CIE A Level Biology复习笔记15.1.11 Ultrastructure of Striated Muscle

• Striated muscle makes up the muscles in the body that are attached to the skeleton
• Striated muscle is made up of muscle fibres
• A muscle fibre is a highly specialised cell-like unit:
  • Each muscle fibre contains an organised arrangement of contractile proteins in the cytoplasm
  • Each muscle fibre is surrounded by a cell surface membrane
  • Each muscle fibre contains many nuclei – this is why muscle fibres are not usually referred to as cells
• The different parts of a muscle fibre have different names to the equivalent parts of a normal cell:
  • Cell surface membrane = sarcolemma
  • Cytoplasm = sarcoplasm
  • Endoplasmic reticulum = sarcoplasmic reticulum (SR)
• The sarcolemma has many deep tube-like projections that fold in from its outer surface:
  • These are known as transverse system tubules or T-tubules
  • These run close to the SR
• The sarcoplasm contains mitochondria and myofibrils
  • The mitochondria carry out aerobic respiration to generate the ATP required for muscle contraction
  • Myofibrils are bundles of actin and myosin filaments, which slide past each other during muscle contraction
• The membranes of the SR contain protein pumps that transport calcium ions into the lumen of the SR

The ultrastructure of striated muscle and of a section of muscle fibre

Myofibrils

• Myofibrils are located in the sarcoplasm
• Each myofibril is made up of two types of protein filament:
  • Thick filaments made of myosin
  • Thin filaments made of actin
• These two types of filament are arranged in a particular order, creating different types of bands and line

Myofibrils parts & descriptions table

The structure of a myofibril