Skeleton System in Humans

Skeletal System in Humans 

  • The skeletal system is made up of bones and cartilages, which are specialized forms of connective tissue. 
  • Its primary function is to provide support and structure to the body, enabling movement and protecting vital organs. 
  • Imagine chewing food without jaw bones or walking without the support of limb bones; the skeletal system is crucial for these basic activities of daily life. 
  • It is groupedinto two main divisions –

the axial skeleton and,

the appendicular skeleton


Axial Skeleton: Core Support Structure

  • The axial skeleton forms the central framework of the body. 
  • The axial skeleton encompasses 80 bones positioned along the body's main axis, including the skull, vertebral column, sternum, and ribs.


1. Skull:

  • Composed of cranial and facial bones totaling 22 bones. 
  • Cranial Bones (8): Form the protective cranium around the brain, ensuring its safety. 
  • Facial Bones (14): Constitute the front part of the skull, contributing to facial structure and features. 
  • Hyoid Bone: A U-shaped bone located at the base of the buccal cavity, supporting the tongue and swallowing. 
  • Ear Ossicles: Three tiny bones (Malleus, Incus, Stapes) in each middle ear, aiding in hearing.





2. Vertebral Column:

  •  Consists of 26 vertebrae arranged in a serial fashion, providing support and protection for the spinal cord. 
  • Differentiated into cervical (7), thoracic (12), lumbar (5), sacral (1 fused), and coccygeal (1 fused) regions. 
  • Atlas: The first vertebra, articulating with the occipital condyles, allowing for head movement. 
  • Function: Protects the spinal cord, supports the head, and serves as the attachment point for ribs and back muscles.





3. Sternum and Ribs:

  • Sternum: A flat bone located in the ventral midline of the thorax, contributing to chest structure and protection. 
  • Ribs (12 Pairs): Twelve pairs of ribs, attached dorsally to the vertebral column and ventrally to the sternum, enclosing and protecting the chest cavity. 

- True Ribs (1-7): Attached dorsally to thoracic vertebrae and ventrally to the sternum via hyaline cartilage. 

- False Ribs (8-10): Indirectly connected to the sternum through cartilaginous extensions from the seventh rib. 

- Floating Ribs (11-12): Not connected ventrally, providing less direct protection but still contributing to rib cage structure.






Functionality: Together, the thoracic vertebrae, ribs, and sternum form the rib cage, which encloses and protects vital organs like the heart and lungs, while also supporting respiratory functions.


Appendicular Skeleton: Limb Support and Mobility

  • The appendicular skeleton consists of the bones of the limbs and their associated girdles, facilitating movement and mobility. 
  • Limb Bones: Each limb contains a specific arrangement of bones, totaling 30 in number. 
  • Divided into the upper and lower limbs, along with their respective girdles.


Forelimb (Hand):

  • Includes the humerus (upper arm bone), radius and ulna (forearm bones), carpals (wrist bones - 8 in number), metacarpals (palm bones - 5 in number), and phalanges (digits - 14 in number).


Hind Limb (Leg):

  • Comprises the femur (thigh bone - the longest bone), tibia and fibula (lower leg bones), tarsals (ankle bones - 7 in number), metatarsals (5 in number), and phalanges (digits - 14 in number). 
  •  Knee Cap: Also known as the patella, a cup-shaped bone covering the knee ventrally, providing protection and support.


Girdle Bones:

  • Pectoral and pelvic girdles facilitate the articulation of the upper and lower limbs with the axial skeleton. 
  • Pectoral Girdle (Shoulder Girdle):

- Composed of two halves, each consisting of a clavicle (collarbone) and a scapula (shoulder blade). 

- The scapula is a large triangular flat bone situated in the dorsal part of the thorax, featuring a spine and acromion process. The clavicle articulates with the acromion, forming the shoulder joint.





  • Pelvic Girdle:

- Formed by the fusion of three bones - ilium, ischium, and pubis, each coxal bone. 

- Supports the lower limbs and facilitates movement, with the acetabulum serving as the point of articulation for the thigh bone. The two halves of the pelvic girdle meet ventrally to form the pubic symphysis, containing fibrous cartilage for flexibility.