Human Skeletal System

Human Skeletal System

Human Skeletal System

Skeletal system is the framework of  bones and cartilages that protect our organs and allow us to move. This system includes all of the bones and joints in the body.

Types of Skeletal System

Skeletal system is divided into following two types

  1. Exoskeleton    The skeleton found on the surface of the body is called exoskeleton. It originates from ectoderm or mesoderm e.g., nails, hairs, etc.
  2. Endoskeleton   The skeleton found inside the body is called endoskeleton. It originates from the mesoderm, e.g., cartilages and bones. 
Some other differences between exoskeleton and endoskeleton are given below

Functions of Skeleton (Skeletal System)

  1. Protection   The skeletal system protects the internal organs from injury. For example, Brain is protected by cranial bones, spinal cord is protected by  vertebrae, while the heart and lungs are protected by ribcage.
  2. Support   Skeletal system gives support to the softer body parts.
  3. Movement     Muscles are attached to bones. Due to the contraction of the muscles, movement takes place. Thus, bones help in bringing out movement.
  4. Mineral Reservation    The bones store minerals, calcium and phosphorus and these  are supplied to other parts of the body on great demand.
  5. Haematopoiesis   The red blood corpuscles and white blood corpuscles and platelets are produced by bone marrow.
  6. Helps in Breathing and Hearing   The cartilages of larynx, sternum ribs and trached helps in breathing and the ear bones transmit the sound vibrations from the tympanic membranes to the internal ear.
  7. Basic Body Form  (shape and size) The skeletal parts provide basic shape and size to  the body.
  8. Body Balance   Skeletal distribution about the main axis provide the balance features  to the body.

Human skeletal system mainly consists of different bones and cartilages.


Human body is made up of 270 bones which are fused variously to form 206  Bones are living tissue in our body having their own blood vessels. They are made up of  living cells, which help them to grow and to repair. These are mainly composed of  proteins, minerals and vitamins. Bone has a very hard matrix due to the presence of  calcium salts in it.

Types of Bones

  1. Long Bone   ::-  Possess an elongated shaft (diaphysis) and 2 expanded ends (epiphyses), shaft has a central medullary cavity, e.g., femur, ulna, etc.
  2. Short Bone  ::-  Broad, short, can be of any shape, e.g., carpals, tarsals, etc.
  3. Pneumatic Bone   ::-  Irregular, contain large air spaces. which make them light, e.g., sphenoid, ethmoid of skull.
  4. Sesamoid Bone   :::-  They are in the form of nodules embedded in tendons and joint capsules, ossification occurs after birth, e.g., patella.
  5. Flat Bone   ::-  Resemble shallow plates and form boundaries of certain body cavities, e.g., scapula, ribs, sternum, etc.
  6. Irregular Bone  ::- Completely irregular in shape, e.g., hip bone, vertebral, bones in the base of skull, etc.


Cartilages are the connective tissues, which have slightly pliable matrix due to chondroitin salts. Matrix of glycoprotein, which is semi-solid, transparent and elastic substance forms cartilage.

 Types of Human Skeletal System

The adult human skeleton consists of 206 bones which are grouped into, the axial skeleton and appendicular skeleton. Out of 206 bones, 6 occur as ear ossicles and the remaining 200 bones are distributed into axial and appendicular skeleton.



The structural arrangements of tissues by which bone and bone or bone and cartilage are joined together are called joints. According to the mobility, joints are classified as

Fibrous, Fixed or Immovable Joints

There is no movement between the bones in such type of joints. Bones are held by white fibrous tissue in the form of sutures, to form the cranium. e.g.,

  • The joints between the bones of skull called sutures.
  • The joints between teeth and the maxilla.
  • The joints between teeth and mandible.

Cartilagenous or Slightly Movable Joints

 In this type, there is a pad of white fibrous cartilage between the ends of bones taking part in the joints, which allow very slight movement. Movement is possible only because of compression of pad of cartilages. e.g., pubic symphysis of pubis and the joints between the vertebrae (intervertebral discs).

Synovial or Freely Movable Joints

Ail synovial joints are freely movable in selected directions and contain synovial cavity, articular cartilage and a synovial membrane .Some joints also have ligaments holding the bones together.

There are six categories of synovial joints 

  • Hinge or Ginglymus Joints  ::- The bone of this type of joint can move in a single plane (monaxial). Examples are the elbow, ankle and interphalangeal joints.
  •  Pivot Joint  ::-  The joint in which a rounded, pointed or conical surface of one bone  articulates within a ring formed partly by another bone and partly by a ligament. Movement is of rotation type and joint is monaxial. e.g., rotation of the head from side to side and movement between the proximal ends of the radius and ulna.
  • Gliding Joint  ::-  The joints in which the articulating surfaces of bone are usually flat,  only side-to-side and back and forth movements are permitted, e.,g,  joints between the carpal bones, tarsal bones, the sternum and clavicle and the scapula and clavicle.
  • Ball and Socket or Sphenoid Joint  :::-  These joints consists of a ball-like surface of one bone filled into a cup-like cavity of another bone. Such a joint permits movement in three planes (triaxial). e.g., shoulder and hip joints.
  • Saddle or Sellaris Joint  ::-  In these joints, the articular surface of one bone is saddle shaped and the articular surface of the other bone is shaped like a rider sitting in the saddle. Movement are side-to-side and back-and-forth (biaxial). e.g., movement between the carpal and metacarpal of the thumb.
  • Ellipsoidal or Condyloid Joint  ::-This is the joint in which oval shaped condyle of one bone fits into an elliptical cavity of another bone. Movements are side-to-side and back-and-forth (biaxial), e.g., movement of the wrist.

Some Common Injuries of the Joints

Dislocation ::-  Occurs when bones are forced out of a joint, often accompanied by sprains, inflammation and joint immobilisation.

Cartilage tears  ::- Cartilage may tear when joints are twisted or when pressure is applied to them.

Sprain ::-  Partially or completely torn ligament.

Functions of Joints

Joints serves following functions in human body

  •  The joints make body flexible.
  • Some joints allow the growth of the structures that they connect to.
  • These are essential for all types of movement.


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