Skeletal Muscles

Introduction to Skeletal Muscles

• Skeletal muscles & tendons: 44% of body mass.
• Accessory structures include:
  • Joints: Allow movement.
  • Nerves: Stimulate contraction.
  • Ligaments: Reinforce joints.
  • Cartilage/bones: Provide attachment for tendons.
  • Tendons: Attach muscles to bones and stabilize joints.

Functions of Skeletal Muscle

• Movement
• Strength
• Support for skin and soft tissues
• Body shape
• Protection
• Heat production
• Facial expression
• Vocalization
• Posture

Naming Skeletal Muscles

• Criteria for naming:
  • Size
  • Shape
  • Location
  • Action
  • Number of origins
  • Direction of fibers
  • Origin and insertion

Skeletal Muscle Actions

• Origin: Immovable end of muscle.
• Insertion: Movable end of muscle.
• Contraction pulls insertion toward origin.

Interaction of Skeletal Muscles

• Agonist (prime mover): Primary muscle in action.
• Synergists: Helper muscles.
• Antagonists: Opposing muscles.
• Fixators: Stabilize the origin of the agonist.

Types of Muscle Contractions

• Isotonic: Muscle length changes.
  • Concentric: Muscle shortens.
  • Eccentric: Muscle lengthens.
• Isometric: No change in muscle length.

Muscle Structure Overview

• Key components:
  • Fascicle
  • Muscle fibers
  • Myofibrils (thick and thin filaments)
• Sarcomere: Functional unit of muscle contraction.

Muscle Contraction Process

• Cross-bridge cycling:
  • $ ext{Ca}^{2+}$ release exposes binding sites on actin.
  • Myosin cross-bridge binds to actin.
  • Power stroke occurs as actin is pulled.
  • ATP is required for myosin to release from actin and reset.

Key Muscles in the Face and Neck

• Corrugator supercilii
• Orbicularis oculi
• Zygomaticus (minor/major)
• Masseter
• Sternocleidomastoid
• Trapezius
• Frontalis

Key Muscles in the Body

• Triceps brachii
• Biceps brachii
• Quadriceps group (Rectus femoris, Vastus lateralis)
• Gastrocnemius
• Gluteus maximus
• Latissimus dorsi