The following article is written mainly for anyone taking the level 3 gym instructor course but as it deals with the different types of muscle it is useful for anyone who exercises, especially where the focus is on muscle growth, strength or power. The more you know about how your body, in this case muscle, works the more effective you can be at getting the results you desire.
There are 3 types of muscle in the human body: skeletal, smooth and cardiac. While they each have a different role to play they are also very similar, for example they are all composed of muscle cells called myofibres and contain 2 types of filaments. One is a protein called actin and the and the other is a protein called myosin, which work together to cause a contraction, which I’ll explain more about later.
Cardiac muscle (myocardium) is found only in the heart. The actin and myosin filaments are arranged in such a way that the muscle appears to be striped or striated, which is also the case with skeletal muscle. Unlike skeletal muscle however, it has 3 main differences:
• Contraction is involuntary as we have no conscious control over it (though the rate can be increased or decreased with practise)
• The muscle cells are connected to form a syncitium (cellular mass) so they can share nutrients and communicate with each other quickly. This allows them to contract in an organised sequence, which is required to pump blood in and out of the heart’s 4 chambers.
• Cardiac muscle cells can only work aerobically, which means they need oxygen to generate energy and contract. Without it an anoxic cell, which is one that is deprived of oxygen, will start to die almost immediately.
Smooth muscle is found surrounding all of the tubes of the body such as the digestive, respiratory, reproductive and urinary tracts, as well as blood vessels. It is involuntary and not striated. Contraction causes a decrease in diameter of whatever it surrounds (constriction) and relaxation causes an increase in diameter (dilation).
Skeletal muscle is the type used to cause a movement or stabilisation of the skeleton. It is mostly voluntary in that a conscious decision can be made to move a certain part of the body, but also involuntary in that the precise way this is done is down to habit and training. Also, postural muscles involuntarily control skeletal alignment beyond our conscious control, unless we decide to alter it consciously.
No matter how large a muscle is it is constructed in the same way. Individual cells are packaged together and protected by connective tissue which is made up of protein collagen fibres and some elastic tissue.
Each cell is surrounded by a sheath of endomysium
Numerous cells are then bundled together into fascicles
The Fascicles are wrapped in the perimysium
This is all bundled together in the outer covering of the muscle which is called the epimysium
Towards the ends of each muscle the irregular collagen fibres of the epimysium become a lot denser and more regularly aligned to form muscle tendon, which fuses with the periosteum (outer membrane) of a bone. It is this that transmits the force generated by the muscle to bring about movement. Also, every muscle is well supplied with blood vessels carrying nutrients and oxygen and with nerve fibres that carry the signal to contract (or relax).
Muscle Cell Structure
As I’ve said, each muscle cell is packed with filaments of two different proteins – actin and myosin. Actin filaments look like 2 beaded necklaces wound around each other, while myosin filaments look like a strand of double-headed golf clubs which stick out and make contact with the actin during a muscle contraction.
The myosin and actin filaments are strictly arranged inside each cell, with parallel rows of myosin each surrounded by 6 rods of actin to form myofibrils. Each myofibril is made up of repeating units called sarcomeres, which are aligned in a way that gives a striped or striated appearance.
As always, any questions or feedback leave a comment below.