First, an overview. Think of it like this.
The 5 Rami become 3 Trunks, the 3 Trunks become 6 Divisions, the 6 Divisions become 3 Cords, the 3 Cords become 6 Branches. The 5 Rami are C5, C6, C7, C8, and T1. The 3 Trunks are Upper, Middle and Lower, going superiority to inferiority, e.g. C5 and C6 merge to form the Upper Trunk. The 6 Divisions are not named (note: in the body 3 are more anterior and 3 are more posterior). The 3 Cords are really important for naming, as labeled above, the Posterior, Lateral, and Medial Cords, so named again due to their location relative to the axillary artery.
Branches (memorize all of this, if you are not familiar with the muscles, google it or wait for an upcoming post)
Off the Rami:
1. Long Thoracic Nerve (C5,C6,C7)- Innervates the Serratus Anterior
2. Dorsal Scapular Nerve (C5)- Innervates the Rhomboid Major, Rhomboid Minor, and Levator Scapulae (all back muscles)
Off the Upper Trunk:
1. Suprascapular Nerve (C5,C6)- Innervates the Supraspinatus and Infraspinatus (back muscles)
2. Subclavius Nerve (C5, C6)- Subclavius (essentially a useless muscle)
Off the Lateral Cord:
1. Lateral Pectoral Nerve (C5,C6,C7)- Innervates Pectoralis Major (clavicular portion)
2. Musculocutaneous Nerve (C5,C6,C7)- Innervates Biceps, Coracobrachialis, Brachialis and does sensory (like all nerves that ends in -cutaneous)
3. Lateral head of Median (C5,C6,C7)
Off the Medial Cord:
1. Medial Pectoral Nerve (C8, T1)- Innervates Pectoralis Minor and Pectoralis Major (sternocostal)
2. Medial head of Median (C8, T1)
3. Ulnar Nerve (C8, T1)- Innervates stuff in the arm, also is the 'funny bone' you hit when you strike your elbow.
4. Medial Brachial Cutaneous Nerve (C8, T1)- Sensory in arm
5. Medial Antebrachial Cutaneous Nerve (C8, T1)- sensory in arm
Off the Posterior Cord:
1. Radial Nerve (C5,C6,C7,C8,T1) - Lots of stuff in the arm
2. Axillary Nerve (C5,C6)- Innervates the Deltoid and the Teres Minor muscles
3. Thoracodorsal (C6,C7,C8)- Innervates the Latissimus Dorsi muscle.
4. Upper Subscapular (C5,C6)- Innervates the upper part of the subscapularis
5. Lower Subscapularis (C5,C6)- take a guess... lower part of the subscapularis.
Practice drawing it, youtube has some good videos (https://www.youtube.com/watch?v=gTas7ijp0YE). Remember to practice both sides!!!
More information- locations and arterial relations. Rami and Trunks are found in the Posterior Triangle of the Neck and are associated with the Subclavian Artery. Divisions are found behind the clavicle and are associated with the Subclavian and the 1st Part of the Axillary Artery. Cords are in the Axilla and associated with the 2nd part of the Axillary Artery. Branches are in the Axilla and associated with the 3rd part of the Axillary Artery.
###The Key Landmark in all this is the large capital M formed by the medial cord, lateral cord, and terminal branches. On a practical you should always find the M, orient yourself, and trace back/fore wards from there.
Brachial Plexopathy: What can go wrong? You can have inflammation or an immune reaction, neoplasms and cancer growths, tears due to wounds, constriction by scar tissue, to name a few. Great test questions ask about someone stabbed in a certain place, or a certain group of muscles in not functioning, and you must reason out which nerve is the problem, to do that you must know it cold.
A few major pathology itemes:
-Erb's Palsy (Erb-Duschenne-Palsy) is the name when C5 and C6 are severed, most common during a difficult childbirth or someone falling awkwardly on their head/shoulder. "The signs of Erb's Palsy include loss of sensation in the arm and paralysis and atrophy of the deltoid, biceps, and brachialis muscles. The position of the limb, under such conditions, is characteristic: the arm hangs by the side and is rotated medially; the forearm is extended and pronated. The arm cannot be raised from the side; all power of flexion of the elbow is lost, as is also supination of the forearm. The resulting biceps damage is the main cause of this classic physical position commonly called "waiter's tip.""
-Klumpke Paralysis: A lower injury, generally C8 and T1, "The subsequent paralysis affects, principally, the intrinsic muscles of the hand and the flexors of the wrist and fingers The classic presentation of Klumpke's palsy is the “claw hand” where the forearm is supinated and the wrist and fingers are flexed."
Practice Test Questions, mix of my own and UofMichigan Medical School
-Answers below-
1. During a fight a man is stabbed in the lateral chest beneath the right arm. The wound does not enter the chest cavity. Physical examination reveals that the vertebral (medial) border of the patient's scapula projects posteriorly and is closer to the midline on the injured side. On return visit the patient complains that he cannot reach as far forward (such as to reach for a door knob) as he could before the injury. The nerve injured which caused these symptoms is the:
1. axillary
2. long thoracic
3. musculocutaneous
4. radial
5. suprascapular
2. Name the 3 muscles innervated by Dorsal Scapular
3. Given their respective locations, what two nerves can be damaged during excision of axillary lymph nodes?
4. A person sustains a left brachial plexus injury in an auto accident. After initial recovery the following is observed: 1) the diaphragm functions normally, 2) there is no winging of the scapula, 3) abduction cannot be initiated, but if the arm is helped through the first 45 degrees of abduction, the patient can fully abduct the arm. From this amount of information and your knowledge of the formation of the brachial plexus where would you expect the injury to be:
1. axillary nerve
2. posterior cord
3. roots of plexus
4. superior trunk
5. suprascapular nerve
5. You suspect a patient of yours has a soft tissue hematoma. He presents with winged scapulae, he has trouble fully abducting, and both scapulae are noticeably protrusive. Where could you reasonably localize the problem to and why?
