UL1.H1.4 +D1 Skeletal Muscle
Skeletal Muscle:
- Skeletal muscle cells are found in a wide range of sizes but some may be very large, with a length measured in millimetres or centimetres
- They are multinucleate cells with some of the larger muscle cells containing many thousands of nuclei
- These nuclei are located at the periphery of the cell
- The remainder of the cell is occupied by the contractile apparatus and support structures, including mitochondria for the supply of energy
- The contractile apparatus is made up of sarcomeres
- Sarcomeres are small units (2-3 microns in length) of actin and myosin filaments in a highly structured order
- Contraction of the muscle cell relies on the actin and myosin filaments actively sliding over each other to reduce the length of the contractile unit, the sarcomere
- Sarcomeres are connected together, end to end, to form long myofibrils which run from one end of the cell to the other along the longitudinal axis
- Skeletal muscle cells contain many myofibrils lying in parallel
- When a sarcomere contracts, its length is reduced by 30%
- The internal organisation of skeletal muscle cells is such that contraction is an all or none response - that is all the sarcomeres will contract together
- Thus the myofibrils, and therefore the cell, will contract by 30%
- Skeletal muscle cells are controlled by the somatic nervous system
Skeletal Muscle Cells:
- Notice that the majority of the cell is occupied by the contractile apparatus (sarcomeres)
- The cross structures shown in this image reflect the highly structured arrangement of sarcomeres and their arrangement into myofibrils
- This highly organised structure maximises the contractile power that can be generated by each muscle cell
Skeletal muscle fibres cut in longitudinal section. Nuclei are arrowed
