Brachial Plexus Anatomy

January 13, 2021 || By : Dr. MhmadFarooq || 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.

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.

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.

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

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.

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