Human body is made up of over 600 different muscles. These muscles are hence divided into three categories considering where they are located. The brain, nerve and skeletal system work collectively towards helping the body with locomotive functions. This article aims to discuss muscles and all the other aspects associated with the same. A few examples of muscles are involuntary muscles, cardiac muscles, biceps brachii, triceps, etc. There are about\(\;630\) muscles in the human body. Muscles need proper oxygen and nutrition to work efficiently.

What is Muscle in Human Body?

Muscles are specialized tissue that is responsible for the movement of different body parts. They are soft tissues and muscle cells are also known as the myocyte. The muscles contain unique proteins called actin and myosin that help in the contraction and relaxation of muscles.

What are the 3 Types of Muscles and Examples?

Muscles are of three types based on location:

1. Striated or Skeletal Muscles
2. Non-Striated or Smooth Muscles
3. Cardiac Muscles

1. Striated or Skeletal Muscles: Striated muscles are responsible for all the movements of body parts that are present throughout the body.

	Striated or Skeletal muscles
Location	Structure	Function
1. They are present in the limb, tongue, body wall, pharynx, and upper part of oesophagus.	1. The muscle fibres are arranged in bundles.	1. They help in the locomotion and movement of the voluntary organs.
	2. The shape is cylindrical.	2. They contract rapidly for a short period of time.
	3. They are unbranched fibres.
	4. They are multinucleated.
	5. They are covered by a covering called sarcolemma.
	6. Myofibril of muscle fibre has dark (A-band) and light bands (I-band) called striped muscle fibres
	7. They are attached to the bones by tendons.
	8. The contractile unit of striated muscle is called the sarcomere.

2. Non-Striated or Smooth Muscles: Smooth muscles are responsible for the movement in internal organs such as the stomach, intestine, and uterus. They are involuntary and controlled by the autonomic nervous system.

	Non-Striated or Smooth muscles
Location	Structure	Function
1. They are present in the wall of the internal organs like stomach, intestine, blood vessels, iris of eye, ureter, bronchi of lungs.	1. They are arranged in layers.	1. They help in the movements of food in the stomach, urine in the ureters, and sex cells in the genetic ducts.
	2. They are spindle-shaped with tapering ends,	2. They contract relatively slowly, and the contraction is for a longer period.
	3. They are unbranched fibres.
	4. They are uninucleate.
	5. They do not have light or dark bands, so they are called unstriped muscle fibres.
	6. They are not attached to the bones.

2. Cardiac Muscles: Cardiac muscles are located in the walls of heart. They are also called myocardium. The rhythmic contraction of cardiac muscles is regulated by the SA node which helps in performing coordinated contractions that allow the heart to pump blood through the circulatory system.

	Cardiac Muscles
Location	Structure	Function
1. They are present in the wall of the heart.	1. They are cylindrical in shape with flat and zigzag ends.	1. They perform rapid and rhythmic contractions.
	2. They are branched fibers.	2. They help in pumping and in distributing blood to different parts of the body.
	3. They form a three-dimensional network.
	4. They have light and dark bands.
	5. They are uninucleate.

Types of Muscles Based on Muscle Action

Muscles are of three types based on location:

1. Voluntary Muscles: The muscles that can be controlled at our will are called voluntary muscles. They are attached to our bones and provide movement to the body parts. Therefore, they are also known as skeletal muscles.
2. Involuntary Muscles: The muscles that cannot be controlled at one’s will are called involuntary muscles. They are found in our internal organs like the oesophagus, stomach, intestines, etc.

Difference between Voluntary muscles and Involuntary muscles.

