Hello everyone! This is Nicole from Kenhub, and welcome to our tutorial on the main nerves of the upper extremity. The first thing you might be wondering before we talked about the main nerves of the upper extremity is, what is a nerve? We'll to help you answer that, we're going to take a couple of minutes to define a nerve. A nerve is a cordlike structure that conveys information and impulses from cell bodies in the brain and spinal cord to and from the peripheral body. They are considered to be part of the peripheral nervous system or the PNS, which you can see highlighted in green on the image on the right.
A nerve acts much like a telephone cable carrying messages along a wire with its central communication center in a cell body or neuron in the brain and the spinal cord. Its affected organ or structure is located in the periphery. A nerve can therefore convey one of two types of information: Motor information – that is, impulses from the brain and spinal cord to affect the motor movement in an organ; or sensory information – that is, information collected by the peripheral body to be sent to the brain and spinal cord although they occasionally have other special functions.
As you can imagine from the image of the PNS and its peripheral nerves on the right, nerves tend to have the following physical structure: A root – that is, the point at which the nerve arises from the brain or the spinal cord so, for example, any of the points along the spinal cord here could be considered a root; a course – that is, the pathway the nerve takes throughout the body and you can see some pathways taking their roots just here; and a structure that is innervated by the nerve – that is, a structure that either receives motor instruction or sensory information so any of the structures that are along the terminal ends of these nerves.
Nerves can generally be divided into cranial nerves which originate in the brain and if you look at the image on the right of the inferior aspect of the cerebral hemispheres – brainstem and cerebellum – you can see several cranial nerves emerging from the brain and the brainstem with the vagus nerve highlighted in green; and spinal nerves which originate in the spinal cord and, on the right here, you can see the spinal nerves of the lower half of the body colored in yellow with the genitofemoral nerves highlighted in green.
Today, however, our focus is going to be on the spinal nerves that are associated with the upper extremity. The upper extremity is an anatomical term for the body parts that make up the upper limb. It consists of the shoulder, the forearm, the wrist and the hand and, therefore, when it comes to talking about the main nerves of the upper extremity, we’re going to be talking about the main nerves that supply structures from the shoulder to the hand.
Before we talk about the major nerves of the upper extremity, however, I want to take a little bit of time to define the brachial plexus. The brachial plexus is a nerve plexus, that is, a complex network of interlacing nerves of the neck and the axilla originating from the anterior rami of the nerves rising from the spinal cord at the level of the fifth cervical to the first thoracic vertebrae. The nerves that arise from this plexus provide innervation for the structures of the shoulder to the hand. In this image, in addition to the brachial plexus highlighted in green, you can also see the cervical plexus above it in yellow.
The brachial plexus can be divided into a supraclavicular part – that is, a part that lies superior to the clavicle; and an infraclavicular part – that is, the part that lies inferior to the clavicle. But we’ll talk about these parts a little bit later on as for the moment I want to talk a little bit about the various levels of the brachial plexus and their branches.
In addition to dividing the brachial plexus into a supraclavicular part and an infraclavicular part, the brachial plexus as we mentioned can be divided into several levels of branches coming together to form the nerves of the upper extremity. So as you can see in the image, the brachial plexus is first formed by the roots which we mentioned in the previous slide, and of course, these roots come together to form the trunks which then form divisions before finally moving on to form cords which then go on to form the nerves that innervate the structures of the upper extremity.
Now that you’ve seen how the branches form from root to nerve, let’s go back a bit and explain exactly what we’re seeing there. So going back to our image of the roots, you can see the nerve roots numbered C5 to T1 just here and of course just for completion sake, let’s list them all – C5, C6, C7, C8 and T1. And I just wanted to point out that these nerve roots are actually the anterior rami, that is, the anterior branch of the nerve arising from the spinal cord at the level of these vertebrae. So when we refer to the roots of C5 and so on throughout the tutorial, just remember that we’re referring specifically to the anterior branches of these roots.
Our next level down as we mentioned above are the trunks and as you can see, there are three trunks – the superior trunk made up of the roots of C5 and C6, a middle trunk which is made up of the root of C7, and an inferior trunk which is made up of the roots of C8 and T1. These trunks are found in the lower part of the neck and superior to the clavicle. After passing behind the clavicle, the trunks then unite to form divisions as you can see in this image. The two divisions can be divided into an anterior division which supply the anterior compartments of the upper extremity and a posterior division which supply the posterior compartments of the upper extremity. And of course finally as you can see, the divisions then come together to form three cords – a lateral cord, a medial cord and a posterior cord – and these cords are named in relation to the axillary artery.
