Arm bones how many

It is positioned in the left upper abdomen, and…. The knee is a complex joint that flexes, extends, and twists slightly from side to side.

The knee is the meeting point of the femur thigh bone in…. A retinaculum refers to any region on the body in which tendon groups from different muscles pass under one connective tissue band. Wrist retinacula….

The elbow is one of the largest joints in the body. In conjunction with the shoulder joint and wrist, the elbow gives the arm much of its versatility….

The distal phalanges are one of three types of finger bones. The human hand and wrist are comprised of three different bone groups.

The carpals are…. The vagus nerve is the longest of the 12 cranial nerves. Here, learn about its anatomy, functions, and the kinds of health problems that can occur. Health Conditions Discover Plan Connect. Medically reviewed by William Morrison, M. Each arm consists of four main parts: upper arm forearm wrist hand Read on to learn more about the bones, muscles, nerves, and vessels of the upper arm and forearm, as well as common arm problems you may encounter.

Anatomy and function of arm bones and joints. Upper arm The upper arm includes the shoulder as well as the area between the shoulder and elbow joint.

The bones of the upper arm include the: Scapula. The scapula is also called the shoulder blade. It attaches the arm to the torso. The clavicle is also called the collarbone. Like the scapula, it attaches the arm to the torso. It also helps to distribute force from the upper part of the arm to the rest of the skeleton.

The humerus is a long bone in the upper arm. Many muscles and ligaments in the arm are attached to the humerus. The upper arm also contains several joints, including the: Acromioclavicular joint. The scapula and the clavicle meet at this joint. Glenohumeral joint. This is the joint where the scapula and humerus meet. Sternoclavicular joint. The clavicle connects to the sternum breastbone at this joint. Forearm The forearm is the area between the elbow joint and the wrist.

Its two major bones are the radius and the ulna: Radius. The radius is located on the side of the forearm closest to the thumb. It twists around the ulna and can change its position depending on how the hand is moved.

There are many muscles attached to the radius that aid in movement of the elbow, wrist, and finger joints. The ulna runs parallel to the radius. Elbow joint The elbow joint is where the humerus bone of the upper arm connects with the radius and ulna bones in the forearm.

The elbow joint is actually composed of three separate joints: Ulnohumeral joint. This is where the humerus connects to the ulna. Radiocapitellar joint. At this joint, the radius connects to an area of the humerus called the capitellum. Proximal radioulnar joint. This joint connects the radius and ulna, allowing for rotation of the hands. Anatomy and function of upper arm muscles.

This movement brings two body parts closer together, such as the forearm and upper arm. This movement increases the space between two body parts. An example of this is straightening the elbow.

This refers to moving a body part away from the center of the body, such as lifting the arm out and away from the body. This refers to moving a body part toward the center of the body, such as bringing the arm back in so it rests along the torso. Anterior compartment The anterior compartment is located in front of the humerus, the main bone of the upper arms. The muscles of the anterior compartment include: Biceps brachii. Often referred to as the biceps , this muscle contains two heads that start at the front and back of the shoulder before joining together at the elbow.

The end near the elbow flexes the forearm, bringing it toward the upper arm. The carrying angle is larger in females. The radius runs parallel to the ulna, on the lateral thumb side of the forearm see Figure 8. The head of the radius is a disc-shaped structure that forms the proximal end. The small depression on the surface of the head articulates with the capitulum of the humerus as part of the elbow joint, whereas the smooth, outer margin of the head articulates with the radial notch of the ulna at the proximal radioulnar joint.

The neck of the radius is the narrowed region immediately below the expanded head. Inferior to this point on the medial side is the radial tuberosity , an oval-shaped, bony protuberance that serves as a muscle attachment point.

The shaft of the radius is slightly curved and has a small ridge along its medial side. This ridge forms the interosseous border of the radius , which, like the similar border of the ulna, is the line of attachment for the interosseous membrane that unites the two forearm bones. The distal end of the radius has a smooth surface for articulation with two carpal bones to form the radiocarpal joint or wrist joint Figure 8. On the medial side of the distal radius is the ulnar notch of the radius.

This shallow depression articulates with the head of the ulna, which together form the distal radioulnar joint. The lateral end of the radius has a pointed projection called the styloid process of the radius. This provides attachment for ligaments that support the lateral side of the wrist joint. Compared to the styloid process of the ulna, the styloid process of the radius projects more distally, thereby limiting the range of movement for lateral deviations of the hand at the wrist joint.

Watch this video to see how fractures of the distal radius bone can affect the wrist joint. Explain the problems that may occur if a fracture of the distal radius involves the joint surface of the radiocarpal joint of the wrist.

The wrist and base of the hand are formed by a series of eight small carpal bones see Figure 8. The carpal bones are arranged in two rows, forming a proximal row of four carpal bones and a distal row of four carpal bones. The small, rounded pisiform bone articulates with the anterior surface of the triquetrum bone. The pisiform thus projects anteriorly, where it forms the bony bump that can be felt at the medial base of your hand.

The hamate bone is characterized by a prominent bony extension on its anterior side called the hook of the hamate bone. Thus, it starts and finishes on the lateral side. The carpal bones form the base of the hand. This can be seen in the radiograph X-ray image of the hand that shows the relationships of the hand bones to the skin creases of the hand see Figure 8.

Within the carpal bones, the four proximal bones are united to each other by ligaments to form a unit. Only three of these bones, the scaphoid, lunate, and triquetrum, contribute to the radiocarpal joint. The scaphoid and lunate bones articulate directly with the distal end of the radius, whereas the triquetrum bone articulates with a fibrocartilaginous pad creating a space in the X-ray in Figure 8.

The distal end of the ulna thus does not directly articulate with any of the carpal bones. The four distal carpal bones are also held together as a group by ligaments.

