Skeletal muscles have three major functions. First, skeletal muscle works with the bones of the skeletal system to produce movement. Second, it muscle provides stabilization. Finally, it generates heat; providing critical support to the regulation of body temperature. Skeletal muscle has four important characteristics that allow for its function. These characteristics are excitability, contractility, elasticity and extensibility.
The excitability and contractility of skeletal muscle refer to its reaction to a nervous electrical impulse. Excitability means the muscle can respond to a stimulus. Contractility means the muscle is able to shorten powerfully. An electrical impulse, or action potential, is carried by a nerve cell to a muscle cell. When the action potential reaches the end of the nerve cell, it is translated into a chemical signal and travels to a specified muscle cell. The muscle cell contracts, or shortens, in response to the signal it receives from the nerve cell. Skeletal muscle returns to its original shape after contracting or lengthening. The ability of a muscle to return to its resting length after stretching is called elasticity. Muscles are attached to bone by tendons. So, when the muscle shortens, it pulls the tendon tight and moves the bone. Muscles can only pull on bones to move them, they never push. So in order for the body to move in many directions, muscles must have opposition. For example, the biceps in the upper arm flex the arm. The triceps – the opposing muscle group to the biceps – extend the arm. The capability of skeletal muscle to stretch is called extensibility. Skeletal muscle can also lengthen beyond normal – this usually occurs as the result of injury. When a muscle is stretched beyond its normal limits, it is called muscle strain.
Muscles provide for the stabilization of joints. Joints are made when bones meet. The ends that meet, or articulate with each other, are covered in a smooth cartilage that reduces friction upon movement of the joint. However, the cartilage doesn’t create a strong bond between the bones. Ligaments connect the joint together to attach bone to bone. However, the most significant stabilizers are the tendons. Tendons connect bone to muscle. The tendons are held tight by the muscles. The muscles maintain a small amount of contraction, even when resting. This is called muscle tone. Good muscle tone is necessary for holding joints together.
Skeletal muscle is also important for maintaining posture. Our muscles make small adjustments all the time to keep us sitting or standing up straight. Without muscles, our bodies would lose the battle against gravity – a force that is constantly pulling us toward the ground.
Skeletal muscle makes up about forty percent of the body's muscle mass. Heat is produced when muscles contract. Since skeletal muscle is such a significant portion of our body’s mass, it is crucial to maintaining proper body temperature. Most of the chemical reactions that occur in your body – from enzyme functions to metabolism reactions – work best at optimum body temperature. Normal body temperature is 98.6 degrees Farenheit or 37 degrees Celcius. Ever wonder why you shiver when you get cold? Shivering is the result of contracting muscles. It is one mechanism employed by the body to warm itself.
- Marieb, Anatomy & Physiology, 7th Ed., 2007