Brachial plexus

BRACHIAL PLEXUS

  • This brachial plexus is a flat fasciculus of nerves placed between the medial face of the shoulder and the thoracic wall.
  • It is formed by the convergence of the ventral primary branches of the sixth, seventh and eighth cervical and the first two dorsal spinal nerves.

  • The plexus appears as a wide, white band at first between the scalenus and longus colli and then between the two divisions of the scalenus.
  • The subscapularis and deep pectoral muscles cover it.
  • Branches from the brachial plexus supply the muscles and integument of the forelimb and some of the muscles of the shoulder girdle and chest wall.
  • The following are the branches of brachial plexus (View image)
    • External thoracic nerve
    • Thoraco dorsal nerve
    • Long thoracic nerve
    • Nerves to pectorals
    • Suprascapular nerve
    • Nerves to subscapularis
    • Nerve to teres major
    • Axillary nerve
    • Ulnar nerve
    • Musculocutaneous nerve
    • Median nerve 
    • Radial nerve
    • This arises from the brachial plexus by a common trunk with the ulnar nerve.
    • It is at first placed medial to the ulnar nerve but leaves its company, passes backward to the deep face of the long head of triceps muscle, then along its deep face in company with the external thoracic vein, if present.
    • It gives off a number of branches to the deep pectoral, cutaneous muscle and terminates in the skin of the abdominal wall and one of its branch unites with the second and third perforating intercostal branches, winds round the ventral border of the latissimus dorsi and passing forwards, ramifies in the omobrachial part of the cutaneous muscle.
    • This nerve supplies latissimus dorsi.
    • Its fibres are derived from the eighth cervical and first dorsal.
    • It ramifies on the deep face of the muscle.
    • The fibres of this nerve are derived from the seventh and eighth cervicals and sometimes from the sixth also and it supplies the serratus thoracis ventralis.
    • It is a thin and wide nerve and at first it passes backward under the deep face of the scalenus dorsalis on the posterior part of the serratus cervicis.
    • After giving a few branches to this muscle it gains the serratus thoracis and distributed to it.
    • These are three or four in number and arise from the anterior part of the plexus and form the loop formed by the musculocutaneous and median nerves.
    • One of these passes to the deep face of the deep pectoral.
    • Another nerve passes to the superficial pectoral and brachiocephalicus.
    • It is the most anterior of all the nerve from the brachial plexus and is fairly large.
    • It derives its fibres from the sixth and seventh cervicals, passes forward, downward and outward, gains the space between the supraspinatus and the subscapularis, turns around the lower fourth of the anterior border of the scapula, gains the supraspinous fossa, gives branch to the supraspinatus continues backward under the acromion process, passes into the infraspinatus muscle and terminates in it and teres minor.
    • They are two or three in number and are derived from the seventh and eighth cervical nerves.
    • These nerves are confounded at the origin with the thoracodorsal nerve, suprascapsular and circumflex nerves.
    • They supply the three divisions of the subscapularis.
    • It is derived from the seventh and eighth cervical nerves.
    • It crosses the subscapularis and the teres major and supplies branches to it and also the posterior part of the subscapularis.
    • It arises from all the cervicals. It runs downward across the medial face of the lower part of the subscapularis, gains the space between the teres major and subscapular artery, gains the company of the posterior circumflex vessels, runs behind the shoulder joint reaches the deep face of the deltoideus.
    • It supplies teres major, deltoideus, teres minor and divides into dorsal and ventral branches.
    • The dorsal branch passes under the acromial head of deltoideus and ends in the terminal part of brachiocephalicus.
    • The ventral branch passes under the scapular head of deltoid, over the lateral head of triceps and continues down as the dorsal or anterior cutaneous nerve of forearm.
    • It derives its fibres from the first dorsal nerve.
    • It arises along with the median nerve by a short common trunk.
    • It first lies behind the brachial vessels then passes down receding from them, but keep company with the median nerve till about posterior, the middle of the arm. Here it detaches a long cutaneous branch to the skin on the posterior face of the forearm.
    • It then leaves the company of the median nerve, reaches the space between the olecranon process and the medial condyle of the humerus, gains the company of the collateral ulnar artery and vein, detaches an articular branch to the elbow and then disappears between the two heads of the flexor carpi ulnaris. Here it gives off branches to the two heads of the flexor carpi ulnaris, superficial flexor and ulnar head of the deep flexor.
