Lecture Notes: Structure of Skeletal Muscle

Characteristics of Muscle Tissue

• Excitability: Muscle tissue is excitable, meaning it can respond to neural stimuli by developing a change in membrane potential.

  • Motor neurons release neurotransmitters (e.g., acetylcholine) which stimulate muscle cells.
  • This stimulation leads to action potentials that cause muscle contraction.

• Contractility: Ability of muscle to contract or shorten forcibly when adequately stimulated.

• Extensibility: Muscle tissue can be stretched beyond its normal resting length.

• Elasticity: Ability of muscle tissue to recoil to its original length after being stretched.

Functions of Muscle

• Locomotion: Produces movement by pulling on bones, allowing movement of the skeleton.
• Posture Maintenance: Maintains posture and body position against gravity.
• Joint Stabilization: Stabilizes joints by surrounding them.
• Heat Production: Generates heat via muscle contractions (e.g., shivering) to maintain body temperature.

Structure of Skeletal Muscle

Connective Tissue Coverings

• Epimysium: The outermost layer surrounding the entire muscle, made of dense fibrous irregular connective tissue.
• Perimysium: Surrounds bundles of muscle fibers called fascicles.
• Endomysium: Surrounds each muscle fiber (cell), made of areolar connective tissue.

Muscle Fiber (Cell)

• Enclosed by a plasma membrane known as the sarcolemma.
• Contains many myofibrils, which are composed of protein filaments.

Myofibrils

• Composed of repeating units called sarcomeres, which are the functional units responsible for contraction.

Connective Tissue Sheaths

• They are interconnected and transmit the force of muscle contraction to the tendons.
• Tendons: Rope-like structures that connect muscle to bone; composed primarily of collagen.
• Aponeurosis: Sheet-like connective tissue serving similar functions to tendons.

Muscle Attachments

• Direct Attachments: Less common; epimysium fuses directly with the periosteum or perichondrium of bone/cartilage.
• Indirect Attachments: More common; involve tendons or aponeuroses.
  • Advantages: Conserve space, more resilient to abrasion due to collagen content.

Key Points

• Muscle contractions pull on connective tissue sheaths, which in turn pull on tendons to move bones and create movement.
• Connective tissue sheaths provide elasticity, resisting excessive stretch.
• Blood vessels and nerve fibers run through connective tissue sheaths, supporting muscle function.

Upcoming Topics

• Detailed look at the sarcomere structure and its role in muscle contraction in the next part of the lecture series.