Illustration of the muscles of a man

Types of muscle

Our bodies contain three main types of muscle

There are approximately 640 muscles in your body, divided into three groups.

Skeletal muscle

Skeletal muscles are our voluntary muscles, meaning that we can control them at will. We use them to govern movement and posture and regulate body temperature.

A light micrograph of stained longitudinal section through striated skeletal muscle

Skeletal muscle: A light micrograph of a stained longitudinal section through striated skeletal muscle. 

CC BY NC ND

Spike Walker/Wellcome Images 

Most often they are found over joints, attached to two bones. They typically control movement through activation by the somatic branch of the peripheral nervous system, with a rapid speed of contraction.

However, while usually voluntarily controlled, they can be used in involuntary reflex responses when fast movement is required. For example, if you touch a hot stove, your skeletal muscles will respond rapidly to instant chemical and electrical impulses from the brain, withdrawing your hand from the dangerous situation without conscious thought.

Skeletal muscles also play a role in temperature regulation, using rapid muscle contractions (shivering) to release heat to raise body temperature – which is another example of their involuntary use.

Skeletal muscle is made up of muscle fibres – which in skeletal muscle come in several different types (see ‘A closer look at skeletal muscles’ for more detail) – and is striated, meaning that its tissue is crossed with light and dark bands. This is a result of how the subunits that make up the muscle fibres are arranged. (You can learn more about the structure of muscle fibres and how they contract in our video on the sliding filament theory of contraction.)

Smooth muscle

Smooth muscle is involuntary muscle tissue controlled by the autonomic nervous system. It lines organs such as the stomach and bladder as well as our blood vessels. 

Smooth muscle contracts much more slowly than skeletal and cardiac muscle. Its purpose is to move substances through an organ or vessel, and it does so by contracting in waves, which is known as peristalsis (and occurs, for example, in the intestines).

A transmission electron micrograph showing a longitudinal section of cardiac (heart) muscle

Cardiac muscle: A transmission electron micrograph showing a longitudinal section of cardiac (heart) muscle, in which the striated structure and a large intercalated disc can be seen.

Credit:

Prof. Giorgio Gabella/Wellcome Images

Cardiac muscle

Cardiac muscle is found only in the heart. Another involuntary muscle controlled by the autonomic nervous system, it stimulates itself using electrical impulses to contract and pump blood around our bodies.

This is made possible by specialised junctions called ‘intercalated discs’, which lie between the heart muscle cells (cardiomyocytes), defining their borders. These discs help conduct impulses from one cell to another rapidly, allowing them to synchronise their contractions.

Like skeletal muscle, cardiac muscle tissue is striated. In between its fibres are intermittent spaces, which contain connective tissue and many capillaries to ensure a constant supply of oxygen.

The thickness of cardiac muscle differs across the heart. For example, the left ventricle has to pump blood all over the body, and is therefore characteristically thick. The wall of the right ventricle is thinner, as it only has to pump oxygen-depleted blood the short distance from the heart to the lungs. 

Summary

Type of muscle

Where found? Voluntary or involuntary? Striated?
Skeletal Over joints, throughout body Voluntary Yes
Smooth

Blood vessels, intestines, stomach, uterus, bladder, lungs

Involuntary No
Cardiac Heart Involuntary Yes

 

Lead image:

El Bingle/Flickr CC BY NC

References

Further reading

About this resource

This resource was first published in ‘Exercise, Energy and Movement’ in August 2016.

Topic:
Physiology
Issue:
Exercise, Energy and Movement
Education levels:
16–19, Continuing professional development