Skeletal System

Skeletal system consists of a framework of bones and a few cartilages. 

This system has a significant role in movement shown by the body.

Swimming, jumping, walking, running are different types of movements shown by Human beings.

Bone and cartilage are specialised connective tissues that help in movement.

1.0Bone

Bone is a specialized connective tissue having very hard matrix. Bone is hard due to presence of calcium salts in its matrix. 

2.0Cartilage

Specialized connective tissue which can be bent. It has slightly pliable matrix with chondroitin salts in it. 

In human beings, this system is made up of 206 bones and a few cartilages. Its two main divisions are the axial skeleton and the appendicular skeleton.

     Axial Skeleton                  Human Skeletal System       Appendicular Skeleton

3.0Axial Skeleton

Axial skeleton comprises 80 bones distributed along the main axis of the body. The skull, vertebral column, sternum and ribs constitute the axial skeleton. 

Skull bones

The Skull is composed of two sets of bones – cranial and facial, that totals to 22 bones. 

Cranial Bones 

Cranial bones are 8 in number. They form the hard-protective outer covering, cranium (brain box) for the brain. They are as follows

1. Frontal Bone –1 2. Parietal Bones – 2           3. Temporal Bones – 2

4. Occipital Bone – 1 5. Sphenoid Bone – 1         6. Ethmoid Bone –1

Cranial bones

• Occipital bone consist of two projections called Occipital condyles therefore our skull is called dicondylic skull.
• The skull region articulates with the superior region of the vertebral column with the help of two occipital condyles (dicondylic skull).

Foramen Magnum 

At the base of skull an opening is present called foramen magnum through which spinal cord comes out.

Facial Bones

The facial region is made up of 14 skeletal elements which form the front part of the skull. The bones of the facial region are:

1. Maxilla – 2 2. Nasal – 2

3. Zygomatic/Malar – 2 4. Lacrimal – 2

5. Palatine – 2 6. Vomer – 1

7. Inferior Nasal (Turbinal bones) –2 8. Mandible – 1

Mandible is the only movable bone of skull.

Facial bones

Hyoid Bone 

• A single U-shaped bone called hyoid is present at the base of the buccal cavity between the mandible and larynx. It is also included in the skull. 
• It is a unique component of the axial skeleton because it does not articulate with any other bone rather it is suspended by ligaments and muscles.
• Tongue is attached with hyoid bone.      

Hyoid bone

Ear Ossicles

• Each middle ear contains three tiny bones - Malleus, Incus and Stapes, collectively called ear ossicles. 
• Stapes is the smallest bone of our body.
• The ear ossicles increase the efficiency of transmission of sound waves to the inner ear.

Ear Ossicles

Hyoid bone, Skull bones and associated bone

Vertebral Column

The human vertebral column is made up of serially arranged vertebrae. 26 vertebrae make up the vertebral column. Vertebral column is the protective bony covering around the spinal cord. It extends from the base of the skull. 

• Each vertebra has a central hollow portion (neural canal) through which the spinal cord passes. 
• The vertebral column is differentiated into Cervical (7), Thoracic (12), Lumbar (5), Sacral (1-fused) and Coccygeal (1-fused) regions starting from the skull. 
• When viewed from the anterior or posterior, a normal adult vertebral column appears straight. But viewed from the side, it shows slight bends called normal curves. The curves of the vertebral column increases it’s strength, helps to maintain balance in the upright position, absorb shocks during walking and helps to protect the vertebrae from fracture. 

Vertebral column lateral and posterior view

Cervical Vertebrae

• The number of cervical vertebrae are seven in almost all mammals including human beings.

Atlas 

• First vertebra is the atlas. 
• Atlas articulates with the occipital condyles of occipital bone and form condylar joint which is responsible for downward and upward movement. 

Atlas

Axis Vertebra

• Second vertebra is called axis.
• Axis form pivot joint with atlas.
• pivot joint is responsible for sideways movement.

Thoracic Vertebrae

• Thoracic Vertebrae are considerably larger and stronger than cervical vertebrae.
• Thoracic vertebrae in human beings are 12 in number. They provide protection to the lungs.
• The feature of the thoracic vertebrae that distinguishes them from other vertebrae is that they articulate with the ribs.

Lumbar Vertebrae

• Lumbar vertebrae are 5 in number.
• Lumbar vertebrae are the heaviest and largest vertebrae
• The lumbar vertebrae’s function is to support the great weight of the body.

Sacrum

• The sacrum is a triangular bone formed by the union of five sacral vertebrae. 
• The sacrum forms the posterior pelvic wall and strengthens and stabilizes the pelvis.

Coccyx

• It is formed by the fusion of usually four coccygeal vertebrae. 
• Coccyx provides weight-bearing support to a person in the seated position.

Functions of Vertebral Column :-

(1) The vertebral column protects the spinal cord, 

(2) Vertebral column supports the head 

(3) Vertebral column serves as the point of attachment for the ribs and muscles of the back.

4.0Sternum

• Sternum is a flat bone on the ventral midline of thorax. 
• There are three parts of sternum- 

(i) Superior part is the prosternum (manubrium) 

(ii) Middle part is the mesosternum (body) 

(iii) Inferior smallest metasternum (xiphoid process)

• The sternum provides spaces for the attachment of the thoracic ribs and abdominal muscles too.
• The sternum is a favoured site for obtaining samples of haemopoietic tissue during diagnosis of suspected blood diseases.

5.0Ribs

• There are 12 pairs of ribs numbered 1-12 from superior to inferior, give structural support to the sides of thoracic cavity. The ribs increase in length from the first through seventh, and then decrease in length to the twelfth rib.
• Each rib is a thin flat bone connected dorsally to the vertebral column and ventrally to the sternum. 
• It has two articulation surfaces on its dorsal end and is hence called bicephalic. 
• Spaces between ribs called intercostal spaces, are occupied by intercostal muscles, blood vessels and nerves.

Structure of Rib Cage  

• First seven pairs of ribs are called true ribs.
• Dorsally, they (1^st to 7^th pair of ribs) are attached to the thoracic vertebrae and ventrally connected to the sternum with the help of hyaline cartilage. 
• The 8^th, 9^th and 10^th pairs of ribs do not articulate directly with the sternum but join the seventh rib with the help of hyaline cartilage (Costal cartilage). These are called false ribs. 
• Last 2 pairs (11^th and 12^th) of ribs are not connected ventrally and are therefore, called floating ribs.
• Thoracic vertebrae, ribs and sternum together form the rib cage.

There are Five Parts of Rib Cage

1. Dorsal part consists of vertebral column and ribs
2. Ventral part consists of sternum and ribs
3. Lateral part consists of ribs
4. Anterior part consists of clavicle
5. Posterior part consists of diaphragm

Significance of Rib Cage

The rib cage protects the organs in the thoracic cavity. It helps in respiration and provides support for the upper extremities.

6.0Also Read