Anatomy of the brachial plexus

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Introduction0:00–0:40

Have you ever fallen asleep with your shoulder in a weird position only to wake up with your arm completely asleep or hit the inside of your elbow, the famous funny bone and cause part of your hand to go numb.
This happens when we compress or bang the nerves found in our arms, all of which originate in the brachial plexus. The brachial plexus is a vast network of nerves originating from the anterior ami of C five to T one which extends through the axilla into the shoulder arm and hand, providing efferent or sensory nerve fibers from the skin as well as efferent or motor nerve fibers to the muscles.
All right. So the brachial plexus is divided into five roots, three trunks, six divisions, three cords and five terminal branches.

Parts of brachial plexus0:40–1:23

The order can be remembered using the mnemonic, remember to drink cold beer. Additionally, there are branches that leave the brachial plexus at various points along its length.
Since the branches that come off of the roots and trunks are located above the clavicle, they are sometimes called the supraclavicular branches of the brachial plexus.
And since the branches that come off of the cords, as well as the terminal branches are located below the clavicle. They're sometimes called the infraclavicular branches of the brachial plexus.
Ok. So, starting with the roots, the five roots come from the anterior rami of the last four cervical nerves, C five through C eight.

Roots1:23–2:13

As well as the anterior ramus of the first thoracic nerve or t one. These roots usually travel between the anterior and middle scaling muscles along with the subclavian artery.
These five roots give off some branches. The long thoracic nerve which arises from C five to C seven and gives motor innervation to the serratus anterior muscle.
The dorsal scapular nerve from C five which gives motor innervation to the rhomboid and levator scapulae muscles. And a contribution to the phrenic nerve from C five, which gives motor and sensory innervation to the diaphragm at the inferior part of the neck.

Trunks2:13–3:02

The five roots combined to form three trunks. C five and C six merge to form the superior or upper trunk.
C seven remains as the middle trunk and C eight and T one merge to form the inferior or lower trunk. The superior trunk gives off another branch.
The suprascapular nerve which travels across the posterior triangle of the neck, which we can see here highlighted in blue and through the scapular notch to give motor innervation to the supraspinatus and infraspinatus muscles.
The superior trunk also gives off the nerve to subclavius which gives motor innervation to the subclavius muscle. Ok.

Quiz3:02–3:17

Now that we've gone over the roots, trunks and the supraclavicular branches. Let's pause and do a quick quiz, pause a video and see if you can identify them.
Moving on each trunk splits into an anterior and a posterior division as they travel through the cervicoaxillary canal or the apex of the axilla, giving rise to a total of six divisions, think of it as traveling through a wormhole.

Divisions and Cords3:17–5:11

And on the other side, the six divisions regroup with each other to form three chords. The cords are named for their relationship to the second part of the axillary artery.
So lateral to the axillary artery, there's a lateral cord which is formed by the anterior divisions of the superior and middle trunks, posterior to the axillary artery.
There's you guessed it, the posterior cord formed by the posterior divisions of the superior, middle and inferior trunks and medial to the axillary artery.
There's a medial cord formed by the anterior division of the inferior trunk, no surprises there. Now, these cords sprout a number of branches.
The lateral cord gives rise to the lateral pectoral nerve which gives motor innervation to the pectoralis major muscle and also the pectoralis minor muscle via a communicating branch to the medial pectoral nerve.
The posterior cord gives rise to the upper and lower subscapular nerves which give motor innervation to the subscapularis and the subscapularis and teres major muscles respectively.
There's a thoracodorsal nerve sometimes called the middle subscapular nerve which gives motor innervation to the latissimus dorsi muscle.
Next, the medial cord gives rise to the medial cutaneous nerve of the arm and the medial cutaneous nerve of the forearm, which gives sensory innervation to the medial skin of the arm and forearm.
And more proximately, there's a medial pectoral nerve which gives motor innervation to the pectoralis minor and major muscles.
And finally, the three cords give rise to the five terminal branches. The median nerve is formed by contributions from both the lateral and medial cords and is made up of fibers from C five to T one.

