Brachial Plexus Anatomy

• The brachial plexus arises from the anterior rami of the cervical spine roots of (C5 – C6 – C7 – C8 – T1).
  • Sometimes C5 receives some fibers from C4 and T1 also receives some fibers from T2.
• Shortly after leaving the intervertebral foramen, each root receives its sympathetic component via a gray ramus.
• The cervical roots receive their sympathetic components from one of the lower cervical sympathetic ganglia and the T1 root from its own sympathetic ganglion after contributing a white ramus to it.
• The brachial plexus begins to form distal to the scalene muscle.
• Brachial Plexus palsy can be seen in infant after birth or in adult patient after trauma or accidents.

Parts of Brachial Plexus:

• The Brachial Plexus consists of ( 5 Roots – 3 Trunks – 6 Divisions – 3 Cords – 5 Terminal Branches) respectively :
  • Roots are the anterior rami of (C5 – C6 – C7 – C8 – T1) as mentioned above.
  • Trunks are ( Upper – Middle – Lower trunk).
  • Divisions are anterior and posterior of each trunks.
  • Cords are ( Lateral – Posterior – Medial)
• The only nerves that arise from the root directly are:
  • Dorsal scapular nerve: arises from C5 root, it’s the first important branch seen when the plexus is explored superior to the clavicle.
  • The Long Thoracic nerve arises from C5 – C6 – C7 cervical roots.

The Trunks:

• There are three trunks formed from the united of the roots.
• They proceed infero-laterally behind the clavicle:
• The three trunks are:
  1. The Upper trunk is formed by the united of C5 & C6 cervical roots.
  2. The Middle trunks is formed by the C7 cervical root alone.
  3. The Lower trunk is formed by the united of the C8 & T1.
• The upper trunk gives arise to:
  1. Suprascapular nerve.
  2. Subclavius nerve.

The Divisions:

• Each trunk is divided into two divisions:
  • Anterior Division.
  • Posterior Division.
• No Nerves arise from the divisions.

The Cords:

• The Lateral Cord is formed by the united of the anterior divisions of the upper and middle trunks, it gives arise to the:
  1. Lateral Pectoral Nerve (C5 – C6 – C7).
• The Posterior Cord is formed by the united of the three posterior divisions, , it gives arise to the (Respectively from proximal to distal):
  1. Upper Subscapular Nerve (C5 – C6)
  2. Thoracodorsal (Middle Subscapular) Nerve (C6 – C7 – C8).
  3. Lower Subscapular Nerve (C5 – C6).
• The Medial Cord is formed by the anterior division of the lower trunk alone, it gives arise to the (Respectively from proximal to distal):
  1. Medial Pectoral Nerve (C5 – C6 – C7).
  2. Medial Brachial Cutaneous Nerve (T1).
  3. Medial Antebrachial Cutaneous Nerve (C8 – T1).
• These cords is named based on their relationship with the axillary artery:
  1. Lateral Cord is located lateral to the axillary artery.
  2. Posterior Cord is located posterior to the axillary artery.
  3. Medial Cord is located medial to the axillary artery.

Notice: The lateral pectoral nerve and the medial pectoral nerve communicate by an anastomotic loop.

Terminal Branches:

1. The Musculocutaneous Nerve (C5 – C6 – C7): arises from the lateral cord.
2. The Axillary Nerve (C5 – C6): arises from the posterior cord.
3. The Radial Nerve (C5 – C6 – C7 – C8 – T1): arises from the posterior cord.
4. The Median Nerve (C5 – C6 – C7 – C8 – T1): arises from the lateral & medial cord.
5. The Ulnar Nerve (C7 – C8 – T1): arises from the medial cord.

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