Skull
The skull is a vital bony structure in vertebrates, particularly in humans, where it serves to protect the brain and support facial features. In adults, the human skull comprises twenty-two bones, divided into the cranium, which encases the brain, and the facial skeleton. Notably, the skull includes movable joints called sutures that connect these bones, allowing for some flexibility. Newborns start with a softer skull made of six bones, featuring fontanels or soft spots that aid in passage through the birth canal and accommodate rapid brain growth. The skull's bony architecture includes various cavities, such as the cranial cavity for the brain and the orbital cavities for the eyes. It also houses sinuses that reduce weight. Skull fractures, although rare due to the strength of the bones, can occur from impacts or falls, and their treatment varies based on severity. Understanding the structure and function of the skull is essential in fields such as medicine, anatomy, and anthropology.
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Skull
In most vertebrates, the skull is the bony structure that forms the head. In humans, the skull consists of two main parts: the cranium, which houses the brain, and the facial skeleton. An adult human skull consists of twenty-two bones, twenty-one of which are movable and connected by sutures, which are fibrous, immovable joints. The main function of the skull is to protect the brain, the most important organ in the human body. Other functions include supporting the facial structures, fixing the distance between the eyes for vision, and fixing the position of the ears to allow for hearing. The sinuses are also contained in the skull. These are air-filled cavities believed to decrease the skull's weight.
Background
A human newborn is born with a skull, but it is significantly different from an adult's skull. While an adult's skull has twenty-two bones, a newborn's skull has only six—one frontal bone that makes up the forehead, two parietal bones that comprise the top and sides of the skull, two temporal bones that are on the side of the head, and one occipital bone that is in the back of the head. A newborn's skull has two spaces that are not covered by bone. These spaces are called fontanels, or soft spots. One fontanel is on the top of the middle of the head, and the other is in the middle of the back of the head.
The fontanels help make a newborn's skull flexible, which enables it to pass through the birth canal more easily. This flexibility also helps accommodate the rapid brain growth that occurs during the first eighteen months of life.
As the baby grows, the spaces between the bones lessen. Between the ages of twenty months and two years, the fontanels close, and the permanent skull is fused together. A child's skull reaches adult size around the age of seven.
As a child's skull grows and develops, the cranial and facial bones form cavities. The largest cavity is the cranial cavity, which houses the brain. The nasal cavity is divided by the nasal septum. The orbital cavities support and protect the eyes. Three small ear bones are in each middle-ear cavity: the malleus, incus, and stapes. The oral cavity is in the mouth.
Overview
The skull is thought generally to contain twenty-two bones: eight in the cranium and fourteen in the facial skeleton. However, sometimes the maxilla, the upper jawbone, is considered one bone instead of two, which decreases the number of bones in the skull to twenty-one. Other times, the three small bones in the inner ear (the malleus, incus, and stapes) and the hyoid, a bone that supports the tongue, are considered skull bones.
Cranium and Cranial Base
The cranium, also known as the neurocranium, is the part of the skull that supports and protects the brain. Anatomically, the cranium can be divided into two parts: the calvarium and the cranial base. The main bones of the calvarium are the frontal bone, which is the forehead; the occipital bone, which is at the back of the skull; and two parietal bones, which are at the top and sides of the skull.
The five bones that make up the cranial base, also called the skull base, are the two frontal bones (in the front under the face), the ethmoid bone (between the frontal bones), the sphenoid bone (behind the frontal bones), the two temporal bones (in the middle of the base), the parietal bone (on the outer base), and the occipital bone (in the back of the base).
The occipital bone has an opening in its center for the spinal cord, the major column of nerves that transmits signals to and from the brain. The cranium and the cranial base are supported by the first and highest vertebra, the atlas.
Facial Skeleton
The facial skeleton is also called the viscerocranium. Its shape determines a person's facial structure. It has several important functions. It protects the brain and the sensory organs connected to smell, sight, and taste. It also serves as a frame for the soft tissue covering the face.
The facial skeleton has fourteen bones, thirteen of which are fused and immovable. The nasal bones are two small bones that are right above the nasal openings in the nose. They form the bridge and roof of the nose. The vomer is a bone that separates the nasal cavity into two sides. The two inferior nasal conchae push out the nasal cavity to make breathing easier. The two zygomatic bones are the cheekbones. The two lacrimal bones are small and fragile and form part of the eye socket. The two maxillae form the upper jaw; the upper teeth are rooted in each maxilla. The maxillae are on each side of the nasal bones and also form the lower portion of the eye socket. Each maxilla has a sinus cavity. The lower teeth are in the mandible (jawbone), the only facial bone that can move. The two palatine bones are in the back of the oral cavity (mouth) and form part of the hard palate.
Sutures
The bones in the cranium are held together by sutures, which are rigid, immovable joints. The main sutures are the coronal suture, sagittal suture, and lambdoid suture. The coronal suture joins the frontal bone with the two parietal bones. The sagittal suture joins the parietal bones to one another, and the lambdoid suture joins the two parietal bones to the occipital bones.
Skull Fractures
The main purpose of the skull is to protect the brain. Skull bones are extremely strong. However, they can sometimes fracture or break. Skull fractures are most often caused by a blow to the head, a fall, or a collision in an automobile. Symptoms of a skull fracture include a bruise on the impacted area, swelling, pain, and bleeding from the nostrils or ears.
Skull fractures are classified by location and severity. Three main types are closed fractures, open fractures, and depressed fractures. In a closed fracture, also called a simple fracture, the skin covering the fracture is not cut. In an open fracture, on the other hand, the skin is cut, and the skull is visible. A depressed fracture is the most serious of the three. In this type of fracture, the skull is indented and extending into the brain cavity.
Treatment of a skull fracture depends on its severity. Minor fractures may require only rest and pain medication, while very serious fractures may require neurosurgery.
Bibliography
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