July 13, 2008

Flex Those Muscles

Human body is so complicated! It contains neural circuitry, the skeletal framework, a heart that tirelessly pumps blood to feed the power-hungry tissues, the excretory system that disposes off metabolic toxins through the kidneys and many others. The muscles on the other hand give us the power of movement and locomotion, participate in respiratory excursions, various reflex actions and of course, something you probably show off to your girlfriend. The way the muscles contract is quite complex and yet not fully understood.

Each muscle fiber has two types of filaments: thin filaments comprising of actin, and thick filaments consisting of myosin. On the surface of G actin molecules (the actin fiber or F actin, is composed of several of these G actin molecules ) a chemical called ADP, for adenosine di phosphate, is found. These places are the putative active sites of contraction of the actin fibers. These active sites have to be covered or else myosin will bind and elicit automatic contractions. This covering is done by another protein called tropomyosin. It is aided by another protein complex, called troponin (consisting of three subunits, Troponin I, T and C). The contraction process require ATP or adenosine tri phosphate as its energy source. Surprisingly, as it may sound, relaxation of the muscles are also energy dependent too.

This video illustrates quite elegantly the molecular events that accompany contraction.

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