Introduction

In this article, students will learn about Muscles in our body, types, structure and functions of Muscles. Let's first know what muscle is.


A muscle is a soft tissue found in both humans and animals. The word muscle is derived from the Latin word “musculus” meaning little mouse as some Muscles resemble the shape of a small mouse or the contraction of Muscles look like a moving mouse.


Muscles are made up of protein filaments of myosin and actin that slide past each other and produce expanding and contracting movements of Muscles. This kind of movement changes both the shape and length of the muscle cells. Muscles function in humans by producing motion and force and help in circulation of blood, changing and maintaining body pressure, movement of internal organs like the movement of food down the digestive tract, and also helps in locomotion.


The human muscular system comprises more than 600 Muscles and makes up about 40-50% of our overall body weight. Muscles are essentially attached to blood vessels, bones and other internal organs. Muscles are composed of special kinds of elastic tissue, tendons, nerves and tissues.


The functioning of Muscles helps in making movements of every kind in the body and internal organs by transferring substances from these organs throughout the body. Muscles function by using up energy by oxidation of carbohydrates and fats, especially from the stored energy molecules adenosine triphosphate (ATP).


Types

There are three types of Muscles found in the body:

  • Cardiac Muscles 

  • Smooth Muscles 

  • Skeletal Muscles 


Out of these three types, cardiac Muscles are involuntary Muscles which means that the movement of cardiac Muscles cannot be controlled by us according to our will.


Skeletal Muscles

Skeletal Muscles are voluntary Muscles and are attached to the bones and involved in different body parts functioning. They come under the central nervous system control of the body. Skeletal Muscles are long and multinucleated. They are cylindrically shaped with branched cells which are attached to the bones by collagen fibres and tendons, which are composed of connective tissues.


The function of Skeletal muscle can be summed up briefly as follows:

  • The primary function of Skeletal muscle is contraction. And thus, contraction helps produce heat in our body.

  • Skeletal muscle helps in maintaining the body posture and joint position by conveying information about the degree of muscle length and stretch to the central nervous system.

  • Skeletal Muscles produce ATP and store glucose in the form of glycogen. Glycogen can be converted into glucose when energy is needed.

Cardiac Muscles

Cardiac Muscles are found only in the heart and are involuntary like movement. They are made up of cylindrical-shaped cells. These are striated Muscles responsible for keeping the heart moving by circulating and pumping blood throughout the body. The interconnected Muscles provide flexibility and strength to the Cardiac muscle tissue and are involved in rhythmic relaxation and contraction of the heart Muscles . Cardiac Muscles are characterised by branched cylindrical fibres and a centrally located nucleus.


Cardiac Muscles are primarily found in humans and regulate rhythmic relaxation and contractions of the heart Muscles for pumping blood. The Cardiac Muscles have a specialised type of tissue called “pacemaker” cells that expand and contract by responding to electrical impulses of the central nervous system.


Smooth Muscles

Smooth Muscles are also involuntary Muscles that are non-striated and are present in major organs whose movements are not controlled by the will, such as the stomach, vessels, bladder, uterus, etc. They are spindle-shaped with a single nucleus. These Muscles are shorter than skeletal Muscles with a length ranging between 20 to 200 μm and thickness between 3-10 µm. These Muscles produce their connective tissue and lack actin, myosin and filaments.


Smooth Muscles perform various tasks in our body which can be given as follows: 

  • Smooth Muscles maintain the diameter of arteries and thereby maintain blood pressure. Arteries have thick walls due to Smooth muscle present there, which helps them carry blood away from the heart. 

  • In the digestive tract, Smooth muscle maintains the peristaltic movement and forces food through the digestive tract. 

  • They are present in the eye responsible for shrinking the size of the pupil.

  • In the respiratory system, Smooth muscle helps air go from the trachea to the lungs.

  • In reproductive systems Smooth muscle helps sperm to move along the male reproductive system, during menstruation Smooth muscle helps to expel the uterine lining.

  • Smooth muscle in the uterus helps women to push out her baby during childbirth.

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FAQs on Muscles

1. Explain about Voluntary and Involuntary muscles?

Depending on the muscle actions, they are further classified as listed below.

  • Voluntary Muscles

  • Involuntary Muscles


Voluntary Muscles

Voluntary muscles are long and multinucleated cells, containing sarcomeres arranged into bundles. These are composed of cylindrical fibres and usually attached to the skin and bones. They play an essential role in allowing the body to move by relaxing and contracting, and their actions lie under the control of the somatosensory nervous system mainly. These voluntary muscles also include skeletal muscles.

 

Involuntary Muscles

Involuntary muscles are branched and striated in cardiac muscle cases. The actions of involuntary muscles are controlled mainly by the body’s autonomic nervous system. These involuntary muscles include smooth and cardiac muscles.

2. Explain the Functions of Skeletal Muscles in brief?

Let us discuss the functions of the Skeletal Muscle in brief.

  • It regulates body temperature and maintains body posture

  • It is responsible for performing muscular involuntary movements

  • It controls and connects to the motions of the skeleton

  • It is also responsible for body movements like extending the arm, typing, writing, breathing, and more

  • It is responsible for the body’s erect posture. The sartorius muscles in thighs take care of body movement

  • These muscles protect the internal organs and tissues from any injuries and provide support to these delicate tissues and organs

  • These muscles also support the entry and exit points of the body

3. What are voluntary and involuntary muscles?

Voluntary muscles are the ones that move or contract under the conscious control of a person. Under control of the somatic nervous system. Voluntary muscles are also known as skeletal muscles or striated muscles. Structurally, the voluntary muscles are unbranched, long cylindrical with the peripherally located nucleus. These muscles may be multinucleated and are rich in mitochondria. The voluntary muscle fibre is surrounded by thick sarcolemma.


Involuntary muscles are the ones that do not move under the free will of a person and are controlled by the autonomic nervous system. So these muscles are myogenic. These muscles are also known as smooth muscles or nonstriated muscles but cardiac muscles are striated. These muscles line the organs like the urinary bladder, blood vessels, stomach, eye etc. And cardiac muscle is present in the heart. Structurally, the smooth involuntary muscles are long, thin, spindle-shaped cells with a centrally located nucleus.

4. What is the function of skeletal muscles?

Skeletal muscles produce ATP and store glucose in the form of glycogen. Glycogen can be converted into glucose when energy is needed. maintaining body posture by keeping it erect and regulating body temperature. Skeletal muscles help in the movement of hands, feet, as well as regulating a part of the digestive tract such as chewing in the mouth and swallowing movements. Skeletal muscles also help in excretion around the anus and urinary tract by expanding and contracting.

5. How do cardiac muscles function in the human body?

Cardiac muscles are exclusively found in humans. Cardiac muscle functions by keeping our heart pumping through involuntary movement. Cardiac muscle is controlled by the autonomic nervous system, which signals our heart cells to contract incorrect patterns.

6. What are the functions of smooth muscles?

Smooth muscles are responsible for the occurrence of goosebumps on our bodies, contracting sphincter muscles and regulating fluid movement across organs. The main functions of this kind of tissue are transporting chyme for intestinal tube contractions and producing connective tissue proteins like elastin, collagen.

7. How do muscles get energy for functioning?

The major fuel source that muscles use for energy is carbohydrates. Any glucose is stored as glycogen in the liver and muscles to be used later as a quick use fuel. Excess amounts of carbohydrates are stored as fats that can be used as slow-release energy.


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