Lecture on Skeletal Muscle Structure

Characteristics of Muscle Tissue

• Excitability: Ability to respond to stimuli, usually neural, by changing membrane potential (action potential).
  • Involves neurotransmitters (e.g., acetylcholine) stimulating muscle cells.
• Contractility: Ability to shorten forcibly when adequately stimulated.
• Extensibility: Ability to be stretched beyond resting length.
• Elasticity: Ability to recoil and return to original length after being stretched.

Functions of Muscle

• Produce Movement: Muscles contract to move the skeleton (locomotion).
• Maintain Posture: Stabilizing body position against gravity.
• Joint Stabilization: Muscles wrap around joints to provide additional stability.
• Heat Production: Muscle activity generates heat, e.g., shivering to produce heat during cold conditions.

Macroscopic Structure of Skeletal Muscle

• Epimysium: Dense irregular connective tissue surrounding the muscle belly.
  • Can form direct attachments to bone (periosteum) or cartilage (perichondrium).
• Fascicle: Bundle of muscle fibers within the muscle.
  • Surrounded by Perimysium, another layer of dense irregular connective tissue.
• Muscle Fiber (Cell): Individual muscle cell within a fascicle.
  • Surrounded by Endomysium, an areolar connective tissue.
  • Covered by the sarcolemma (plasma membrane).

Connective Tissue Sheaths

• Continuous Structure: Epimysium, perimysium, and endomysium are continuous, transmitting force from muscle fibers to tendons.
• Function:
  • Transmit muscle contraction force to tendons and bones.
  • Contribute to muscle elasticity.
  • Contain blood vessels and nerve fibers.

Muscle Attachments

• Direct Attachments: Less common, where epimysium fuses directly with periosteum or perichondrium.
• Indirect Attachments: More common, involves tendons (rope-like) or aponeuroses (sheet-like).
  • Tendons conserve space and resist abrasion/friction.

Microstructure: Myofibrils

• Myofibrils: Rod-like structures within muscle fibers, composed of proteins.
• Sarcoplasmic Reticulum: Surrounds myofibrils, stores calcium.
• Muscle Fiber Characteristics:
  • Multinucleated and cylindrical.
  • Striated appearance due to sarcomeric structure.

Upcoming Topics

• Detailed structure of the sarcomere in part two.

Note:

• The lecture also mentioned future discussions on neuromuscular junctions and excitation-contraction coupling.