Humerus
Encyclopedia
The humerus is a long bone
in the arm
or forelimb
that runs from the shoulder
to the elbow
.
Anatomically, it connects the scapula
and the lower arm (consisting of the radius
and ulna
), and consists of three sections. The upper extremity consists of a rounded head, a narrow neck, and two short processes (tubercles, sometimes called tuberosities.) Its body
is cylindrical in its upper portion, and more prism
atic below. The lower extremity
consists of 2 epicondyle
s, 2 processes (trochlea & capitulum
), and 3 fossae (radial fossa
, coronoid fossa, and olecranon fossa
). As well as its true anatomical neck, the constriction below the greater and lesser tubercles of the humerus is referred to as its surgical neck
due to its tendency to commonly get fractured, thus often becoming the focus of surgeons.
originates on the lateral third of the clavicle
, acromion and the crest of the spine
of the scapula. It is inserted on the deltoid tuberosity
of the humerus and has several actions including abduction, extension, and circumduction of the shoulder. The supraspinatus also originates on the spine of the scapula. It inserts on the greater tubercle of the humerus, and assists in abduction of the shoulder.
The pectoralis major, teres major, and latissimus dorsi insert at the intertubercular groove of the humerus. They work to adduct and medially, or internally, rotate the humerus.
The infraspinatus and teres minor insert on the greater tubercle, and work to laterally, or externally, rotate the humerus. In contrast, the subscapularis muscle inserts onto the lesser tubercle and works to medially, or internally, rotate the humerus.
The biceps brachii, brachialis, coracobrachialis, and brachioradialis
(which attaches distally) act to flex the elbow. (The biceps, however, does not attach to the humerus.) The triceps brachii and anconeus extend the elbow, and attach to the posterior side of the humerus.
The four muscles of supraspinatus, infraspinatus, teres minor and subscapularis form a musculo-ligamentous girdle called the rotator cuff
. This cuff stabilizes the very mobile but inherently unstable glenohumeral joint
. The other muscles are used as counterbalances for the actions of lifting/pulling and pressing/pushing.
. More distally, at the elbow, the capitulum of the humerus articulates with the head of the radius
, and the trochlea of the humerus articulates with the olecranon process of the ulna
.
is located at the proximal end, against the shoulder girdle. Dislocation of the humerus's glenohumeral joint
, has the potential to injure the axillary nerve or the axillary artery
. Signs and symptoms of this dislocation include a loss of the normal shoulder contour and a palpable depression under the acromion.
The radial nerve
follows the humerus closely. At the midshaft of the humerus, the radial nerve travels from the posterior to the anterior aspect of the bone in the spiral groove. A fracture of the humerus in this region can result in radial nerve injury.
The ulnar nerve
at the distal end of the humerus near the elbow is sometimes referred to in popular culture as 'the funny bone'. Striking this nerve can cause a tingling sensation ("funny" feeling), and sometimes a significant amount of pain.
s had little, if any, shaft connecting the upper and lower extremities, making their limbs very short. In most living vertebrates, however, the humerus has a similar form to that of humans. In many reptile
s and some primitive mammal
s, the lower extremity includes a large foramen, or opening, into which nerves and blood vessels pass.
Long bone
The long bones are those that are longer than they are wide. They are one of five types of bones: long, short, flat, irregular and sesamoid. Long bones, especially the femur and tibia, are subjected to most of the load during daily activities and they are crucial for skeletal mobility. They grow...
in the arm
Arm
In human anatomy, the arm is the part of the upper limb between the shoulder and the elbow joints. In other animals, the term arm can also be used for analogous structures, such as one of the paired forelimbs of a four-legged animal or the arms of cephalopods...
or forelimb
Forelimb
A forelimb is an anterior limb on an animal's body. When referring to quadrupeds , the term foreleg is often instead used....
that runs from the shoulder
Shoulder
The human shoulder is made up of three bones: the clavicle , the scapula , and the humerus as well as associated muscles, ligaments and tendons. The articulations between the bones of the shoulder make up the shoulder joints. The major joint of the shoulder is the glenohumeral joint, which...
to the elbow
Elbow
The human elbow is the region surrounding the elbow-joint—the ginglymus or hinge joint in the middle of the arm. Three bones form the elbow joint: the humerus of the upper arm, and the paired radius and ulna of the forearm....
.
