MCEM Part A Study Guide/Anatomy/Upper Limb
|Muscle name||Surface markings||Action||Nerve supply||Picture|
Covers much of the anterior thoracic wall. Occasionally a gap is visible between the two parts. Its sternal origin presents a border which bounds, and determines the width of, the sternal furrow.
The upper margin is generally well-marked medially and forms the medial boundary of a triangular depression, the infraclavicular fossa, which separates the pectoralis major from the deltoid; it gradually becomes less marked as it approaches the tendon of insertion and is closely blended with the deltoid. The lower border of pectoralis major forms the rounded anterior axillary fold.
|Adduction and medial rotation of humerus.
||Lateral + medial pectoral nerves (C5+C6, clavicular head; C7-T1, sternocostal head)|
Lies underneath pectoralis major When the arm is raised, the lowest slip of origin of pectoralis minor produces a fullness just below the anterior axillary fold and serves to break the sharp outline of the lower border of pectoralis major.
|Holds scapula in position against thoracic wall||Medial pectoral nerve (C8+T1)|
The anterior border presents as a slight ridge running downward and forward from the superior nuchal line of the occipital bone to the junction of the intermediate and lateral thirds of the clavicle. The inferior border of the muscle forms an undulating ridge passing downward and medialward from the root of the spine of the scapula to the spinous process of the twelfth thoracic vertebra.
|Action||Spinal accessory nerve (CN XI)|
The lateral border may be traced, when the muscle is in action, as a rounded edge starting from the iliac crest and slanting obliquely forward and upward to the axilla, where it takes part with the teres major in forming the posterior axillary fold.
|Action||Thoracodorsal nerve (C6+7)|
|Serratus anterior||The origin causes a very characteristic surface marking. When the arm is abducted the lower five or six serrations form a zigzag line with a general convexity forward; when the arm is by the side the highest visible serration is that attached to the fifth rib.||Action||Long thoracic nerve (C6+7)|
Five of the muscles share a common origin from the medial humeral epicondyle: pronator teres, flexor carpi radialis, flexor carpi ulnaris, palmaris longus and parts of flexor digitorum superficialis. (You do not need to know other attachments or relations in detail.)
|Muscle name||Surface topography||Action||Nerve supply||Picture|
On the front of the elbow are two muscular elevations, one on either side, separate proximally but converging distally so as to form the medial and lateral boundaries of the antecubital fossa. The medial elevation consists of the pronator teres and the flexors, and forms a fusiform mass, pointed above at the medial epicondyle and gradually tapering off below. The pronator teres is the most lateral of the group.
|Pronates and flexes forearm at the elbow.||Median nerve (C6+C7)|
|Flexor carpi radialis||This muscle, lying to the medial side of pronator teres, is the most prominent and may be traced downward to its tendon, which is situated nearer to the radial than to the ulnar border of the front of the wrist and medial to the radial artery.||Flexes and abducts hand at the wrist.||Median nerve (C6+C7)|
|Flexor digitorum superficialis||Does not directly influence surface anatomy; the position of its four tendons on the front of the distal part of the forearm is indicated by an elongated depression between the tendons of palmaris longus and flexor carpi ulnaris.||Flexes PIP joints of the 2nd-5th digits; with strong action, flexes MCP joints of the 2nd-5th digits and also flexes the wrist.||Median nerve (C7-T1)|
|Palmaris longus||Presents no surface marking proximally, but distally, its tendon stands out when the muscle is in action as a sharp, tense cord in front of the middle of the wrist.||Weakly flexes hand at the wrist, and tenses the palmar aponeurosis.||Median nerve (C7+C8)|
|Flexor carpi ulnaris||This forms the medial border of the forearm, and is separated from the extensor group of muscles by the ulnar furrow produced by the subcutaneous dorsal border of the ulna; its tendon is evident along the ulnar border of the lower part of the forearm, and is most marked when the hand is flexed and adducted.||Flexes and adducts hand at the wrist.||Ulnar nerve (C7+C8)|
There are three other deeper muscles in the anterior forearm:
|Muscle name||Surface topography||Action||Nerve supply||Picture|
|Flexor digitorum profundus||
Mirrors the course of the flexor digitorum superficialis, but inserts more distally.
|Flexor pollicis longus||Performs the equivalent role for the thumb as the flexor digitorum muscles do for the other digits.||Flexes MCP and IP joints of thumb.||Anterior interosseus nerve, from median nerve (C8+T1)|
|Pronator quadratus||A small, flat, quadrilateral muscle, extending across the front of the lower parts of the radius and ulna. It helps to bind the two bones together.||Pronates forearm.||Anterior interosseus nerve, from median nerve (C8+T1)|
The brachial artery normally bifurcates in the distal cubital fossa, opposite the neck of the radius. It becomes the radial and ulnar arteries.
The radial artery appears, from its direction, to be the continuation of the brachial, but it is smaller in calibre than the ulnar. It commences at the bifurcation of the brachial, just below the bend of the elbow, and passes along the radial side of the forearm to the wrist. Its upper part is overlapped by the fleshy belly of the brachioradialis; the rest of the artery is superficial. It then winds backward to continue around the lateral side of the carpus.
On the palmar aspect of the distal radius, medial to the styloid process and lateral to flexor carpi radialis, a portion of the radial artery is superficial and is used clinically for observations on the pulse.
The ulnar artery begins deeply seated, lying upon brachialis and flexor digitorum profundus. Immediately below the radial tuberosity it gives rise to the common interosseous artery, which passes backward to the upper border of the interosseous membrane. It is then crossed by the median nerve, and continues on the ulnar aspect of the forearm in close relation to the ulnar nerve, lying on flexor digitorum profundus. The artery is overlapped in its middle third by flexor carpi ulnaris.
The ulnar artery pulse may be palpated distally in the forearm, lateral to flexor carpi ulnaris.