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Brachial Plexus
Brachial Plexus
Roots
- Typically formed from the C5–T1 roots (their ventral rami).
Trunks
- Upper (superior) trunk: C5, C6
- Middle trunk: C7
- Lower (inferior) trunk: C8, T1
Divisions
- Posterior divisions all join to form the posterior cord.
- Anterior division lower trunk forms the medial cord.
- Anterior division upper and middle trunks form the lateral cord.
Cords
- Posterior cord forms the radial nerve and the axillary nerve.
- Medial cord forms the ulnar nerve and a portion of the median nerve.
- Lateral cord forms the musculocutaneous nerve, and branches from the lateral and medial cords join to form the median nerve.
Major Terminal Nerves
- Radial nerve
- Innervates extensor musculature.
- Ulnar nerve
- Innervates medial (pinky side of the hand) flexors that lie below the elbow.
- Median nerve
- Innervates lateral (thumb side of the hand) flexors that lie below the elbow.
Derived from the Roots
Relevant Anatomical Landmarks
Posteriorly
- Scapula
- 1st rib
Medially (posteriorly)
- Vertebral bodies of levels: C4, C5, C6, C7, and T1.
- C5, C6, and C7 roots lie above their corresponding vertebrae T1.
- C8 root lies below C7/above T1.
- T1 root lies below its vertebra.
Laterally
- Humerus
- Coracobrachialis muscle in the supero-medial shoulder
Transverse
- Clavicle
Axillary Artery
The axillary artery and its relationship to the brachial plexus
- A continuation of the subclavian artery.
- It climbs over the first rib, passes over the posterior cord, & beneath the lateral and medial cords.
- The cords are named by their relationship to the axillary artery (specifically the 2nd portion of it):
- Lateral cord lies lateral.
- Posterior lies posterior.
- Medial lies medial.