Human Muscular System - Human Muscles - and Busiest Muscle in the Body

Human Muscular System

The human muscular system is an organ system composed of skeletal muscles, smooth muscles and cardiac muscles. There are at least 639 muscles in a human body. The muscular system in human is controlled through nervous system and brain, except that in the case of some muscles like heat muscles the control is autonomous.

Functions of Muscles

The main functions of muscles in human body include:

  1. muscles aid in the movement of the body
  2. muscles helps circulate blood in the body
  3. muscle gives body its posture
  4. muscles provides strength and balance to the body

Types of Muscle Tissue

There are three types of muscle tissues namely:

  1. Skeletal muscles (striated muscle) – These are the muscles that aid in the movement of body parts. Skeletal muscles are the bulk of muscles in the body. Skeletal muscles are controlled through peripheral nervous system and brain – they are voluntary muscles as they are under your conscious control.
  2. Smooth muscles are involuntary muscles controlled by autonomic nervous system. These are muscles of body internal organs such as muscle layers in the digestive system, urinary bladder, arteries, etc.
  3. Heart muscles, also known as cardiac muscles, are a cross between smooth muscles and striated muscle. Striated muscle is the same as skeletal muscle, and the term ‘striated’ is usually used for ‘skeletal’ to distinguish skeletal muscles from smooth muscles. The heart muscles are controlled by sinus node, and sinus node is by extension controlled by the central nervous system (or autonomic nervous system).

How Muscles Work - Contracting and Relaxing

Muscles work by contracting and relaxing. Muscles can only pull, they can not push. To get a pull, a muscle will have to contract. Reversing the pull to its original position, another muscle will have to contract to pull in the opposite direction. This therefore means that muscles works in pair - whilst one muscle is a synergist, the other muscle to undo the action is antagonist. Let’s take an example: Muscle No.1 contracts (synergist) to move a joint, then at the same time, muscle No.2 will stretch (antagonist) to allow the joint to move. Muscle No.2 is stretched and is in essence exerting an opposing pull which will reverse the direction of movement, if need be. When the direction of movement is reversed, muscle No.1 will relax.

Definitions on Description of Muscles Functions

The definitions of words used in description of muscles functions are as follows.

  1. Flexors are muscles that bend a limb are flexors.
  2. Extensors are muscles that straighten a limb.
  3. Abductors are muscles that move a limb to the side, away from the body.
  4. Adductors are muscles that move a limb sideways toward the body.
  5. Elevators are muscles whose contraction raises a part of the body.
  6. Depressors are muscle whose contraction pulls down the part of the body to which it is attached.
  7. Rotators are muscles whose contraction causes/assists in the rotation of a part of the body.
  8. Dorsiflexors are muscles whose contraction dorsiflexes the hand or foot. E.g. dorsiflexion can refer to the movement which decreases the angle between the superior surface of the foot and the leg, so that the toes are brought closer to the shin.
  9. Planar flexors are the muscles whose contractions will increases the approximate 90 degree angle between the front part of the foot and the shin like when depressing car pedal.
  10. Palmar flexors are muscles whose contraction will bend the hand or fingers toward the palmar surface.

Smallest Muscle in Human Body

The smallest muscle in humans is the stapedius muscle. Stapedius muscle has a length of 1.27 mm and is located in the middle ear. Stapedius muscle controls the smallest bone in humans, the stapes bone, which aids the ears in vibrations through the middle ear.

The Largest Muscle in Human Body

The largest muscle in humans is the buttocks. The buttocks are the gluteal muscles comprising the gluteus minimus and maximus.

The Strongest Muscle in Human Body

The strongest muscle in humans is the jaw muscle which has the advantage of working over a shorter lever arm relative to other muscles. Your jaw bite can be as much as 2000 N per second.

The Longest Muscle in Human Body

The longest muscle in the human body is the sartorius muscle. The sartorius muscle is a muscle of the anterior hip and thigh group that is connected to the ilium and the tibia.

