gross anatomy of brachial plexus

suprascapular nerve origin

upper (superior) trunk of brachial plexus, receiving fibers from C5, C6, and sometimes C4

suprascapular nerve anatomical course

• passes laterally across the posterior triangle of the neck and deep into the trapezius muscle

• runs along the superior border of the scapula and enters the suprascapular notch and then enters the suprascapular fossa

• curves around the lateral border of the spine of scapula through spinoglenoid notch to reach infraspinous fossa

suprascapular nerve function

• supraspinatus muscle: helps in initiation of arm abduction by assisting deltoid

• infraspinatus muscle: lateral (external) rotation of arm

• provides articular branches to glenohumeral joint

dorsal scapular nerve origin

posterior aspect of the anterior ramus of C5

dorsal scapular nerve anatomical course

pierce middle scalene muscle to descend deep to levator scapulae and rhomboid muscles

dorsal scapular nerve function

• innervates rhomboid minor, rhomboid major, and occasionally levator scapulae muscles

• contracts rhomboid minor and major muscles: retraction and downward rotation of scapula

• contracts levator scapulae: elevation of scapula and rotation of inferior angle medially

upper subscapular nerve origin

posterior cord of brachial plexus; receives fibers from C5

upper subscapular nerve anatomical course

passes posteriorly and directly enters subscapularis muscle

upper subscapular nerve function

innervates subscapularis, which controls adduction and medial rotation of arm

lower subscapular nerve origin

posterior cord of brachial plexus; receives fibers from C6

lower subscapular nerve anatomical course

passes inferolaterally deep into subscapular vessels

lower subscapular nerve function

innervates subscapularis which controls adduction and medial rotation of arm, and teres major whose contraction also results in adduction and medial rotation of arm

subclavian nerve origin

upper trunk of brachial plexus, receiving fibers from C5, C6, and sometimes C4

subclavian nerve anatomical course

descends posteriorly to clavicle and anterior to brachial plexus and subclavian artery, often giving an accessory root to phrenic nerve

subclavian nerve function

innervates sternoclavicular joint and subclavius muscle (which anchors, depresses, and stabilizes the clavicle, along with assisting in lifting the ribs during respiration)

long thoracic nerve origin

posterior aspect of anterior rami of C5, C6, C7

long thoracic nerve anatomical course

descends through cervicoaxillary canal, posterior to axillary vessels and deep to clavicle

long thoracic nerve function

innervates serratus anterior muscle, whose contraction stabilizes scapula, causes protraction of scapula, and assists in upward rotation of scapula

thoracodorsal nerve

posterior card of brachial plexus, receiving fibers from C6, C7, C8

thoracodorsal nerve anatomical course

arises between upper and lower subscapular nerves, and runs inferolaterally along posterior axillary wall, follows course of subscapular artery to the latissimus dorsi

thoracodorsal nerve function

innervates latissimus dorsi, causing the adduction, medial rotation, and extension of humerus

lateral pectoral nerve origin

lateral cord of brachial plexus, receiving fibers from C5, C6, C7

lateral pectoral nerve anatomical course

pierces costocoracoid membrane to reach deep surface of pectoral muscles

lateral pectoral nerve function

• innervates pectoralis major whose contraction causes flexion, adduction, and medial rotation of humerus

• acromioclavicular and glenohumeral joints

medial pectoral nerve origin

medial cord of brachial plexus, receiving fibers from C8 to T1

medial pectoral nerve anatomical course

passes between the axillary artery and vein, pierces pectoralis minor and enters the deep surface of pectoralis major, lies lateral to lateral pectoral nerve

medial pectoral nerve function

innervates pectoralis minor (depresses the point of shoulder, drawing scapula superior towards thorax and moves its inferior angle posteriorly) and pectoralis major (flexion, adduction, and medial rotation of humerus)

axillary nerve origin

terminal branch of posterior cord of brachial plexus, receiving fibers from C5 to C6

axillary nerve anatomical course

• initially lies posterior to axillary artery, anterior to subscapularis muscle

• passes through quadrangular space with posterior circumflex humeral artery

axillary nerve function

• innervates deltoid (shoulder abduction along with flexion, abduction, rotation of arm), teres minor (lateral rotation of upper arm at shoulder joint), acromioclavicular and glenohumeral joints

• gives off the superolateral cutaneous nerve, which innervates skin of superolateral arm

• vulnerable to injury during shoulder dislocation, and fracture of surgical neck of humerus

musculocutaneous nerve origin

terminal branch of lateral cord, receives fibers from C5 to C7

musculocutaneous nerve anatomical course

musculocutaneous nerve function

innervates biceps brachii (flexion of elbow joint, supination of forearm), brachialis (flexion of forearm), coracobrachialis (contraction results in weak flexion and adduction)

gives off lateral antebrachial cutaneous nerve of forearm which innervates skin of lateral aspect of anterior forearm

injury to lateral cord of brachial plexus can lead to weakness in biceps brachii, brachialis, coracobrachialis muscles

median nerve origin

• lateral root originates in terminal branch of lateral cord (C6, C7)

• medial root originates in terminal branch of media cord (C8, T1)

pronator teres

pronation of radioulnar joint

flexor carpi radialis

flexion and adduction of wrist

palmaris longus

flexion of wrist, tensing of palmar aponeurosis

flexor digitorum superficialis

flexion of proximal interphalangeal joints of 2nd, 3rd, 4th, 5th fingers

pronator quadratus

pronation of forearm

flexor digitorum profundus

flexion of wrist at metacarpophalangeal and interphalangeal joints

flexor pollicis longus

flexion of phalanges of the thumb

flexor pollicis brevis

flexion of thumb at metacarpophalangeal joint & flexion and medial rotation of 1st metacarpal bone at carpometacarpal joint

adductor pollicis brevis

abduction of thumb at metacarpophalangeal and carpometacarpal joints

opponens pollicis

flexion of the thumb’s metacarpal at the first carpometacarpal joint, which aids in opposition of thumb

1st and 2nd lumbricals

flex the metacarpophalangeal joints while extending the interphalangeal joints of the digit on which they insert

palmar cutaneous nerve

innervates the skin at the lateral part of the palm

palmar digital cutaneous nerve