what is muscle?

Glucose from carbohydrates in our diet fuels our muscles. To work properly, muscle tissue also needs particular minerals, electrolytes and other dietary substances such as calcium, magnesium, potassium and sodium.

A range of problems can affect muscles – these are collectively known as myopathy. Muscle disorders may cause weakness, pain or even paralysis.

Different types of muscle

The three main types of muscle include:

• Skeletal muscle – the specialised tissue that is attached to bones and allows movement. Together, skeletal muscles and bones are called the musculoskeletal system (also known as the locomotor system). Generally speaking, skeletal muscle is grouped into opposing pairs such as the biceps and triceps on the front and back of the upper arm. Skeletal muscles are under our conscious control, which is why they are also known as voluntary muscles. Another term is striated muscles, since the tissue looks striped when viewed under a microscope.
• Smooth muscle – located in various internal structures including the digestive tract, uterus and blood vessels such as arteries. Smooth muscle is arranged in layered sheets that contract in waves along the length of the structure. Another common term is involuntary muscle, since the motion of smooth muscle happens without our conscious awareness.
• Cardiac muscle – the muscle specific to the heart. The heart contracts and relaxes without our conscious awareness.

Make-up of muscle

Skeletal, smooth and cardiac muscle have very different functions, but they share the same basic composition. A muscle is made up of thousands of elastic fibres bundled tightly together. Each bundle is wrapped in a thin transparent membrane called a perimysium.

An individual muscle fibre is made up of blocks of proteins called myofibrils, which contain a specialised protein (myoglobin) and molecules to provide the oxygen and energy required for muscle contraction. Each myofibril contains filaments that fold together when given the signal to contract. This shortens the length of the muscle fibre which, in turn, shortens the entire muscle if enough fibres are stimulated at the same time.

The neuromuscular system

The brain, nerves and skeletal muscles work together to cause movement. This is collectively known as the neuromuscular system. A typical muscle is serviced by anywhere between 50 and 200 (or more) branches of specialised nerve cells called motor neurones. These plug directly into the skeletal muscle. The tip of each branch is called a presynaptic terminal. The point of contact between the presynaptic terminal and the muscle is called the neuromuscular junction.

To move a particular body part:

• The brain sends a message to the motor neurones.
• This triggers the release of the chemical acetylcholine from the presynaptic terminals.
• The muscle responds to acetylcholine by contracting.

Shapes of skeletal muscle

Generally speaking, skeletal muscles come in four main shapes, including:

• Spindle – wide through the middle and tapering at both ends, such as the biceps on the front of the upper arm.
• Flat – like a sheet, such as the diaphragm that separates the chest from the abdominal cavity.
• Triangular – wider at the bottom, tapered at the top, such as the deltoid muscles of the shoulder.
• Circular – a ring-shape like a doughnut, such as the muscles that surround the mouth, the pupils and the anus. These are also known as sphincters.

Muscle disorders

Muscle disorders may cause weakness, pain, loss of movement and even paralysis. The range of problems that affect muscles are collectively known as myopathy. Common muscle problems include:

• Injury or overuse, including­ sprains or strains, cramps, tendonitis and bruising
• Genetic problems, such as muscular dystrophy
• Inflammation, such as myositis
• Diseases of nerves that affect muscles, such as multiple sclerosis
• Conditions that cause muscle weakness, such as metabolic, endocrine or toxic disorders; for example, thyroid, and adrenal diseases, alcoholism, pesticide poisoning, medications (steroids, statins) and myasthenia gravis
• Cancers, such as soft tissue sarcoma.

Where to get help

• Your doctor
• Physiotherapist
• Exercise physiologist ESSA Exercise & Sports Science Australia
• Osteopath
• NURSE-ON-CALL Tel. 1300 60 60 24 – for expert health information and advice 24 hours, 7 days

Things to remember

• There are about 600 muscles in the human body.
• The three main types of muscle include skeletal, smooth and cardiac.
• The brain, nerves and skeletal muscles work together to cause movement – this is collectively known as the neuromuscular system.

  Muscles are pieces of soft tissue throughout your body. They help you do everything from holding your body still to running a marathon. Muscles also move and support your organs. Your heart is a hard-working muscle that beats thousands of times a day to keep you alive.

  Because you have so many muscles, injuries and health conditions that affect them are common. Everyone has a sore muscle every once in a while, but long-term muscle pain, weakness and other symptoms can be signs of serious issues. Visit a healthcare provider if you experience muscle pain for more than a week, or if you’re having trouble moving. Go to the emergency room if it’s hard to breathe or swallow.

  Function

  What are muscles’ function?

  Muscles move your body. They perform two types of movements:

  • Voluntary movements: Voluntary movements are actions you control. You choose to perform an action and your muscles move your body to make it happen. You use your nervous system to control these movements. Flicking your thumb to scroll through this article on your phone and sprinting around a track are both voluntary movements.
  • Involuntary movements: Involuntary movements happen automatically without you thinking about them. The muscles in and around your organs move involuntarily to keep your body working properly. Your heart beating and muscles in your chest and back moving your ribs when you breathe are examples of involuntary movements.

  Your muscles use a combination of voluntary and involuntary movements to work with nearly all your body’s systems and functions. Different kinds of muscles help with:

  • Vision.
  • Hearing.
  • Breathing, speaking and swallowing.
  • Digesting food and getting rid of waste (peeing and pooping).
  • Moving, sitting still and standing up straight.
  • Pumping blood through your heart and blood vessels.
  • Giving birth.

  Muscles also store and release energy your body uses as part of your metabolism.

  Anatomy

  What is the anatomy of muscles?

  Your muscles are made of thousands of small fibers woven together. These fibers stretching and pressing together is what moves your organs or body. Your muscles weave together like a quilt that covers your body. They run in all directions and work together to move you.

