The skeleton of the vertebral head is called the "skull." Anatomy allows him to carry a protective function due to bones firmly and immovably bonded to each other (the exception is only the mandible and hyoid bone). The skull is a kind of box that preserves the brain and sensory organs. It is the skeleton for the nasal and oral cavities, has a system of holes and channels in which nerve fibers, arteries and veins pass.
Development in phylogenesis
Over time, during natural selection, the animals developed a nervous system and appeared nerve ganglia, and later the brain. The skeleton in these places was supposed to protect the nervous tissue and sensory organs to the maximum, so the cartilaginous skull first appears in cyclostomes. Its bones by their origin are divided into replacing cartilage, integument and visceral. In fish, a bone skull first appears. The connection of the bones of the skull is through the cartilage, which replaces the bone tissue. Bones located outside appeared from ossification in the layers of the dermis.
The visceral parts of the vertebral skull are nothing more than modified gill arches from cartilaginous tissue; therefore, in the process of embryogenesis at the early stages of development, the beginnings of gill openings are laid. Later, muscles and bones of the visceral skeleton will form at this place.
Types of bone joint
Numerous flat, mixed and pneumatic bones form the skull. The connection of the bones of the skull occurs through the following types of attachments: continuous (synarthrosis), discontinuous (joints or diarthrosis).
Synarthrosis is distinguished by the type of connective tissue:
- Syndesmosis (from fibrous tissue) is represented by ligaments, sutures, interosseous membranes, fontanelles and knockings (connection of the root of the tooth with the jawbone).
- Synchondrosis (from cartilage) can be constant throughout life or replaced by bone tissue over time.
- Syndesmosis - are formed when the cartilage of the synchondrosis is replaced by bone.
Synchondrosis, in the thickness of which there is a cavity, is a symphysis, this type of connection is present in the pelvis, connecting the pubic bone.
Diarthrosis is the usual moving joints covered with cartilage. They are a connective tissue capsule that forms a cavity with synovial fluid inside. Diarthrosis is distinguished by the shape of the articular surfaces and the number of their components.
Brain skull
The skull of an adult is formed by 23 main bones, 3 bones in the auditory canal, as well as 32 teeth. The skull is divided into a neurocranium (cerebral) and facial (visceral).
Cranial bones :
1. Unpaired:
- occipital (four parts);
- sphenoid (body, large and small wings, wing processes);
- frontal (also has four parts)
- ethmoid (has a labyrinth) - it is sometimes referred to the facial skeleton.
2. Paired: parietal, temporal.
The temporal bone of the skull has a complex structure, because it is in it that the auditory canal is located. It consists of three parts, which in the perinatal period and after birth are represented by different bones, eventually merging into one. Thus, three components are distinguished: scaly, drum and stony parts, separated by intermediate seams.
The scaly part includes the zygomatic process involved in the formation of the mandibular joint. From here begins the auditory passage, which passes into the tympanum (localization of the middle ear), where the auditory ossicles are located: the malleus, anvil and stapes, as well as a small lenticular cartilage between them. These elements are involved in capturing sound waves, transmitting their vibrations to the inner ear.
The stony bone is very strong and acts as a skeleton for the organs of hearing and balance. Behind the tympanic cavity is a complex bone system, which is a kind of labyrinth, which is the basis of the inner ear. In addition, there is a system of holes and channels conducting nerve fibers and blood vessels.
So, thanks to its complex device, the temporal bone of the skull performs several functions at once.
Inside the frontal bone is a cavity.
Visceral skull
Bones of the visceral part of the skull are:
1. Unpaired: opener, mandibular (the result of fusion of paired dental bones) and hyoid (fixes the tongue, muscles of the pharynx and larynx) of the bone.
2. Paired:
- maxillary (fused to the brain);
- incisal (front bones of the jaw);
- palatine bones (forming the bottom of the skull);
- pterygoid bones;
- zygomatic bones (create a zygomatic arch and partly an orbit).
In the alveoli of the maxilla and mandible in adults, 32 teeth are attached. The facial skull is involved in the formation of the orbit.
In the maxillary bone there are sinuses, which together with those of the frontal and sphenoid ossicles, as well as the labyrinth of the ethmoid bone, make the paranasal sinuses lined with the mucous membrane.
In the seams and fontanelles there are inconsistent bones of the skull.
The structure of the bones of the skull
The skull is formed by flat bones, consisting of a compact substance and spongy (diploe). From the side of the brain, the plate of such a substance is very fragile and easily breaks when injured. The periosteum is attached to the bones in the suture area, forming in other areas the subperiosteal space, which has a loose structure. The hard shell of the brain protrudes from the inside.
