Muscle Tissue Types and Functions

Types of Muscle Tissue

• Skeletal muscle is attached to bones and primarily responsible for movement; its activity is generally voluntary, controlled by the somatic nervous system.
  • Some skeletal muscles operate subconsciously, like the diaphragm for breathing and muscles maintaining posture.
• Cardiac muscle is exclusive to the heart; its contraction and relaxation are involuntary, driven by an internal pacemaker (autorhythmicity) that determines heart rate.
• Smooth muscle is found in the walls of hollow internal structures, like blood vessels, airways, and organs. It lacks striations, unlike skeletal and cardiac muscle.
  • Its contractions are usually involuntary and often exhibit autorhythmicity.
  • Peristalsis, the rhythmic movement of food through the digestive tract, is driven by smooth muscle contractions.

Functions of Muscular Tissue

• Producing body movements: Skeletal muscles, bones, and joints work together to produce movement.
• Stabilizing body positions: Muscle contractions help maintain postures like standing or sitting.
• Storing and moving substances: Sphincters, ring-like bands of smooth muscle, control the storage and movement of substances within the body.
• Generating heat: Muscle contraction produces heat (thermogenesis). Shivering, involuntary skeletal muscle contractions, increase heat production.

Structure of Skeletal Muscle Tissue

• Muscle fibers (myocytes): Elongated cells forming the structure of skeletal muscle.
• Connective tissue: Surrounds and protects muscle tissue.
  • Subcutaneous tissue (hypodermis): Areolar and adipose tissue separating muscle from skin. It stores triglycerides, insulates, and protects muscle.
  • Fascia: A dense connective tissue sheet lining the body wall and limbs. It supports and surrounds muscles and organs.

Layers of Connective Tissue

• Epimysium: The outer layer surrounding the entire muscle; composed of dense irregular connective tissue.

• Perimysium: Dense irregular connective tissue surrounding bundles of muscle fibers called muscle fascicles.

• Endomysium: Mostly reticular fibers, surrounding individual muscle fibers within a fascicle.

• Connective tissue attachments: The epimysium, perimysium, and endomysium extend beyond the muscle fibers to form tendons or aponeuroses:

  • Tendons: Rope-like structures attaching muscle to bone.
  • Aponeurosis: Broad, flat sheets attaching muscle to other structures.

Tendon vs. Aponeurosis

• Tendon: Rope-like, tough, and common for movement and flexibility.
• Aponeurosis: Delicate, sheath-like, for strength and stability.

Skeletal Muscles

• Muscular System: The system of voluntarily controlled skeletal muscles.
• Movement: Skeletal muscle contraction moves bones by exerting force on tendons, which pull on bones or other structures.
• Joint Movement: Most muscles cross at least one joint, and contraction pulls one bone towards the other.
• Origin & Insertion: Muscles attach to bones at two points:
  • Origin: The more stationary attachment point.
  • Insertion: The attachment point that moves when the muscle contracts.