As we mentioned, the brachial plexus can also be divided into a supraclavicular part and an infraclavicular part. For the moment, we’re going to be focused on the branches of the infraclavicular part which we’ll talk through over the next slides.
As we mentioned, the terminal branches or the peripheral nerves are formed from the branches of the three cords. These terminal branches make up the bulk of the infraclavicular part will be the focus of our tutorial from now on. As you can see, there are five terminal branches – the musculocutaneous nerve, the median nerve, the ulnar nerve, the radial nerve, and the axillary nerve – and we’ll talk through these branches over the next few slides. In addition to the above five nerves, we’re also going to change a little and tell you a little bit about the superior subscapular nerve and the inferior subscapular nerve as they are significant branches emerging from the posterior cord.
The first major terminal branch of the brachial plexus and the terminal branch of the lateral cord is the musculocutaneous nerve. As you can tell from the image, the musculocutaneous nerve carries fibers from the roots of C5, C6 and C7. In terms of its course, I’m just going to show you this image so you can imagine it a bit more clearly. As it’s descending down the arm, you can see that the nerve is piercing the coracobrachialis muscle then descending between the brachialis and biceps brachii muscles before continuing as the lateral cutaneous nerve of the forearm which you can see a bit more clearly in this image on the right. And as you’ll be able to get from its course, the musculocutaneous nerve innervates the muscles of the anterior compartment of the arm as well as the skin of the lateral aspect of the forearm by the lateral cutaneous nerve.
The median nerve as you can see in the image arises from both the lateral and medial cords. With regards to its nerve contributions, it carries fibers from all five roots – C5 to T1. However, do note that the lateral root of the median nerve more specifically is the terminal branch of the lateral cord and therefore C6 and C7 while the medial root of the median nerve is the terminal branch of the median cord and that is C8 and T1. The median nerve does not give off any branches in the arm which you can see in this image just here. And though it’s a bit difficult to imagine in this image, the nerve’s pathway includes the nerve descending lateral to the brachial artery before entering the forearm via the cubital fossa and then finally entering the hand at the carpal tunnel.
There are also a couple of major branches that are worth talking about with regards to the median nerve. In the forearm, the median nerve gives off the anterior interosseus nerve and the palmar cutaneous branch, while in the carpal tunnel, the median nerve divides into the recurrent branch as well as common and proper palmar digital nerves. The median nerve also gives off muscular branches to the pronator teres as it passes the elbow. And finally, the median nerve supplies the muscles of the anterior compartment of the forearm except the flexor carpi ulnaris and the ulnar part of the flexor digitorum profundus, the thenar and intrinsic hand muscles, and the skin of the palmar aspect of the lateral three and a half fingers.
The ulnar nerve is a large terminal branch arising from the medial cord carrying fibers from C8 to T1 and from time to time C7. Like the median nerve, the ulnar nerve gives no branches in the upper arm and as you can see in this image, it has a fairly long course traversing the whole arm and hand. In the arm, the ulnar nerve descends through the medial arm to pass behind the medial epicondyle of the humerus which you can see here in this image. In the forearm, the ulnar nerve descends along the ulnar aspect. The ulnar nerve then enters the hand superficial to the flexor reticulatum where it divides into the dorsal branch of the ulnar nerve and the palmar branch of the ulnar nerve which as you can see divides quickly into a deep branch of the palmar branch of the ulnar nerve and the superficial branch of the palmar branch of the ulnar nerve. And of course the ulnar nerve supplies the flexor carpi ulnaris and the ulnar half of the flexor digitorum profundus within the forearm, the hypothenar muscles and the intrinsic muscles of the hand, and the skin of the medial one and a half fingers.
The radial nerve is the largest branch of the brachial plexus and the larger branch of the posterior cord. As you can see, the radial nerve arises from the roots C5 to T1. The radial nerve as we can see in this posterior view emerges from the axilla to run posterior to the axillary artery which we can see in our image just here to then pass behind the humerus as you can see in this image before passing anterior to the elbow and dividing into two branches. And of course we want to briefly mention these branches which are the deep branch which you can see running along here in this section of the radial nerve inferior to the elbow and the deep branch becomes the posterior interosseus nerve around about here; and the superficial branch which enters the hand to give off the dorsal digital branches which are not visible in this image but they run along the dorsal aspect of the first three and a half fingers along with the dorsal digital arteries.
