Upper Limb. Brachial Plexus Part 2 CORDS
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00:00Brachial plexus, the cords and their branches. These cords will be found in the axilla having
00:10some branches and they are three in number named according to the relation they are having
00:15with the axillary artery running in the axilla. One of the cord is lateral to the artery hence
00:20called lateral cord, one is medial so medial cord and one of them is running posterior
00:24to the axillary artery hence called as the posterior cord of brachial plexus. Now regarding
00:30their branches, the medial cord of brachial plexus will continue medially and contribute
00:35to the ulnar nerve running with the ulnar bone whereas the lateral cord of brachial
00:39plexus contributes to musculocutaneous nerve, the nerve of the anterior arm and when it
00:44comes to the posterior cord of brachial plexus, lying posterior to axillary artery contributes
00:50to radial nerve which passes posterior to the humerus bone and supplies the muscles
00:54of posterior arm. As the name is suggesting this radial nerve is going to follow the radius
01:00bone laterally. Then we have got some more branches to discuss contributed by these cords
01:05and for that purpose we need to look at some more diagrams. As we understand the brachial
01:10plexus is having five components that is the roots, trunks, divisions, cords and branches.
01:17When it comes to the roots and trunks they are found in the neck region. There are five
01:22roots which are contributing in various combinations for the three trunks in the neck region upper,
01:28middle and lower. Now each trunk is giving one anterior one posterior division so totally
01:33there will be three anterior and three posterior divisions total six divisions which are passing
01:39behind the bone clavicle. So these divisions which are six in number three anterior three
01:45posterior they pass behind the bone clavicle to enter the axilla and contribute to three
01:50cords of brachial plexus which will be giving certain branches in the axilla. So our focus
01:56should remain on the three cords of brachial plexus in the axilla how they are contributed
02:01by the divisions and then we can see what are the terminal branches they are going to
02:06give. Now coming to the schematic diagram here we need to focus upon the cords in the
02:11axilla total three in number this is the lateral cord of brachial plexus and then we
02:17have got the posterior cord of brachial plexus and here is the middle cord of brachial plexus.
02:23Now how are they contributed? We have discussed this earlier as well the lateral cord of brachial
02:28plexus is contributed by the anterior divisions of the upper trunk and anterior division of
02:35the middle trunk as well whereas the anterior division of the lower trunk is going to contribute
02:40towards the medial cord of brachial plexus. Then what about the posterior divisions of
02:45these trunks? As we'll find the posterior divisions of the three trunks contribute to
02:50the posterior cord of brachial plexus as seen in the diagram this is the posterior division
02:55of the upper trunk and posterior division of the middle trunk and the posterior division
03:00of the lower trunk all these divisions are passing behind the bone clavicle to enter
03:05the axilla and contribute to the cords. Here it is the posterior cord and this posterior
03:10cord is giving us terminally the radial nerve. Radial nerve is the continuation of the posterior
03:16cord of brachial plexus contributed by posterior division of the three trunks of brachial plexus.
03:22Then what is the continuation of the lateral cord of brachial plexus? Lateral cord of brachial
03:27plexus continue as the musculo-cutaneous nerve as shown in the diagram and what about the medial
03:33cord of brachial plexus then? If we are talking about the medial cord of brachial plexus it will
03:38continue as the ulnar nerve as evident here. So ulnar nerve which is continuation of the
03:44medial cord of brachial plexus was contributed by anterior division of the lower trunk of
03:49brachial plexus comes from the root value C8 and T1 chiefly but be careful it is given by
03:57Grey's anatomy that ulnar nerve is going to have additional C7 root value as well by a
04:03different pathway. This C7 root the axons they somehow track a path and jump into the ulnar
04:10nerve so that finally ulnar nerve is maybe having the chief value C8 T1 but additionally has C7 as
04:18well that comes as MCQ. First answer should always be C8 T1 additionally C7. Now ulnar nerve is
04:25supplying chiefly the hand muscles whereas radial nerve is a nerve of posterior compartment supplies
04:31the muscles of extension in the upper lip. Musculo-cutaneous nerve is supplying some
04:35muscles in the anterior arm. What about this axillary nerve and the medial nerve how they
04:40are formed and for that purpose we need to look at the next diagram. As we mentioned the three
04:45cords of brachial plexus in the axilla are named according to their relation with the axillary
