Nerves - Brachial Plexus

Question 1

What is the brachial plexus?

Where does it originate?

Answer 1

It is a network of nerve fibres that supplies the skin and musculature of the upper limb.

It begins in the root of the neck.

Question 2

Which spinal segments contributes to the brachial plexus?

The brachial plexus can be divided into five parts…

Answer 2

The anterior rami of the C5, C6, C7. C8 and T1 spinal nerve roots.

Pneumonic: Read That Damn Cadaver Book.

R - roots

T - trunks

D - divisions

C - cords

B - branches

Question 3

Roots

Answer 3

At each vertebral level paired spinal nerves arise from the intervertebral foramina.

These spinal nerves then divides into an anterior and posterior ramus.

The roots of the brachial plexus arises from the anterior ramus of the spinal nerves

Note on the posterior ramus: it innervates the skin and muscles of the intrinsic back muscles.

These nerves then pass between the anterior and medial scalene muscles to enter the base of the neck.

Question 4

Trunks

Answer 4

The roots of the brachial plexus then converge to form the trunks and are named depending on their relative location:

1) Superior trunk - C5 and C6
2) Middle trunk - C7
3) Inferior trunk - C8 and T1

The trunks traverse laterally passing the posterior triangle.

Question 5

Divisions

Answer 5

Each trunk divides into two branches - anterior and posterior - within the posterior triangle.

The anterior branch moves towards the front of the body.

The posterior branch moves towards the back of the body.

Therefore we have 3 anterior branches and 3 posterior branches. They pass into the axilla, where they recombine into cords of the brachial plexus.

Question 6

Cords

Answer 6

From the anterior and posterior divisions, we have 3 cords, named by their relative position from the axillary artery:

1) Lateral cord - formed by the:
- anterior division of the superior trunk
- anterior division of the middle trunk
2) Posterior cord - formed by the:
- posterior cord of the superior trunk
- posterior cord of the middle trunk
- posterior cord of the inferior trunk
3) Medial cord - formed by the:
- anterior divison of the inferior trunk

Question 7

There are five major branches of the brachial plexus. These are…

Answer 7

1) Musculotaneous
2) Axillary
3) Median
4) Radial
5) Ulnar

Question 8

Musculotaneous

Roots?

Motor?

Sensory?

Answer 8

Roots - C5, C6. C7

Motor - brachialis, biceps brachii, coracobrachialis

Sensory -

• lateral cutaneous branch of the forearm - lateral half of the anterior forearm.
• lateral portion of the posterior forearm.

Question 9

Axillary

Answer 9

Roots - C5, C6

Motor - teres minor, deltoids

Sensory -

• superior lateral cutaneous nerve - inferior region of the deltoid (regimental badge area)

Question 10

Median nerve

Answer 10

Roots - C6, C7, C8, and T1

Motor - most flexor muscles of the forearm, thenar, two lateral lumbricals associated with the index and middle fingers.

Sensory -

• palmar cutaneous branch - lateral part of the palm
• digital cutaneous branch - lateral 3 and a half fingers - palmar side

Question 11

Radial nerve

Answer 11

Roots - C5, C6, C7. C8, T1

Motor - triceps brachii, posterior compartment of the forearm (primarily the extensors of the wrist and fingers).

Sensory -

• Posterior aspect of the arm and forearm and posterolateral aspect of the hand

Question 12

Ulnar nerve

Answer 12

Roots - C8 and T1

Motor - muscles of hand (except thenar and lateral lumbricals), flexor carpi ulnaris, and medial half of flexor digitorum profundus.

Sensory -

• anterior and posterior surfaces of the medial 1 and a half fingers - palmar surface.

Question 13

Practical relevance: dissection of brachial plexus

Answer 13

It can be diffucult to find the brachial plexus on a specimen.

It’s important to look for an ‘M’ shape, formed by the musculotaneous, median and ulnar nerves, usually superficial to the axillary artery.

You can then work backwards to figure out where the cords and divisions are.