Theory:

In the human body along with the skeletal and nervous systems, the muscular system  is responsible for the various body movements.
 
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Muscular system
 
Muscles are tissues that can contract and therefore they help in movement of the other body parts. It is a tissue that helps in maintaining the posture and position of a body.
Movement of bones in the joints:
Bones cannot move on their own. The muscle brings about the movement of bones. The muscle is the prominent tissue that plays a significant role in the movement of the bones. Muscle is a tissue that works in pairs as they cannot push. The movement of the bone is brought about the contraction of one of the muscle.
 
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Muscles movement
 
Among the pairs of the muscles, when one of the muscle contracts the other relaxes. The bone is moved in the direction in which the muscle contracts. To move the bone in the opposite direction, the muscle under relaxation contracts to pull the bone towards its original position. During this, the other muscle relaxes.
 
The lower arm's movement in upwards and downwards direction is regulated by two muscles such as biceps and triceps. When a person raises his lower hand, the front's biceps become short by contraction and the triceps muscle at the backstretch to pull up the arm. Hence, when a person lowers the arm the triceps at the back contract and biceps stretch to pull the arm down.
Types of muscle:
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Anatomy of muscle
 
There are three types of muscles. They are:
  • Skeletal muscle
  • Smooth muscle
  • Cardiac muscle
Skeletal muscles:
 
The muscles of the body that are attached to the bones are known as skeletal muscles. These are voluntary muscles as they can be controlled consciously by our will.
For example: Muscles of the arm.
 
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Skeletal muscle
 
Smooth muscles:
 
These are the muscles that are found in the digestive tract walls, urinary bladder, arteries and other internal organs. They are also known as involuntary muscles as our will does not control them.
 
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Smooth muscle
 
Cardiac muscles:
  
These are the muscles that make up the walls of the heart. They have the ability to perform continuous rhythmic contractions and are also involuntary in nature.
 
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Cardiac muscle
 
This video is a summary regarding the muscular system of the human body.
 
Reference:
https://www.freepik.com/free-vector/human-muscular-skeletal-systems-informative-poster_6168812.htm
https://courses.lumenlearning.com/cuny-csi-ap-1/chapter/muscular-levels-of-organization/
https://www.vecteezy.com/vector-art/434408-different-systems-of-human-body-diagramhttps://www.vecteezy.com/vector-art/1928991-movement-process-of-the-arm-muscle-biceps-and-triceps
https://www.freepik.com/free-vector/type-muscle-cells_11573851.htm#page=1&query=cardiac%20muscle&position=0