Muscle - Definition, Function, Types and Structure | Biology Dictionary (2023)

Muscle Definition

A muscle is a group of muscle tissues which contract together to produce a force. A muscle consists of fibers of muscle cells surrounded by protective tissue, bundled together many more fibers, all surrounded in a thick protective tissue. A muscle uses ATP to contract and shorten, producing a force on the objects it is connected to. There are several types of muscle, which act on various parts of the body.

Structure of Muscle

A muscle consists of many muscle tissues bundled together and surrounded by epimysium, a tough connective tissue similar to cartilage. The epimysium surrounds bundles of nerve cells that run in long fibers, called fascicles. These fascicles are surrounded by their own protective layer, the perimysium. This layer allows nerves and blood to flow to the individual fibers. Each fiber is then wrapped in an endomysium, another protective layer. As seen in the image below, a muscle is arranged in a basic pattern of bundled fibers separated by protective layers.

These layers and bundles allow different parts of a muscle to contract differently. The protective layer surrounding each bundle allows the different bundles to slide past one another as they contract. The epimysium connects to tendons, which attach to the periosteum connective tissue that surrounds bones. Being anchored to two bones allows movement of the skeleton when the muscle contracts. A different type of muscle surrounds many organs, and the epimysium connects to other connective tissues to produces forces on the organs, controlling everything from circulation to food processing.

Function of Muscle

Whether it is the largest muscle in your body or the tiny muscle controlling the movement of your eye, every muscle functions in a similar manner. A signal is sent from the brain along a bundle of nerves. The electronic and chemical message is passed quickly from nerve cell to nerve cell and finally arrives at the motor end plate. This interface between the muscle and nerve cells releases a chemical signal, acetylcholine, which tells the muscle fiber to contract. This message is distributed to all the cells in the fiber connected to the nerve.

(Video) Musculoskeletal System | Muscle Structure and Function

This signal causes the myosin proteins to grab onto the actin filaments around them. These are the purple proteins in the image below. Myosin uses ATP as an energy source to crawl along the green filament, actin. As you can see, the many small heads of the myosin fibers crawling along the actin filaments effectively shortens the length of each muscle cell. The cells, which are connected end-to-end in a long fibers, contract at the same time and shorten the whole fiber. When a signal is sent to an entire muscle or group of muscles, the resulting contraction results in movement or force being applied.

A muscle can be used in many different ways throughout the body. A certain muscle might contract rarely with a lot of force, whereas a different muscle will contract continually with minimal force. Animals have developed a plethora of uses for the forces a muscle can create. Muscles have evolved for flying, swimming, and running. They have also evolved to be pumps used in the circulatory and digestive systems. The heart is a specialized muscle, which is uses exclusively for pumping blood throughout the body. These different types of muscle will be discussed below.

Types of Muscle

Skeletal Muscle

When you think of a muscle, most people generally think of a skeletal muscle. The biceps, triceps, and quadriceps are all common names for muscles that body builders tend to focus on. In fact, these general muscles are often composed of many small muscles that attach to different places to give a joint its full range of motion. Skeletal muscle is a striated muscle. This means that each muscle fiber has striations, or linear marks, which can be seen when this muscle is put under a microscope. The striations correspond to the sarcomeres present in striated muscles, which are highly organized bundles of muscle cells which can contract quickly in concert.

Skeletal muscle is controlled via the somatic nervous system, also known as the voluntary nervous system. Point your finger to the ceiling. This is your somatic nervous system in action, controlling your skeletal muscles.

(Video) The Muscular System Explained In 6 Minutes

Cardiac Muscle

Cardiac muscle, while similar to skeletal muscle in some ways, is connected to the autonomous nervous system. This system controls vital organs such as the heart and lungs and allows us to not have to focus on pumping our heart each time it needs to beat. While there is a certain amount of conscience control we have over the autonomous nervous system, it will always kick in when we are unconscious. For instance, you can hold your breath if you like but you do not have to remember to breathe all the time. Cardiac muscle surround the chambers of the heart and is used to pump blood through the body.

Cardiac muscle is similar to skeletal muscle in that it is striated. Unlike skeletal muscle, cardiac muscle fibers are arranged in a branching pattern instead of a linear pattern. Both skeletal muscle and cardiac muscle need to contract quickly and often, which is why the striations can be seen.

Smooth Muscle

Unlike skeletal and cardiac muscle, smooth muscle is not striated. This is because the individual muscle cells are not perfectly aligned into sarcomeres. Instead, they are displaced throughout the fibers. This gives smooth muscle the ability to contract for longer, although the contraction happens more slowly. Consider the muscle that contracts the sphincter on your bladder. This muscle may need to stay clamped shut for hours at a time and only gets a minute of relief when you go to the bathroom. Many other smooth muscles operate in the same manner.

