Brachial Plexus

Question 0

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

Answer 0

1) Brachial C5-T1
2) Cervical C1-C4
3) Lumbar T12/L1-L4
4) Sacral L5-S5

Question 1

Which component of the spinal nerve is responsible for the formation of a plexus (ie. brachial plexus)? What happens to the dorsal rami?

Answer 1

The ventral ramus. The dorsal rami remain segmental

Question 2

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

Answer 2

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

Question 3

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

Answer 3

The ventral rami

Question 4

List the three trunks of the brachial plexus. How are they formed? What are they named after?

Answer 4

Superior, middle, inferior trunks. The roots fuse to form trunks. Named for their anatomical relationship to one another.

Question 5

List the various trunks and what forms each one.

Answer 5

Superior: roots of C5 and C6
Middle: continuation of the root of C7
Inferior: roots of C8 and T1

Question 6

How does each trunk terminate?

Answer 6

Each trunk terminates by dividing into the anterior and posterior divisions.

Question 7

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

Answer 7

Posterior: fusion of all 3 posterior divisions
Lateral: fusion of upper 2 anterior divisions
Medial: remaining lower trunk anterior division
They are named for their relationship to the axillary artery.

Question 8

List the branches off the roots of the brachial plexus and what each innervates. Which of the three trunks exhibits branches?

Answer 8

Dorsal scapular: levator scapulae, rhomboid major, rhomboid minor
Long Thoracic: serratus anterior

Only the upper superior trunk gives rise to branches

Question 9

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

Answer 9

Upper trunk: suprascapular n. (supraspinatus m. & infraspinatus m.) and the nerve to the subclavis (subclavius m.)

Question 10

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

Answer 10

1) Lateral pectoral n. –> lateral pectoral m.
2) musculocutaneous n. –> motor to muscles of flexor compartment of arm / sensory to lateral aspect of forearm
3) lateral root of medial nerve –> joins to form median n.

Question 11

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

Answer 11

1) Medial pectoral n. –> pectoralis minor & pectoralis major
2) Medial cutaneous n. to arm
3) Medial cutaneous n. to forearm
- ->these both supply sensory to the region
4) Medial root of median nerve –> joined by lateral cord to form median n. (motor to forearm muscles)
5) Ulnar nerve –> supplies muscle and skin of forearm.

Question 12

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

Answer 12

1) Axillary –> deltoid & teres minor, lateral cutaneous innervation of arm
2) Radial –> in axilla gives branches to teh triceps brachii and anconeus, passes into forearm
3) Upper subscapular
4) Lower subscapular
- -> both innervate subscapularis and teres major
5) Thoracodorsal–> latissimus dorsi m.

Question 13

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

Answer 13

1) Musculocutaneous
2) Median
3) Ulnar

Question 14

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

Answer 14

Axillary vein is superficial (inferiorly) to the axillary artery.

Question 15

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

Answer 15

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

Question 16

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

Answer 16

The radial nerve lies posterior to the axillary artery