6. The cords of the brachial plexus are:
1. above the clavicle, medial to the scalenus anticus (anterior scalene).
2. above the clavicle, behind the scalenus anticus (anterior scalene).
3. at or below the clavicle, closely related to the axillary artery.
4. at or below the clavicle, closely related to the axillary vein.
7. In a diving accident that severed the spinal cord below the sixth cervical vertebra, which muscle would be affected?
1.Deltoid
2. Infraspinatus
3. Latissimus dorsi
4. Levator scapulae
5. Trapezius
8. During a strenuous game of tennis a 55 year old woman complained of severe shoulder pain that forced her to quit the game. During physical examination it was found that she could not initiate abduction of her arm, but if her arm was elevated to 45 degrees from the vertical (at her side) position, she had no trouble fully abducting it. Injury to which muscle was responsible?
1. deltoid
2. infraspinatus
3. supraspinatus
4. teres major
5. trapezius
Answers (with explanations)
1. Long thoracic
Remember--an injury to the long thoracic nerve denervates serratus anterior, meaning that there will be no muscle protracting the scapula and counteracting trapezius and the rhomboids, powerful retractors of the scapula. The long thoracic nerve is derived from the nerve roots of C5-7; this nerve is particularly vulnerable to iatrogenic injury during surgical procedures because it is located on the superficial side of serratus anterior.
The axillary nerve innervates teres minor and deltoid. It wraps around the surgical neck of the humerus and is endangered by fractures of the surgical neck. If the axillary nerve was damaged and deltoid was denervated, the patient would be unable to abduct his upper limb beyond 15 to 20 degrees. The musculocutaneous nerve innervates biceps brachi, coracobrachialis, and brachialis. If this nerve was disrupted, the patient would be unable to flex her or his forearm, and have weakened arm flexion. The radial nerve innervates extensors of the forearm and triceps brachi--if this nerve was injured, the patient would no longer be able to extend forearm, but only have slightly weakened arm extension (latissimus is the powerful extensor of the arm). Finally, the suprascapular nerve innervates supraspinatus--the muscle that initiates abduction. Damage to this nerve would prevent the patient from starting to abduct her or his arm.
2. Rhomboid Major, Rhomboid Minor, and Levator Scapulae
3. Thoracodorsal and Long Thoracic
4. Suprascapular nerve
Let's take the observations one by one to break down this question. If the diaphragm is functioning normally, you know that the phrenic nerve is probably uninjured, which means that the C5 root has not been damaged. Since the scapula is not winged, there was no damage to the long thoracic nerve or the C5-7 nerve roots. Finally, since the patient cannot initiate abduction of the arm, you know that the suprascapular nerve is injured and supraspinatus has been denervated. But, the patient can abduct the arm once it is lifted to 45 degrees, so the deltoid muscle and the axillary nerve must be intact.
Taking the answer choices one by one: The axillary nerve is ok, because deltoid is functioning. The posterior cord of the brachial plexus must also be intact, since this cord gives off the axillary nerve. The roots of the brachial plexus are ok, since the phrenic nerve and long thoracic nerve (which are derived from the roots) are still functioning. The superior trunk of the brachial plexus must also be undamaged, since this trunk contributes to the posterior cord which is intact. So, this means that the injury must be to the suprascapular nerve.
5. The area of C5-C7, his long thoracic nerve is affected, classically presenting with a weakened winged scapulae.
6. at or below the clavicle, closely related to the axillary artery
The cords of the brachial plexus are closely related to the axillary artery, at or below the level of the clavicle. You should have seen this in the dissection--the cords were wrapped around the axillary artery. The axillary vein is anterior to the axillary artery and is not associated with the cords of the brachial plexus. As far as the scalene muscles go, you'll learn more about this in the head and neck, but know that the roots, not the cords, of the brachial plexus are the structures found between the anterior and middle scalene muscles.
7. latissimus dorsi
If the spinal cord was severed beneath the 6th cervical vertebra, all nerve roots below C6 would be affected. So, latissimus dorsi, which is innervated by the thoracodorsal nerve (C6, C7, C8) would be affected. Deltoid is suplied by the axillary nerve (C5, C6). Infraspinatus is supplied by the suprascapular nerve (C5, C6). Levator scapulae is supplied by the dorsal scapular nerve (C5). Trapezius is supplied by the accessory nerve (CN XI). All of these nerves would be intact, so these muscles would not be affected after the accident.
8. supraspinatus
Supraspinatus is responsible for initiating abduction of the arm, while deltoid is responsible for continuing abduction of the arm past the first 15 or 20 degrees. Since this patient can abduct her arm when it is lifted to 45 degrees, deltoid seems to be intact. But, she can't initiate the motion, so you know that she has probably injured supraspinatus. Infraspinatus rotates the arm laterally, and teres major rotates the arm medially. Trapezius elevates and depresses the scapula--a problem with this muscle is most evident if a patient has trouble raising the acromion of her shoulder.
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