04:51artery whether they are lateral, medial or posterior to the axillary artery and we can name
04:57them here in the diagram as well. We need to zoom it a little bit and as we do that it is understood
05:04that the three cords of brachial plexus the lateral cord lying lateral to axillary artery as shown
05:10here then we have got the medial cord of the brachial plexus and the third one is the posterior
05:16cord lying posterior to axillary artery. So we need to know what are their continuations further
05:22distally and for that we need to zoom out a little bit. As we'll notice the medial cord of brachial
05:28plexus continues medially and it is passing behind the medial epicondyle to run with the medial lying
05:35bone the ulnar bone and hence accordingly called as the ulnar nerve. The ulnar nerve which is
05:41continuation of the medial cord of brachial plexus is chiefly supplying the hand muscles. Now running
05:47with the ulnar is ulnar nerve what about the radius bone? With the radius bone we have the radial nerve
05:52as is evident here. Then how the radial nerve is contributed in the axilla? As we follow the radial
05:59nerve upwards we know it has been contributed by the posterior cord of the brachial plexus. The
06:05radial nerve given in the axilla passes posterior to the humerus bone supply the extensor muscles
06:10in the arm then extensor muscles in the forearm get some branches and it follows the radius bone
06:15there. If there is a fracture mid-shaft of humerus then the radial nerve can be damaged whereas if
06:21there is a fracture on the medial epicondyle then the ulnar nerve will be damaged. What about the
06:27continuation of the lateral cord of brachial plexus that becomes the musculocutaneous nerve? As you can
06:33see here lateral cord continues as musculocutaneous nerve and supplying the muscles of the anterior
06:39arm. Let us represent the three terminal branches of the three cords of brachial plexus in this
06:45diagram as well. So here we see the lateral cord of brachial plexus running lateral to the axillary
06:51artery. What will be its continuation? As we can follow lateral cord running lateral to axillary
06:56artery continues as the musculocutaneous nerve as is evident here. Then what about the medial
07:04cord of brachial plexus? As we understand medial cord was running medial to the axillary artery
07:08and further will continue as the ulnar nerve which we can show in the diagram here. Ulnar nerve
07:15keep running as a medial nerve with the medial bone ulnar bone. And what about the posterior
07:20cord of brachial plexus? We can see the posterior cord of brachial plexus continue as the radial
07:26nerve. As is evident here the posterior cord of brachial plexus comes posterior to the axillary
07:31artery and then further will continue as the radial nerve, the nerve of the posterior compartment
07:38supplying the extensor muscles. So here we have seen the three cords of brachial plexus contributing
07:43to three major nerves. What about the median nerve? How the median nerve is formed? The median nerve
07:48actually gets contribution from both the lateral cord as well as the medial cord. You will notice
07:54in the diagram it is the lateral cord which is contributing partly to the median nerve and the
07:59other contribution is coming from the medial cord of brachial plexus. So medial cord and the lateral
08:05cord contributing to the median nerve keeps running in the midline and chiefly supplies the
08:11muscles of the anterior forearm though it is also contributing to some muscles of the hand towards
08:18the thumb side. Let us show the median nerve running in the median plane in this diagram as
08:24well. So here is the median nerve as we said running in the median plane it is being contributed by
08:30the medial cord of brachial plexus and the lateral cord of brachial plexus as well. Then what about
08:36this axillary nerve? Where is this axillary nerve is coming from? For that purpose we have to look
08:43at the further branches of the posterior cord of brachial plexus and we can draw one schematic
08:48diagram for the same ourselves as well. In this schematic diagram we'll be looking at the right
08:54axilla, the right axillary artery and the three cords of brachial plexus in relation to that. So
08:59here is the axillary artery and then we can draw the three cords as well. Lateral to the artery,
09:06lateral cord of brachial plexus shown here, medially we have got the medial cord of brachial
09:11plexus and then we can also look posterior to the axillary artery, the posterior cord of brachial
09:17plexus. This posterior cord of brachial plexus passing posterior to the artery will continue as
09:23the radial nerve which you can show here. Then what about the lateral and medial cord? Let us look at
09:29them as well. The lateral cord continues as the muscular cutaneous nerve as we have mentioned
09:35earlier supplying the muscles of anterior arm whereas the medial cord of brachial plexus continues
09:41as the ulnar nerve. Now what about the medial nerve? How was it contributed? The medial nerve which
