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Anatomy of Human bones

Bones are integral part of inner framework in a human body. Interestingly, new born baby has approx 270 bones which are reduced to around 206 bones by adulthood after some bones get merged together. Generally all the bones in the human body develop and acquire maximum bone mass around the age of 21years. Primary functions of these bones are to support weight and give protection to body organ.

…continued from the previous post (Types of Bones in Human Body)

3. Flat Bones

As the name suggests they have a flat shape, not rounded such as skull and rib bones. These bones have two prominent surfaces. They are similar to shallow plates and form boundaries of certain body cavities. Flat bones are made up of a layer of spongy bone between two thin layers of compact bone. These bones have marrow, but they do not have a bone marrow cavity.

It's important to note that many of these bones aren't truly flat and have a curve to them so the name 'flat bone' is a wrong notion.

Being a base for muscular attachment flat bones main role is to protect internal vital organs such as the brain, heart, and pelvic organs. There are flat bones in the scapula, skull (occipital, parietal, frontal, nasal, lacrimal, and vomer), the thoracic cage (sternum and ribs), and the pelvis (ilium, ischium, and pubis).

Following are the main functions of flat bones:

  • give shield to a important body parts like the brain, the heart and lungs
  • support broad and largely flat surface area whereby a muscle(s) can attach, such as the shoulder blade

4.  Irregular Bones

An irregular bone is a type of bone classified according to its shape. These bones do not fall into any other category, due to their uneven shape. They have complicated shapes which is neither long, nor short or flat such as bones of vertebrae, hip, sacrum, mandible (lower jaw) and atlas bone in the neck. They primarily consist of cancellous bone, with a thin outer layer of compact bone.

Following are the different functions of the irregular bones :

  • protection of nervous tissue (the vertebrae protect the spinal cord)
  • affording multiple anchor points for skeletal muscle attachment (as with the sacrum)
  • maintaining pharynx and trachea support, and tongue attachment (such as the hyoid bone).

Pneumatic bones:These are considered as part of the irregular bones because of their unusual shape but yet a slight difference makes them index individually. Presence of large air space in these pneumatic bones makes them light in weight which gives shape to the major part of the skull as sphenoid, ethmoid and maxilla. It also helps in resonance of sound and as air conditioning chambers for the inspired air.

5.  Sesamoid Bones

The word ‘sesamoid’ is taken from the Greek language which means sesame-seed like, which indicates small, smooth structure of the bones.

Sesamoid bone is a tiny and to some extent rounded mass (independent bone or bony nodule) developed in some tendons generally related to joint surfaces where it passes over an angular structure, usually in the hands and feet.

These are not like the other types of bones because they are in the form of nodules. Also these bones are short in size and irregular in shape.

Examples of sesamoid bones are as follows:

  • Patella — this is largest sesamoid bone, present within the quadriceps tendon in the knee.
  • Fabella (or flabella) — this is a small sesamoid bone found in the tendon of the lateral head of the gastrocnemius muscle behind the lateral condyle of the femur.
  • In the hand—Two sesamoid bones in the distal portions of the first metacarpal bone (within the tendons of adductor pollicis and flexor pollicis brevis).

‎Sesamoid bones provide a mechanical advantage to the joint as they improve efficiency of movement and power production, thus are very important for normal function. These bones adjust force, to reduce abrasion and sometimes changes muscle pull direction.

The sesamoid bones are positioned under the base of the big toe in each foot to form the mass in joint. Sesamoid bones in the feet are also very important for ensuring normal way of walking and proper power production.

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