Anatomically, it connects the scapula
Scapula
In anatomy, the scapula , omo, or shoulder blade, is the bone that connects the humerus with the clavicle ....
and the lower arm (consisting of the radius
Radius (bone)
The radius is one of the two large bones of the forearm, the other being the ulna. It extends from the lateral side of the elbow to the thumb side of the wrist and runs parallel to the ulna, which exceeds it in length and size. It is a long bone, prism-shaped and slightly curved longitudinally...
and ulna
Ulna
The ulna is one of the two long bones in the forearm, the other being the radius. It is prismatic in form and runs parallel to the radius, which is shorter and smaller. In anatomical position The ulna is one of the two long bones in the forearm, the other being the radius. It is prismatic in form...
), and consists of three sections. The upper extremity consists of a rounded head, a narrow neck, and two short processes (tubercles, sometimes called tuberosities.) Its body
Body of humerus
The body or shaft of the humerus is almost cylindrical in the upper half of its extent, prismatic and flattened below, and has three borders and three surfaces.- Anterior :...
is cylindrical in its upper portion, and more prism
Prism (geometry)
In geometry, a prism is a polyhedron with an n-sided polygonal base, a translated copy , and n other faces joining corresponding sides of the two bases. All cross-sections parallel to the base faces are the same. Prisms are named for their base, so a prism with a pentagonal base is called a...
atic below. The lower extremity
Lower extremity of humerus
The lower extremity of the humerus is flattened from before backward, and curved slightly forward; it ends below in a broad, articular surface, which is divided into two parts by a slight ridge.Projecting on either side are the lateral and medial epicondyles....
consists of 2 epicondyle
Epicondyle
Epicondyle may refer to:...
s, 2 processes (trochlea & capitulum
Capitulum of the humerus
In human anatomy of the arm, the lateral portion of the articular surface of the humerus consists of a smooth, rounded eminence, named the capitulum of the humerus....
), and 3 fossae (radial fossa
Radial fossa
Above the front part of the capitulum is a slight depression, the radial fossa, which receives the anterior border of the head of the radius, when the forearm is flexed....
, coronoid fossa, and olecranon fossa
Olecranon fossa
The olecranon fossa is a deep triangular depression on the posterior side of the humerus, superior to the trochlea, in which the summit of the olecranon is received during extension of the forearm.-External links: *...
). As well as its true anatomical neck, the constriction below the greater and lesser tubercles of the humerus is referred to as its surgical neck
Surgical neck of the humerus
The surgical neck of the humerus is a constriction below the tubercles of the greater tubercle and lesser tubercle.It is much more frequently fractured than the anatomical neck of the humerus. A fracture in this area is most likely to cause damage to the axillary nerve...
due to its tendency to commonly get fractured, thus often becoming the focus of surgeons.
Muscles attached to the humerus
The deltoidDeltoid muscle
In human anatomy, the deltoid muscle is the muscle forming the rounded contour of the shoulder. Anatomically, it appears to be made up of three distinct sets of fibers though electromyography suggests that it consists of at least seven groups that can be independently coordinated by the central...
originates on the lateral third of the clavicle
Clavicle
In human anatomy, the clavicle or collar bone is a long bone of short length that serves as a strut between the scapula and the sternum. It is the only long bone in body that lies horizontally...
, acromion and the crest of the spine
Spine of scapula
The spine of the scapula is a prominent plate of bone, which crosses obliquely the medial four-fifths of the scapula at its upper part, and separates the supra- from the infraspinatous fossa....
of the scapula. It is inserted on the deltoid tuberosity
Deltoid tuberosity
In human anatomy, the deltoid tuberosity is a rough, triangular area on the anterolateral surface of the middle of the humerus to which the deltoid muscle attaches.-Development:...
of the humerus and has several actions including abduction, extension, and circumduction of the shoulder. The supraspinatus also originates on the spine of the scapula. It inserts on the greater tubercle of the humerus, and assists in abduction of the shoulder.
The pectoralis major, teres major, and latissimus dorsi insert at the intertubercular groove of the humerus. They work to adduct and medially, or internally, rotate the humerus.
The infraspinatus and teres minor insert on the greater tubercle, and work to laterally, or externally, rotate the humerus. In contrast, the subscapularis muscle inserts onto the lesser tubercle and works to medially, or internally, rotate the humerus.
The biceps brachii, brachialis, coracobrachialis, and brachioradialis
Brachioradialis
Brachioradialis is a muscle of the forearm that acts to flex the forearm at the elbow. It is also capable of both pronation and supination, depending on the position of the forearm...
