[Biology Class Notes] on Axial Skeleton Pdf

The skeletal system of humans comprises a framework of bones and cartilages. They together form the endoskeleton and play a crucial role in providing shape to the body and facilitating locomotion. The human skeletal system is classified into two broad groups, the axial and appendicular skeleton. The axial skeleton encapsulates all the bones along the human body’s long axis, the skull, laryngeal skeleton, vertebral column, and thoracic cage. The appendicular skeleton includes all the bones in the upper and lower limbs, the shoulders, and the pelvic girdles.

The primary difference between axial and appendicular skeletons is based on their locations. The axial skeleton comprises all the bones along the human body’s center, whereas the appendicular skeleton comprises bones that embody extremities. The axial skeleton includes the components like the skull, the vertebral column, ribcage, and sternum. On the flip side, the appendicular skeleton includes the pectoral girdle, humerus, radius and ulna, carpals, metacarpals, and phalanges. Now that we have talked about the rudimentary differences between the axial skeleton and appendicular skeleton let us study the nitty-gritty of the former.

Axial Skeleton Bones 

The axial skeletal system has 80 bones and six parts. Let us dissect the various parts of the axial skeleton in further detail.

• Thoracic Cage – It is an integral part of the axial skeleton bones. The thoracic cage comprises the ribs and sternum, which safeguard various internal organs and extend attachment to muscles that work towards respiration and upper limb locomotion. There are 12 pairs of ribs, and the ribs 1 to 7 are deemed true ribs as they directly communicate to the sternum. On the contrary, ribs 8 to 10 are known as false ribs. The last two ribs, 11 and 12, are called floating ribs as they are not attached to the sternum and simply hang free. The total number of bones in the thoracic cage is 25, one sternum and 24 ribs.

• The Skull – It comprises the cranial bones and the facial skeleton. The former encompasses the top and back of the skull and encloses the brain, whereas the latter makes up the skull’s face. The facial skeleton has 14 bones that form the entry points to the respiratory and digestive tract. The facial skeleton comprises the following bones.

1. Mandible

2. Maxillae

3. Zygomatic

4. Lacrimals

5. Left and Right Nasals

6. Left and Right Palatines

7. Left and Right Nasal Conchae

Likewise, the cranial bones of the skull protect and safeguard the brain. The occipital bone, the left and light temporal bone, the left and right frontal bone, sphenoid, and the ethmoid together make up the cranial bones.

• Vertebral Column – It is the third component of the axial skeleton bones. Immediately after birth, human babies have 33 separate vertebrae. In due course of time, they fuse together to form 24 vertebras. The vertebral column is a flexible column that has 24 vertebrae and the sacrum and coccyx. We commonly use the word ‘spine’ to refer to our vertebrae. It extends from the roots of the skull to the base of the pelvis. The spinal cord moves from the foramen magnum of the skull through the vertebral canal within the vertebral column. We can group the vertebral column into five regions, the cervical spine, the thoracic spine, the lumbar spine, the sacral spine, and the coccygeal spine. 

Now that we have talked about the various parts of the axial skeletal system let us explore its functions.

Functions of the Axial Skeletal System

The skull, a fundamental part of the axial skeleton, provides protection and security to the precious human brain. It also forms the orbit of the eyes, provides attachment to various muscles, and gives structure to the face. The thoracic cage also offers protection to the lungs, heart, and kidneys. It supports these organs and makes sure that they are safe and functioning. Lastly, the vertebral column protects the spinal cord and supports our head. It offers space for the settlement of ribs and bones of the pelvic girdle. The spine or the vertebrae is also responsible for providing flexibility to human backs.

Differences between the Axial Skeleton and the Appendicular Skeleton

The primary function of the axial skeletal system is to keep the body in an upright position and protect specific precious organs like the brain and lungs. They also provide spaces for the attachment of muscles and thereby facilitate movement. On the contrary, the appendicular system supports the various appendages or extremities of the human structure. It consists of 126 bones. The multiple sections of the axial skeleton system and the appendicular system are tabulated below.

 

Here, we have discussed the various parts of the axial skeleton and their functions. For a better understanding, you can have a look at the axial skeleton labeled diagram. The axial skeletal system is crucial for the overall functioning of the human body.