1. In general, there are 3 types of muscle tissues.
- Skeletal muscle: which is striated and voluntary
- Cardiac muscle: which is striated and involuntary
- Smooth muscle: which is non striated and involuntary
2. Skeletal muscle tissue:
- involuntary muscle (can be made contract or relax by conscious control through the nervous system)
- striated or striped muscle because of the presence of alternating dark & light bands on the muscle fibre.
The structure of skeletal muscle:
1. Is made up of a large number of cylindrical cells called muscle fibres or myofibres.
(myofibre = a muscle cell)
2. Each myofibre/muscle fibre is covered by a plasma membrane called sarcolemma, has many nuclei, & contains many protein fibres (called myofibrils) which enable the muscle fibre to contract.
3. Each skeletal tissue consists of bundles of muscle fibres & these bundles are separated by connective tissue (also called epimysium)
What is myofibrils?
1.Myofibrils are composed of individual contractile proteins called myofillaments. These myofilaments are generally divided into thick and thin myofilaments.
2. The thin myofilaments are composed mainly of a protein known as actin. Actin filaments are anchored into the z-line of a sarcomere.
3. The thick myofilaments are composed mainly of the protein myosin. It is the orderly overlapping of the actin and myosin filaments that give cardiac and skeletal muscle their striated appearance (light and dark bands). - The contraction of skeletal muscle tissue comes from the collective contractions of each single muscle fibre, whose contraction in turn comes from the contractions of the protein fibres (myofibrils).
- The contraction of skeletal muscle requires energy (ATP) produced by mitochondria within the muscle fibres. (sarcosome = the mitochondria of muscle cell).
What is cardiac muscle?
- Cardiac muscle cells are not as long as skeletal muscles cells and often are branched cells.
- Cardiac muscle cells may be mononucleated or binucleated. In either case the nuclei are located centrally in the cell.
- Cardiac muscle is also striated.
- In addition cardiac muscle contains intercalated discs.
What is smooth muscle?
- Smooth muscle cells are described as spindle shaped. That is they are wide in the middle and narrow to almost a point at both ends.
- Smooth muscle cells have a single centrally located nucleus.
- Smooth muscle cells do not have visible striations although they do contain the same contractile proteins as skeletal and cardiac muscle, these proteins are just laid out in a different pattern.
