Joints and Muscles Overview

Joints and Muscles

• Joints connect bones, enabling movement.
• Muscles produce movement by pulling on bones.
• Joints are classified by their movement and structure:
  • Fibrous joints: Immovable or have slight movement.
  • Cartilaginous joints: Connected by cartilage; limited movement.
  • Synovial joints: Have a fluid-filled cavity; most mobile.
    • These joints have articular cartilage, a capsule, ligaments, and synovial fluid.

Types of Joints

• Fibrous joints:

  • Offer little to no movement.
  • Examples: Sutures of the skull, distal tibiofibular joint.
  • Function: Hold bones tightly together.

• Cartilaginous joints:

  • Allow limited movement.
  • Examples: Pubic symphysis, intervertebral discs.
  • Function: Provide cushioning and slight flexibility.

• Synovial joints:

  • Highly mobile joints.
  • Examples: Knee, hip, shoulder.
  • Function: Enable wide range of motion.

Types of Synovial Joints

• Classified by shape:
  • Ball-and-socket: Wide range of motion (e.g., shoulder, hip).
  • Hinge: Flexion and extension (e.g., elbow, knee).
  • Pivot: Rotation (e.g., atlas and axis).
  • Saddle: Bends in two directions (e.g., thumb).
  • Plane: Sliding movement (e.g., intercarpal joints).
  • Condylar: Movement in two directions (e.g., metacarpophalangeal joints).

Anatomical Axes

• Sagittal axis: Runs from front to back.
• Vertical axis: Runs from top to bottom.
• Frontal axis: Runs from side to side.

Types of Movement

• Flexion: Decreases the angle between two bones.
• Extension: Increases the angle between two bones.
• Abduction: Movement away from the body's midline.
• Adduction: Movement toward the body's midline.
• Rotation: Movement around a central axis.
• Circumduction: Circular movement.
• Supination: Rotation of the forearm so the palm faces forward.
• Pronation: Rotation of the forearm so the palm faces backward.
• Inversion: Movement of the sole of the foot inward.
• Eversion: Movement of the sole of the foot outward.
• Dorsiflexion: Bending the foot upward.
• Plantar flexion: Bending the foot downward.

Muscle Types

• Skeletal muscle: Voluntary movement, attached to bones.
• Cardiac muscle: Involuntary, found in the heart.
• Smooth muscle: Involuntary, found in the digestive system and other organs.

Skeletal Muscle Function

• Movement production
• Heat generation
• Stabilization
• Posture maintenance

Terminology of Muscles

• Origin: Point of attachment of muscle to stationary bone.
• Insertion: Point of attachment of muscle to movable bone.
• Tendon: Cord of fibrous tissue connecting muscle to bone.
• Aponeurosis: Flattened, sheet-like tendon.
• Contraction: Muscle shortening.
  • Isometric: No change in muscle length.
  • Isotonic: Change in muscle length.

Motor Units

• Motor neuron and all muscle fibers it innervates.
• Not all motor units need to contract simultaneously.

Naming Muscles

• Based on shape, location, size, action, number of origins.

Shoulder Girdle (Deltoid)

• Rounding the shoulder
• Abduction
• Flexion
• Extension

Brachial Region (Biceps Brachii)

• Flexion
• Supination

Brachii Region (Triceps Brachii)

• Extension of forearm

Hip Region (Iliopsoas)

• Flexion of the thigh

Gluteus Maximus

• Hip extension

Gluteus Medius

• Hip abduction

Femoral Region (Quadriceps Femoris)

• Knee extension
• Hip flexion

Crural Region (Tibialis Anterior)

• Dorsiflexion of ankle

Crural Region (Triceps Surae)

• Plantar flexion of ankle

Thoracic Region (Pectoralis Major)

• Adduction of the arm
• Rotates arm upward

Diaphragm

• Important muscle for respiration
• Separates the thoracic and abdominal cavities.

Dorsal Region (Trapezius)

• Prevents shoulder collapse

Abdominal Region

• Assists in movement, pressure, and organ functions.

Facial Muscles

• Control facial expressions
• Originate from bones or fascia, insert into facial skin.