The Brachial Plexus

List the four plexuses (or three if 3 and 4 are considered a singular plexus) that arise from the spinal cord.

1. Cervical plexus; 2. Brachial plexus; 3. Lumbar plexus; and 4. Sacral plexus. (Lumbosacral plexus if singular)

How does each trunk terminate?

Each trunk terminates by dividing into an anterior and posterior division.

Give the root values for each of these 3(4) plexuses.

Cervical: C1-C4. Brachial: C5-T1. Lumbar plexus: T12/L1-L4. Sacral plexus: L5-S5.

Name the three branches from the lateral cord and indicate what they innervate.

Branches from the lateral cord: lateral pectoral n. (C5,6,7): pectoralis major m.; musculocutaneous n. (C5,6,7): motor to the muscles of the flexor compartment of the arm (and sensory to lateral aspect of the forearm); lateral root of the medial nerve (C6,7): joins to form the median n.

Name the branches of the medial cord cord and indicate what they innervate.

Branches from the medial cord: medial pectoral n. (C8,T1): pectoralis minor m.; medial cutaneous n. of the arm and medial cutaneous n. of the forearm: sensory to these regions; medial root of the median nerve (C8,T1): joined by lateral cord to form median which is motor to mm. of the forearm; ulnar nerve (C8,T1): supplies mm. and skin of the forearm (terminal br. of the medial cord).

Name the branches of the posterior cord cord and indicate what they innervate.

Branches from the posterior cord: upper and lower subscapular nn. (C5,C6): subscapularis and teres major mm.; thoracodorsal n. (C6,7,8): latissimus dorsi m.; axillary n. (C5,6): deltoid and teres minor mm. + lateral cutaneous innervation of arm.; radial nerve (C5-8,T1): in axilla gives branches to the triceps brachii and anconeus, passes into forearm - it is the terminal branch of the posterior cord.

List the branches off the roots of the brachial plexus and what each innervates.

Branches from the roots: dorsal subscapular n. (C5): levator scapulae, rhomboideus major and minor; long thoracic n. (C5,6,7): serratus anterior.

Name the branches of this/these trunk(s) and what they innervate.

Branches from the upper trunk: suprascapular n. (C5,6): supraspinatus and infraspinatus mm.; n. to the subclavius (C5,6): subclavius m.

How are the cords of the plexus named?

For their relationship to the axillary artery.

What three nerves form the M over the surface of the axillary artery?

Musculocutaneous, median and ulnar nn.

Which of the three trunks exhibits branches?

Only the upper trunk gives rise to branches.

Identify the anatomical region where you would find the following portions of the brachial plexus: roots, trunks, divisions, and cords.

Roots: prevertebral musculature. Trunks: posterior triangle. Divisions: behind clavicle. Cords: in axilla.

List the three trunks of the brachial plexus.

Superior, inferior and middle trunks.

What is the relationship of the axillary vein to the axillary artery?

The axillary v. is superficial (inferiorly) to the axillary artery.

What is the relationship of the median nerve to the axillary artery?

The median nerve lies superficial (anteriorly) to the axillary artery.

How is each of the cords of the brachial plexus formed?

The posterior cord is formed by the fusion of all 3 posterior divisions; the lateral cord is formed by the fusion of the upper two anterior divisions; the medial cord forms from the remaining anterior division from the lower trunk.

What is the relationship of the radial nerve to the axillary artery?

The radial nerve lies posterior to the axillary artery.

How are the trunks of the brachial plexus formed?

The roots fuse to form trunks.

List the various trunks and what forms each one.

The roots of C5 and C6 unite to form the superior trunk; the root of C7 continues to become the middle trunk; and the lower two roots (C8 and T1) unite to form the inferior trunk.

Which division of a spinal nerve forms the roots of the brachial plexus.

The ventral rami.

Which component of the spinal nerve is responsible for the formation of a plexus (ie. brachial plexus)?

The ventral ramus

How do these trunks get their anatomical names?

They are named for their anatomical relationship to one another.

What happens to the dorsal rami of these spinal nn.?

They remain segmental (dorsal rami always remain segmental).