And last but not least, the radial nerve innervates the muscles of the posterior compartments of the arm and forearm, the skin of the posterior and inferolateral arm and the posterior forearm, and the skin of the dorsal aspect of the lateral three and a half fingers.
The axillary nerve is the terminal branch of the posterior cord and as you can see in the image, it carries fibers from C5 and C6. And of course, we can see its course a little more clearly in this ventral image of the axillary nerve as the nerve enters the quadrangular space before wrapping around the surgical neck of the humerus. And you can see this pathway a little more clearly in this dorsal image of the axillary nerve and some of its associated structures such as the posterior humeral circumflex artery that travels with it. In terms of its major branches, the axillary nerve gives rise to the superior lateral brachial cutaneous nerve which you can see just here. The superior lateral brachial cutaneous nerve is also the terminal branch of the posterior cord. And of course the axillary nerve provides innervation to several structures including the glenohumeral joint, the teres minor and deltoid muscles and the skin overlying the deltoid muscle.
And as we mentioned, we're just going to sneak in a couple more branches of the posterior cord even though they're not part of the five terminal branches of the brachial plexus as these branches give off some important nerves. And the nerves we're going to talk about in this part of the tutorial are the two subscapular nerves – a superior and an inferior one. Let's begin as always with the superior one.
The superior subscapular nerve also known as the upper subscapular nerve arises from the posterior cord and carries fibers from C5. And as you see in this image as it's a side branch of the posterior cord, its course is relatively short traveling posteriorly from the brachial plexus. And as you can probably guess, the superior subscapular nerve has no further branches and instead supplies the superior part of the subscapularis muscle.
The inferior subscapular nerve also known as the lower subscapular nerve arises as a side branch of the posterior cord and carries fibers from C6. Similar to the superior subscapular nerve, the inferior subscapular nerve has a short course running inferior and lateral to the brachial plexus and gives off a single branch to the teres major muscle which I'm pointing out with my arrow just here. The inferior subscapular nerve innervates the inferior part of the subscapularis muscle as well as the teres major muscle. And just to give you a sense of how the superior and inferior subscapular nerves come together as a whole, I just want to show you this image which is a ventral view of the two nerves emerging from the brachial plexus as well as the subscapularis muscle and the scapula amongst other structures. And in this image, you can see the superior subscapular nerve as it innervates the superior portion of the subscapularis muscle as well as the inferior subscapular nerve innervating the lower half of the subscapularis as well as the teres major.
As we mentioned earlier in the tutorial, the brachial plexus can be divided into a supraclavicular part and an infraclavicular part and for most of the tutorial we discussed the infraclavicular part. Now, however, I'd like to talk very briefly about the supraclavicular part and some of its major branches.
The supraclavicular part of the brachial plexus as we mentioned is made up of nerves that arise in the brachial plexus superior to the clavicle although there are several nerves that arise from this region. Today we're just going to briefly mention the four branches that arise from the trunks and the roots of the brachial plexus itself – that is, the dorsal scapular nerve, the long thoracic nerve, the suprascapular nerve and the subclavian nerve. There are other branches that arise from the brachial plexus, however, they arise from a combination of various roots. For the purpose of this tutorial, we're going to finish off by focusing on only one of these nerves – the suprascapular nerve.
The suprascapular nerve as you can see in the image is a nerve that arises from the superior trunk and carries fibers from C5 and C6. To help you visualize the course of this nerve a little bit, I'm just going to show this image here of the suprascapular nerve from a posterior view where you can see the nerve in relation to the skeleton and as you can see, it's basic pathway is descending inferolaterally across the posterior triangle of the neck to pass through the scapular notch to enter the supraspinous fossa. And in this image, you can see more clearly how the nerve interacts with the structures it innervates. As you can probably guess from looking at the image, the suprascapular nerve innervates the supraspinatus muscle and the infraspinatus muscle and the acromioclavicular joint and the glenohumeral joint. It's important not to confuse this nerve with the superior or inferior subscapular nerve which we talked about in previous slides.
And that's it for this basics tutorial. Thanks for watching.
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