What is Structure and Function of the Axial Skeleton?

The skeletal system present in our body is distinguished as the axial and appendicular skeleton. The appendicular skeleton has upper and lower limb bones. The axial skeleton is the bones that are present in the upper part of the body. The axial skeleton is made up of bones found in the head and the trunk region. The bones are the skull bones, ossicles of the ear, hyoid bone (throat bone), rib cage, sternum, and the vertebral column. The ear ossicles consists of the auditory ossicles; the three small bones. The auditory ossicles enable the sound to reach the brain. The axial skeleton helps in attaching the skeletal muscles so that the parts of the body can be moved.

Skull

The skull is a bony structure; it is a cavity that protects the brain and supports the face. The skull consists of the cranium (neurocranium), and mandible (viscerocranium). The bones of the skull support the structures.

Note: Neurocranium is the brain cage and the upper part of the skull.

Note: The Viscerocranium is the facial skeleton that is not the part of the brain cage.

What Bones are Present on the Anterior Part of the Skull?

The bones of the skull are present in the axial skeleton. The anterior part of the skull holds the frontal and facial bones, as the face contains the eyes, nose, and other structures these bones support them. Firstly, the orbit is the one that holds the eyeball and it contains the muscles which move them. Besides the supraorbitals margin, there is an opening that allows the sensory nerve to skin present on the forehead and that is called the supraorbital foramen. The infraorbital foramen provides the passage for the sensory nerves that reach the frontal face; it is present below the orbit.

Nasal cavity

The nasal septum divides the cavity into two; the perpendicular plate of the Ethmoid bone forms the upper part of the nose. The vomer bone is the part present below.  The nose is triangular on each side and bony plates are seen anteriorly.

The braincase

The braincase provides protection for the brain present in it. The cranial cavity occupies the brain that is surrounded by the calvarias (skull cap). The flat bones of the skull form the upper part and the sides of this braincase. The base of the braincase has several openings for the movement of the cranial nerves, spinal cord and, blood vessels to the regions of the axial skeleton and the vertebral column. The braincase contains two parietal bones, two temporal bones, frontal, occipital, sphenoid, and Ethmoid bones.

The parietal bone

The paired parietal bones are present on both sides to form the upper skull. Each of them is additionally bounded by the frontal bone and inferior is the temporal bone and, the occipital bone is placed posteriorly.

Temporal bone

The lateral side of the skull is formed by the temporal bone. The temporal bone is divided into many regions. The squamous portion is flattened and present above. The zygomatic process is placed below the temporal bone; forms the posterior portion. The mastoid portion is present to the posterior side, just behind the ear lobe and this helps in the attachment of the muscles.

Frontal bone

The forehead is formed by this bone, the supraorbital foramen is found in the middle of the supraorbital margin and it is thickened at the eyebrow, this also allows the nerves to pass through the forehead.

Occipital bone

The posterior skull and the base of the cranial cavity form the occipital bone. The external occipital protuberance is a minute protrusion found at the midline of the posterior neck. The neck is attached to the skull at the superior point of the nuchal lines that are covered by the scalp of the skull. The foramen magnum is present at the base of the skull; through this, the spinal cord is placed. There is a presence of the occipital condyle which supports the skull which has been placed on the vertebral column.

Sphenoid bone

The single bone in the central skull is the sphenoid bone; it joins with almost all the bones in the skull to give a defined skull.  The pituitary gland is encased by the hypophyseal fossa that is round and depressed on the floor of sellaturcica. The two bony plates formed here are thin in the sphenoid bone and it is oriented in a vertical way. Those are the medial pterygoid plate and the lateral pterygoid plate. The lateral pterygoid plate acts as a site that attaches the muscles which are meant for chewing and play as the mandible.

Ethmoid bone

The perpendicular plate of the ethmoid bone in the nasal cavity forms the nasal septum and the lateral wall in the upper portion. The orbit and the nasal cavity contain the lateral portions of the ethmoid bone.

Hyoid bone

Note: The hyoid bone is not the part of the skull as it is an independent bone.

The hyoid bone is located at the upper neck shaped as the alphabet ‘U’. The base of the tongue is attached to the larynx and starts at the hyoid bone. It helps in swallowing the food that is ingested and also for speech. The movement is interlinked with the tongue, larynx, and pharynx.

The Vertebral Column

The vertebral column is the backbone; it is a part of the axial skeleton which is attached to the appendicular skeleton. The vertebral column is flexible and supports the neck head and body. The spinal cord, the canal, and the cavity are encased by the vertebral column. The appendicular skeleton is the portion of the skeleton vertebrates. Adjacent to the vertebrate the intervertebral disc, to keep the vertebrae united the intervertebral disc acts as ligaments. To allow movement of the vertebral column to sit, bend and other works the disc forms the fibrocartilaginous joint. There are curvatures present in the vertebral column.  The cervical vertebra does not carry a heavy bodyweight. The cervical vertebrae can be found in the finger and they can be distinguished by the features as the thoracic and lumbar vertebrae. The scapulae and the clavicles make up the shoulder girdles. A shoulder girdle is present in the appendicular skeleton.

Content and Applications

This topic is significant in the professional exams for both undergraduate and graduate courses, especially for;

• B.Sc. in Zoology
• B.Sc. General Physiology
• M.Sc. in Human anatomy and Physiology
• M.Sc. in medicine
• Masters in Medicine

Related Concepts

• Anatomy and physiology
• Axial skeleton and its functions
• The vertebral column of the human system