CH 9 Skeletal Muscle Microscopic Anatomy

Muscle Fibers

• Definition: Individual skeletal muscle cells.
• Surrounded by a specialized cell membrane called sarcolemma.
• "Sarco" means flesh and "lemma" means layer.
• Identical to the phospholipid bilayer (fluid mosaic model) known from prior studies.

Sarcoplasm

• Definition: Cytoplasm of muscle fibers (muscle cells).
• Has a special name due to its association with muscle.

Structure of Sarcolemma

• Not smooth; features invaginations known as T-tubules (transverse tubules).
• Function: Allow electrical currents, or action potentials, to flow into the cell.
• Important for muscle contraction.

Electrical Activity

• Action potentials: Electrical energy flows into muscle cells, triggering contractions.

Organelles in Sarcoplasm

• Contains familiar organelles: multiple nuclei, endoplasmic reticulum (ER), and mitochondria.
• Special organelles:
• Sarcoplasmic Reticulum (SR)
  • Specialized ER that stores calcium ions (Ca²⁺).
  • Calcium is crucial for muscle contraction and also plays a significant role in nervous and skeletal systems.
• Myofibrils
  • Long contractile rods that occupy most of the muscle fiber's volume.
  • Composed of proteins known as myofilaments.

Fascicles and Muscle Structure

• Muscle organ composed of bundles called fascicles.
• A muscle fiber’s composition includes:
• Sarcolemma (membrane).
• Sarcoplasm (cytoplasm).
• Organelles such as mitochondria.
• Myofibrils that give a striated appearance.

Visualizing Sarcolemma and Related Structures

• Sarcolemma surrounds myofibrils and has T-tubules for conduction of action potentials.
• Sarcoplasmic Reticulum (SR) appears net-like, storing calcium for contraction initiation.
• Formation of triads occurs when T-tubules and SR are in close proximity.

Details of Myofibrils

• Myofibrils give insight into muscle tissue at the microscopic level, focusing on their protein composition and functional role in muscle contraction.