  What are the types of muscles?

  Healthcare providers organize muscles by tissue type. There are three types of muscle tissue in your body:

  • Skeletal.
  • Cardiac.
  • Smooth.

  Skeletal muscles

  Skeletal muscles are part of your musculoskeletal system. They work with your bones, tendons and ligaments to support your weight and move you. Tendons attach skeletal muscles to bones all over your body.

  Skeletal muscles are voluntary — they move when you think about moving that part of your body. Some muscle fibers contract quickly and use short bursts of energy (fast-twitch muscles). Others move slowly, like your back muscles that help with posture.

  Cardiac muscle

  Cardiac muscle (myocardium) makes up the middle layers of your heart. It doesn’t exist anywhere else in your body. Cardiac muscle squeezes and relaxes to pump blood through your cardiovascular system.

  Your heart is an involuntary muscle — it beats on its own without your input.

  Smooth muscles

  Smooth muscles are involuntary muscles that line the inside of some organs. They do essential jobs like moving waste through your intestines and helping your lungs expand when you breathe.

  Smooth muscles play an important role in many body systems, including the:

  • Female reproductive system and male reproductive system.
  • Urinary system.
  • Respiratory system.
  • Digestive system.

  How many muscles are in the human body?

  There are more than 600 muscles located almost everywhere throughout your body.

  Your first thought when picturing muscles might be the biceps in your upper arms or the quads in your thighs, but muscles support almost every part of your body, many of which you’ll never notice.

  Conditions and Disorders

  What are common injuries or health conditions that affect muscles?

  Muscle strains (pulled muscles) are the most common muscle injury. They happen when you overuse a muscle. The strands of muscle fiber are stretched beyond their limit and tear apart. You’ve seen this happen if you’ve ever tried to use an old bungee cord to hold something in place.

  Many health conditions can affect your muscles, too, including:

  • Fibromyalgia.
  • Myopathies.
  • Myositis and polymyositis.
  • Infections, including the flu (influenza) and COVID-19.
  • Amyotrophic later sclerosis (ALS).
  • Cardiovascular disease.

  Muscle symptoms

  The most common symptoms of a muscle injury or health condition include:

  • Muscle pain.
  • Muscle weakness.
  • Stiffness.
  • Muscle spasms (cramps).
  • Swelling.
  • Bruising.
  • Skin discoloration.

  Muscle tests

  A healthcare provider may use a few different kinds of tests to diagnose muscle conditions or injuries:

  • Blood tests.
  • Electromyography (EMG).
  • Magnetic resonance imaging (MRI).
  • Ultrasound.
  • Muscle biopsy.

  How do healthcare providers treat muscle issues?

  Which treatments you’ll need depends on the health condition or injury you have. Some conditions that affect your muscles are short-term issues. Others are chronic conditions and you’ll need to manage your symptoms for a long time.

  You can manage many muscle injuries at home with the RICE method:

  • Rest: Avoid the activity that caused the injury. Try not to use the injured part of your body while it heals.
  • Ice: Apply a cold compress to your injury 15 minutes at a time, a few times a day. Wrap ice packs in a towel or thin cloth so they’re not directly touching your skin.
  • Compression: Wrap an elastic bandage around your injured muscle to help reduce swelling. Your provider can show you how to apply a compression wrap safely.
  • Elevation: Keep your injured muscle above the level of your heart as often as you can.

  Care

  How can I take care of my muscles?

  Stretching and warming up before exercise or physical activity are the best ways to prevent muscle injuries. Increasing your overall flexibility will also protect your muscles from injuries. The more flexible you are, the more room your muscle fibers have to stretch before they begin to tear.

  Increase your activity level gradually. Don’t suddenly ramp up your training intensity or start exercising way more often than you usually do.

  When should I see a healthcare provider?

  Visit a provider if you’re experiencing muscle pain that doesn’t get better in a week with rest and other at-home treatments. Go to the emergency room if you have any of the following symptoms:

  • Sudden chest pain or other heart attack symptoms.
  • Trouble breathing or swallowing.
  • Severe pain, muscle spasms or muscle weakness.
  • Loss of balance.
  • Suddenly worse vision.
  • Problems controlling your bladder or bowels.

  Additional Common Questions

  Is a muscle an organ or a tissue?

  Muscles are tissue. Smooth muscle tissue lines some of your organs, but most organs are also made of other types of tissue, too. Providers sometimes refer to the muscular system as one anatomical group that includes all your muscles. They might also include muscles as parts of other systems throughout your body.

  Your heart is the only organ that’s also a muscle. It’s made of a special type of muscle tissue called cardiac muscle. Your heart is the only place in your body that has cardiac tissue.

  What are muscle groups?

  Fitness trainers or physical therapists may talk about strengthening or working out specific muscle groups. These are usually loosely defined.

  It’s common to group muscles together by their location (like your chest muscles, leg muscles or back muscles) or what kind of movement they perform (abductors, flexors or extensors, for example).

  Healthcare providers usually only classify muscles based on the type of tissue they’re made of.

  A note from Cleveland Clinic

  You have more than 600 muscles, and you use them constantly whether you’re thinking about them or not. Some muscles you can see and feel (especially after a big workout). Others — like your heart and the muscles that line some organs — silently keep you alive. It’s normal to feel sore or achy sometimes, but visit a healthcare provider if you’re constantly feeling muscle pain. You shouldn’t feel sore or painful all the time. Muscle pain can often be a sign of a condition a provider needs to diagnose and treat.

  Remember, you don’t have to look like a muscular professional athlete to be healthy. Talk to your provider about ways to support your muscle (and overall) health. They’ll suggest exercises, movements or physical activities that’ll keep you strong, safe and healthy.