Week 5 Brachial Plexus

brachial plexus overview

major nerve network for upper limb, consists of C5- T1, passes between the anterior and middle scalene muscles and subclavian artery

brachial plexus trunks

superior trunk: C5, C6 roots, middle trunk: C7, inferior trunk: C8, T1

brachial plexus divisions

each trunk divides into anterior (flexor) and posterior (extensor)

brachial plexus cords

lateral cord: anterior divisions of superior and middle trunks

posterior cord: posterior divisions of all trunks

medial cord: anterior division of inferior trunk

brachial plexus branches

includes important nerves like the dorsal scapular nerve and long thoracic nerve, terminal branches are the musculocutaneous, median, ulnar, radial, and axillary nerves

dorsal scapular

origin: posterior aspect of anterior ramus of C5 with frequent contribution from C4

course: pierces middle scalene, descends deep to levator scapular dn rhomboids

innervates: rhomboids, levator scapulae

long thoracic n

origin: posterior aspect of anterior rami of C5, C6, C7 and oftern C4

course: passes through cervico-axillary canal, descends posterior to C8 and T1 roots of plexus, runs inferiorly on superfical surface of serratus anterior

innervates: serratus anterior

suprascapular n

origin: superior trunk, receiving fibers from C5, C6, and often C4

course: passes laterally across lateral cervical region, superior to brachial plexus, then through scapular notch inferior to superior transverse scapular ligament

innervates: supraspinatus and infraspinatus, glenohumeral joint

subclavian n

origin: superior trunk, receiving fibers from C5, C6, and often C4

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

innervates: subclavius and sternoclavicular joint (the accessory root to phrenic nerve innervates diaphragm)

lateral pectoral n

comes from the lateral cord, fibers from C5, C6, C7, innervates pectoralis major primarily but some also to pectoralis minor, AC joint, and glenohumeral joint

musculocutaneous n

origin: terminal branch of lateral cord, receiving fibers from C5-C7

course: exits the axila by piercing coracobrachialis, descends between biceps brachii and brachialis, continues at the lateral cutaneous nerve of forearm

innervates: coracobrachialis, biceps brachii, brachialis, skin of lateral aspect of forearm

median n

origin: lateral root of medial nerve is a terminal branch of the lateral cord (C6, C7), medial root of median nerve is a terminal branch of the medial cord

course: lateral and medial roots merge to form median n lateral to axillary artery, descends through arm adjacent to brachial artery, with nerve gradually crossign anterior to artery to lie medial to artery in cubital fossa

innervates: muscles of the anterior compartment of the forearm (except FCU and medial ½ of FDP) and 5 intrinsic muscles in the thenar half of palm and palmar skin

medial pectoral n

branch from the medial cord, fibers from C8, T1, innervates pectoralis minor and sternocostal part of pectoralis major

medial cutaneous n of arm and forearm

branches from medial cord of brachial plexus, supplies the skin of the medial forearm and arm

ulnar n

origin: larger terminal branch of medial cord, recieving fibers from C8, T1 and often C7

course: descends medial arm, passes posterior to medial epicondule of humerus, then descends ulnar aspect of forearm to hand

innervates: FCU and medial ½ of FDP, most intrinsic muscles of hand, skin of hand medial to axial line of digit 4

upper subscapular n

branches from the posterior chord, fibers from C5, innervates the superior part of subscapularis

lower subscapular n

branches from the posterior chord, fibers from C6, innervates the inferior portion of subscapularis and teres major

thoracodorsal n

branch of posterior cord, fibers from C6, C7, C*, innervates latissimus dorsi

axillary artery

origin: terminal branch of posterior cord, fibers from C5, C6

course: exits axillary fossa posteriorly, passing through the quadrangular space with posterior humeral circumflex a, gives rise to superior lateral brachial cutaneous nerve, then winds around surgical neck of humerus deep to deltoid

innervates: AC and glenohumeral joint, teres minor and deltoid muscles, skin of superolateral arm

