Muscle System Blog

Bones have attachments of tendons which is attached to the epimysium, and it seperates the muscle from surrounding tissue. Inside the epimysium is the perimysium which divides the muscle into compartments called fascicles. In depth of the perimysium is the endomysium, and that seperates each fiber and ties closer fibers together. Inside the endomysium are muscle fibers, they contain organelles and tightly packed myofibrils. Myofibrils make up 80% of cellular volume and they contain myofilaments which have I-band (thin filament: Actin- Z line) and A-band (thick filament: Myosin- M line). Inside the muscle fibers is the sarcolemma and it is a muscle cytoplasm with glycosomes and myoglobin, and inside that is the sarcoplasmic reticulum and that modifies and elaborates smooth endoplasmic reticulum which stores calcium ions and releases on demand. T-tubules are continuations of sarcolemma that penetrate into cell. The mitochondria is between the myofibrils and it produces energy.

 

 

 

The muscles contract and contain energy by the sodium potassium pump (Na+ K+ Pump). At the neuromuscular junction ACh is released by synaptic terminal and binds to receptors on sarcolemma. Resulting change in membrane potential leads to production of an action potential that spreads across the entire surface of muscle fiber and along the T-tubules. Sarcoplasmic reticulum releases stored calcium ions, increasing calcium concentration in the sarcoplasm. Calcium ions bind to troponin, resulting in movement of tropomyosin and exposure of active sites on the thin filaments. Crossbridge form when myosin heads bind to active sites. Contraction begins as repeated cycles of crossbrigde binding, pivoting, and detachment occur, powered by the breakdown of ATP. These events produce filament sliding, and muscle fiber shortens. Action potential generation ceases ACh is broken down by AChE. The sarcolplasmic reticulum reabsorbs calcium ions in the sarcoplasm declines. When calcium ion concentration approach normal resting levels, the troponin and tropomyosin molecules return to their normal positions. This recovers the active sites. With the active sites no longer accessible, crossbridge formation cannot occur. Without crossbridge interactions, further sliding cannot take place, and the contraction ends. Muscle relaxtion occurs, and the muscle returns passively to its resting length.