Terminal branches5:11–6:57

The other terminal branch of the lateral cord is the musculocutaneous nerve which receives contributions from C five to C seven in the axilla.
The median nerve is anterior to the axillary artery. The musculocutaneous nerve quickly exits the axilla by piercing the Caraco brachialis muscle.
The posterior cord divides into two terminal branches which are the axillary nerve, which is made up of contributions from C five and C six.
And the radial nerve which is made up of contributions from C five to T one. The axillary nerve travels with the posterior circumflex humeral artery, which is one of the branches of the third part of the axillary artery and exits the axilla through the quadrangular space to travel around the surgical neck of the humerus.
The radial nerve passes posterior to the axillary artery to exit the axilla and travel in the spinal groove of the humerus finally, the medial cord gives rise to two terminal branches, the medial contribution to the median nerve and the ulnar nerve, which is made up of fibers from C eight T one and occasionally C seven.
I think you'll agree that the brachial plexus can be pretty overwhelming. So one tip for orienting yourself and finding those terminal branches is to look for the letter M that is formed by the musculocutaneous nerve laterally, the ulnar nerve medially and the median nerve in the middle.
All right, we're almost there now that we've gone over the divisions, cords and terminal branches. Let's go ahead and do another quiz.

Quiz6:57–7:13

See if you can identify the cords and their branches as well as the terminal branches. Since the terminal branches of the brachial plexus, each have many motor and sensory functions.

Median nerve7:13–8:09

Let's go ahead and summarize them here, starting at the shoulder joint and moving our way down towards the fingertips. First, the median nerve gives motor innervation to the muscles of the anterior forearm, except for flexor carpi, ulnaris and the ulnar or medial half of flexor digitorum profundus.
In the hand, it innervates the thenar muscles which act on the thumb and the lateral lumbrical. It also carries sensory innervation from the skin of the hand.
On the palmer side, it innervates the lateral 3.5 digits and the adjacent palm on the dorsal side, it innervates the distal aspects of the lateral 3.5 digits the musculocutaneous nerve gives motor innervation to the muscles of the anterior arm.

Musculocutaneous nerve8:09–8:25

It then continues as the lateral cutaneous nerve of the forearm to supply sensory innervation to the lateral side of the forearm.
The axillary nerve carries motor innervation to the teres minor and deltoid muscles. It also carries sensory information from the glenohumeral joint or shoulder joint and the skin covering the inferior portion of the deltoid.

Axillary nerve8:25–8:49

This area of skin innervated by the axillary nerve is also known as a Sergeant's patch. The radial nerve gives motor innervation to all of the muscles of the posterior arm and forearm.

Radial nerve8:49–9:13

It also provides sensory innervation to the skin of the posterior arm and forearm. In the hand, it only supplies sensory innervation on the dorsal side.
Here, it innervates the lateral hand, the thumb and the proximal second to fourth digits. And finally, the ulnar nerve carries motor information to the flexor carpi ulnaris and the ulnar half of the flexor digitorum profundus.

Ulnar nerve9:13–10:10

In the hand, it innervates most of the intrinsic muscles except for a couple that are innervated by the median nerve just like the median and radial nerves.
It also carries sensory information from the skin of the hand. On the palmer side.
It supplies the medial 1.5 digits and the adjacent palm on the dorsal side. It also innervates the medial 1.5 digits and the adjacent skin of the hand.
Let's take one more pause here before we recap. Here's a picture of the palmar and dorsal sides of the hand.
Can you remember which nerves carry sensory information from each region? All right.

Review10:10–10:47

As a quick recap, the brachial plexus originates from C five to T one. These five roots combine to form three trunks.
Each trunk splits into an anterior and a posterior division for a total of six divisions which then regroup with each other and form three chords.
Finally, the cords divide and give rise to five terminal branches which are the musculocutaneous nerve, the axillary nerve, the radial nerve, the median nerve and the ulnar nerve.