Overview of Skeletal Muscle Structure

Sep 12, 2024

Structure of Skeletal Muscle Lecture Notes

Characteristics of Muscle Tissue

  • Excitable
    • Muscle cells can respond to neural stimuli.
    • Motor neurons release neurotransmitters (e.g., acetylcholine) which cause a change in the muscle cell's membrane potential.
    • This can lead to an action potential and muscle contraction.
  • Contractility
    • Muscles can shorten forcibly when adequately stimulated.
  • Extensibility
    • Muscles can be stretched beyond their normal resting length.
  • Elasticity
    • Ability to recoil and return to the original length after being stretched.

Functions of Muscles

  • Produce Movement
    • Move the skeleton by contracting and pulling on bones.
  • Maintain Posture
    • Support body posture against gravity.
  • Stabilize Joints
    • Muscles wrap around joints, adding stability.
  • Generate Heat
    • Muscle contractions produce heat, aiding in body temperature regulation.

Structure of Skeletal Muscle

  • Epimysium
    • Dense fibrous irregular connective tissue covering the entire muscle belly.
    • Can fuse with the periosteum of the bone to form direct attachments.
  • Fascicles
    • Bundles of muscle fibers within the muscle.
    • Surrounded by Perimysium, a dense fibrous irregular connective tissue.
  • Muscle Fibers (Muscle Cells)
    • Covered by Endomysium, an areolar connective tissue.
    • Each fiber has a plasma membrane or Sarcolemma.
  • Connective Tissue Sheaths
    • Continuous from endomysium, perimysium, to epimysium.
    • They contribute to muscle elasticity and are involved in the transmission of force from the muscle to the tendon.

Tendons and Aponeuroses

  • Tendons
    • Rope-like collagen-rich structures that attach muscle to bone.
    • Resilient to abrasion, allowing for friction with bones.
  • Aponeuroses
    • Sheet-like connective tissues that connect muscles to bones.
  • Direct and Indirect Attachments
    • Direct: Epimysium fuses with the periosteum or perichondrium of bone.
    • Indirect: More common, involve tendons or aponeuroses.
    • Tendons are preferred due to their small size and resilience.

Microscopic Structure

  • Myofibrils
    • Composed of proteins, hundreds to thousands per muscle cell.
    • Provide the striated appearance of muscle fibers.
  • Sarcoplasmic Reticulum
    • Surrounds myofibrils, stores calcium.
  • Sarcomere
    • The functional and structural unit of the muscle cell.
    • Will be discussed further in the next lecture video.