The proximal and distal rows of carpal bones articulate with each other to form the midcarpal joint see Figure 8. Together, the radiocarpal and midcarpal joints are responsible for all movements of the hand at the wrist.

The distal carpal bones also articulate with the metacarpal bones of the hand. In the articulated hand, the carpal bones form a U-shaped grouping. A strong ligament called the flexor retinaculum spans the top of this U-shaped area to maintain this grouping of the carpal bones Figure 8. The flexor retinaculum is attached laterally to the trapezium and scaphoid bones, and medially to the hamate and pisiform bones. Together, the carpal bones and the flexor retinaculum form a passageway called the carpal tunnel , with the carpal bones forming the walls and floor, and the flexor retinaculum forming the roof of this space.

The tendons of nine muscles of the anterior forearm and an important nerve the median nerve pass through this narrow tunnel to enter the hand. Overuse of the muscle tendons or wrist injury can produce inflammation and swelling within this space. This produces compression of the nerve, resulting in carpal tunnel syndrome, which is characterized by pain or numbness, and muscle weakness in those areas of the hand supplied by this nerve.

The palm of the hand contains five elongated metacarpal bones. These bones lie between the carpal bones of the wrist and the bones of the fingers and thumb see Figure 8. The proximal end of each metacarpal bone articulates with one of the distal carpal bones.

Each of these articulations is a carpometacarpal joint see Figure 8. The expanded distal end of each metacarpal bone articulates at the metacarpophalangeal joint with the proximal phalanx bone of the thumb or one of the fingers. The distal end also forms the knuckles of the hand, at the base of the fingers. The metacarpal bones are numbered 1—5, beginning at the thumb.

The first metacarpal bone, at the base of the thumb, is separated from the other metacarpal bones. Our forearm contains two long, parallel bones: the ulna and the radius. The ulna is the longer and larger of the two bones, residing on the medial pinky finger side of the forearm.

It is widest at its proximal end and narrows considerably at its distal end. At its proximal end, the ulna forms the hinge of the elbow joint with the humerus.

The end of the ulna, known as the olecranon, extends past the humerus and forms the bony tip of the elbow. At its distal end, the ulna forms the wrist joint with the radius and the carpals. Compared to the ulna, the radius is slightly shorter, thinner, and located on the medial side of the forearm. The radius is narrowest at the elbow and widens as it extends towards the wrist. At its proximal end, the rounded head of the radius forms the pivoting part of the elbow joint that permits rotation of the lower arm and hand.

Frequently, the hamate can break when people use the hand for punching. Also, the hook of the hamate can fracture during a fall or if struck directly, such as when a baseball player swings a bat or golfer swings a golf club.

The pisiform is a small sesamoid bone a bone within a tendon that sits in the wrist and is in the flexor carpi ulnaris tendon. Like other sesamoid bones, it changes the direction of pull of the tendon to which it is attached. Occasionally, the pisiform can break or can have arthritis in the joint it makes with the triquetrum. The metacarpals of the fingers make up the bone structure of most of the hand.

They are all similar in shape and have joints in the wrist on one end, and the finger at the other end. The index and middle finger metacarpals have very little motion, while the metacarpals of the ring and little finger move much more. The proximal phalanx of the fingers is the proximal, or first bone, in the fingers when counting from the hand to the tip of the finger.

There are three phalanges in each finger. The proximal phalanx is the largest of the three bones in each finger. The proximal phalanx has joints with the metacarpal and with the middle phalanx. The middle phalanx of the finger is the middle or second of the three bones in each finger when counting from the hand to the tip of the finger.

The middle phalanx has joints with the proximal phalanx and with the distal phalanx of the finger. The distal phalanx of the finger is the distal or third of the three bones in each finger when counting from the hand to the tip of the finger. The distal phalanx has a joint just with the middle phalanx. On the tip of the phalanx is a bulbous tuft of bone that helps give the finger its rounded appearance.

The distal phalanx is also important for supporting the fingernail. The thumb metacarpal is similar in shape to the metacarpals of the fingers, but it is thicker. The thumb metacarpal has significantly more motion than the other metacarpals. It makes a joint with the trapezium that allows much of the thumb motion.

This joint allows the thumb to move in a way that allows pinching. This is largely due to the unusual shape of the base of the metacarpal and the trapezium.

The head of the metacarpal has a large joint surface next to the thumb proximal phalanx. The thumb sesamoids are two small round bones at about the level of the thumb metacarpophalangeal joint These bones, as with all sesamoid bones, lie within tendons.

The flexor pollicis brevis tendon and the adductor pollicis attach to the thumb sesamoids. Sesamoid bones help change the line of pull for their tendons which can help increase the force of tendon pull across the joint. The thumb proximal phalanx is a short and stout bone between the metacarpal and distal phalanx. There is no middle phalanx in the thumb. The thumb distal phalanx is a short bone with a rounded tuft at the end that makes a joint with the proximal phalanx.

The bulbous tuft at the end of the bone gives the thumb its rounded end. This bone supports the thumb nail. The coronoid process is a small projection of bone off of the ulna bone that sits in the front of the elbow and on the inside of the elbow On and very near the coronoid process are attachment sites for muscles and ligaments of the elbow joint. The coronoid process is important for adding stability to the elbow.

The radial head is a somewhat rounded cup that joins with the humerus and ulna to make up a portion of the elbow joint.

The radial head has cartilage surfaces for both the humerus and the ulna to allow bending and extending of the elbow and twisting of the forearm. It also can add a significant amount of stability to the elbow joint.

The radial tuberosity is a small, smooth projection on the surface of the radius bone near the elbow. It is the attachment site for the biceps tendon in the forearm. Because of the position of the tuberosity on the radius, the biceps tendon twists the hand palm up the forearm.