraction
in skeletal muscle
Let's take a look at what occurs within a skeletal muscle, from excitation to contraction to relaxation:
An electrical signal (action potential) travels down a nerve cell, causing it to release a chemical message (neurotransmitter) into a small gap between the nerve cell and muscle cell. This gap is called the synapse.
The neurotransmitter crosses the gap, binds to a protein (receptor) on the muscle-cell membrane and causes an action potential in the muscle cell.
The action potential rapidly spreads along the muscle cell and enters the cell through the T-tubule.
The action potential opens gates in the muscle's calcium store (sarcoplasmic reticulum).
Calcium ions flow into the cytoplasm, which is where the actin and myosin filaments are.
Calcium ions bind to troponin-tropomyosin molecules located in the grooves of the actin filaments. Normally, the rod-like tropomyosin molecule covers the sites on actin where myosin can form crossbridges.
Upon binding calcium ions, troponin changes shape and slides tropomyosin out of the groove, exposing the actin-myosin binding sites.
Myosin interacts with actin by cycling crossbridges, as described previously. The muscle thereby creates force, and shortens.
After the action potential has passed, the calcium gates close, and calcium pumps located on the sarcoplasmic reticulum remove calcium from the cytoplasm.
As the calcium gets pumped back into the sarcoplasmic reticulum, calcium ions come off the troponin.
The troponin returns to its normal shape and allows tropomyosin to cover the actin-myosin binding sites on the actin filament.
Because no binding sites are available now, no crossbridges can form, and the muscle relaxes.
As you can see, muscle contraction is regulated by the level of calcium ions in the cytoplasm. In skeletal muscle, calcium ions work at the level of actin (actin-regulated contraction). They move the troponin-tropomyosin complex off the binding sites, allowing actin and myosin to interact.
我猜用作肌肉收縮的鈣不會導致骨骼發育不良,而且鈣的daily recommanded intake是成人1000mg,如果你的飲食均衡,應該不用擔心不夠鈣吧.
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