radial n

origin: larger terminal branch of posterior cord, fibers from C5-T1

course: exits axillary fossa posterior to axillary artery, passes posterior to humerus in radial groove with deep brachial a, between lateral and medial heads of triceps, enters cubital fossa, dividing into superficial (cutaneous) and deep (motor) radial nerves

innervates: all muscles of posterior compartment of arm and forearm, skin of posterior and inferolateral arm, posterior forearm, and dorsum of hand lateral to axial line of digit 4

cutaneous nerves of the upper limb

cutaneous nerves of upper limb follow a developmental pattern, lateral aspect innervated by cranial spinal cord segments, medial aspect innervated by more caudal segments, most are derived from brachial plexus, shoulder nerves arise from the cervical plexus, located deep to sternocleidomastoid muscle

supraclavicular nerves (cutaneous)

C3, C4, from the cervical plexus, pass anterior to clavicle, immediately deep to platysma, and supply skin over clavicle and superolateral aspect fo pectoralis major

superior lateral cutaneous nerve of arm

C5, C6, from terminal branch of axillary artery, emerges from beneath posterior margin of deltoid and supplied skin over lower part of this muscle and on lateral side of midarm

inferior lateral cutaneous n of arm

C5, C6, from radial nerve (or posterior cutaneous nerve of arm), perforates lateral head of triceps, passing close to cephalic vein to supply skin over inferolateral aspect of arm

posterior cutaneous n of arm

C5-C8, from radial n in axilla, crosses posterior to and communicates with intercostobrachial n and supplies the skin of posterior arm as far as olecranon

posterior cutaneous nerve of forearm

C5- C8, from radian n (with inferior lateral cutaneous n of arm), perforates lateral head of triceps, descends laterally in arm, then runs along and supplies the posterior forearm to wrist

lateral cutaneous n of forearm

C6, C7, from musculocutanous n, emerges lateral to biceps tendon deep to cephalic vein, supplying skin of anterolateral forearm to wrist

medial cutaneous n of forearm

C8, T1, from medial cord of brachial plexus, descends medial to brachial artery, pierces deep facia with basilic vein in midarm, dividing into anterior and posterior branches hat enter the forearm and supply skin of anteromedial aspect to wrist

medial cutaneous nerve of arm

C8- T2, from medial cord of brachial plexus, communicates with intercostobrachial nerve, continuing to supply skin of medial aspect of distal arm

intercostobrachial nerve

T2, from second intercostal nerve (as its lateral cutaneous branch), extends laterally, communicating with posterior and medial cutaneous nerves of arm, supplying skin of axilla and medial aspect of proximal arm

dermatome

a region of skin supplied by a single spinal nerve root, there is overlap between adjacent and much variation

C3, C4

dermatome for region at base of neck, extending laterally over shoulder

C5

dermatome for lateral aspect of arm

C6

dermatome for lateral aspect of forearm and thumb

C7

dermatome for middle three fingers and center of posterior aspect of forearm

C8

dermatome for little finger, medial side of hand and forearm (ie inferior aspect of abducted arm)

T1

dermatome for medial aspect of forearm and inferior arm

T2

dermatome for medial aspect of superior arm and skin of axilla

myotome

groups of muscles controlled by a single spinal nerve root, linked to a unilateral muscle mass and innervated by a single spinal cord nerve, upper limn muscles receive motor fibers from multisegmental peripheral nerves, intrinsic muscles of the hand are innervated by a single myotome (T1)

C5 (M)

myotome for deltoid, can test abduction and shoulder flexion to test

C5, C6 (M)

myotome for biceps (can test elbow flexion to test ) and extensor carpi radialis longus and brevis (test wrist extension)

C7 (M)

myotome for triceps (test extension of elbow) and flexor carpi radialis and ulnaris (test wrist flexion)

C8 (M)

myotome for flexor carpi ulnaris and extensor carpi ulnaris (test ulnar deviation/adduction)

T1 (M)

myotome for interossei, test with digit abduction (for dorsal) and adduction (for palmar)