The skeleton serves as a point of attachment for muscles, is a support for soft tissues, protection and a receptacle for internal organs. It develops from the mesenchyme. The human skeleton consists of about two hundred individual bones. The axial skeleton and the accessory skeleton are made up of different bones, but almost all of them form a single whole with the help of ligaments, joints and other connections.
Skeletal changes throughout life
The skeleton is constantly changing throughout life. The cartilaginous skeleton of the fetus, for example, during fetal development is gradually replaced by bone. This process continues after birth, for several years. A newborn baby has almost 270 bones in its skeleton. This is much more than in an adult, in which it consists of 200-208. This difference arose because the skeleton of a newborn contains many small bones. Only by a certain age they grow together into large ones. This applies, for example, to the bones of the spine, pelvis and skull. The sacral vertebrae fuse into the sacrum (singlebone) only at the age of 18-25.
Which bones are not directly related to the skeleton?
The skeleton does not directly relate to the six special bones that are in the middle ear, three on each side. They connect only with each other and take part in the work of the organ of hearing. These bones transmit vibrations to the inner ear from the eardrum.
Features of some bones
The hyoid bone in the human body is the only one that is not directly connected to others. It is located on the neck, but it is traditionally attributed to the bones of the skull (facial region). It is suspended from it by muscles and connected to the larynx. The femur is the longest in the skeleton, and the stirrup located in the middle ear is the smallest.
Skeleton organization
In humans, the skeleton is arranged according to the principle common to vertebrates. Its bones are divided into the following two groups: axial and accessory skeleton. The first includes the bones that form the skeleton of the body. They lie in the middle - these are all the bones of the neck and head, the sternum, ribs, spine. The axial skeleton of animals is built on the same principle. Additional - these are the shoulder blades, collarbones, bones of the upper and lower extremities and the pelvis.
Subgroups of bones of the axial skeleton
All bones of the skeleton are divided into subgroups. The axial skeleton consists of the following.
1. The skull is the bone base of the head, as well as the seat of the brain, the organs of smell, hearing and vision. It has two sections: facial and cerebral.
2. Examining the human skeleton(axial skeleton), the chest should also be noted, which in shape is a compressed truncated cone. This is a container for various internal organs. It consists of 12 pairs of ribs, 12 thoracic vertebrae, as well as the sternum.
3. The spine (otherwise - the spinal column) is the support of the entire skeleton, the main axis of the body. The spinal cord runs inside the spinal canal.
Subgroups of bones of the accessory skeleton
The following subgroups are distinguished in it.
1. The belt of the upper limbs, which provides attachment to the axial skeleton of the upper limbs. It consists of paired clavicles and shoulder blades.
2. The upper limbs, which are most adapted for the implementation of labor activity. They consist of three sections: hand, forearm and upper arm.
3. Belt of the lower extremities, which provides attachment to the axial skeleton of the lower extremities. In addition, it is a support and receptacle for the organs of the reproductive, urinary and digestive systems.
4. The lower limbs, which provide movement of the human body in space.
Bones and divisions of the axial skeleton
As you can see, the bones of the skeleton belong to two groups. We briefly reviewed the axial and accessory skeleton. We will not dwell on the additional one in detail, since this is not part of our task. Let us now consider the various sections and bones that together make up the axial skeleton.
Spinal column
This is the mechanical support of the body. It consists of 32 to 34vertebrae connected to each other. Five departments stand out in the spine: coccygeal, sacral, lumbar, thoracic, cervical. Connections in the lumbar and cervical regions are mobile, and in the sacral and thoracic - inactive. The spinal column has four physiological bends. The lumbar and cervical bend is directed forward, forming a lordosis, and the sacral and thoracic curve is directed backward (kyphosis). In different departments, the sizes of the vertebrae are not the same. They depend on the magnitude of the load falling on one or another of them and on the development of the muscles. The sacral and lumbar vertebrae reach their maximum size. Intervertebral discs act as a shock absorber - they distribute pressure between different vertebrae, and also provide the necessary strength and mobility.
The axial skeleton develops throughout life. In a newborn, the vertebral column is almost straight, after a while, bends of the spine appear. There are two bends back and two forward (kyphosis and lordosis).
Their main purpose is to weaken the concussion of the torso and head when running, walking, jumping. Scoliosis (curvature of the spine in any direction) is observed in many people. It is often the result of painful changes in the spine.
Vertebrae
The vertebrae belong to the axial skeleton. They have a round body, as well as an arch closing the vertebral foramen. They have processes that connect the articulating vertebrae. The spinal cord passes through all the openings. The tunnel they formed is calledspinal canal. This is a reliable bone protection for the spinal cord located in it. The composition of the vertebra includes: the dura mater (protective membrane); a spiny bone process that connects it to the muscles; spinal cord and blood vessels. On the section of the intervertebral disc, a biconvex nucleus pulposus and fibrous rings can be seen. The spinous process is turned back, and the body of the vertebra is turned forward. In the middle is the vertebral foramen. Let's say a few words about arcs. There are depressions on the arches of the vertebrae, which together form the intervertebral foramina through which the spinal nerves pass.
