The Structure of Skeletal Muscle (AQA A Level Biology): Revision Note

Skeletal muscle structure

• Skeletal muscle, also known as striated, or striped, muscle, is the muscle that contracts to move the skeleton

  • Other types of muscle include cardiac muscle in the heart, and smooth muscle in the walls of the internal organs

• Skeletal muscle is made up of bundles of muscle cells

  • Muscle cells are usually known as muscle fibres

  • In a muscle fibre the:

    • cell surface membrane = sarcolemma

    • cytoplasm = sarcoplasm

    • endoplasmic reticulum = sarcoplasmic reticulum

• Muscle fibres have the following features:

  • each muscle fibre is an elongated cell that contains many nuclei

  • the sarcoplasm contains an organised arrangement of contractile proteins that form myofibrils

  • the sarcolemma has many deep tube-like projections that fold in from its outer surface; these are known as T-tubules

  • many mitochondria in the sarcoplasm generate ATP for muscle contraction

Myofibrils

• Myofibrils are long, rod-like structures made of protein filaments

• The protein filaments found in myofibrils are:

  • myosin, also known as thick filaments

  • actin, also known as thin filaments

• Myofibrils can be divided up into sections known as sarcomeres, which shorten during muscle contraction as myosin and actin filaments slide past each other

  • This is the sliding filament model of muscle contraction

• Each sarcomere contains the following features: