Section 3 - Brachial Plexus

What system is the brachial plexus a part of?

Peripheral nervous system

Which spinal nerves become the interior trunk?

C8, T1

5 roots: ventral rami of C5-8 and T1 give out three nerves:

1. Dorsal scapular nerve (C5) - innervates rhomboid and levator scapulae 2. Phrenic (C3, 4, 5) - innervates diaphragm 3. Long thoracic nerve (C5, 6, 7) - innervates serratus anterior

The medial cord is formed from the continuation of the anterior division of the inferior trunk. Carries fibers from C8 and T1. Three branches:

1. Medial pectoral nerve (C8, T1) - innervates pec major and pec minor 2. Medial cutaneous nerve of the arm (medial brachial cutaneus) (C8, T1) - supplies the skin on the medial side of the arm and the superior part of the forearm 3. Medial cutaneous nerve of the forearm (medial antebrachial cutaneus) (C8 and T1) - supplies the skin on the medial side of the forearm

Which spinal nerve becomes the middle trunk?

C7

The superior trunk (from the union of C5 and C6 roots) gives out two nerves:

1. Nerve to the subclavius (C5) - innervates the subclavius 2. Suprascapular nerve (C4, 5, 6) - innervates supraspinatus, infraspinatus and glenoid joint

The posterior cord is formed by the posterior divisions of all three trunks. Carries fibers from C5 to T1. Three branches:

1. Upper subscapular nerve (C5, 6) - innervates subscapularis muscle 2. Thoracodorsal nerve (C6, 7) - supplies latissimus dorsi muscle 3. Lower subscapular nerve (C6, 7) - supplies teres major and the inferior part of the subscapularis

How many cords are in the brachial plexus?

3 (lateral, medial, posterior) *Named for relationship to axillary artery

How many trunks are in the brachial plexus?

3 (superior, middle, inferior)

How many terminal branches are in the brachial plexus?

5

How many roots are in the brachial plexus?

5 (C6-T1)

How many divisions are in the brachial plexus?

6 (each trunk divides into anterior and posterior divisions)

Brachial plexus block

A local anesthetic method when operating on the upper limb without using general anesthesia. Injection of anesthetic solution into the angle between the posterior border of the sternocleidomastoid and the clavicle. The injustion has to be into the axillary sheath containing the cords. DO NOT INJECT INTO THE VESSELS. This procedure blocks all the deep structures of the upper limb and the skin distal to the middle of the arm.

Injury of the axillary nerve

Abduction of the shoulder joint beyond the first 15 degrees, then continued abduction against resistance

5 terminal branches

Axillary - posterior cord Musculocutaneous - lateral cord Median - lateral & medial cords Radial - posterior cord Ulnar - medial cord (Most Alcoholics Must Really Urinate)

The inferior trunk is from the union of what?

C8 & T1

What is the relationship between the brachial plexus and axilla?

Brachial plexus has five terminal branches

What is the relationship between the brachial plexus and scalene muscles?

Brachial plexus travels between anterior and middle scalenes

What is the relationship between the brachial plexus and clavicle?

Brachial plexus travels under the clavicle

What is the relationship between the brachial plexus and axillary artery?

Brachial plexus wraps around the axillary artery

Which spinal nerves become the superior trunk?

C5, C6

Brachial plexus is formed by the union of the anterior (ventral) rami of which spinal nerves?

C5, C6, C7, C8, and T1

The middle trunk is a continuation of which root?

C7

Fracture of the surgical neck

Can damage the axillary nerve Common in elderly people Caused by fall on hand Fracture is stable due to ligaments surrounding the region Patient can still move the injured arm passively with little pain Identified by X-Ray or CT scan

Erb's palsy (superior part injury)

Cause - excessive separation of the head and neck, such as falling with shoulder on ground Shoulder dystocia, head delivers but baby's shoulders get stuck in birth canal. Excessive stretching baby's head away from shoulder while trying to deliver the rest of the baby. Appearance - (sneaky) waiter's tip position - the injured limb hangs by the side in medial rotation. Loss of sensation on the lateral aspect of the upper limb. Muscle paralysis - deltoid, biceps, brachialis, and brachioradialis

Brachial plexus injuries

Cause - typically injuries, sometimes cancers Presents - paralysis or anesthesia Superior part injuries (C5, 6) - Erb's palsy *more common Inferior part injuries (C8, T1) - Klumpke's Palsy *less common

Compression of cords of the brachial plexus (superior part injury)

Caused by hyperabduction of the arm - i.e., painting a ceiling. Pain running down the arm, numbness and tingling.

What is a condition associated with the root region of brachial plexus?

Cervical rib could compromise the long thoracic nerve

Root, trunk and divisions are not seen without cutting away what?

Clavicle

6 Divisions

Formed from trunks. Each trunk divides into anterior and posterior divisions resulting in six pieces of nerve fibers. There are no branches in this section. The anterior division nerves mainly innervate the muscles in the anterior region of the upper limb (the flexor muscles). The posterior division nerves mainly innervate muscles in the posterior region of the upper limb (extensor muscles).

The lateral cord is formed from the union of the anterior division of superior and middle trunks. Carries fibers from C5, 6 and 7. One branch:

Lateral pectoral nerve (C5, 6, 7) - innervates pectoralis major muscle

What does the dorsal scapular nerve innervate

Levator scapulae Rhomboids

Backpacker's Palsy (superior part injury)

Micro injury of the superior trunk of the brachial plexus due to carrying a heavy backpack. It results in sensory deficits in the distribution of the musculocutaneous nerve and radial nerve. It may also produce muscle spasms.

How are the cords of the brachial plexus named?

Named for their relationship to the axillary artery

What does the brachial plexus carry

Nerve fibers from motor neurons and autonomic nervous system (sympathetic) neurons

Variations of the brachial plexus

Prefixed brachial plexus - the plexus is formed from C4 to C8 instead of C5 to T1 Postfixed brachial plexus - the plexus is formed from C6 to T2. In this case, the inferior trunk of the plexus may be compressed by the 1st rib, producing neurovascular symptoms in the upper limb. Formation of trunks, divisions and cords may be different. Origin and combination of branches may be different However, the makeup of the terminal branches is unchanged. The median nerve may be formed from two branches of the medial cord. This is common!

Inferior part injury (C8, T1)

Sudden pull of the arm superiorly such as grasping a tree branch to stop a fall or during delivery. The short muscles of the hand are affected resulting in a "clawhand" when trying to form a fist. Klumpke's palsy similar to ulnar nerve damage

Anatomy of suprascapular nerve and artery

Suprascapular artery (army) goes over, the nerve (Navy) goes under the bridge (superior transverse scapular ligament) which covers the notch

Nerve and vessel injuries related to humerus fractures

Surgical neck - axillary nerve Radial groove (mid humeral) - radial nerve and deep arm vessels Distal end of humerus - median nerve Medial epicondyle - ulnar nerve

What travels between scalene muscles?

The root region of brachial plexus (anterior and middle) The long thoracic nerve (middle and posterior)

Anatomy of long thoracic nerve

Travels between middle and posterior scalene myscles. It is found superficial (rare for innervation of a muscle) to the serratus anterior muscle. Swimmers can have hypertrophy of middle and posterior scalene muscle that compresses and lose function of serratus anterior by overuse.