muscle tissue of human body

Did you know that approximately 40 – 50% of the human body mass consist of skeletal muscle tissue?

Skeletal muscle tissue is the largest tissue in humans and likely the tissue that is most affected by movement, such as physical activity and exercise.

Muscle Tissue

Human possess three types of muscle tissue; 1) cardiac muscle; 2) smooth muscle; and 3) skeletal muscle (see picture 1).

Picture 1: The three different types of muscle tissue

Each type of muscle tissue has different functional and anatomical features.

Smooth muscle tissue appears in many tissues and is non-striated. It is found in the walls of hollow organs, like the gastrointestinal tract, and in the walls of passageways, such as blood vessels and the tracts of the respiratory system. Smooth muscle is fundamentally different from skeletal muscle and cardiac muscle in terms of structure, function, and contraction.

Cardiac muscle tissue is only present in the heart. It shares several common features with skeletal muscle as both appear striated (striped) (see picture), and both contract or shorten in a similar manner. Activity of cardiac muscle, as well as smooth muscle, occurs involuntarily. This means a general absence of conscious control as to how fast the heart beats, or how fast food moves through the digestive system.

Skeletal muscle tissue operates under voluntary control, as in curling a 25-lb barbell or hitting a golf ball. As an individual you can easily control the velocity of the movement in the barbell curl, the range of motion during the lifting movement, and the number of repetitions completed. In golf, the player controls all aspects of the coordinated, and hopefully perfectly timed, movements of the arms, legs, and torso during the backswing and downswing. Skeletal muscle, of course, attracts most interest in sports and exercise.

Skeletal muscles

Did you know that a human body possesses approximately 600-plus skeletal muscles (depending on the source consulted)? And do you know which muscle is the biggest and which the smallest?

A large muscle is the quadriceps. This is the muscle on the front side of your upper leg, which actually consists of 4 (‘quadri’) parts. The gluteus maximus muscle, so your buttocks, is also a large muscle. Both, quadriceps and gluteus, are well developed in power athletes and can generate lots of force.

On your upper body the deltoid muscle (shoulder), the latissimus dorsii (‘lat’ or back muscle) - connecting your head with your shoulder and upper back -, and the biceps brachii are large muscles (see picture 2).

Picture 2: Example of some skeletal muscles

The smallest has only a size of 1-2 mm and can be found in your ear. It is the stapedius muscle and support the smallest bone in the body (the stapes), which helps conduct vibrations to the inner ear.

Anatomy Skeletal muscle (see picture 3)

Skeletal muscles are made up of long fibres. Fibre length varies from a few millimetres in the eye muscles to nearly 30 cm in the large leg muscles. An individual skeletal muscle may be made up of hundreds, or even thousands, of muscle fibres bundled together and wrapped in connective tissue. Each muscle is surrounded by a connective tissue sheath called the epimysium. Fascia, connective tissue outside the epimysium, surrounds and separates the muscles. Portions of the epimysium project inward to divide the muscle into compartments. Each compartment contains a bundle of muscle fibres. Each bundle of muscle fibre is called a fascicle and is surrounded by a layer of connective tissue called the perimysium. Within the fascicle, each individual muscle cell, or muscle fibre, is surrounded by connective tissue called the endomysium.

Picture 3: Skeletal muscle anatomy

Besides muscle cells, skeletal muscles have an abundant supply of blood vessels and nerves. This is directly related to the primary function of skeletal muscle: contraction. Before a skeletal muscle fibre can contract, it has to receive an impulse from a nerve cell. Blood vessels supply the muscle with oxygen and nutrients, and remove products, such as carbon dioxide, lactate and protons (H⁺).