(which attaches distally) act to flex the elbow. (The biceps, however, does not attach to the humerus.) The triceps brachii and anconeus extend the elbow, and attach to the posterior side of the humerus.
The four muscles of supraspinatus, infraspinatus, teres minor and subscapularis form a musculo-ligamentous girdle called the rotator cuff
Rotator cuff
In anatomy, the rotator cuff is the group of muscles and their tendons that act to stabilize the shoulder. The four muscles of the rotator cuff, along with the teres major muscle, the coracobrachialis muscle and the deltoid, make up the seven scapulohumeral muscles of the human body.-Function:The...
. This cuff stabilizes the very mobile but inherently unstable glenohumeral joint
Glenohumeral joint
The glenohumeral joint, or shoulder joint, is a multiaxial synovial ball and socket joint and involves articulation between the glenoid fossa of the scapula and the head of the humerus...
. The other muscles are used as counterbalances for the actions of lifting/pulling and pressing/pushing.
Articulations
At the shoulder, the head of the humerus articulates with the glenoid fossa of the scapulaScapula
In anatomy, the scapula , omo, or shoulder blade, is the bone that connects the humerus with the clavicle ....
. More distally, at the elbow, the capitulum of the humerus articulates with the head of the radius
Radius (bone)
The radius is one of the two large bones of the forearm, the other being the ulna. It extends from the lateral side of the elbow to the thumb side of the wrist and runs parallel to the ulna, which exceeds it in length and size. It is a long bone, prism-shaped and slightly curved longitudinally...
, and the trochlea of the humerus articulates with the olecranon process of the ulna
Ulna
The ulna is one of the two long bones in the forearm, the other being the radius. It is prismatic in form and runs parallel to the radius, which is shorter and smaller. In anatomical position The ulna is one of the two long bones in the forearm, the other being the radius. It is prismatic in form...
.
Nerves
The axillary nerveAxillary nerve
The axillary nerve or the circumflex nerve is a nerve of the human body, that comes off the of the brachial plexus at the level of the axilla and carries nerve fibers from C5 and C6...
is located at the proximal end, against the shoulder girdle. Dislocation of the humerus's glenohumeral joint
Glenohumeral joint
The glenohumeral joint, or shoulder joint, is a multiaxial synovial ball and socket joint and involves articulation between the glenoid fossa of the scapula and the head of the humerus...
, has the potential to injure the axillary nerve or the axillary artery
Axillary artery
In human anatomy, the axillary artery is a large blood vessel that conveys oxygenated blood to the lateral aspect of the thorax, the axilla and the upper limb...
. Signs and symptoms of this dislocation include a loss of the normal shoulder contour and a palpable depression under the acromion.
The radial nerve
Radial nerve
The radial nerve is a nerve in the human body that supplies the upper limb. It supplies the medial and lateral heads of the triceps brachii muscle of the arm, as well as all 12 muscles in the posterior osteofascial compartment of the forearm and the associated joints and overlying skin.It...
follows the humerus closely. At the midshaft of the humerus, the radial nerve travels from the posterior to the anterior aspect of the bone in the spiral groove. A fracture of the humerus in this region can result in radial nerve injury.
The ulnar nerve
Ulnar nerve
In human anatomy, the ulnar nerve is a nerve which runs near the ulna bone. The ulnar collateral ligament of elbow joint is in relation with the ulnar nerve. The nerve is the largest unprotected nerve in the human body , so injury is common...
at the distal end of the humerus near the elbow is sometimes referred to in popular culture as 'the funny bone'. Striking this nerve can cause a tingling sensation ("funny" feeling), and sometimes a significant amount of pain.
In other animals
Primitive fossil amphibianAmphibian
Amphibians , are a class of vertebrate animals including animals such as toads, frogs, caecilians, and salamanders. They are characterized as non-amniote ectothermic tetrapods...
s had little, if any, shaft connecting the upper and lower extremities, making their limbs very short. In most living vertebrates, however, the humerus has a similar form to that of humans. In many reptile
Reptile
Reptiles are members of a class of air-breathing, ectothermic vertebrates which are characterized by laying shelled eggs , and having skin covered in scales and/or scutes. They are tetrapods, either having four limbs or being descended from four-limbed ancestors...
s and some primitive mammal
Mammal
Mammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...
s, the lower extremity includes a large foramen, or opening, into which nerves and blood vessels pass.