Let's take a closer look at some vertebrae, considering the structure of the axial skeleton. Atlas is the first cervical vertebra. He is missing a body. This vertebra articulates with the 2nd cervical vertebra and with the occipital bone of the skull. Epistropheus (2nd cervical vertebra) has an odontoid process that connects to the atlas (its anterior arch). The spinous process at the 7th cervical vertebra is not bifurcated. It is easily palpable. This process protrudes above the neighboring vertebrae, their spinous processes. It is more noticeable in men. There are articular fossae on the thoracic vertebrae. They are needed to attach the ribs. The spinous processes of the thoracic vertebrae are directed downward and backward, they are the longest. The most massive are the lumbar vertebrae. Their spinous processes deviate backward. The sacrum consists of 5 fused vertebrae. There is a wide upper part (base), two side parts and a narrow lower part (top). Nerves pass through the holes in the sacrum, and insideis the sacral canal. It is a continuation of the spinal canal. The pelvis is attached to the sacrum. The coccygeal bone of the axial skeleton is divided into 4-5 underdeveloped vertebrae fused together. These are the remains of the tail that the ancestors of man had. The vertebrae are connected to each other with the help of joints, cartilage and ligaments. The spine can unbend and bend, twist, lean to the side. Its most mobile sections are cervical and lumbar.
Chest
Another department that has an axial skeleton is the chest. It consists of the sternum (highlighted in red in the photo), ribs and thoracic vertebrae. The length of the sternum in adults is from 16 to 23 cm. This is an unpaired flat bone of the axial skeleton. The following three parts are distinguished in it: the xiphoid process, the middle (body) and the upper (handle). Ribs are made up of cartilage and bone. The first of them is located almost horizontally. Seven pairs of ribs with their cartilages at the anterior ends are connected to the sternum. The other five pairs do not connect with it. The 8th, 9th and 10th pairs are attached to the cartilage of the overlying rib. The 11th and 12th freely end with the anterior ends in the muscles. In humans, the chest contains the lungs, heart, esophagus, trachea, nerves and large vessels. It participates in respiration - its volume during exhalation and inhalation decreases and increases due to rhythmic movements. In a newborn, the chest has a pyramidal shape. However, it changes along with the growth of the chest. In women, it is smaller than in men, and also its upper part is relatively wider. A change in the chest is possible after past illnesses. For example, chicken breast develops with severe rickets (in which case the sternum protrudes sharply forward).
Skull bones
Describing the axial skeleton, you need to talk about the skull. Its bones consist of the following parts: nasal bone, frontal bone, parietal, zygomatic, occipital, mandibular and maxillary bones and teeth. The skull (skeleton of the head) has a cavity where the brain is located. There are, in addition, cavities of the mouth, nose, receptacles for the organs of hearing and vision. Considering the axial skeleton of animals and humans, the facial and cerebral sections of the skull are usually distinguished. All of his bones, except for the lower jaw, are interconnected by sutures. Two paired bones make up the medulla. We are talking about the temporal and parietal. 4 unpaired ones are also distinguished in it - occipital, ethmoid, wedge-shaped, frontal. The facial region is represented by six paired bones (upper jaw, lacrimal, nasal, palatine, zygomatic and inferior nasal concha), as well as two unpaired ones. The latter include the vomer and lower jaw. The hyoid bone is also the bone of the face. Many bones of the skeleton of the head have channels and openings for the passage of blood vessels and nerves. Some of them have cells or cavities filled with air (they are called sinuses). The brain part of the skull in humans prevails over the facial.
Sutures of cranial bones
The sutures that connect the bones of the skull are different. They are flat (smooth edges adjoin each other).to each other the bones of the facial section), scaly (this is how the parietal and temporal bones are connected), serrated (they are characteristic of the main part of the bones of the skull and are the most durable). Most of the sutures in adults and especially in the elderly ossify. With the help of the temporomandibular combined joint, the lower jaw is connected to the temporal bones. There is cartilage in this joint, the joint capsule is strengthened with ligaments.
More about the structure of the skull
The roof is called the upper part of the cerebral skeleton of the head. The bottom one is the base. It has a large foramen magnum. The facial bone (with the exception of the lower shell), as well as the roof of the skull, go through 2 stages in their development: first membranous, then bone. For other bones of the skull, three stages are characteristic: membranous, cartilaginous and bone. The remnants of the membranous skull (they are called fontanelles) are found in the roof of the skull of a newborn. There are only six of them: two mastoid, two wedge-shaped, posterior and anterior. The largest of them are the rear and front. The anterior is located at the junction of the parietal and frontal bones (at the crown). By the age of one and a half, he ossifies. The occipital (posterior) fontanel overgrows already 2 months after the birth of the child. In full-term children, lateral fontanelles, as a rule, are absent, and if they are, they also quickly overgrow (on the 2nd or 3rd month of life). In a newborn, the facial region is less developed than in the brain than in an adult: teeth are absent, the airways of the cranial bones are not developed. Seams ossify in old age, and the spongy layer in the bones also decreases.substances - the skull becomes fragile and light. Its growth is completed by the age of 25-30. The skull of men is relatively larger than that of women, which is related to the overall size of the body. The tubercles and protrusions on the cranial bones are less pronounced in a woman than in a man.
So, we have examined the main sections of the axial skeleton. Recall that we talked about the additional only briefly, since it is not the topic of this article. Now you know that the axial skeleton is made up of various bones that have different structures and functions.