Like cardiac muscle, smooth muscle is mostly controlled by the autonomous nervous system. The many muscles that line your digestive tract work together to move food through the digestive system. Muscles attach to your hair follicles that all your hairs to stand up when it’s cold. Smooth muscle is almost everywhere in your body and aids in everything from circulation to digestion.


1. A big, strong bear goes in a cave to hibernate for winter. In the spring a skinny, weak bear emerges. What happened to the bear’s muscles?
A. They stayed the same size, they were just hidden under fat
B. The bear used them as energy during hibernation
C. The bear’s fur is thinner, making him look weaker

(Video) Structure & function of skeletal MUSCLES: Myofibrils, sarcomere, sliding filament theory.

Answer to Question #1

B is correct. Muscles that aren’t being used are wasted energy. The bear will use the protein and nutrients available in its muscle and fat cells to survive through the winter. Some muscles, like the diaphragm used to control breathing, will not see a loss in mass. Other muscles, like the leg muscles, are not needed during hibernation and will be allowed to atrophy, or decrease in size.

2. Growing muscles is known as hypertrophy. Body builders do this when they work out to increase the size of their muscle. Often, days after a good workout, the muscle that got worked will hurt slightly. What causes this?
A. Lactic Acid buildup
B. Not enough Protein!
C. Microscopic tears in the muscle fibers

Answer to Question #2

(Video) Structure of Skeletal Muscle Explained in simple terms

C is correct. When you really push your muscles to the limits, they begin to tear. If you try to lift too much weight, you will tear you muscles in half. By doing repetitive sets of a heavy weight, a muscle will obtain tiny tears in various muscle fibers. When these tears heal, more muscle cells are used and the overall mass and size of the muscle increase.XX

3. Endurance runners are told to eat pasta the night before a big run. Why is this helpful?
A. Pasta doesn’t slosh around while you are running
B. Carbohydrates help you soak up more water, which helps you run
C. Carbohydrates break down easily and load your cells with ATP

Answer to Question #3

C is correct. The carbs found in pasta can easily be broken down into glucose, which muscle cells convert to ATP to store energy. This ATP is then used to activate the myosin heads and help them walk along the actin filament. In reality, any balanced meal will load your cells up with glucose and prepare you for exercise.


  • Lodish, H., Berk, A., Kaiser, C. A., Krieger, M., Scott, M. P., Bretscher, A., . . . Matsudaira, P. (2008). Molecular Cell Biology 6th. ed. New York: W.H. Freeman and Company.
  • Nelson, D. L., & Cox, M. M. (2008). Principles of Biochemistry. New York: W.H. Freeman and Company.


What are the structures and functions of muscles? ›

The basic function of muscle is to generate force. Secondarily, muscles can provide some shape and form to the organism. Anatomically and functionally, muscle can be divided into two types, smooth and striated. Striated or striped muscle can be further divided into skeletal muscle and cardiac (heart) muscle.

What are the 5 main functions of the muscular system describe each function? ›

The 5 main functions of the muscular system are movement, support, protection, heat generation, and blood circulation.
  • Movement. Skeletal muscles pull on the bones causing movements at the joints. ...
  • Support. Muscles of the body wall support the internal organs. ...
  • Protection. ...
  • Heat generation. ...
  • Blood circulation.

What are the different types of muscles explain their function? ›

Each type of muscle tissue in the human body has a unique structure and a specific role. Skeletal muscle moves bones and other structures. Cardiac muscle contracts the heart to pump blood. The smooth muscle tissue that forms organs like the stomach and bladder changes shape to facilitate bodily functions.

What are the 7 functions of muscle? ›

The main functions of the muscular system are as follows:
  • Mobility. The muscular system's main function is to allow movement. ...
  • Stability. Muscle tendons stretch over joints and contribute to joint stability. ...
  • Posture. ...
  • Circulation. ...
  • Respiration. ...
  • Digestion. ...
  • Urination. ...
  • Childbirth.
May 30, 2018

What's the definition of muscle? ›

mus·​cle ˈməs-əl. often attributive. : a body tissue consisting of long cells that contract when stimulated and produce motion see cardiac muscle, smooth muscle, striated muscle.

What are the 6 major types of muscles? ›

6.3: Types of Muscle Tissue
  • Work Those Eye Muscles!
  • What is Muscle Tissue?
  • Skeletal Muscle Tissue. Skeletal Muscle Pairs. Skeletal Muscle Structure. Slow- and Fast-Twitch Skeletal Muscle Fibers.
  • Smooth Muscle. Structure of Smooth Muscle. Functions of Smooth Muscle.
  • Cardiac Muscle. Feature: Human Body in the News.
May 13, 2020

What are the 6 major muscles and their functions? ›

The six major muscle groups you want to train are the chest, back, arms, shoulders, legs, and calves. You want to train each of these muscle groups at least once every 5 to 7 days for maximum muscle gain.

