Bones also protect the body's organs. The skull protects the brain and forms the shape of the face. The spinal cord, a pathway for messages between the brain and the body, is protected by the backbone, or spinal column. The ribs form a cage that shelters the heart and lungs, and the pelvis helps protect the bladder, part of the intestines, and in women, the reproductive organs.
Bones are made up of a framework of a protein called collagen, with a mineral called calcium phosphate that makes the framework hard and strong. Bones store calcium and release some into the bloodstream when it's needed by other parts of the body. The amounts of some vitamins and minerals that you eat, especially vitamin D and calcium, directly affect how much calcium is stored in the bones.
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In this soft bone is where most of the body's blood cells are made. The bone marrow contains stem cells, which produce the body's red blood cells and platelets, and some types of white blood cells. Red blood cells carry oxygen to the body's tissues, and platelets help with blood clotting when someone has a cut or wound. White blood cells help the body fight infection.
Bones are fastened to other bones by long, fibrous straps called ligaments (LIG-uh-mentz). Cartilage (KAR-tul-ij), a flexible, rubbery substance in our joints, supports bones and protects them where they rub against each other.
The bones of kids and young teens are smaller than those of adults and contain "growing zones" called growth plates. These plates consist of multiplying cartilage cells that grow in length, and then change into hard, mineralized bone. These growth plates are easy to spot on an X-ray. Because girls mature at an earlier age than boys, their growth plates change into hard bone at an earlier age.
Even when we sit perfectly still, muscles throughout the body are constantly moving. Muscles help the heart beat, the chest rise and fall during breathing, and blood vessels regulate the pressure and flow of blood. When we smile and talk, muscles help us communicate, and when we exercise, they help us stay physically fit and healthy.
The movements that muscles make are coordinated and controlled by the brain and nervous system. The involuntary muscles are controlled by structures deep within the brain and the upper part of the spinal cord called the brain stem. The voluntary muscles are regulated by the parts of the brain known as the cerebral motor cortex and the cerebellum (ser-uh-BEL-um).
When you decide to move, the motor cortex sends an electrical signal through the spinal cord and peripheral nerves to the muscles, making them contract. The motor cortex on the right side of the brain controls the muscles on the left side of the body and vice versa.
The cerebellum coordinates the muscle movements ordered by the motor cortex. Sensors in the muscles and joints send messages back through peripheral nerves to tell the cerebellum and other parts of the brain where and how the arm or leg is moving and what position it's in. This feedback results in smooth, coordinated motion. If you want to lift your arm, your brain sends a message to the muscles in your arm and you move it. When you run, the messages to the brain are more involved, because many muscles have to work in rhythm.
Muscles move body parts by contracting and then relaxing. Muscles can pull bones, but they can't push them back to the original position. So they work in pairs of flexors and extensors. The flexor contracts to bend a limb at a joint. Then, when the movement is completed, the flexor relaxes and the extensor contracts to extend or straighten the limb at the same joint. For example, the biceps muscle, in the front of the upper arm, is a flexor, and the triceps, at the back of the upper arm, is an extensor. When you bend at your elbow, the biceps contracts. Then the biceps relaxes and the triceps contracts to straighten the elbow.
Subchondral tissue. This is the smooth tissue at the ends of bones, which is covered with another type of tissue called cartilage. Cartilage is a specialized, rubbery connective tissue.
The tough, thin outer membrane covering the bones is called the periosteum. Under the hard outer shell of the periosteum are tunnels and canals. Through these, blood and lymphatic vessels carry nourishment for the bone. Muscles, ligaments, and tendons may attach to the periosteum.
Bones give shape and support for the body. They give protection to some organs. Bone also serves as a storage site for minerals. And soft bone marrow in the center of certain bones is where blood cells are formed and stored.
Bone markings are crucial for identifying bones and understanding anatomy. These distinctive features benefit various professionals, including clinicians and forensic scientists. Bone markings are easily overlooked but serve essential functions like facilitating joint movement, locking bones in place, and supporting and protecting soft tissues.