The Busiest Muscle in the Human Body - The Eye Muscles

The busiest muscle in the human body is the eye muscles. The eye muscles are called extraocular muscles. The extraocular muscles are small, strong and efficient. Humans have six extraocular muscles in each eye. These six muscles are constantly moving the eye in order to follow a target for a sharp distinct vision. The six extraocular muscles that rotates the eye vertically, horizontally and antero-posterior are:

  1. Inferior Rectus
  2. Superior Oblique
  3. Inferior Oblique
  4. Medial Rectus
  5. Lateral Rectus
  6. Superior Rectus

So, the eyes muscles are the busiest muscles in humans. Other busy muscles are cardiac (heart) muscles and diaphragm (breathing) muscles since they work nonstop.

When A Person Dies What Stops First, Heart Or Brain?

And is the brain a muscle? The answer is no. Brain is an organ, and it's the key organ in the nervous system. The brain is the organ that instructs the body what to do. When a person dies what stops first, heart or brain? The heart shuts down first. The brain does not shut down until everything else is completely done.

Human Muscular System - Functions of Muscles - Labeled from the Back Side

Below find an image of human muscular system showing muscle labeling (posterior) of some of the major muscles.

Human Muscular System with labeling from back view. Image Credit: Mikael Häggström via Wikimedia Commons.
Human Muscular System with labeling from back view. Image Credit: Mikael Häggström via Wikimedia Commons.


  1. Peroneus Brevis Muscle is for turning the foot outward and upward
  2. Peroneus Longus Muscle is a superficial muscle in the lateral compartment of the leg that causes dorsi flexion and turns the foot outward.
  3. Tibialis Posterior Muscle is a deep muscle of the leg arising from the tibia that provides for the movement of the foot.
  4. Soleus Muscle is a broad flat muscle in the calf of the leg under the gastrocnemius which helps in standing and walking.
  5. Gastrocnemius Muscle is main muscle in the back part of the leg that forms the greater part of the calf. Gastrocnemius muscle flexes the knee and foot.
  6. Semimembranosus Muscle is a muscle in the back of the thigh. The semimembranosus muscle provides in straightening the hip joint and flexing the knee joint, as well as to medially rotate the knee.
  7. Semitendinosus Muscle is one of the hamstrings. It is located in the back of the thigh. The Semitendinosus muscle, like Semitendinosus muscle, also helps in straightening of the hip joint and flexing the knee joint, as well as medially rotating the knee.
  8. Biceps Femoris Muscle is a muscle of the the back thigh. It has two parts – the short head and the long head. Biceps femoris muscle perform knee flexion, and is involved in hip extension.
  9. Gluteus Maximus Muscle is the muscle of the buttock. It’s the biggest muscle in the human body. This muscle forms the bulk of the buttocks. Gluteus maximus muscle helps in extending the upper leg, spread it, and turn it outward.
  10. Triceps Brachii Muscle is a large muscle that extends the entire length of the posterior surface of upper limb. The triceps has a long head, a lateral head, and a medial head. The functions of triceps brachii are to extend the forearm and to adduct and extend the arm.
  11. Rotator Cuff Muscles forms the supporting structure of the shoulder consisting of the muscles and tendons that attach the arm to the shoulder joint and stabilize the shoulder. It also enables the arm to move.
  12. Rhomboid Muscle is a blade rhombus-shaped muscle. Rhomboid muscle functions in helping to move the shoulder.
  13. Levator Scapulae Muscle is a skeletal muscle found at the back and side of the neck. The Levator scapulae muscle functions in lifting the scapula.
  14. Trapezius Muscle is a flat triangular muscle of the shoulder and upper back. There are two such muscles at the shoulders and upper back. Trapezius muscles function in moving the scapulae and arms.
  15. Deltoid Muscle is triangular muscle covering the joint of the shoulder. The deltoid muscle functions in raising the arm away from the side of the body.
  16. Brachioradialis Muscle is a muscle of the foream. The Brachioradialis muscle functions in flexing the elbow joint. This muscle is also capable of pronation and supination. Brachioradialis muscle is also known as the “beer drinker muscle”.
  17. Latissimus Dorsi Muscle is a flat muscle at either side of the back. Latissimus dorsi muscle runs from the spine, hip and ribs to the upper arm. Latissimus dorsi muscle functions in extending and rotating the arm medially as well as moving the shoulder down and back.

Human Muscular System – Functions of Muscles – Labeled from the Front Side

Below find an image of human muscular system showing labeling (anterior) of some of the major muscles.

