6 - Brachial Plexus

*RAMI/ROOTS* of brachial plexus

*Anterior* rami (*R*oots) are most proximal portion of brachial plexus - two nerves arise directly from rami 1. Dorsal scapular nerve C5 2. Long thoracic nerve C5-7

*DIVISIONS* of brachial plexus

*NO NERVES ARISE DIRECTLY FROM DIVISIONS OF BP* 3 posterior divisions and 3 anterior divisions - each trunk splits into a posterior and an anterior division - In anatomical position, posterior divisions are deep to anterior divisions

Organization of brachial plexus

*R*each *T*o *D*rink *C*old *B*eer *R*oots (*R*ami) *T*runks *D*ivisions *C*ords *B*ranches

Lateral pectoral nerve C5-7

- arises superiorly to the lateral cord - innervates the clavicular head of the pectoralis major muscle

Injuries to upper part of brachial plexus usually result from... (CLINICAL)

...excessive separation of neck and shoulder - rami of nerves C5-6 may be pulled out of spinal cord - superior trunk of BP can also be torn These lesions are known as *Erb-Duchenne paralysis* - AKA *waiter's tip*!!!

An accessory (cervical) rib can stretch and damage the... (CLINICAL)

...inferior trunk C8T1, causing cervical rib syndrome

Damage to long thoracic nerve can cause... (CLINICAL)

...paralysis of serratus anterior muscle - causes medial border of scapula to become unusually prominent - *Winged Scapula*!

Injuries to lower part of brachial plexus usually result from... (CLINICAL)

...upper limb suddenly being pulled superiorly - can happen during childbirth - involve C8T1 nerves - thus, will paralyze most of intrinsic hand muscles This injury is known as *Klumpke's paralysis* - AKA *claw hand*

Reflection of embryology

Anterior and posterior divisions reflect emrbryology of upper limb - anterior supplies preaxial muscles (front of bone) - posterior supplies postaxial muscles (behind bone)

Terminal *B*ranches of Lateral Cord

Arise directly from lateral cord of BP - distal to lateral pectoral nerve

Terminal *B*ranches of Medial Cord

Arise directly from medial cord of BP - distal to medial pectoral nerve, medial brachial cutaneous nerve, medial antebrachial cutaneous nerve

Terminal *B*ranches of Posterior Cord

Arise directly from posterior cord of BP - distal to upper subscapular nerve, thoracodorsal nerve, lower subscapular nerve

Posterior triangle of neck

Basically behind earn and runs down neck to top middle of shoulder - contains 3 trunks of BP

Medial *C*ord C8T1 of brachial plexus

Bottom line on diagram, continuation of anterior division of lower/inferior trunk - gives rise to 5 nerves 1. Medial pectoral nerve C8T1 2. Medial brachial cutaneous nerve C8T1 3. Medial antebrachial cutaneous nerve C8T1 4. Ulnar nerve C8T1 (TERMINAL BRANCH) 5. Medial root of medial nerve C8T1 (TERMINAL BRANCH)

Winged scapula (CLINICAL)

Caused by damage to long thoracic nerve - causes medial border of scapula to protrude an abnormal amount

Middle *T*runk of brachial plexus

Continuation of C7 ramus, does NOT give rise to any nerves

Musculocutaneous nerve C5-7

First of 2 terminal branches of lateral cord of BP - innervates the 3 flexor muscles in the arm (coracobrachialis, biceps brachii, and brachialis) - also supplies elbow joint and skin on lateral side of forearm

Ulnar nerve C8T1

First of 2 terminal branches of medial cord of BP - innervates 1 1/2 muscles of flexor forearm and most of the hand's intrinsic muscles - also supplies elbow joint, wrist joint, and skin on medial surfaces of hand (palmar and dorsal) - runs along medial side of elbow - AKA the "funny bone"

Axillary nerve C5-6

First of 2 terminal branches of posterior cord - innervates deltoid and teres minor muscles - also supplies glenohumeral joint, skin over inferior half of deltoid and adjacent arm - travels through the quadrangular space

Medial pectoral nerve C8T1

First of 3 nerves that arise inferiorly from medial cord of BP - innervates pectoralis minor and sternocostal head of pectoralis major

Upper subscapular nerve C5-6

First of 3 nerves that arise inferiorly from posterior cord of BP - innervates part of the subscapularis muscle

Superior/upper *T*runk

Formed by Rami of C5-6 and directly gives rise to 2 nerves 1. Suprascapular nerve C5-6 2. Nerve to the Subclavius C5-6

Inferior/lower *T*runk of brachial plexus

Formed by Rami of C8-T1, does NOT give rise to any nerves

Posterior divisions of brachial plexus

Middle line on diagram, dives under (deep/posterior to) the axillary artery - basically forms an angled E or arrowhead shape as they come together to form posterior cord