Types of connection of the skull bones
The main type of bone compounds of the neurocranium is syndesmosis. Most of these mergers are represented by serrated joints; only between the temporal and parietal bones does a scaly suture pass. The facial skull has flat scars. Anatomically, a suture is often referred to by the names of the bones connecting with it, forming the skull. The connection of the bones of the skull includes one sagittal suture (using it connects the paired parietal bone of the skull), coronary (connects the parietal and frontal bones) and lambdoid (connects the occipital and parietal bones).
Inconsistent sutures may also occur, sometimes resulting from insufficient ossification of the skull.
Teeth attachment
Types of connection of the skull bones include nibbling - this is a type of syndesmosis represented by attaching a tooth to the jaw - mandible and maxilla.
The teeth consist of the following layers: on top they are covered with enamel, under it is a solid substance, dentin, inside it is formed a pulp cavity containing pulp (passing vessels and a nerve). Below the root there is also cement - a fibrous fabric reinforced with lime. The tooth is attached to the alveolar bone of the jaw using cement and periodontal ligaments.
These jaw processes are formed using two cortical plates and a spongy substance between them. The space between the plates is divided by means of interdental septa into separate alveoli. The tooth roots are surrounded by a periodontal ligament - it is a connective tissue formed from fibers of different types and different orientations, it is it that attaches the tooth root to the jaw.
Temporomandibular joint
The joint is paired (two mandibular joints act together as a complex), combined (there is a joint disk), ellipsoidal. It forms a mandible (like the movable bone of the skull), or rather its articular head, and processes of the temporal bone. The capsule is free, the joint has ligaments both inside and outside.
The joint is capable of performing the following movements:
- up and down (opening and closing the mouth);
- lateral movements;
- pushing the jaw forward.
Atlantooccipital joint
The skull, the anatomy of which allows it to carry mainly a protective function, can also make various movements thanks to the joint connecting the occipital bone and the first vertebra (atlas). On his side, the joint is formed by the condyles of the occipital bone; it is paired (since two condyles are connected to the articular fossae of the atlas) ellipsoid, has two membranes (anterior and posterior), as well as lateral ligaments.
Skull development in ontogenesis
Perinatal development includes three stages: membranous, cartilage and bone. The first phase passes from two weeks, the second - from two months of age the formation of the embryo. Moreover, in many parts of the skull, development passes the second stage.
The skull originates from the front of the chord, mesenchyme and primordia of gill arches. As the brain, nerves and blood vessels grow, it forms around them. Bones are divided into primary (originating from connective tissue) and secondary (originating from cartilage). At some point in the cartilage foci of ossification appear, which grow inland, forming plates of compact and spongy substance.
Features of the structure of the skull in newborns
The skeleton of a newborn is very different from what can be seen in an adult. The skull is highly developed relative to the rest of the body and has a large circle, and the brain is much larger than the facial. However, their main difference is the presence of fontanelles - cartilaginous joints, remnants of the membranous skull, which over time will be replaced by bone tissue. Their presence allows the head bones to move, thereby helping it to pass through the birth canal at birth, protecting it from various kinds of bruises. They are also a compensatory mechanism that protects the brain during head injuries at the beginning of life.
A large (front) fontanel is the most extensive, located where the frontal and parietal bones of the skull are attached, it closes when the child reaches two years of age.
The small (posterior) fontanel is located between the parietal and occipital bones, it closes faster - already in the second or third month of development of the child.
There are also small wedge-shaped and mastoid fontanelles located on the lateral surfaces of the skull and ossifying soon after birth.
Features of the structure of the skull at a young age
The human body grows and develops up to 20-25 years. Up to this point, there is such a type of connection of the bones of the skull as synchondrosis, formed by fibrous cartilage. It is present between the sphenoid and occipital bone, as well as between the four parts of the occipital bone. At the base of the skull are stony-occipital synchondrosis, as well as a layer of cartilage at the junction of the sphenoid bone and the ethmoid. Over time, bone tissue develops in their place, and syndesmosis appears.
Thus, it is clear what complex functions the human skull carries. The junction of the bones of the skull is designed so that the entire bone structure is extremely durable, acting as a defense for the brain, sensory organs, major vessels and nerve fibers. Therefore, it is very important to keep your head from bumps, bruises and various kinds of injuries.
When riding a horse, motorcycle, scooter, ATV and other vehicles, a safety helmet should be worn, it will be able to protect the skull from damage in the event of a fall or accident.