Classification of skeleton: Axial-1

Classification of the Skeletal System

The 206 named bones in the mature human skeleton are divided into two main divisions. The axial and appendicular skeletons are what they are. The appendicular skeleton is made up of body bones from the axial group, while the axial skeleton is made up of bones that are located around the axis. They are annexes. Appendicular skeleton includes the bones of the upper and lower extremities as well as girdle bones.

Axial Skeleton

The skull, the vertebral column, the ribs, and the sternum make up the axial skeleton, which serves as the body's axis. There are 80 bones in the axial skeleton. The brain, spinal cord, and organs in the thorax are all protected by this portion of the skeleton, which also supports the head, neck, and trunk.

Skull

The 22 bones that make up the cranium (but including 1 hyoid and 3 pairs of auditory ossicles there are 27 bones). The skull is supported by the top of the spinal column, and it has two distinct bony sections:

• The cranial bone (cranium) or neurocranium
• The facial bone (Face) or viscerocranium

Cranium

Numerous flat and crooked bones make up the skull, which protects the brain, eyes, and ears as well as the brain cavity. A base and a vault/calvaria make up the skull. The vault that surrounds and covers the brain's topmost resting place is called the cranial base. The base is made up of uneven temporal and sphenoid bones, whereas the vault is made up of flat bones (frontal, parietal, and occipital). The eight cranial bones that make up the cranium are:

• Frontal bone: 1
• Occipital bone: 1
• Temporal bones: 2
• Sphenoid bone: 1
• Ethmoid bone: 1
• Parietal bones: 2
   
• Frontal bone: The bone in the forehead is this. It contributes to the formation of the supraorbital borders, the conspicuous ridges above the eye, and the orbital cavities (eye sucket). There are two air-filled cavities called sinuses within the bone just above the supraorbital margins. The frontal and parietal bones are connected by the coronal suture.
• Parietal bone: The sides and roof of the skull are made up of the two parietal bones. They connect at the sagittal suture, the coronal suture at the frontal bone, the lambdoidal suture at the occipital bone, and the squamous suture at the temporal bones.
• Temporal bones: On the base of the skull and on each side are these bones. Together with the parietal, sphenoid, and zygomatic bones, they form an immovable joint. The four parts that make up each temporal bone develop during development.
• Occipital bone: These bones make up a large portion of the base and the back of the skull (occipital). The lower portion of the bone contains a sizable opening called the foramen magnum. Within this foramen, the medulla oblongata joins the spinal cord. The atlanto-occipital joint is formed by the articulation of the occipital condyles, or rounded projections, on either side of the foramen magnum with the first cervical vertebra, or atlas.
• Sphenoid Bone: According to legend, the sphenoid bone is formed like a bat. Between the frontal and temporal bones on the side of the skull, its larger wing protects. The cranial floor is made up of all the cranial bones that articulate with one another and hold them all together. The pituitary gland rests in a small depression called the sella turcica on the superior surface of the bone in the middle of the body.
• Ethmoid bone: At the base of the skull, between the orbits, on the roof of the nose, is a thin, spongy bone called the ethmoid bone. It is located behind the nasal bones and ahead of the sphenoid.

Craniometric points of cranium

• Pterion (Greek: wing): Junction of the frontal, parietal, squamous temporal, and greater wing of the sphenoid bones.
• Lamda (Greek; letter L): Point on the calvaria where the lambdoid and sagittal sutures converge.
• Bregma (Greek; forepart of head): Point on the calvaria where the coronal and sagittal sutures converge.
• Vertex (Latin; whirl, whorl): Middle of neurocranium's superior point, with Frankfort or orbitomeatal plane of the skull aligned.
• Asterion (Greek; asterios, starry): It has a star-like shape and is situated where the parietomastoid, occipitomastoid, and lambdoid sutures meet.
• Glabella (Latin; smooth, hairless): Smooth prominence; most noticeable in men; located on the frontal bones above the nose's root; the frontmost projecting portion of the forehead.
• Inion (Greek; back of head): Largest protuberance on the external occipital bone.
• Nasion (Latin; nose): The region of the skull where the frontonasal and internal sutures converge.

