Brachial Plexus

Question 1

Formation of Brachial Plexus

Answer 1

• Ventral primary rami of C5-T1

- Occasionally receives contributions from C4 and/or T2

Question 2

Successive levels of organization.

Answer 2

Read That Damn Cadaver Book

• Roots (five, not the same as ventral or dorsal roots)
• Trunks (three)
• Division (three anterior + three posterior=six)
• Cords (three)
• (Terminal) Branches (five principal branches + eleven smaller branches)

Question 3

Levels of Organization

Answer 3

• Roots form trunks (deep into the neck/posterior triangle)
• Trunks form divisions (posterior to the clavicle/cervico-axillary canal)
• Divisions form cords (in the axilla)
• Cords form terminal branches (in the axilla/posterior to pectoralis minor muscle/named after relationship with axillary artery)

Question 4

Roots to trunks

Answer 4

• Roots C5 and C6 for the superior trunk
• Roots C7 forms the middle trunk
• Roots C8 and T1 form the inferior trunk

Each of the three trunks splits into anterior and posterior divisions

Question 5

Anterior divisions

Answer 5

Generally innervate flexor/pronators (muscles)-anterior compartment of the upper limb

Question 6

Posterior divisions

Answer 6

Generally innervate extensors/supinators (muscles)- posterior compartment of the upper limb

Question 7

Divisions

Answer 7

• anterior divisions of the superior and middle trunks form the lateral cord (C5, C6, C7)
• anterior division of the inferior trunk form the medial cord (C8-T1)
• posterior divisions of all three form the posterior cord (C5, C6, C7, C8, T1)

Question 8

Musculocutaneous nerve

Answer 8

Formed by lateral cord

Question 9

Median nerve

Answer 9

Formed by lateral and medial cord

Question 10

Axillary and Radial nerves

Answer 10

Formed by posterior cord

Question 11

Ulnar nerve

Answer 11

Formed by medial cord

Question 12

Supraclavicular branches

Answer 12

1. Four
2. Arising from roots or trunks
3. C5- dorsal scapular nerve
4. C5-C7- long thoracic nerve
5. Superior trunk (C5-C6) nerve to the subclavius and suprascapular nerve

Question 13

Infraclavicular branches

Answer 13

1. Twelve
2. Arising from cords
3. Lateral cord: musculocutaneous nerve (C5-C7), lateral cord contribution to median nerve (C6-C7), lateral pectoral nerve (C5-C7)
4. Medial cord: medial cord contribution to median nerve (C8-T1), ulnar nerve (C8-T1), medial pectoral nerve (C8-T1), medial cutaneous nerve of the arm (C8-T1), medial cutaneous nerve of forearm (C8-T1)
5. Posterior cord: axillary nerve (C5-C6), Radial nerve (C5-T1), upper subscapular nerve (C5-C6), thoracodorsal nerve (C6-C8), lower subscapular nerve (C5-C6)

Question 14

Relevant Topographic Relationships

Answer 14

• anterior scalene muscle
• middle scalene muscle
• first rib
• clavicle
• pectoralis minor muscle
• subclavian artery
• sympathetic trunk