    • The nerve then runs downwards under cover of flexor carpi ulnaris and between it and superficial flexor, then between the superficial flexor and ulnaris lateralis, detaches a few branches to the tendons and skin and divides about the lower third of the forearm into superficial and deep branches.
      • The superficial branch emerges between the two muscles, runs down subcutaneously behind the insertion of the tendon of the flexors, runs superficially over the carpal sheath downward and outward over the metacarpal region and is continued as the lateral dorsal abaxial digital nerve on the abaxial aspect of the lateral digit.
      • The deep branch descends deeply under the deep fascia behind the carpus over the carpal sheath, supplies branches to the suspensory ligament below the carpus, unites about the fetlock with a branch of the lateral branch of the median and runs subcutaneously as the lateral volar abaxial digital nerve on the lateral digit.
    • This nerve arises from the anterior part of the brachial plexus close behind the suprascapular nerve and derives its fibres chiefly from the seventh and eighth cervical nerves.
    • It descends on the medial face of the shoulder joint below which it joins the median nerve by a large short branch to from a loop in which the brachial artery passes.
    • One or two pectoral branches are given off from this nerve to the loop.
    • The nerve then runs in front of the median, in the space between the division of the coracobrachialis in company with the anterior circumflex vessels, gives off a branch to this muscle and reaches the biceps brachii and terminates in it.
    • It derives its fibres from the eighth cervical and the first dorsal nerves.
    • It is united at its origin by a branch from the musculocutaneous nerve to form a loop in which the brachial artery is suspended.
    • It at first descends on the medial face of the brachial artery which it crosses obliquely, then runs down the arm in front of the brachial artery and at the elbow it crosses over it and gains its posterior aspect and lies on the medial ligament of the elbow.
    • It again crosses the artery below the elbow joint and lies behind the radius at the lower part of the medial ligament.
    • It passes below the elbow beneath the pronator teres. It then runs down along the forearm between the bone and the flexor carpi radialis.
    • It passes through the carpal sheath descends to the lower third of the metacarpus and divides into lateral and medial branches. 
  • Collateral branches
    • The musculo-cutaneous branch arises off from this nerve at about the middle of the humerus from its anterior face passes under the cover of biceps brachii and divides into muscular and cutaneous branches. The muscular branch supplies the brachialis.
    • The cutaneous branch supplies the skin in front and medial aspect of forearm.
    • Immediately below this, it gives off muscular branches to pronator teres, flexor carpi radialis, superficial flexor, humeral and radial heads of the deep flexor and a small interosseous nerve that accompanies the artery of the same name.
    • The terminal branches are medial and lateral.
    • The medial branch divides into medial and lateral divisions. Of which the former, after giving some small branches to the rudimentary digit is continued down as medial volar abaxial digital nerve.
    • The lateral division joins the medial division of the lateral branch to form the volar common digital nerve.
    • The lateral branch divides similarly into medial and lateral divisions.
    • The medial branch forms the volar common digital nerve and the lateral division joins the deep branch of the ulnar nerve to form the lateral volar abaxial digital nerves.
    • The volar common digital nerve passes into the interdigital space and divides into two volar axial digital nerves to supply the digits.
    • It is the largest nerve in the brachial plexus .
    • It remians subcutaneous below the elbow and prone to external pressure or injuries.
    • Its fibres are derived from the seventh and eighth cervical and first dorsal nerves.
    • The nerve passes downward and backward across the subscapularis and teres major and disappears in the space between the scapula, humerus and long head of triceps, passes in the musculospiral groove between the triceps and brachialis, reaches the anterior aspect of the elbow between the brachialis and extensor carpi radialis and emerges from under the lower part of the lateral head of triceps and descends on the anterior face of the forearm on the extensor carpi radialis over the deep fascia.
    • It continues down the anterior face of forearm in relation to cephalic vein and then down the carpus and metacarpus.
    • At about the middle of metacarpus it detaches the medial dorsal abaxial digital nerve and continues down the metacarpus to divide into two dorsal axial digital nerves at the upper part of the interdigital space.
Last modified: Sunday, 16 October 2011, 8:03 AM