We review the bones that make up the human arm, and explain their characteristics.
The reason why this limb can perform this type of movement is the fact that, thousands of years ago, our ancestors began to move bipedally, freeing their hands and allowing them to be used to manipulate objects.
Let’s see in depth what is meant by arm from the field of anatomyas opposed to its most popular meaning, in addition to going into detail about all the bones that make up this joint.
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What exactly is the arm?
Strictly speaking, the arm is the upper part of the upper limbs, that is, the segment that runs from the elbow to the scapula. However, in a more general sense, it is used as a synonym for the entire limb.
Thus, starting from the most popular definition in general culture, the arm is not only composed of the humerus bone, but also of two others, the radius and the ulna, which are located in the part of the forearm, in addition to the bones of the hand and wrist.
In this article we are going to mention all the bones that are part of the human upper extremity, but we are going to present them according to how it is segmented into anatomy, that is, dividing it into arm, forearm, wrist and hand.
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Arm bones
Next we are going to know the only bone of the arm , its anatomy and other interesting information. We are talking about the humerus.
1. Humerus
As we have indicated, it is the bone that constitutes the section that, anatomically and strictly speaking, forms the arm.
This bone, whose scientific name is “humerus”, is the main bone of the limb and is the fourth longest bone in the human body . It connects to the back through the scapula or scapula, which forms the shoulder, and to the rest of the arm through the ulna and radius bones, forming the elbow.
The pectoral girdle, which is formed by the clavicle and the scapula, articulates with the arm through the shoulder. In this section of the humerus bone is the humeral head, a spherical structure that is what forms the shoulder itself.
When this limb moves, the muscles involved are the trapezius, deltoid, rhomboid, and rotator cuff muscles.
forearm bones
The forearm is made up of two bones: the ulna and the radius . We are going to know its anatomy and its characteristics.
2. Ulna
It is also called “ulna” and is, along with the radius, one of the two bones of the forearm, being the longest and largest.
The ulna is practically straight, with a slight concave curvature, and has three faces and three borders . At its proximal end is the olecranon, a section with a shape that is similar to that of a wrench, which allows it to articulate with the other bone of the forearm, forming and protecting the elbow.
3. Radio
Like the ulna, the radius or “radius” has three faces and three edges , and is positioned almost parallel to the other bone of the forearm.
It differs from the ulna in that it is more curved and concave, as well as being slightly smaller and thinner.
Thanks to not being straight, it enables mobility of the limb, allowing it to extend and flex.
In the part that forms the elbow, unlike the ulna, the radius ends with a rounded shape and fits into the olecranon.
At its most distal end, the radius widens and forms the joint of the forearm together with the wrist.
Bones of the wrist and hand
The skeleton of the hand is divided into the carpus, metacarpus, palm, and phalanges .
Thanks to its bony and muscular characteristics, the hand allows delicate and complex movements, such as writing, crafts or even a surgical operation.
4. Carpus or carpal bones
It is a structure composed of eight bones, which form the wrist.
The eight bones are arranged in two rows:
- Proximal row : scaphoid, lunate, pyramidal and pisiform.
- Distal row : trapezium, trapezoid, capitate, and hamate.
5. Metacarpus or metacarpal bones
These are five bones that make up the bony part of the palm of the hand . They are located between the fingers and the wrist.
These bones are named after ordinal numbers: first, second, third, fourth, and fifth metacarpal bones.
6. Phalanges or finger bones
The phalanges are small bones that make up the fingers .
The little, ring, middle, and index fingers each have three phalanges: proximal phalanx, middle phalanx, and distal phalanx. The thumbs have only two, since they lack the middle phalanges. In total, each human hand has 11 phalanges.
Thanks to the fact that the thumbs are fingers with fewer bones and are located away from the rest of the fingers, they have greater freedom, in addition to acquiring the important function of acting as hooks when manipulating objects.
These phalanges are very similar to those that form the toes, which are also called phalanges.
Principal functions
The bones of the arm allow, together with the muscles and nerves found in the extremity, to carry out the following movements.
1. Extension movement
It is the movement of this joint that gives rise to the greatest angle between two bones of the arm.
2. Bending movement
Reduces the angle they meet at the joint.
3. Supination movement
It consists of placing the palm of the hand facing forward, and it is usually the position in which the human body is found when it is anatomically represented.
The brachial and brachial muscles supinate the forearm by pulling on the radius. These muscles cause the bone to radius in the opposite direction to that of the pronator muscles.
4. Pronation
It is a rotational movement of the hand by rotating the joint that joins it to the radius, without involving the shoulder joint.
This movement is performed by the action of the square and round pronator muscles.
Other functions of the bones of the arm and forearm
In addition to giving structure to the arms, forearms, and hands, the bones of the upper extremities are involved in maintaining body homeostasis. This is because, along with the rest of the bones in the body, they serve as a storehouse for minerals such as calcium.
In addition to this, they participate in the process of hematopoiesis, that is, they contribute to the formation and maturation of blood cells such as platelets and leukocytes.
They also fulfill very important locomotor functions, something that can be seen when running, since it allows the arms to be positioned in such a way that less air resistance can be presented. In addition to this locomotor function, they serve to extend the arms before the loss of balance, and thus distribute the weight in a more homogeneous way.
References
- Clarke, B. (2008). Normal Bone Anatomy and Physiology. Clinical Journal of the American Society of Nephrology, 3(3): 131–S139.
- Palastanga, N. (2000). Human anatomy and movement: structure and functioning. Barcelona: Paidotribo.
- Aramburo, F. (1984) Guide to human anatomy. Barcelona, Spain. Fontalba Publishing House.
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