The skeleton of the head of vertebrates is called the "skull". Anatomy allows him to carry out a protective function due to the bones firmly and immovably fastened to each other (the only exceptions are the mandible and the 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 through which nerve fibers, arteries and veins pass.
Development in phylogenesis
Over time, in the course of natural selection, the nervous system developed in animals and nerve ganglia appeared, and later the brain. The skeleton in these places was supposed to protect the nervous tissue and sensory organs to the maximum, therefore, for the first time, a cartilaginous skull appears in cyclostomes. Its bones, according to their origin, are divided into replacing cartilage, integumentary and visceral. For the first time, a bony skull appears in fish. The connection of the bones of the skull goes through cartilage, which replaces the bone tissue. The bones located on the outside have arisen from ossification in the layers of the dermis.
The visceral parts of the vertebrate skull are notnothing more than modified gill arches made of cartilaginous tissue, therefore, in the process of embryogenesis, the rudiments of gill openings are laid in the early stages of development. Later, the muscles and bones of the visceral skeleton will form in this place.
Types of bone connections
Multiple flat, mixed and pneumo 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:
- Syndesmoses (from fibrous tissue) are represented by ligaments, sutures, interosseous membranes, fontanelles and impactions (connection of the tooth root to the jawbone).
- Synchondrosis (from cartilage) can be permanent throughout life or replaced by bone tissue over time.
- Syndesmoses - are formed when the cartilage tissue of 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.
Diarrhosis are ordinary mobile joints covered with cartilage. They are a connective tissue capsule that forms a cavity with synovial fluid inside. Diarthroses are distinguished by the shape of the articular surfaces and the number of their components.
Cerebral skull
The skull of an adult is formed by 23 main bones, 3 bones in the auditory canal, and 32 teeth. The skull is divided into neurocranium (brain) and facial(visceral).
Cranium bones:
1. Unpaired:
- occipital (four parts);
- wedge-shaped (body, large and small wings, wing processes);
- frontal (also has four parts)
- lattice (has a labyrinth) - it is sometimes referred to as 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, which eventually merge into one. Thus, three components are distinguished: scaly, drum and stony parts, separated by intermediate sutures.
The squamous part includes the zygomatic process involved in the formation of the mandibular joint. From here, the auditory passage begins, which passes into the tympanic cavity (localization of the middle ear), where the auditory ossicles are located: the hammer, anvil and stirrup, as well as a small lenticular cartilage between them. These elements are involved in capturing sound waves, transmitting their vibrations to the inner ear.
Stony bone is very strong and acts as a skeleton for hearing and balance. Behind the tympanic cavity is a complex skeletal 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 that conduct nerve fibers and blood vessels.
Thus, thanks to its complex structure, the temporal bone of the skull performs immediatelymultiple functions.
There is a cavity inside the frontal bone.
Visceral skull
The bones of the visceral part of the skull are:
1. Unpaired: vomer, mandibular (the result of the fusion of paired dentary bones) and hyoid (fixes the tongue, muscles of the pharynx and larynx) bones.
2. Paired:
- maxillary (fused to the medulla);
- incisive (front jaw bones);
- palatine bones (forming the bottom of the skull);
- pterygoids;
- zygomatic bones (create the zygomatic arch and part of the 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 eye socket.
There are sinuses in the maxillary bone, which, together with those of the frontal and sphenoid bones, as well as the labyrinth of the ethmoid bone, make up the paranasal sinuses lined with mucous membrane.
In the sutures and fontanelles, unstable bones of the skull are observed.
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 in case of injury. The periosteum is attached to the bones in the area of the sutures, 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 bones of the skull
The main type of neurocranium bone jointsis syndesmosis. Most of this kind of fusion is represented by jagged sutures; only between the temporal and parietal bones is a scaly suture. The facial skull has flat scars. Anatomically, the suture is often named after the bones that connect with it to form the skull. The connection of the bones of the skull includes one sagittal suture (with the help of which the paired parietal bone of the skull is connected), coronal (connects the parietal and frontal bones) and lambdoid (connects the occipital and parietal bones).
Intermittent sutures may also be seen, sometimes resulting from insufficient ossification of the skull.
Attachment of teeth
Types of connection of the bones of the skull include hammering - this is a type of syndesmosis, represented by attaching a tooth to the jaws - the mandible and maxilla.
Teeth consist of the following layers: on top they are covered with enamel, under it there is a solid substance dentin, a pulp cavity containing pulp (passing vessels and nerve) is formed inside it. At the bottom of the root there is also cement - a fibrous tissue reinforced with lime. The tooth is attached to the alveolar process of the jaw with cement and periodontal ligaments.
These jaw processes are formed by two cortical plates and a spongy substance between them. The space between the plates is divided by interdental partitions into separate alveoli. The roots of the tooth are surrounded by the periodontal ligament - this is a connective tissue formed from fibers of different types and different directions, it is she who attaches the root of the tooth to the jaw.
Temporomandibular joint
The joint is paired (two mandibular joints act together, being a complex), combined (there is an articular disc), ellipsoid. It is formed by the mandible (as a 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 the following movements:
- up-down (mouth opening and closing);
- lateral movements;
- jaw thrust forward.
Atlantococcipital joint
The skull, whose anatomy allows it to carry out mainly a protective function, can also perform various movements thanks to the joint connecting the occipital bone and the first vertebra (atlas). On its side, the joint is formed by the condyles of the occipital bone; it is paired (since the two condyles connect to the articular fossae of the atlas), ellipsoid, has two membranes (anterior and posterior), as well as lateral ligaments.
Development of the skull in ontogeny
Perinatal development includes three stages: membranous, cartilaginous and bone. The first phase takes place from two weeks, the second - from the age of two months of embryo formation. At the same time, development bypasses the second stage in many parts of the skull.
The skull originates from the anterior part of the notochord, mesenchyme and primordia of the gill arches. As the brain, nerves, and vessels grow, it forms around them. Bones are divided into primary (originating from connective tissue) and secondary (originating fromcartilage). At a certain point, foci of ossification appear in the cartilage, which grow deeper, 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 strongly developed relative to the rest of the body and has a large circumference, and the brain region is much larger than the facial region. However, their main difference lies in the presence of fontanelles - cartilaginous joints, remnants of a membranous skull, which will eventually be replaced by bone tissue. Their presence allows the bones of the head 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 from head injuries early in life.
The large (anterior) 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.
The small (posterior) fontanel is located between the parietal and occipital bones, it closes faster - already in the second or third month of the child's development.
There are also small wedge-shaped and mastoid fontanelles located on the lateral surfaces of the skull and ossifying shortly 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 tissue. It is present between the sphenoid and occipital bones, as well as between the four parts of the occipital bone. At the base of the skull there is a stony-occipital synchondrosis, as well as a layer of cartilaginous tissue at the junction of the sphenoid bone and the ethmoid bone. Over time, bone tissue develops in their place, and syndesmosis appears.
Thus, you can see what complex functions the human skull has. The connection of the bones of the skull is arranged in such a way that allows the entire bone structure to be extremely strong, acting as a protection for the brain, sensory organs, the most important vessels and nerve fibers. Therefore, it is very important to protect your head from blows, bruises and various kinds of injuries.
While riding a horse, motorcycle, scooter, ATV and other vehicles, you should wear a safety helmet, it can protect the skull from damage in case of a fall or accident.
