Human Skull - Medical Terminology

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HUMAN SKULL

The skull is a bony structure that forms the head in vertebrates, It supports the structures of the face and provides cavity for the brain.
In human being skull is formed by two sets of bones.

• Cranium
• Facial Bones
  
  

CRANIUM:
The cranium encloses and protects the fragile bone tissue and is composed of eight large flat bones, which are:

1. Frontal bone
2. Two Parietal bones
3. Two Temporal bones
4. Occipital bones
5. Sphemoid bone
6. Ethmoid bone

1. FRONTAL BONE
The frontal bones forms the forehead, the bony projection under the eyebrows, and the superior part of each eye's orbit.

2. PARIETAL BONE:
The paired (two in number) parietal bones formed most of the superior and lateral walls of the cranium; they meet in the middle line of the skull at the sagittal suture. In front they meet the frontal bone by coronal suture.

3. TEMPORAL BONE:
The temporal bones lie inferior to the parietal bones; and join them at the squamous suture.

4. OCCIPITAL BONE:
The occipital bone joins the parietal bones anteriorly at the lamboid suture. In the base of the occipital bone is a large opening, the foreman magnum, which surrounds the lower part of the brain and allows the spinal cord to connect with the brain.

5. SPHENOID BONE:
The butterfly-shaped sphenoid bone spans the width of the skull and forms the floor of the cranial cavity; In the middle line of sphenoid bone there is a small depression called the Sella Turcica or Turk's Saddle, which forms a snug enclosure for the Pituitary glands.

6. ETHMOID BONE:
The ethmoid bone is very irregular in shape, and lies anterior to the sphenoid bone. It forms the roof of the nasal cavity and part of the medial walls of the eye's orbits.

FACIAL BONES
Face's bone composed of fourteen bones, Twelve facial bones are paired, only Mandible and Vomer are single bones. Here are Facial bones:

1. A Pair of Maxillae bones
2. A Pair of Palatine bones
3. A Pair of Zygmatic bones
4. A pair of Lacrimal bones
5. A pair of Nasal bones
6. A pair of Inferior Nasal Conchea
7. Single Mandible bone
8. Single Vomer bone

SUTURES FOUND IN BRAINS
The sutures of the skull, also referred to as the cranial sutures, are fibrous connective tissue composed mainly of collagen. Sutures of an adult skull are categorized as synarthroses. Synarthrosis is an immobile joint under normal circumstances. It also doesn't have a capsule or joint cavity. Thus suture form immobile articulations or joints with a fracture-like appearance that connect the bones of the skull.
Sutures can be further subdivided according to their location into:

• Sutures of the neurocranium
• Sutures of the viscerocranium
• Sutures between the neuro- and viscerocranium.

SUTURES OF NEUROCRANIUM:
Six primary sutures of the cranial vault exist, including the paired:

1. Sagittal Suture: Between the both parietal bones in the midline.
2. Coronal Suture: Between the frontal bone with the parietal bones.
3. Lambdoid Suture: Between the parietal bones with the occipital bone (between the parietal and interparietal bones).
4. Squamosal Suture: Between the temporal bone with the parietal bones.
5. Metopic Suture: (or frontal suture): Between the both frontal bones. Found in childrren.
6. Sphenoid Suture: is consists of:
   * Sphenofrontal suture (2): Between spenoid bone and frontal bone.
   * Sphenoparietal suture (2): Between spenoid bone and parietal bone.
   * Sphenopetrosal suture (2): Between the sphenoid bone and the temporal bone.
   * Sphenoethmoidal suture: Between sphenoid bone and the ethmoid bone.

Sub division Of Sutures:

• Frontoethmoidal suture (2): Between the orbital process of the frontal bone and the orbital plate of the ethmoid bone.
• Occipitomastoid suture(2): Between the articulation of the squamous part of the occipital bone and the temporal bone's mastoid part.
• Petrosquamous suture (2): Between the medial petrous and the lateral squamous parts of the temporal bones.
• Petroclival suture (2): The petroclival suture, also called the petro-occipital or petroclival fissure, is the articulation between the lateral surface of the occipital bone's basilar part and the apex of the temporal bone's petrous part.
• Parietomastoid suture (2): Closer to the mastoid part of the parietal bone, the squamous suture transforms into and continues as the parietomastoid suture. Parietotemporal suture (2): Between the parietal and temporal bones, is the parietotemporal suture.

SUTURES OF VISCEROCRANIUM:
These are facial sutures are seen on the anterior part of the skull. The sutures of the viscerocranium are:

• Intermaxillary suture: Between two maxilla.
• Median palatine suture: Between the horizontal plates of the palatines.
• Lacrimomaxillary suture (2): Between the anterior border of the lacrimal bone and the frontal process of the maxilla.
• Nasomaxillary suture (2): Between the later sides of the nasal bones and the frontal process of the maxillary bones.
• Zygomaticomaxillary suture (2): Between the zygomatic bone and maxilla bone.

SUTURES BETWEEN NEURO AND VISCEROCRANIUM:
These include:

• Frontolacrimal suture (2): Between the inferior border of the frontal bone's orbital part and the superior border of the small and delicate lacrimal bones.
• Frontonasal suture (2): Between the frontal and the nasal bone.
• Frontomaxillary suture (2): Situated on both sides of the nasal bones between the frontonasal suture and frontolacrimal suture.
• Frontozygomatic suture (2): Between the frontal and the zygomatic bone.
  (Note: The combination of the six sutures - two frontolacrimal, two frontomaxillary and two frontonasal sutures - looks like one continuous suture.)
• Sphenozygomatic suture (2): connects greater wing of the sphenoid bone with the zygomatic bone and its medial part participates in forming the lateral wall of the orbit.

FONTANELLES:
In new born child, the sutures are incompletely fused, leaving membranous gaps called fontanelles. Fontanelles are also often called soft-spots. There are two major and four minor fontanelles:
Major Fontallenes:

1. Occipital fontanelle: also known as posterior fontanelle, located at the junction between the sagittal and lambdoid suture, typically closes around the first and second months of age.
2. Frontal fontanelles: It is also known as the anterior fontanelle, is found at the junction of the coronal and sagittal sutures. The frontal fontanelle closes between 12 and 18 months of age.

Minor Fontallenes:
The minor fontanelles are paired. They are smaller and situated on the sides of the skull. These are

1. Mastoid fontanelles(2): is situated between the temporal, occipital, and parietal bones.
2. Sphenoid fontanelles (2): is located between the sphenoid, temporal, frontal, and parietal bones.

LANDMARKS SITUATED ALONG THE SUTURE OF THE SKULL:
Where the sutures intersect, bony landmarks like elevations or depressions can be observed. These landmarks are anatomically important features, and are used as craniometric points of reference in radiology and anthropological measurements. There are following landmarks on the skull:

• Bregma: It is the intersection of the coronal and sagittal sutures.
• Lambda: It is formed at the convergence between the sagittal and lambdoid sutures (resemble to a greek letter 'Lambda'.
• Asterion (2): It is formed on the posteroinferior part of the skull at the junction of the parietomastoid, occipitomastoid and lambdoid sutures.
• Nasion: It is a midline bony depression between the two orbits.
• Obelion: It is formed at the intersection of the sagittal suture and an imaginary line that connects the two parietal foramina.
• Pterion (2): It is an H-shaped point of junction between four bones: the sphenoid, temporal, frontal and parietal bone.
• Vertex: It is a single midline landmark found between the bregma and lambda, almost at the midpoint of the sagittal suture. The vertex of the human skull is formed at the juncture of four bones: frontal bone, parietal bones (2) and occipital bone.