Human Skeletal System – Notes for Quick Exam Revision

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Human Skeletal System
Short Notes for Quick Exam Revision

⇒What is Bone?

Bone is the hardest connective tissue in the human body.
Human skeleton

Main Functions of Bone

  • Provides support and gives body shape
  • Helps in movement with muscles
  • Protects internal organs
  • Stores minerals, especially calcium and phosphorus
  • Bone marrow produces red and white blood cells

⇒ Bone Structure: Bone has two main layers:

Compact Bone

  • Hard, dense outer layer
  • Gives strength to bone

Spongy Bone

  • Soft inner layer
  • Contains marrow and blood vessels

Bone Cells

Mature bone cells are called osteocytes

Bone Marrow

  • Red marrow produces blood cells
  • Yellow marrow stores fat

⇒Human Skeleton: 

An adult human skeleton has 206 bones.
Babies have about 300 bones; many fuse during growth.

The human skeleton is divided into two main parts:

Axial Skeleton (80 bones): It forms the central axis of the body.

Includes:

  • Skull
  • Vertebral column
  • Ribs
  • Sternum

Appendicular Skeleton (126 bones): It helps in movement.

Includes:

  • Shoulder girdle
  • Arms and hands
  • Pelvic girdle
  • Legs and feet

⇒Skull: The skull protects the brain.

Skull Bones
  • Total bones = 22
  • 8 cranial bones protect the brain
  • 14 facial bones form the face

Important Skull Bones

  • Frontal bone
  • Parietal bones
  • Temporal bones
  • Occipital bone

⇒Vertebral Column: Also called backbone or spine.

Function: Supports body & Protects spinal cord

  • Total Vertebrae = 33
  • 7 cervical
  • 12 thoracic
  • 5 lumbar
  • 5 sacral (fused)
  • 4 coccygeal (fused)

⇒Rib Cage: The rib cage protects the heart and lungs.


Total Ribs = 12 pairs (24 ribs)

  • 7 true ribs
  • 3 false ribs
  • 2 floating ribs

⇒Limbs

Forelimbs (Arms)

Each arm has:

  • Humerus
  • Radius
  • Ulna
  • Carpals
  • Metacarpals
  • Phalanges

Hind Limbs (Legs)

Each leg has:

  • Femur
  • Patella
  • Tibia
  • Fibula
  • Tarsals
  • Metatarsals
  • Phalanges

⇒Joints: A joint is the place where two bones meet.


Types of Joints
  • Fixed joint → skull
  • Hinge joint → elbow, knee
  • Ball and socket joint → shoulder, hip
  • Pivot joint → neck

⇒Cartilage: Cartilage is softer than bone.

Functions

  • Reduces friction in joints
  • Gives flexibility
  • Supports nose and ear

⇒Ligaments and Tendons

Ligament: Connects bone to bone
Tendon: Connects muscle to bone

Quick Exam Facts ⭐

Longest bone = Femur
Smallest bone = Stapes (ear)
Strongest bone = Femur
Hardest substance in body = Tooth enamel





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