Skeletal System - Summary Notes

The Skeletal System

Components

  • Bones: Primary organs of the skeletal system.
  • Cartilages: Fetal template for bone formation; covers bone ends at joints.
  • Ligaments: Connect bone to bone, support joints, limit movement.
  • Tendons: Connect muscle to bone.
  • Joints: Where bones meet.

Functions of Bones

  • Support.
  • Protection: Vital organs protected by the skeletal system (e.g., skull protects brain, rib cage protects heart and lungs).
  • Storage of minerals: Calcium and phosphorus.
    • Calcium: 99%99\% located in the skeleton.
  • Blood cell production: Occurs in red bone marrow.
  • Movement/leverage.

Bone Categories

  • Long bones: Longer than wide (e.g., femur, humerus).
  • Short bones: Length nearly equal to width (e.g., carpals, tarsals).
  • Flat bones: Flat, thin surfaces (e.g., cranial bones).
  • Irregular bones: Complex shapes (e.g., vertebrae).

Skeletal Divisions

  • Axial skeleton (80 bones): Bones along central body axis (skull, vertebral column, thoracic cage).
  • Appendicular skeleton (126 bones): Bones of upper and lower limbs; girdles attach limbs to axial skeleton.
    • Pectoral girdle: Holds upper limbs.
    • Pelvic girdle: Holds lower limbs.
  • Typically, there are about 206 bones.

Axial Skeleton Components

  • Skull.
  • Sternum.
  • Ribs.
  • Vertebral Column.

Appendicular Skeleton Components

  • Upper Extremities.
  • Lower Extremities.
  • Shoulder Girdle.
  • Pelvic Girdle (hip girdle).

The Skull

  • Bony framework of the head.
    • Cranium (8 bones).
    • Facial bones (14 bones).
  • Bones joined by sutures.

Cranium Bones

  1. Occipital bone.
  2. Frontal bone (forehead).
  3. Temporal bones (2).
  4. Parietal bones (2).
  5. Sphenoid.
  6. Ethmoid.
  • Occipital bone surrounds the foramen magnum.
  • Sphenoid and ethmoid form part of the eye orbit and help to form the floor of the cranium.

Fetal Skull

  • Fontanelles: "Soft spots" on baby’s head.
    • Fibrous membranes connecting cranial bones.
    • Allow brain growth.
    • Anterior fontanelle closes around 15-24 months.

Bony Thorax

  • Thoracic cage.
    • Sternum (anteriorly).
    • Ribs (laterally).
    • Thoracic vertebrae (posteriorly).
  • Protects major organs.

Sternum

  • Breastbone, flat bone in the middle of the chest.
  • Protects heart, lungs, and major blood vessels.
    • Manubrium: Superior portion, articulates with clavicles.
    • Body: Longest part.
    • Xiphoid process: Tip of sternum.

Ribs

  • Thin, flat, curved bones forming a protective cage.
    • True ribs (1-7): Connect individually to the sternum.
    • False ribs (8-12): Costal cartilages not directly attached.
    • Floating ribs (11-12): No connection to sternum.

Vertebral Column

  • Backbone, spine, or spinal column.
  • Vertebrae separated by intervertebral discs.
  • Normal curvature.
  • 33 irregularly shaped bones (vertebrae).
    1. Cervical vertebrae (7).
    2. Thoracic vertebrae (12).
    3. Lumbar vertebrae (5).
    4. Sacral (4-5 fused segments): Sacrum is fused bone.
    5. Coccyx (3-4 fused segments): Tail bone.
  • The sacrum protects the digestive, urinary & reproductive systems.

Four Curves of the Spine

  1. Cervical.
  2. Thoracic.
  3. Lumbar-characterized by an inward curvature.
  4. Sacral/ pelvic curves.

Abnormal Spinal Curvatures

  • Scoliosis: Abnormal lateral curve.
  • Kyphosis: Exaggerated thoracic curvature (hunchback).

Spina Bifida

  • Congenital defect where vertebrae fail to form a complete vertebral arch.
  • Folic acid reduces risk.

Appendicular Skeleton

  • Includes bones of upper & lower limbs and pectoral & pelvic girdles.
    • Limbs (appendages).
    • Pectoral girdle.
    • Pelvic girdle.

Pectoral Girdle

  • Shoulder girdle.
    • Clavicle: Collarbone.
    • Scapula: Shoulder blade.
  • Supports upper limbs.

Upper Limb

  • Humerus: Single long bone, longest in upper extremity.
  • Forearm:
    • Ulna: Longer, larger, and more medial.
    • Radius: More lateral and slightly shorter.
  • Hand:
    • Carpals: Wrist.
    • Metacarpals: Palm.
    • Phalanges: Fingers.

Pelvic Girdle

  • Hip girdle.
  • Bony pelvis: Two hip bones, sacrum, and coccyx.
  • Hip bones:
    1. Ilium (largest hipbone).
    2. Ischium (posteriorly).
    3. Pubic bone (anteriorly).
  • Protects reproductive organs, urinary bladder, and part of the large intestine.

The Pelvis

  • Divided into false and true pelvis.
    • True/lessor pelvis: Reproductive organs.
    • False/greater pelvis: Bony structures and bowel.

Male and Female Pelvis

  • Male pelvis: Funnel-shaped, narrower outlet, heavier, and stronger.
  • Female pelvis: Basin-shaped, wider, broader, and lighter, accommodates fetus and childbirth.

Lower Limbs

  • Femur: Thighbone, longest, largest, and strongest bone.
  • Patella: Kneecap, protects knee joint.
  • Leg:
    • Tibia (medial side).
    • Fibula (lateral side).
  • Foot:
    • Tarsus: Ankle.
    • Metatarsals: Sole.
    • Phalanges: Toes.