Human Muscular System, labeling on the front view. Image Credit: Mikael Häggström via Wikimedia Commons
Human Muscular System, labeling on the front view. Image Credit: Mikael Häggström via Wikimedia Commons


  1. Tibialis Anterior Muscle is a deep muscle of the leg arising from the tibia. It functions in dorsiflexing and inverting the foot - it turns the foot inward and flexes the toes backward. Tibialis anterior muscle is both an antagonist and a synergist of the tibialis posterior.
  2. Adductor Muscle is a muscle of the thigh. The adductor brevis, adductor longus, adductor magnus, adductor minimus, pectineus, gracilis, and obturator externus muscles forms a group of adductor muscles that function to draw body parts toward a balance/median line.
  3. Peroneus Brevis Muscle is a muscle that arises from the side of the lower part of the fibula and lies under peroneus longus. The peroneus brevis muscle functions in everting and pronating the foot.
  4. Peroneus Longus Muscle is a muscle at the back of the ankle. Peroneus longus muscle functions in everting and plantar flexing the ankle.
  5. Quadriceps Femoris Muscle is a muscle of the thigh that extends the leg. The quadriceps femoris muscles are also known as quadriceps or quadriceps extensor. Quadriceps femoris muscle is a large extensor muscle of the knee that stabilizes the patella and the knee joint during gait. It’s crucial for walking and running.
  6. Iliopsoas Muscle is a compound muscle composed of the psoas major, psoas minor and iliacus muscles. These are muscles of the lower back and hips that flex the hip.
  7. Abdominal External Oblique muscles are lower abdominal muscles that are diagonally arranged on either side of the torso. Abdominal External Oblique muscles acts in diminishing the capacity of the abdomen and as well as drawing the chest down.
  8. Rectus abdominis muscle is a large muscle in the front of the abdomen. In humans, rectus abdominis muscle is a paired muscle that runs vertically on each side of the anterior wall of the abdomen. Rectus abdominis muscle is also known as six pack. These muscles help in breathing and in respiration. Rectus abdominis muscles also keep the internal organs intact and create intra-abdominal pressure when lifting heavy objects.
  9. Pectoralis Major Muscle is a muscle on the upper front chest that extends from the breastbone to the upper arm. Pectoralis major muscle functions in adducting and rotating the arm.
  10. Deltoid Muscle is a triangular muscle covering the joint of the shoulder. The deltoid muscle functions in raising the arm away from the side of the body.
  11. Rotator cuff muscles forms the supporting structure of the shoulder consisting of the muscles and tendons that attach the arm to the shoulder joint and stabilize the shoulder. It also enables the arm to move.
  12. Biceps Brachii Muscle is a muscle positioned in the arm roast/chop. This is what is simply referred to as biceps. Biceps brachii muscle functions in rotating the forearm and flexing the elbow.
  13. Brachialis Muscle is a muscle in the upper arm.Brachialis muscle lies deeper than the biceps. Brachialis muscle is a synergist that helps the biceps brachii in flexing the elbow joint.
  14. Pronator Teres Muscle is a muscle positioned mainly in the forearm. The Pronator teres muscle together with the pronator quadratus muscle, acts to pronate the forearm. To pronate forearm means to turn so that the palm faces posterior.
  15. Brachioradialis Muscle is a muscle of the foream. The Brachioradialis muscle functions in flexing the elbow joint. This muscle is also capable of pronation and supination. Brachioradialis muscle is also known as the “beer drinker muscle”.


I hope the contents of this article provides its readers with a useful study in understanding the basics of human muscular system.

If you have liked this article, and you would want this page to keep up and improved, you can help in any way you can. A free way to help would be to link back to this webpage from your web page, blog, or discussion forums.

The Author’s page is designed to help beginners and average readers make some money as an extra income to supplement what they may be earning elsewhere - details of which you can find in My Page, if you will.

More by this Author


Comments 2 comments

rebeccamealey profile image

rebeccamealey 4 years ago from Northeastern Georgia, USA

Wow! Lot's of information on muscles, and some very nice illustrations.


AnniesHealthTalk profile image

AnniesHealthTalk 4 years ago from United States

Great information! I voted up and linked to this in one of my hubs!

    Sign in or sign up and post using a HubPages Network account.

    0 of 8192 characters used
    Post Comment

    No HTML is allowed in comments, but URLs will be hyperlinked. Comments are not for promoting your articles or other sites.


    Click to Rate This Article
    working