6.3.2 The Structure of Skeletal Muscle

Key Features of Skeletal Muscle Structure:

1. Attachment to Bones:

• Skeletal muscles are attached to bones by tendons (not ligaments).
• Contraction of these muscles moves the skeleton at joints.

2. Muscle Cells and Myofibrils:

• Muscle cells (muscle fibres) are long, cylindrical cells grouped together for greater strength.
• Inside muscle fibres are myofibrils, which are specialised protein structures that perform contraction.

3. Myofibrils and Filaments:

• Myofibrils give muscles their strength and are responsible for their banded appearance.
• Made of thick filaments (myosin) and thin filaments (actin) that overlap.

4. Actin and Myosin:

• Actin (thin filament):
• Composed of two actin molecules twisted together to form a filament.
• Myosin (thick filament):
• Contains myosin heads which bind to specific sites on actin during muscle contraction.

5. Banding in Myofibrils:

• Overlap of filaments gives skeletal muscle its striated appearance under a microscope.
• Areas of overlap are critical for contraction, forming the sarcomere, the functional unit of contraction.