The rhomboid major is a skeletal muscle on the back that connects the scapula (shoulder blade) with the vertebrae of the spinal column. There are two rhomboid muscles; the rhomboid major and the rhomboid minor. Often simply called the rhomboids, they are rhombus-shaped muscles associated with the scapula (shoulder blade) and are chiefly responsible for its retraction. In human anatomy, the rhomboid minor is a small skeletal muscle on the back that connects the scapula with the vertebrae of the spinal column. Located inferior to levator scapulae and superior to rhomboid major, it acts together with the latter to keep the scapula pressed against the thoracic wall. It lies deep to trapezius but superficial to the long spinal muscles.
Neuromuscular Anatomy and Function
Tulio E. Bertorini MD, in Neuromuscular Case Studies, 2008
Nerves of the Brachial Plexus
The suprascapular nerve arises from the C5 to C6 roots through the upper trunk supplying the supraspinatus and the infraspinatus muscles.
The subscapular nerve from C5 to C6 roots innervates the teres major muscle. The anterior thoracic nerve from the C5 to C8 roots innervates the pectoralis major and minor, and the thoracodorsal nerve from C6 to C8 roots innervates the latissimus dorsi muscle.
The axillary nerve is formed by fibers of the C5 to C6 roots which go through the posterior cord of the plexus and innervate the deltoid and teres minor muscles, as well as part of the skin of the lateral shoulder.
The musculocutaneous nerve originates in the lateral cord from fibers of the C5 to C6 roots and innervates the biceps, brachialis, and choracobrachialis muscles as well. Its sensory branch, the lateral antebrachial cutaneous nerve, innervates the lateral aspect of the forearm.
The radial nerve is formed of axons from C5 to C8 roots going through the posterior cord and innervates the tricepsand the anconeus muscles in the arm; then, after passing the spiral groove of the humerus, it gives off a sensory branch, the posterior antebrachial cutaneous nerve which innervates the skin of the lateral and dorsal forearm. After the groove, the nerve supplies the brachioradialis and the extensor carpi radialis longus. After entering the forearm, the radial nerve divides into the motor posterior interosseus nerve and its sensory branch, the superficial radial nerve, which innervates the skin of the lateral aspect of the dorsum of the hand. The posterior interosseus nerve innervates the supinator, extensor carpi radialis brevis, abductor pollicis longus, extensor carpi ulnaris, extensor digitorum communis, extensor pollicis longus and brevis, extensor digiti minimi, and extensor indicis.
The median nerve originates from axons of the C6 to T1 roots which travel through the lateral and medial cords of the brachial plexus. The nerve supplies the flexor carpi radialis, pronator teres, palmaris longus, and flexor digitorum superficialis. Before entering the carpal tunnel, the nerve gives off a sensory branch that innervates the skin of the thenar eminence. The nerve then passes through the carpal tunnel and supplies the lumbricals I and II and forms the recurrent thenar nerve which innervates the abductor pollicis brevis, the opponens pollicis, and the flexor pollicis. The latter is also partially innervated by the ulnar nerve.
In the forearm the median nerve also gives rise to a purely motor branch, the anterior interosseus nerve, which innervates the pronator quadratus, flexor pollicis longus, and flexor digitorum profundus I and II.
The sensory axons of the distal median nerve innervate the skin of the lateral aspect of the palm, the dorsal surface of the terminal phalanges, and the volar surface of the first three digits and the middle of the fourth. The axons innervating the skin of the thumb come from the C6 roots and part of C7; the index and the middle fingers, from the C7 root.
The most common anomalous cross-innervations in the arm are crossovers between the median and ulnar nerves. Their fibers, which originate from the median nerve, travel with the ulnar nerve to innervate muscles that are normally innervated by the ulnar nerve.
The ulnar nerve originates from the C8 and T1 roots through the medial cord of the plexus and travels in the arm next to the brachial artery and the median nerve. After entering the forearm, it supplies the flexor carpi ulnaris and flexor digitorum profundus III and IV, then also gives rise to the dorsal cutaneous branch, which innervates the skin of the medial dorsal aspect of the hand. It then passes the medial aspect of the wrist, then the hand, and gives origin to its superficial branch supplying the palmaris brevis muscle and the skin of the medial aspect of the hand, the hypothenar eminence, and the fifth digit and half of the fourth digit. The motor branch innervates the muscles of the hypothenar eminence and then innervates the dorsal interossei and lumbricals III and IV, the three volar interossei, and half of the flexor pollicis brevis.
The median antebrachial cutaneous nerve originates directly from the medial cord (from the lower trunk) and supplies the skin over the medial aspect of the forearm. This nerve is important in electrodiagnosis, because it could be affected in plexopathies, helping to differentiate them from ulnar neuropathies and C8-T1 radiculopathies, in which it is not involved.