• 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