09:46runs in the midline has contribution from the lateral cord as well as the medial cord of brachial
09:51plexus and as you see this is the contribution from lateral cord, here we have got the medial
09:57cord and the formation of medial nerve which actually is found running anterior to axillary
10:02artery comparatively so this is the medial nerve. Now we wanted to know where is the axillary nerve
10:09coming from and we mentioned axillary nerve is a branch from the posterior cord of brachial plexus
10:15in fact we need to know the five branches from the posterior cord of brachial plexus one of
10:20them we have seen is the radial nerve and now we have to discuss four more branches so total
10:26five branches those five branches can be remembered by the mnemonic stars so what is the extension of
10:33this mnemonic stars here we have got one upper S and one lower S what is this upper S and lower S
10:42actually these nerves are going under the scapula bone to supply a muscle under the scapula the
10:48subscapularis muscle and since the subscapularis muscle is being supplied by upper subscapular
10:55nerve and lower subscapular nerve it becomes actually one of the hybrid muscles a hybrid
11:02muscle is the one which has more than one motor nerve supply then what about this T here? T is
11:10thoracodorsal nerve going dorsal to the thorax to supply a muscle of lower back latissimus dorsi
11:16let us write it down here so T is the thoracodorsal nerve going dorsal to thorax and supplying
11:22latissimus dorsi muscle what about this A the axillary nerve can you tell me what is this
11:28axillary nerve supplying? it will have motor and cutaneous supply it was actually supplying two
11:34muscles namely the deltoid and tereus minor the deltoid muscle being a powerful abductor at the
11:41shoulder joint and tereus minor is a lateral rotator. R is of course the radial nerve of the
11:48posterior compartment supplying the extensor muscles in the upper limb now as you see the
11:54stars here we have got upper S lower S there is a T there is a A and R is already there so stars
12:03now we need to look at their anatomical location as well in the next diagram as we focus upon the
12:10five branches of the posterior caudal brachial plexus we are looking at the right upper limb
12:15a muscle coming from the lower back the latissimus dorsi is being shown here in the diagram as it
12:20comes from the lower back it is going to insert into the floor of the bicipital groove and this
12:27latissimus dorsi muscle as it lies on the dorsum of the thorax nerve is going there to supply it
12:34hence named accordingly thoracodorsal nerve and this thoracodorsal nerve is a branch from the
12:41posterior caudal of the brachial plexus as we have seen the posterior caudal brachial plexus
12:46was contributed by posterior divisions of the three trunks of brachial plexus and these posterior
12:53divisions are passing behind the bone clavicle to enter the axilla to form the posterior caudal
12:59brachial plexus this posterior caudal brachial plexus will give us five branches the stars in
13:05which we have one upper s and lower s as well let us represent them here the upper subscapular nerve
13:11and the lower subscapular nerve they are actually sandwiching the thoracodorsal nerve so since there
13:18are two motor nerves supplying the muscle under scapula the subscapularis muscle the muscle becomes
13:24a hybrid muscle but we need to zoom this area to look at some more details as we have seen the
13:30posterior caudal brachial plexus giving upper s lower s and the t here what about the a the axillary
13:37nerve and as you notice the axillary nerve coming from the posterior caudal brachial plexus is
13:42followed by one artery the artery which is going posterior to the humerus and around the humerus
13:48that's why the name is posterior circumflex humeral artery it is a branch of the axillary artery which
13:55is also in the axilla and together with the axillary nerve it is lying in the quadrangular
14:00space as you notice here so in the quadrangular space you have got posterior circumflex humeral
14:07artery along with the axillary nerve and both of them after passing the quadrangular space go
14:13posterior to the humerus wind around the surgical neck of the humerus and that is where they are
14:20prone to injury if there is a fracture at the surgical neck of the humerus and you know deltoid
14:25muscle t-reach minor will get compromised and then you can tell about the continuation of the
14:31posterior caudal brachial plexus which is the radial nerve the radial nerve is given in the
14:36axilla then it passes posterior to the bone humerus in the radial groove and continues to sleep towards
14:43the radius bone radial nerve is the nerve of extension in the arm muscle or maybe forearm
14:49muscle and is going to work upon the joints like for elbow extension the wrist extension the mcp
14:57metacarpophalangeal joint extension so here we have located the five branches of the posterior
15:02caudal brachial plexus these stars