LOCOMOTION

Movement is one of the significant features of living beings. Some of the movements result in a change of place or location. Such voluntary movements are called locomotion. All locomotions are movements but all movements are not locomotions.

TYPES OF MOVEMENT IN HUMAN

Cells of the human body exhibit three main types of movement :

Ciliary Movement 

Eg. Cilia in the Trachea (to remove the foreign particles) & Female reproductive tract (for passage of ova).


Muscular Movement 

Eg. Movement of our limbs, jaws, tongue, etc.

MUSCLES

The study of muscle is called Myology / Sarcology. Muscle is a specialized tissue of mesodermal origin. About 40-50 percent of the body weight of a human adult is contributed by muscles. Muscles have special properties like excitability, contractility, extensibility,  and elasticity. 


BASED ON THEIR LOCATION, THREE TYPES OF MUSCLES ARE IDENTIFIED 

1. Voluntary or Skeletal muscles 
2. Involuntary or Smooth muscles 
3. Cardiac muscles


VOLUNTARY MUSCLES 

Closely associated with the skeletal components of the body. Have a striped appearance under the microscope and hence are called Striated muscles.  


STRUCTURE OF STRIATED MUSCLES 


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STRUCTURE OF STRIATED MUSCLES FIBER

Muscle fibers are lined by plasma membrane (sarcolemma) enclosing the sarcoplasm. A characteristic feature of the muscle fiber is the presence of a large number of parallelly arranged filaments in the sarcoplasm called myofilaments or myofibrils. Each myofibril has alternate dark and light bands on it. The light bands contain actin and are called I-band or Isotropic bands, whereas the dark band called A- band or Anisotropic band contains myosin.


MAYOFIBRIL



SARCOMERE


The portion of myofibril between two successive Z lines is considered the functional unit of contraction and called a Sarcomere.
Sarcomere = Structural and Functional unit of muscle fiber.
The Length of the Sarcomere is 2.5 µm. (Actin rod = 1µm, myosin = 1.5 mm)

STRUCTURE OF STRIATED MUSCLES FIBER

Actin filaments are thinner as compared to the myosin filaments, hence are commonly called thin and thick filaments respectively. In the center of each I-band is an elastic fibre called ‘Z’ line which bisects it. The thin filaments are firmly attached to the Z line. The thick filaments in the A-band are also held together in the middle of this band by a thin fibrous membrane called ‘M’ line. The ‘A’ and ‘I’ bands are arranged alternately throughout the length of the myofibrils.   

CONTRACTILE PROTEINS - ACTIN & MYOSIN

Actin protein:- 

Each actin (thin) filament is made of two F (filamentous) actins helically wound to each other. Each F actin is a polymer of monomeric G (Globular) actins.
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REGULATORY PROTEINS - TROPOMYOSIN & TROPONIN

Tropomyosin:-

It is one type of contractile protein. In the relaxed state of the muscle situated in such a way, the active sites remain covered by the Tropomyosin and attached at the terminal end of actin.

Troponin:- 

It is one type of protein that is attached to one of the ends of the tropomyosin molecules. Troponin is made up of three subunits : 
(a) Troponin I (Inhibitory site) 
(b) Troponin T (Tropomyosin site) 
(c) Troponin C (Ca+2 binding site)

MYOSIN PROTEIN

Many monomeric proteins called Meromyosins constitute one thick filament. Each meromyosin has two important parts, a globular head with a short arm and a tail. The head and short arm projects outwards at a regular distance and angle from each other from the surface of a polymerized myosin filament and is known as the cross arm. The globular head is an active ATPase enzyme and has binding sites for ATP and active sites for actin.


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