MUSCLES

MUSCLES:

      Muscles acts like a machine. Muscles provide the forces that put the body into motion. When muscles contract it become shorter and thickened. But when it relaxes, it lengthens and become shorter. Muscles convert their stored chemical potential energy into mechanical energy in the form of work and heat. This work produces movement like walking, eating, heartbeat and breathing.

TYPES OF MUSCLES

    There are three types of muscles which are the following.

 1. Cardiac muscles: 

      These are voluntary muscles that can be moved according to your will or wish. These muscles are composed of chain of single cells. These chains are organized into fibers. Group of fibers from a network. 

      The muscles of the heart are called cardiac muscles. They are very strong and their action is involuntary, rhythmic and automatic. They are not under the direct control of central nervous system, i.e. do not depend on the will or wish.

2. Smooth muscles: 

      Smooth cells are arranged forming sheets. Smooth muscles are found in stomach, intestines and blood vessels. They are also involuntary muscles and not under control. They contract slowly.

 3. Skeletal or voluntary or striated muscles:

          Skeletal muscles are attached to bones. These are responsible for the movements of the limbs and other parts of the body. These muscles are under the control of the central nervous System. They are called striated muscles, because their fibers have light and dark transverse bands. These muscles are much stronger than smooth muscles. Skeletal muscle cells are long and cylinder, have many nuclei and also muscle fibers. If muscles are not use, they become weak and decrease in size.

Working of muscles (skeletal muscles): 

        To bring a movement in the bone, two pairs of muscles are required. When one muscle contract the bone moves to one direction. When the second muscle contracts, the bone moves to the opposite direction. Thus two sets of muscles are required for the proper movement of a bone. 

Attachment of muscles:

       Muscles are attached to the bone by two types; origin and insertion.

1. Origin

      If end of a muscle is attached to an immovable and rigid bone, is known as the origin. Muscles may have more than one origin. It remains fixed during contraction.   

2. Insertion

      If the end of a muscle is attached to a movable bone, it is known as insertion.

TENDONS AND LIGAMENTS

Tendons: 

      Skeletal muscles are joined to bones by tendons. Tendons are very tough white straps/bands that do not stretch. They are made of collagen fibers. One end of the tendon is attached to a non moving bone while the other ends with a moveable bone. When a muscle contract tendon exerts a pulling force on the attached bone, making it to move.   

Ligaments

     Ligaments are strong and flexible bands of connective tissues which hold the relevant bones of the joints together. Ligaments prevent the dislocation of bones at joints during their movement. They also hold tendons in place and control their direction.

Antagonistic arrangement of muscles:

      To move a bone to and fro, there are two sets of muscles. When one set contracts, it moves the bone in one direction, and when the other set contracts, it moves the bone in the opposite direction i.e. these two sets of muscles are antagonistic to each other.

       When one pair of antagonistic muscles Contracts, the other relaxes. Such movement is known as antagonistic movement or antagonism.

For example, movement of arm muscles.

 Flexor 

       Bending of the arm at elbow Joint is called flexion and the muscle that causes this movement is called flexor.

Extensor

       Straightening of the arm at elbow joint is called extension and the muscle that causes this movement is called extensor.

       To bring about movement in the hinge joint, bicep muscles undergo flexion, here called flexor while triceps muscle act as extensor.