What are the 4 main functions of the muscular system? ›

Four functions of muscle contraction are movement, posture, joint stability, and heat production. Three types of muscle are skeletal, smooth, and cardiac.

What are 5 important major muscles in your body? ›

Here are the 5 most important muscle groups you should know about:
  • Shoulder and back muscles. Slouching over our screens and sitting too much makes it crucial to work your shoulder and back muscles. ...
  • Chest and arm muscles. ...
  • Abdominal muscles. ...
  • Leg muscles. ...
  • Calves muscles.

What are the 4 organs in the muscular system? ›

A whole skeletal muscle is considered an organ of the muscular system. Each organ or muscle consists of skeletal muscle tissue, connective tissue, nerve tissue, and blood or vascular tissue.

What are the types of muscles? ›

The 3 types of muscle tissue are cardiac, smooth, and skeletal.

What is the structure of muscles? ›

Each muscle is made up of groups of muscle fibers called fascicles surrounded by a connective tissue layer called perimysium. Multiple units of individual muscle fibers within each fascicle are surrounded by endomysium, a connective tissue sheath.

What are the 7 ways muscles are named? ›

There are seven ways that muscles can be named. Muscles can be named based on their location and muscle attachment points. They are also named on their size, shape, action, the number of divisions, and muscle fiber direction.

What muscles are named for their function? ›

Muscles Named for Action
  • flexor carpi radialis – flexes wrist.
  • abductor magnus – abducts the thigh.
  • extensor digitorum – extends the fingers.
  • levator – lifts a structure.

What are the 8 main muscles of the body? ›

Muscles of the human body
  • Rectus femoris.
  • Sartorius.
  • Tensor fascia latae.
  • Iliopsoas.
  • Pectineus.

What are the 8 muscle groups? ›

Muscle groups
  • chest.
  • back.
  • arms.
  • abdominals.
  • legs.
  • shoulders.
May 28, 2020

What are the 12 major muscles in the body? ›

12 Major Muscle Groups
  • Gluteus. The gluteus can be found on the buttocks. ...
  • Hamstrings. Your hamstrings can be found on the back of your thigh. ...
  • Biceps. Deltoids are located on the top of your shoulder. ...
  • Abdominal Muscles. Deltoids.
  • Gastrocnemius & Soleus. ...
  • Latissimus Dorsi & Rhomboids. ...
  • Erector Spinae. ...
  • Pectoralis.

What are the 4 types of muscles and examples? ›

Types of Muscles
  • Skeletal or striated muscles.
  • Cardiac muscles.
  • Smooth muscles.

What is the best definition of the origin of a muscle? ›

What is the origin of a muscle? The origin muscle definition is the site where bone and muscle are attached, but do not move during contraction. The origin is typically the tissues' proximal attachment, the one closest to the torso. Muscles always pull.

How do you show muscle definition? ›

Consider pushups or a dumbbell press. Go to max effort, doing as many reps as you can, then rest for a minute. Go for one more round to break down the muscle as much as possible. This will help stimulate hypertrophy, which builds muscle size and improves muscle definition.

What are the 7 core muscles? ›

The major muscles of your core include your transverse abdominis, multifidus, internal and external obliques, erector spinae, diaphragm, pelvic floor muscles, and (of course) your abs, the rectus abdominis.

What are the 3 parts of a muscle? ›

Epimysium: The outermost layer of tissue surrounding the entire muscle. Perimysium: The middle layer surrounding bundles of muscle fibers. Endomysium: The innermost layer surrounding individual muscle fibers.

What are the 6 rules of muscles? ›

Six Rules to Follow When You're Trying to Build Muscle
  • #1 – Give your muscles adequate time to recover. ...
  • #2 – Consume adequate calories to help fuel your muscles. ...
  • #3 – Consume high-quality protein throughout the day as needed. ...
  • #4 – Consume carbohydrates to help fuel your muscles. ...
  • #5 – Hydrate!
Sep 6, 2019

What are the 5 major structural parts the muscular system is made up of? ›

Your musculoskeletal system includes bones, muscles, tendons, ligaments and soft tissues. They work together to support your body's weight and help you move.

What are 3 main functions of the muscular system? ›

The muscular system is a complex network of muscles vital to the human body. Muscles play a part in everything you do. They control your heartbeat and breathing, help digestion, and allow movement. Muscles, like the rest of your body, thrive when you exercise and eat healthily.