Bone markings arise through a combination of genetic programming, mechanical stimuli, and adaptation to functional demands, resulting in a diverse array of features that serve various anatomical and physiological roles.[1][2] Bone markings hold significant importance in surgery as they serve as crucial landmarks for surgical procedures.[3] Surgeons rely on bone markings to guide incisions, identify anatomical structures, and navigate around critical areas such as nerves and blood vessels. On the other hand, maladaptive bony prominences can impair normal anatomical function and contribute to musculoskeletal dysfunction and pain. Understanding bone markings enables clinicians to evaluate and manage various musculoskeletal conditions.
Common bone markings are distinctive features on bone surfaces that serve various anatomical, functional, and developmental roles. These markings provide essential reference points for understanding skeletal structure, identifying specific bones, and comprehending their interactions within the body (see Image. Labeled Bone Markings). The following are common bone markings:
The upper limb is involved in a wide range of movements essential for daily activities and physical function. Thus, the upper limb's bone markings are particularly relevant for clinical and anatomical study.
The scapula serves as the upper limb's mobile platform. One can think of this bone as a massive construction crane with jacks that anchor the cab to the ground, like how muscles and connective tissues attach the scapula to the body. The crane also has a long, mobile arm, resembling the upper limb. The scapula has medial, lateral, and superior borders. The inferior pole is the junction of the medial and lateral borders.
The acromion (acromial process) lies at the scapular spine's lateral end. The acromial process is one of the deltoid muscle's proximal insertion sites. The deltoid is a triangular muscle named after the capital Greek letter delta. The scapula's medial border is an insertion site for the rhomboid minor and major muscles. The teres minor originates from the scapula's lateral border, while the teres major arises from the inferior scapular angle.
The humeral midshaft's lateral surface exhibits the deltoid tuberosity, the deltoid insertion site. This muscle abducts the arm beyond the first 15 to 20. The deltoid's anterior fibers rotate the arm medially, while the posterior fibers laterally rotate the arm.[10]
The humeral midshaft's posterior aspect demonstrates the radial spiral groove, which ordinarily lies between the triceps brachii's lateral and medial heads. This groove transmits the radial nerve and profunda brachii artery.
The arm bone's inferior aspect contains the lateral and medial epicondyles. The lateral supracondylar ridge, which contains the proximal insertion point of the brachioradialis and extensor carpi radialis longus, flows into the lateral epicondyle. The lateral epicondyle is a bony prominence where the extensor carpi radialis brevis, extensor digitorum, extensor digiti minimi, and extensor carpi ulnaris originate.
The olecranon fossa lies on the arm bone's posterior aspect between the lateral and medial epicondyles. This region receives the ulna's olecranon process at the elbow joint. The distal humeral articulating surfaces include the laterally located capitulum (Latin for "little head") and the trochlea (Greek for "pulley").[11]
The head comprises the proximal radial end and articulates with the capitulum, allowing rotation for supination (palm up) and pronation (palm down). This mobility, while beneficial, makes the radius susceptible to dislocation, as in "nursemaid's elbow." The radial tuberosity serves as an insertion site for the biceps brachii. The radial shaft leads to the large styloid process at the distal end, where the brachioradialis muscle inserts. The radius articulates with the scaphoid and lunate at the radiocarpal joint.[12]
The proximal ulnar end contains the coronoid process, which articulates with the humeral trochlea. This articulation is strong, only permitting flexion and extension. The ulnar tuberosity is where the brachialis muscle distally inserts. This muscle is a pure forearm flexor.[13] The distally located ulnar head articulates with the radius.
The 8 carpal bones are divided into proximal and distal rows. The proximal wrist bones articulate with the radius. The proximal row includes the scaphoid, which resembles the prow of a ship and articulates with the trapezium distally. The trapezium then connects to the 1st metacarpal bone that supports the thumb. Moving from lateral to medial, the proximal row continues with the lunate (resembling the moon), triquetrum (which has 3 corners), and the rounded pisiform. The pisiform can be palpated on the hand's anterior aspect. This bone moves with hand motion, confirming its location within the wrist rather than the forearm.
The distal carpal row starts with the laterally located trapezium (which resembles a 4-sided figure with 2 parallel sides), articulating with the thumb and index finger metacarpals. Medial to the trapezium is the trapezoid, shaped similarly to the trapezium, and capitate, the largest wrist bone. The hamate is medially located and features a prominent hook. The Guyon canal is the space between the pisiform and the hamate's hook that transmits the ulnar nerve. A hamate hook fracture can damage this nerve. 152ee80cbc
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