Voluntary Muscles	Involuntary Muscles
1. They are striated muscles.	1. They are non-striated and cardiac muscles.
2. They are cylindrical and unbranched-shaped muscles.	2. They are spindle-shaped and have small muscles.
3. They are multinucleated.	3. They are uninucleated.
4. They are attached to bones.	4. They are attached to the walls of internal organs.
5. They require more energy for contraction and relaxation.	5. They require low energy for contraction and relaxation.
6. The nucleus is present at the periphery.	6. The nucleus is present at the center.
7. They can be controlled by will.	7. They cannot be controlled by will.
8. They have thick sarcolemma.	8. They have a thin sarcolemma.
9. Sarcomeres are present.	9. Sarcomeres are absent.
10. They are controlled by the somatic nervous system.	10. They are controlled by the autonomic nervous system.

Muscles in the Body

A human body has more than \(630\) muscles. The important muscles of human body are mentioned below:

How do Muscles Work?

Muscles provide movement to the body parts by contracting and relaxing. They work as pairs of flexors and extensors. Muscles are attached to the bones by tendons that help them to move.

The steps involved in the contraction of muscles are:

1. The process of contraction of muscles begins in the central nervous system.
2. Acetylcholine causes its depolarization which creates an action potential.
3. Action potential triggers the release of Ca²⁺ ions.
4. Ca²⁺ ions bind to troponin, which removes the blocking action of tropomyosin from the actin-binding sites.
5. The actin filaments and myosin head form a cross-bridge that ATP breaks. 
6. ATP then breaks down to ADP and phosphate, and energy released in the myosin head.
7. Energized myosin head binds to actin filament to form a cross bridge.
8. The myosin heads then pull the actin filaments inward, release the ADP and phosphate and return to their original position.
9. Now the myosin head moves the actin filaments towards the center of the sarcomere.
10. The sliding of actin along with myosin shortens the sarcomere that results in muscle contraction.

The steps involved in the relaxation of muscles are:

1. The nerve impulse stops.
2. Acetylcholine is no longer released at the neuromuscular junction.
3. Calcium ions are now pumped back into the sarcoplasmic reticulum.
4. ATP breaks the link between actin and myosin results in the relaxation of muscles.

Disorders of Muscles

The common disorders of muscles are:

1. Inflammatory myopathies
2. Muscular dystrophy
3. Myasthenia gravis
4. Amyotrophic lateral sclerosis
5. Cardiomyopathy
6. Rickets
7. Muscle paralysis

Fun Facts!

1. Just to smile we use \(14\) muscles.
2. Heart is the hardest working muscle in the body.
3. Largest muscle of the body is gluteus maximus and the smallest muscle of the body is the stapedius.

Summary

As discussed in this article muscle is a tissue that allows active movement of the body and the body organs. The characteristics of muscle tissue are based on its appearance, control, and functionality.

Muscles are present in both the external and internal organs of the body. Some muscles are in our control and work as per our will, but some are not in our control. Muscles are a very special part of our body that helps us to stay active and perform movements.

Frequently Asked Question (FAQs) on Muscles

Frequently asked questions related to muscles are listed as follows:

Q.1. What are muscles called?
Ans: Muscles are contractile tissues that are involved in the contraction and relaxation of body organs. 

Q.2. What is a muscle in the human body?
Ans: Muscles are specialized tissue that is responsible for the movement of different body parts.

Q.3. What are the 8 muscles?
Ans: The eight muscles are masseter, biceps brachii, triceps brachii, deltoid, pectoralis major, pectoralis minor diaphragm, and intercoastal.

Q.4. What are the 3 types of muscles and examples?
Ans: The three types of muscles are skeletal, smooth, and cardiac muscles.

Q.5. Which is the strongest muscle in the human body?
Ans: The masseter is the strongest muscle in the human body. 

Q.6. What are the five major types of muscles?
Ans: The five major types of muscles are skeletal, smooth, cardiac, voluntary, and involuntary muscles.

Q.7. Is your tongue a muscle?
Ans: Yes, the tongue is an extremely movable muscle.

Q.8. Which body part has no muscle?
Ans: Appendix has no muscle. 

Q.9. What are muscles made from?
Ans: Muscles are made up of thousands of elastic tissues which are bundled together.

Learn About Muscle Fatigue

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