What is the strongest muscle? ›

The strongest muscle based on its weight is the masseter. With all muscles of the jaw working together it can close the teeth with a force as great as 55 pounds (25 kilograms) on the incisors or 200 pounds (90.7 kilograms) on the molars.

What is biggest muscle in body? ›

The largest muscle in the body is the gluteus maximus. Located at the back of the hip, it is also known as the buttocks. It is one of the three gluteal muscles: medius.

Which muscle is most important? ›

The human heart is the most incredible muscle in the body, beating about 100,000 times to send 3,600 gallons of blood through 75,000 miles of blood vessels each day. Sure, skeletal muscles are vital to our ability to function, but the heart is truly a step above.

What are muscles made of? ›

Muscles and Joints. Tendons are bands of fibrous tissue that connect muscles to bones. Muscles are all made of the same material, a type of elastic tissue (sort of like the material in a rubber band). Thousands, or even tens of thousands, of small fibers make up each muscle.

How many muscles in the body? ›

It's estimated that there are over 650 named skeletal muscles in your body. Other muscle tissue, such as smooth muscle, typically occurs on a cellular level, meaning that you can actually have billions of smooth muscle cells. The muscles of your body perform a variety of vital functions.

Is the brain a muscle? ›

As it turns out, your brain isn't actually a muscle. It's an organ — one that actually plays a huge role in controlling muscles throughout your body. Muscle is made up of muscle tissue, which is muscle cells grouped into elastic bundles that contract together to produce motion and/or force.

How is muscle made? ›

The Physiology Of Muscle Growth

After you workout, your body repairs or replaces damaged muscle fibers through a cellular process where it fuses muscle fibers together to form new muscle protein strands or myofibrils. These repaired myofibrils increase in thickness and number to create muscle hypertrophy (growth).

What are the 3 types of muscles and their main differences? ›

The three main types of muscle include:
  • Skeletal muscle – the specialised tissue that is attached to bones and allows movement. ...
  • Smooth muscle – located in various internal structures including the digestive tract, uterus and blood vessels such as arteries. ...
  • Cardiac muscle – the muscle specific to the heart.

Which muscle closes the eye? ›

The orbicularis oculi muscles circle the eyes and are located just under the skin. Parts of this muscle act to open and close the eyelids and are important muscles in facial expression.

What muscle is used in smiling? ›

The Muscle Used in Smiling — Zygomaticus Major. Known as the Smiling Muscle, the zygomaticus major is most responsible for our smile. It works in conjunction with up to 43 other facial muscles to provide a wide array of smiles.

What are the 5 ways muscles are named? ›

These include naming the muscle after its shape, its size compared to other muscles in the area, its location in the body or the location of its attachments to the skeleton, how many origins it has, or its action.

What are the 6 ways muscles are named? ›

These include naming the muscle after its shape, size, fiber direction, location, number of origins or its action.

What are the 3 structure of muscles? ›

The 3 types of muscle tissue are cardiac, smooth, and skeletal.

What are the 3 main structures of the muscular system? ›

The three main types of muscle include:
  • Skeletal muscle – the specialised tissue that is attached to bones and allows movement. ...
  • Smooth muscle – located in various internal structures including the digestive tract, uterus and blood vessels such as arteries. ...
  • Cardiac muscle – the muscle specific to the heart.

What are 4 important functions of muscles? ›

Four functions of muscle contraction are movement, posture, joint stability, and heat production. Three types of muscle are skeletal, smooth, and cardiac.

What are the 4 main types of muscles? ›

Muscle Types
  • Skeletal Muscle. Skeletal muscle, attached to bones, is responsible for skeletal movements. ...
  • Smooth Muscle. Smooth muscle, found in the walls of the hollow internal organs such as blood vessels, the gastrointestinal tract, bladder, and uterus, is under control of the autonomic nervous system. ...
  • Cardiac Muscle.

What are the 5 major muscles of the muscular system? ›

To achieve these benefits, it is important to know the body's five (5) major muscle groups. Chest, Back, Arms & Shoulders, Abs, Legs & Buttocks and their functions.

What are the 3 most important muscles? ›

Here are the 5 most important muscle groups you should know about:
  1. Shoulder and back muscles. Slouching over our screens and sitting too much makes it crucial to work your shoulder and back muscles. ...
  2. Chest and arm muscles. ...
  3. Abdominal muscles. ...
  4. Leg muscles. ...
  5. Calves muscles.

What are the three main functions of the muscular? ›

The muscular system is a complex network of muscles vital to the human body. Muscles play a part in everything you do. They control your heartbeat and breathing, help digestion, and allow movement.


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