Facial Bones

The remaining 14 bones of the skull are facial bone that have no contain with brain. These bones are as follows:

• Maxillae: 2
• Nasal bones: 2
• Palatine bones: 2
• Interior nasal conches: 2
• Lacrimal bones: 2
• Zygomatic bones: 2
• Vome: 1
• Mandible: 1
   
• Maxillae (upper jaw bone): The two maxillae fuse together to produce the maxillae. Alveolar processes and a body make up each maxilla. The body is a component of the face, as well as the lateral walls, nasal cavity floor, and orbital floor. The upper teeth are carried by the alveolar process. The anterior and significant portion of the hard palate is made up of the horizontal or palatine processes. The palatine processes of the maxillae and the horizontal plates of the palatine bones combine to form the hard palate, which is the bony roof of the mouth.
• Palatine bone: The palatine bones make up the nasal cavity's wall and the remaining portion of the hard palate. Palatine bones are all L-shaped. The horizontal plate is a part of the hard palate, while the upright portion (perpendicular plate) is a part of the lateral walls of the nasal cavity. The palate divides the nasal and oral cavities and forms the roof of the mouth. It is made up of a fleshy soft palate in the back and a bony hard palate up front. By palatine process, the majority of the hard palate is created.
• Zygomatic bone: The cheek prominences and a portion of the lateral wall and floor of each orbit are formed by the zygomatic (check) bones.
• Nasal bones: The bridge of the nose is made up of two tiny, flat nasal bones. The remaining cartilages make up the nose's supporting tissue.
• Lacrimal bones: The nasal bones are located lateral and posterior to these two little bones. They are a component of the orbital cavities' medial wall. The lacrimal sac is located in a groove (fossa) that is present on each lacrimal bone. Tears are collected in the lacrimal sac before they enter the nasal cavity. The canal is where the tear duct travels.
• Inferior nasal conchae: Each concha is a bone with a scroll-like shape that projects into the nasal cavity and makes up a portion of the lateral wall. Prior to entering the lungs, air is filtered by the superior, middle, and inferior pairs of nasal conchae.
• Vomer: The lower half of the nasal septum is made up of a thin, triangular bone called the vomer. The perpendicular plate of the ethmoid bone forms the superior half of the nasal septum.
• Mandible (lower Jaw): It is the only moveable and the strongest bone in the skull. It provides attachment for the facial expression and chewing muscles as well as support for the bottom teeth that make up the lower jaw. It has two upright rami and a body that forms the chin. This "Y"-shaped bone has two processes: the anterior coronoid process, where the temporalis muscle inserts, and the posterior condylar process, which connects to the mandibular fossa of the temporal bone to form the temporomandibular joint.

Hyoid Bone

Despite not actually being a part of the skull, the horseshoe-shaped hyoid bone is closely linked to the mandible and temporal bone. The hyoid bone is a special bone in the body because it is suspended from the tip of the styled process of the temporal bone rather than articulating directly with any other bone. It is used for the attachment of the tongue-moving and speech- and swallow-improving muscles. It is palpable in the neck, just above the thyroid cartilage's edge.

The Skull in Infancy and Childhood

If the skull bones had fused at birth, the infant's head would not be able to fit through the mother's pelvic outlet. Although shifting of the skull during birth may make the baby appear malformed, the head soon takes on a more typical appearance. Fontanels are the spaces between the unfused skull bones. The intra-membranous ossification will be finished in this membrane, which connects the bones at these locations. The posterior fontanel typically ossifies at two to three months after birth, and the anterior fontanel can be palpated at 18 to 24 months after birth. Most fontanels ossify by the time the baby is a year old.

Fontanels

A newly formed embryo's skeleton is made up of cartilage or fibrous membrane components. The Ossification process gradually replaces the cartilage or fibrous membranes with bone. Fontanels are membrane-filled spaces on the skull that are present at birth. They are located between the bones of the skull. Six fontanels make up the majority of the fetal skull.

Functions of Fontanels:

• They allow the fetus's skull to change shape during delivery as it travels through the birth canal.
• They allow the baby's brain to develop quickly.
• They act as a landmark (anterior fontanel) to allow the superior sagittal sinus to be drained of blood.
• They assist in figuring out the fetal position before birth.