Sliding filament Theory

Muscles and bones are present in the human body which supports locomotion and movement of the human body. Muscles are present all over the body and are of three types. They are cardiac muscles, skeletal muscles, and smooth muscles. Skeletal muscles are mainly related to the locomotion and movement of body parts. About all over 650 muscles are present.  These muscles are specialized tissue that consists of a huge number of muscle fibers. These muscle fibers are of two types, thin and thick filaments. Contraction of muscles is necessary for the movement of the body organs.  This occurs when tension-generating sites become activated within the muscles. This can be described as the sliding filament theory.

What is Sliding Filament Theory?

Sliding filament theory is the theory that describes the contraction of muscles when two filaments of actins and myosin slide over each other in the presence of ATP to enable the contraction of muscles. This theory was proposed independently by two groups of scientists, one is Andrew Huxley and Rolf Niedergerke from the University of Cambridge and the other group consists of Hugh Huxley and Jean Hanson from the Massachusetts Institute of technology.   

What are actins and myosin?

Actin and myosin represent the two types of protein, out of which these muscles are made. These two proteins are solely responsible for the contraction of muscles. Actin and myosin along with some regulatory proteins like troponin, tropomyosin, and meromyosin regulate the contraction of muscles and movements of body organs.  The actin is made up of two proteins, troponin, and tropomyosin. Myosin is made of meromyosin. This meromyosin has a head part that connects with the active binding site of actin and is made of heavy chain meromyosin. The tail part is made up of light chain meromyosin.

Sarcomere:

A group of basic structural units of actin and myosin in an alternative pattern that forms the striations in skeletal muscle is known as sarcomeres. They are arranged in stacks throughout the muscle. A single muscle cell consists of a number of sarcomeres and can be replicated. During contraction, the length of the sarcomere decreases. In a single sarcomere, there are alternative arrangements of actin and myosin protein. 

• The A band shows consistency in length during the contraction of muscles. This band is present in the middle of the sarcomere which is the place of overlapping for other filaments.
• Sarcomere has an H zone which is made up of thick myosin.
• The I band in the sarcomere consists of thin filaments.
• The Z line is mostly responsible for the striped nature of the muscles.

Process:

The myosin formed the thick filament and actin formed the thin filament. The myosin consists of an actin-binding site and an ATP binding site. In case of action, the active site of myosin is covered with troponin and tropomyosin. When the nerve impulse comes to the muscle-nerve junction, the sarcoplasmic reticulum that is present in the nerve cells releases calcium ions. These calcium ions join with the troponin protein and activate the myosin binding site within the actin. In the case of myosin, in the protein, the ATP is transformed into ADP in the presence of the enzyme ATPase. The head of the myosin joins, therefore, joins with the myosin-binding site of action and pulls inward. Again another ATP molecule joins with the myosin head and the cycle continues. This is how contraction in muscle occurs. The sarcomere contracts during the process. 

Conclusion:

Muscles and bones are present in the human body which supports locomotion and movement of the human body. Muscles are present all over the body and are of three types. They are cardiac muscles, skeletal muscles, and smooth muscles. Skeletal muscles are mainly related to the locomotion and movement of body parts. Actin and myosin represent the two types of protein, out of which these muscles are made. These two proteins are solely responsible for the contraction of muscles. Actin and myosin along with some regulatory proteins like troponin, tropomyosin, and meromyosin regulate the contraction of muscles and movements of body organs. Sliding filament theory is the theory that describes the contraction of muscles when two filaments of actin and myosin slide over each other in the presence of ATP to enable the contraction of muscles.