What are Skeletal Muscles?
Skeletal muscles are a type of striated muscle that attaches to the bones via tendons, i.e. they attach to the bones of the skeleton, hence their name.
As a result, skeletal muscles are responsible for the voluntary movement of the body and its various parts. They are the most abundant type of muscle in the human body and account for about 40% of total body weight. They are composed of long, cylindrical cells called muscle fibres which are arranged in bundles or fascicles.
Force and Movement
The primary role of skeletal muscles is to generate force and movement. When a muscle contracts, it pulls on the bone to which it is attached, causing movement of the body part. The subsequent application of additional energy then creates force or pressure.
Skeletal muscles work in pairs, with one muscle contracting while the other relaxes to allow movement in both directions. This is known as agonist-antagonist muscle action. Movement pairs include:
- flexion and extension, as in bending and straightening the knee or elbow, and
- abduction and adduction, as in rolling your knees inward and outward while laying on your back, or the rolling of the shoulders forwards and out, and back and inward. The latter example is sometimes referred to as protraction and retraction of the scapula.
Remedial Massage and Physiotherapy are common treatments for ensuring that your skeletal muscles, long nerves, and associated joints function to their fullest ability.
Support and Structure
In addition to movement, skeletal muscles also play a role in maintaining posture and stabilising joints.
For example, the muscles of the lower back and abdomen work together to support the spine and maintain proper posture.
Similarly, the muscles of the shoulder and hip joints work together to stabilise these joints during movement.
Our skeletal muscles are constantly stabilising and adjusting all day, every day, to provide support to our bodies.
Other Types of Muscle
The human body also contains smooth muscles and cardiac muscles.
- Smooth muscles are found in the walls of internal organs, such as the digestive tract, blood vessels, and uterus. Other smooth muscles include sphincters and muscles of the eye. This muscle group is responsible for involuntary movements, such as the contractions that move food through the digestive tract or the dilation, making hairs stand erect (arrector pili), and constriction of blood vessels.
- Another type of smooth muscle, sometimes treated as a sub-classification, are sphincters. These are circular muscles that control the flow of substances through tubes or openings in the body, such as the oesophagus, stomach, intestines, urinary tract, and iris of the eye. Sphincters can open and close to allow the passage of materials in a controlled manner. They may also be encased in striated muscle.
- Cardiac muscles are found exclusively in the heart. They are responsible for the rhythmic contractions that pump blood throughout the body. Like skeletal muscles, cardiac muscles are striated, but they are involuntary and are regulated by the autonomic nervous system.
- Extraocular muscles are a type of striated muscle with both voluntary and involuntary controls that control the outer movements of the eye.