BRACHIAL PLEXUS
I. BRACHIAL PLEXUS - network of nerves that innervate upper limb
A. Contents - mixed nerves = motor + sensory
1. Motor to skeletal muscles
2. Sensory from skin, tendons etc.
3. Autonomic - blood vessel, sweat glands
B. Formation
- originates in the neck; at this time we will only see the portion within the axilla
1. Origin: Formed by ventral primary rami of C5-T1 (roots)
2. 5 rami (roots) form 3 trunks
a. C5-6 - Superior trunk
b. C7 - Middle trunk
c. C8, T1 - Inferior trunk
3. 3 trunks separate into anterior (3) and posterior (3) divisions
a. Anterior division - innervates preaxial structures (original ventral parts of limb)-flexors
b. Posterior division - innervates postaxial structures (original dorsal parts of the limb)-extensors
4. 6 divisions unite to form 3 cords (cords are named for their position relative to the second part of the axillary artery)
a. 3 posterior divisions - posterior cord
b. Superior and middle anterior divisions - lateral cord
c. Inferior anterior division - medial cord
5. 3 cords each divide into two terminal branches - arranged like an "M" on axillary a.
a. Posterior cord
i. Axillary nerve
ii. Radial nerve
b. Lateral cord
i. Musculocutaneous nerve
ii. Median nerve (lateral root)
c. Medial cord
i. Ulnar nerve
ii. Median nerve (medial root)
C. Branches of the brachial plexus
1. Supraclavicular branches - from rami (roots) and trunks
a. Dorsal scapular nerve (ventral ramus - C4-5) – to rhomboids
b. Long thoracic nerve (ventral ramus - C5-7) – to srratus anterior
c. Nerve to subclavius m. (superior trunk - C5) – to subclavius m.
d. Suprascapular nerve (superior trunk, C5-6) - to dorsal scapula
2. Infraclavicular branches-from cords
a. Lateral cord has 3 branches
i. Lateral pectoral nerve (C5-7)
ii. Musculocutaneous nerve (C5-7)
iii. Branch to median nerve
b. Medial cord has 5 branches
i. Medial pectoral nerve (C8, T1)
ii. Medial brachial cutaneous nerve (C8, T1)
iii. Medial antebrachial cutaneous nerve (C8, T1)
iv. Ulnar nerve (C8, T1)
v. Branch to median nerve
c. Posterior cord has 5 branches
i. Upper subscapular nerve (C5-6)
ii. Thoracodorsal nerve (C6-8)
iii. Lower subscapular nerve (C5-6)
iv. Axillary nerve (C5-6)
v. Radial nerve (C5-8, T1)
D. Functional analysis of brachial plexus
1. Anterior and posterior divisions correspond to innervation of anterior and posterior mesodermal masses during development of the limb - related to anatomical position
2. Preaxial = compartment and structures anterior to axis of limb
a. musculocutaneous nerve: muscular in arm, cutaneous in forearm
b. ulnar nerve: forearm and hand
c. median nerve: forearm
d. includes muscles of clavicle and coracoid process
3. Postaxial = compartment and structures posterior to axis of limb
a. radial nerve: supplies all musculature
b. includes scapular muscles
E. Axillary nerve (C5-6)
1. sensory - over lower deltoid
2. motor - to deltoid and teres minor m.
3. lesion - inability to abduct partially abducted arm
F. Musculocutaneous nerve (C5-6)
1. sensory - anterior-lateral forearm (lateral antebrachial cutaneous n)
2. motor - flexor muscles of upper arm
3. lesion - loss of biceps reflex, and flexion at elbow, weak supination
G. Radial nerve (C6-T1)
1. sensory - posterior arm, forearm, dorsum of hand (radial side to digit 4)
2. motor -
a. extensors of elbow
b. extensors of wrist
c. extensors of thumb and fingers
d. supinator muscle
3. lesion
a. extensor paralysis
b. loss of triceps and radial reflex
c. “wrist drop”
H. Median nerve (C6-T1)
1. sensory - palm, palmar thumb and fingers through digits 2-5, distal dorsal fingers
2. motor
a. flexors of wrist on radial side
b. flexors of digits (except digit 5)
c. pronators
d. thenar muscles (abductor, flexor and opponens)
3. lesion – causes either “preacher’s/orator’s hand / ‘hand of benediction’” or “ape (simian) hand” =>
a. loss of flexion, weak pronation
b. loss of thenar mm. (can still adduct and extend)
c. carpal tunnel lesion - at wrist level
I. Ulnar nerve (C8-T1)
1. sensory - both palmar and dorsal hypothenar region, digiti minimi, and ulnar half of digit 4
2. motor -
a. flexor of wrist on ulnar side
b. flexor digiti minimi
c. hypothenar mm. (flex and abduct digit 5)
d. deep mm. of hand
i. ABduct and ADduct all digits
ii. ADduct thumb
iii. help extend fingers
3. lesion
a. loss of abduction and adduction of fingers
b. loss adduction of thumb
c. weak wrist flexion and adduction
d. “claw hand” - extension of distal fingers 4 & 5 flexion of distal fingers 2 & 3
J. Brachial plexus lesions
1. Loss of muscular movement (paralysis)
2. Loss of cutaneous sensation (anesthesia)
3. Most upper brachial plexus injuries from motorcycle accidents
4. Stab and bullet wounds
5. Lower plexus injuries less common