Posterior *C*ord C5-8T1 of brachial plexus

Middle line on diagram, formed from posterior divisions of all 3 trunks - gives rise to five nerves (3 proximal and then 2 Branches distally) 1. Upper subscapular nerve C5-6 2. Thoracodorsal nerve C6-8 3. Lower subscapular nerve C5-6 4. Axillary nerve C5-61 (TERMINAL BRANCH) 5. Radial nerve C5-8T1 (TERMINAL BRANCH)

Brachial plexus

Network of nerves formed by *ANTERIOR* rami of nerves C5-8 and T1 - Extends from spinal cord through cervicoaxillary canal in neck, passes over first rib, and then goes into armpit - supplies afferent and efferent nerve fibers to chest, shoulder, arm, and hand

Long thoracic nerve C5-7

One of 2 nerves to arise from roots/rami of BP - arises inferiorly from three rami C5-7 - innervates serratus anterior

Dorsal scapular nerve C5

One of 2 nerves to arise from roots/rami of brachial plexus - arises superiolaterally from C5 slightly distal to long thoracic nerve C5-7 - innervates inferior slips of levator scapulae and rhomboids major/minor

Glenohumeral joint of shoulder

One of 4 joints that attaches upper extremity to the trunk - composed of head of humerus and the glenoid fossa of the scapula

Suprascapular nerve C5-6

One of two nerves directly arising from superior/upper Trunk of BP - so it arises from C5-6 - innervates supraspinatus and infraspinatus muscles - also gives an articular (sensory) branch to glenohumeral joint of shoulder

Anterior divisions of brachial plexus

Outer lines on diagram, crosses over (superficial/anterior) the axillary artery - the 2 on top come together into lateral cord - the one on bottom continues into medial cord

Klumpke's paralysis (CLINICAL)

Proper name for *claw hand* - results from damage to lower part of BP (C8T1 nerves) - injury caused by arm being pulled superiorly suddenly

Erb-Duchenne paralysis (CLINICAL)

Proper name for *waiter's tip* - results from damage to C5-6 or superior trunk of BP (separation of shoulder and neck can cause this)

Nerve to the subclavius C5-6

Second of 2 nerves arising directly from superior/upper Trunk of BP - innervates the subclavius muscle (duh)

Lateral root of median nerve C5-7

Second of 2 terminal branches of lateral cord of BP - joins with root from Medial Cord to form Median nerve C5-8T1 - Median nerve runs lateral to brachial artery until midarm, then crossed to medial side and descends middle of flexor forearm towards wrist - supplies 6 1/2 muscles of flexor forearm and 5 muscles in hand - also supplies elbow joint, wrist joint, skin of palmar hand

Medial root of median nerve C8T1

Second of 2 terminal branches of medial cord of BP - joins with root from Lateral Cord to form Median nerve C5-8T1 - Median nerve runs lateral to brachial artery until midarm, then crossed to medial side and descends middle of flexor forearm towards wrist - supplies 6 1/2 muscles of flexor forearm and 5 muscles in hand - also supplies elbow joint, wrist joint, skin of palmar hand

Radial nerve C5-8T1

Second of 2 terminal branches of posterior cord - innervates all extensor muscles of the arm and forearm - also supplies elbow joint, wrist joint - also supplies skin of posterior arm, some of posterior forearm, and some of hand's dorsal side

Medial brachial cutaneous nerve C8T1

Second of 3 nerves that arise inferiorly from medial cord of BP - provides cutaneous innervation to medial side of arm

Thoracodorsal nerve C6-8

Second of 3 nerves that arise inferiorly from posterior cord of BP - innervates the latissimus dorsi muscle

Terminal *BRANCHES* of brachial plexus

These are nerves that arise directly from the cords of the BP and are distal to the cords - 2 terminal branches per cord - most distal part of BP

Medial antebrachial cutaneous nerve C8T1

Third of 3 nerves that arise inferiorly from medial cord of BP - provides cutaneous innervation to medial side of forearm

Lower subscapular nerve C5-6

Third of 3 nerves that arise inferiorly from posterior cord of BP - innervates teres major and subscapularis muscles

*TRUNKS* of brachial plexus

Three *T*runks, located in posterior triangle of neck - Superior (formed from C5-6) - Middle (continuation of C7) - Inferior (formed from C8T1)

*CORDS* of brachial plexus

Three Cords located in the axilla and named with respect to part of axillary artery that is deep to pectoralis minor (2nd part) - Lateral cord C5-7 - Medial cord C8T1 - Posterior cord C5-8T1

Lateral *C*ord C5-7 of brachial plexus

Top line on diagram, formed from anterior divisions of superior and middle trunks - gives rise to 3 nerves in total (one proximal and then 2 Branches distally) 1. Lateral pectoral nerve C5-7 2. Musculocutaneous nerve C5-7 (TERMINAL BRANCH) 3. Lateral root of medial nerve C5-7 (TERMINAL BRANCH)

Plexus

a network of nerves or vessels in the body, often interlacing