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Locomotion and Movement - Notes | Class 11 | Part 3: Human Skeletal System

Human Skeletal System

Human Skeletal System

  • It consists of a framework of bones (206) & few cartilages.
  • Human skeletal system has 2 parts: axial & appendicular.

Axial Skeletal System (80 bones)

  • Includes bones of head, vertebral column, sternum & ribs.

Bones of Head (29 bones)

  • It includes skull, Hyoid and Ear ossicles.
  • Skull (22): Include cranial bones and facial bones.
    • Cranial bones (8): Include Frontal (1), Parietals (2), Temporals (2), Occipital (1), Sphenoid (1) & Ethmoid (1).
    • Facial bones (14): Include Nasals (2), Maxillae (2), Zygomatics (2), Lacrimals (2), Palatines (2), Inferior nasals (2), Mandible (1) and Vomer (1).
  • Skull articulates with First vertebra (atlas) with the help of 2 occipital condyles (dicondylic skull).
  • Hyoid bone (1): U-shaped bone seen below buccal cavity.
  • Ear ossicles (3 x 2 = 6): Malleus (2), Incus (2) & stapes (2).

Vertebral Column

  • Formed of 26 vertebrae. It includes:
    • Cervical vertebrae (7)
    • Thoracic vertebrae (12)
    • Lumbar vertebrae (5)
    • Sacral vertebrae (1-fused)
    • Coccygeal vertebrae (1-fused)
  • Vertebra has a central hollow portion (neural canal) through which the spinal cord passes.
  • Number of cervical vertebrae are 7 in almost all mammals.
  • The vertebral column protects the spinal cord, supports the head and serves as the point of attachment for the ribs and musculature of the back.

Sternum or Breast Bone (1)

  • Flat bone on the ventral midline of thorax.

Ribs (12 pairs)

  • True ribs (first 7 pairs): They are attached to thoracic vertebrae and ventrally connected to sternum with the help of Hyaline cartilage.
  • Vertebrochondral (false) ribs (8th, 9th & 10th pairs): They do not articulate directly with the sternum but join the 7th rib with the help of Hyaline cartilage.
  • Floating ribs (11th & 12th pairs): They are not connected ventrally (no connection with sternum or other ribs).
  • Each rib has 2 articulation surfaces on its dorsal end and is hence called bicephalic.

Appendicular Skeletal System (126 bones)

Bones of Fore-limbs (30 x 2 = 60)

  • Humerus (1)
  • Radius (1)
  • Ulna (1)
  • Carpals (wrist bones-8)
  • Metacarpals (palm bones-5)
  • Phalanges (digits-14)

Bones of Hind-limbs (30 x 2 = 60)

  • Femur (thigh bone- 1)
  • Patella (knee cap- 1)
  • Tibia (1)
  • Fibula (1)
  • Tarsals (ankle bones-7)
  • Metatarsals (5)
  • Phalanges (digits-14)

Pectoral Girdles (2x2=4)

  • Include clavicle (2) & scapula (2).
  • Scapula (shoulder blade) is a large triangular flat bone situated in the dorsal part of the thorax between the second and 7th ribs.
  • Scapula has a slightly elevated ridge (spine) which projects as a flat, expanded process (acromion). The clavicle (collarbone) articulates with this.
  • Below the acromion is glenoid cavity which articulates with the head of humerus to form the shoulder joint.

Pelvic Girdles (2)

  • Formed of 2 coxal bones.
  • Each coxal bone is formed by the fusion of 3 bones- Ilium, Ischium & pubis.
  • At the point of fusion of Ilium, Ischium and Pubis is a cavity (Acetabulum) to which the thigh bone articulates.
  • The 2 halves of the pelvic girdle meet ventrally to form pubic symphisis containing fibrous cartilage.

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