Human Skeleton Notes

Types of Skeletons

  • Hydrostatic Skeleton: Fluid-filled cavity for support. Examples: jellyfish, earthworms. Limited in size; risk of drying out.
  • Exoskeleton: External covering made of chitin. Found in arthropods like crustaceans and insects. Supports, protects, and allows movement. Limits growth, requiring molting (ecdysis).
  • Endoskeleton: Internal skeleton of bone or cartilage. Present in vertebrates. Supports body, allows growth, protects organs, and provides muscle attachment. Exterior not protected.

Human Skeleton Functions

  • Support: Holds organs and tissues in place.
  • Protection: Protects vital organs (e.g., cranium protects the brain).
  • Movement: Bones act as levers for muscle attachment.
  • Production & Storage: Produces blood cells and stores minerals like calcium.
  • Aids hearing – malleus, incus, stapes

Structure of the Human Skeleton

  • Axial Skeleton: Skull, vertebral column, and ribcage.
  • Appendicular Skeleton: Pectoral girdle (shoulders, arms, hands) and pelvic girdle (pelvis, legs, feet).

Axial Skeleton Details

  • Skull:

    • Cranial bones (cranium) protect the brain.
    • Facial bones form the face.
    • Foramen magnum: Opening for the spinal cord.

  • Vertebral Column:

    • 33 vertebrae connected by ligaments.
    • Protects the spinal cord.
    • Intervertebral discs act as shock absorbers.

  • Ribcage (Thorax):

    • 12 thoracic vertebrae, 12 pairs of ribs, and the sternum.
    • Protects vital organs and aids in breathing.
    • True ribs, false ribs, and floating ribs.
    • Intercostal muscles facilitate breathing.

Appendicular Skeleton Details

  • Pectoral Girdle:

    • Clavicles (collarbones) and scapulae (shoulder blades).
    • Attaches upper limbs to the axial skeleton.
    • Glenoid cavity: socket for the humerus.

  • Upper Limbs:

    • Humerus (arm), radius and ulna (forearm), carpals (wrist), metacarpals (palm), phalanges (fingers).
    • Enables movement and fine motor skills.

  • Pelvic Girdle:

    • Ilium, ischium, and pubis.
    • Attaches lower limbs to the axial skeleton, supports body weight, and protects organs.

  • Lower Limbs:

    • Femur (thigh bone), patella (kneecap), tibia (shin bone), fibula, tarsals (ankle bones), metatarsals (foot bones), phalanges (toe bones).
    • Supports body weight and enables movement.

Joints

  • Points where bones meet, allowing movement.
  • Types:
    • Fibrous (immovable): Sutures of the skull.
    • Cartilaginous (partially movable): Joints between vertebrae.
    • Synovial (freely movable): Fluid-filled cavity for smooth movement.
      • Types of Synovial Joints: Ball-and-Socket, Hinge, Pivot, Gliding, Saddle, Condyloid
  • Synovial Joint Structure:
    • Hyaline cartilage: Reduces friction.
    • Synovial membrane: Secretes synovial fluid.
    • Synovial fluid: Lubricant.
    • Capsular ligament: Provides stability.
    • Ligaments: Connects bones to bones;
    • Tendons: Connects muscles to bones.

Skeletal Diseases

  • Arthritis: Joint inflammation causing pain and stiffness.
    • Osteoarthritis: Cartilage wears down.
    • Rheumatoid arthritis: Autoimmune disease attacking joints.
  • Osteoporosis: Weak bones due to loss of density.
  • Scoliosis: Spine curves into an "S" or "C" shape.
  • Rickets: Soft, weak bones due to vitamin D deficiency.

Skeletal Muscles

  • Attached to the skeleton by tendons.
  • Antagonistic Muscles: Pairs of muscles that work in opposition (e.g., biceps and triceps).
  • Biceps: Contract while triceps relax to bend the arm.
  • Triceps: Contract while biceps relax to straighten the arm.