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Pronator Teres – Origin, Nerve Supply, Functions

Pronator Teres is a muscle (located mainly in the forearm) that, along with the pronator quadratus, serves to pronate the forearm (turning it so that the palm faces posteriorly when from the anatomical position). It has two attachments, to the medial humeral supracondylar ridge and the ulnar tuberosity, and inserts near the middle of the radius.

Anatomy of Pronator Teres

Pronator Teres – A rectangular muscle located in the superficial region of the anterior compartment.

Attachments: The pronator teres has two origins, one on the proximal end of the humerus and one of the distal end of the ulna. It attaches to the mid-region of the radius.
Function: Pronation of radio-ulnar joint and Pronates the forearm.
Origin: Coronoid process and medial epicondyle of humerus
Insertion: Lateral surface of the radius
Innervation: Median nerve (C6, C7)

Structure

The pronator teres has two heads—humeral and ulnar.

The humeral head, the larger and more superficial, arises from the medial supracondylar ridge immediately superior to the medial epicondyle of the humerus, and from the common flexor tendon (which arises from the medial epicondyle).
The ulnar head (or ulnar tuberosity) is a thin fasciculus, which arises from the medial side of the coronoid process of the ulna, and joins the preceding at an acute angle.

The median nerve enters the forearm between the two heads of the muscle, and is separated from the ulnar artery by the ulnar head. The muscle passes obliquely across the forearm, and ends in a flat tendon, which is inserted into a rough impression at the middle of the lateral surface of the body of the radius, just distal to the insertion of the supinator.

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The lateral border of the muscle forms the medial boundary of the triangular hollow known as the cubital fossa, which is situated anterior to the elbow.

Nerve Supply of Pronator Teres

The pronator teres is innervated by the median nerve.

To stimulate the pronator teres, a signal begins in the precentral gyrus in the brain and goes down through the internal capsule. It continues down the corticospinal tracts through the capsule, midbrain, and pons where it arrives at the medullar pyramids. Once at the pyramids, the corticospinal tracts decussate and the signal goes down the lateral corticospinal tract until it reaches the ventral horns of C5, C6, C7, C8, and T1.^[rx] The signal then goes through the ventral rami and down the root ganglions of C5, C6, C7, C8, and T1 (which together form the brachial plexus). Next, the signal goes down the median nerve branch of the brachial plexus and stimulates the pronator teres to contract causing the hand to pronate.^[rx]

Blood Supply of Pronator Teres

The vascularization for pronator teres muscle comes from three arteries;

Branches of the ulnar artery; common interosseous artery, anterior ulnar recurrent artery
Branch of the radial artery; radial recurrent artery
Branches of the brachial artery; inferior ulnar collateral arteries

Functions of Pronator Teres

Pronator teres pronates the forearm, turning the hand posteriorly. If the elbow is flexed to a right angle, then pronator teres will turn the hand so that the palm faces inferiorly. It is assisted in this action by the pronator quadratus. It also weakly flexes the elbow, or assists in flexion at the elbow when there is strong resistance.
As its name suggests, the main action of pronator teres is the pronation of the forearm, which is an exclusive upper limb movement. The muscle pulls the radius medially, causing its head to rotate around the proximal part of ulna at the proximal radioulnar joint.
This action rotates the palm of the hand as well, bringing it into a position to face the ground, i.e. pronation. Since it crosses the elbow joint, pronator teres also assists in the flexion of the forearm.

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References