Shoulder/Brachial Plexus view

[Diane]

Here is a new series, starting with a view of the brachial plexus in situ. I haven't seen views like this before, and am loving getting in there and finding spatial orientations for these nerve origins. I'll bring more images to this thread from other views too. I have nearly all the branches mapped and will bring those images here too. Spelling mistake: that should be "intercostobrachial", not intecosto...

From Gray's, P. 813: The trunks of the brachial plexus lie in the posterior triangle of the neck in the angles between the clavicle and lower posterior border of sternocleidomastoid, where they are palpable through the skin, platysma and deep fascia.

The initial course of the radial nerve (http://www.somasimple.com/forums/showpost.php?p=31547&postcount=20) may be indicated on the posterior aspect of the arm. It passes laterally from the start of the brachial artery to the junction of the upper and middle thirds of a line between the lateral epicondyle and deltoid tuberosity, and then continues anteriorly as far as the lateral epicondyle, a finger's breadth to the lateral side of the tendon of biceps. From here its course in the forearm can be mapped out along a line descending vertically to a point on the dorsum of the wrist midway between the head of the ulna and the dorsal tubercle of the radius. The point at which the posterior interosseus nerve winds round the upper end of the radius may be indicated by placing the index finger of the contralateral hand on the dorsal aspect of the head of the radius, and aligning the middle and ring fingers below the index finger. The ring finger then lies over the posterior interosseous nerve. This is an important surgical landmark in making an incision for exposure and removal of a fractured head of radius: the incision should not extend more than a finger's breadth below the head of the radius. The terminal branches of the superficial radial nerve can be palpated in the region of the anatomical snuffbox as they pass over the tendon of extensor pollicis longus.

The median nerve (http://www.somasimple.com/forums/showpost.php?p=31549&postcount=22) is intimately related to the brachial artery throughout its course in the upper arm. Its course can be marked on the surface by a line from the medial side of the brachial artery in the cubital fossa along the midline of the forearm to the wrist.

The ulnar nerve (http://www.somasimple.com/forums/showpost.php?p=31548&postcount=21) can be palpated and rolled by the examining fingers as it passes posterior to the medial epicondyle of the humerus. In the forearm its course corresponds to a line drawn from the base of the posterior aspect of the medial epicondyle of the humerus to the radial side of the pisiform and across the hook of the hamate. Deep pressure at these bony landmarks will produce paresthesia. In the lower part of the forearm the line of the nerve lies along the radial side of the tendon of flexor carpi ulnaris medial to the ulnar artery and its venae comitantes.

[Diane]

Brachial Plexus:
Here are some more images. Three of them are simplistic schema from various anatomy books that I have color coded. The fourth is from the CD, showing the brachial plexus and its offspring in situ, a medial view. I added the color key/legend alongside.

What you'll see right away is that in situ, the whole plexus is much more complex, and the offshoots much more extensive, especially from the upper trunk (C5,6), which supplies most of the cutaneous nerves/sensation for most of the arm and some of the chest wall.

I will be bringing all these nerves here individually as well. I'm sad that most of the big, long, extensively branched cutaneous nerves are completely ignored in PT school with all the focus on only the Famous Three. I feel like I'm only just now making their acquaintance.

From P. 803, Gray's: The brachial plexus is a union of the ventral rami of the lower 4 cervical nerves and a greater part of the first thoracic ventral ramus. The fourth ramus usually gives a branch to the fifth, and the first thoracic frequently receives one from the second. These ventral rami are the roots of the plexus and are almost equal in size but variable in their mode of junction. Contributions to the plexus by C4 and T2 vary. When the branch from C4 is large, that from T2 is frequently absent and the branch from T1 is reduced, forming a 'prefixed' type of plexus. If the branch from C4 is small or absent, the contribution from C5 is reduced but that from T1 is larger and there is always a contribution from T2: this arrangement constitutes a 'postfixed' type of plexus.

Close to their exit from the intervertebral foramina, the 5th and 6th cervical ventral rami receive grey rami communicantes from the middle cervical sympathetic ganglion, ad the 7th and 8th receive grey rami from the cervicothoracic ganglion. The first thoracic ventral ramus receives a grey ramus from, and contributes a white ramus to, the cervicothoracic ganglion.

The most common arrangement of the brachial plexus is as follows: the 5th and 6th rami unite at the lateral border of scalenus medius as the upper trunk; the 8th cervical and the 1st thoracic rami join behind scalenus anterior as the lower trunk; the 7th cervical ramus becomes the middle trunk. The three trunks incline laterally, and either just above or behind the clavicle each bifurcates into anterior and posterior divisions. The anterior divisions of the upper and middle trunks form a lateral cord that lies lateral to the axillary artery. The anterior division of the lower trunk descends at first behind and then medial to the axillary artery and forms the medial cord, which often receives a branch from the 7th cervical ramus. Posterior divisions of all three trunks for the posterior cord, which is at first above and then behind the axillary artery. The posterior division of the lower trunk is much smaller than the others and contains few, if any, fibres from the first thoracic ramus. It is frequently derived from the 8th cervical ramus before the trunk is formed.

From p. 848: BRACHIAL PLEXUS LESIONS. Lesions of the brachial plexus commonly affect either the upper part of the plexus, i.e., C5 and C6 roots and the upper trunk or the lower part of the plexus, i.e., C8 and T1 roots and the lower trunk. Lesions affecting the upper part are usually traumatic, whereas those affecting the lower part may be caused by trauma but may also be produced by malignant infiltration or a thoracic outlet syndrome. Severe trauma may affect the whole plexus.

Upper Plexus Palsies: Downward traction of an infant's arm during birth, or, in adults, a severe fall on the side of the head and the shoulder, forcing the two apart, s frequently occurs in a motor cycle injury, may tear the roots of C5 and 6. This will result in paralysis of deltoid, the short muscles of the shoulder, and of brachialis and biceps. The last two are both elbow flexors, and biceps is also a powerful supinator of the superior radioulnar joint. The arm therefore hangs by the side, with the forearm pronated and the palm facing backwards,like a waiter hinting for a tip (Erb-Duchenne paralysis). There is sensory loss over the lateral aspect of the upper arm.

Lower Plexus Palsies: Upward traction on the arm, e.g., in a forcible breech delivery, may tear the lowest root, T1, which provides the segmental supply to the intrinsic muscles of the hand. The hand assumes a clawed appearance reflecting the unopposed action of the long flexors and extensors of the fingers (Klumpke's paralysis). There is sensory loss along the medial aspect of the forearm and there is often an associated Horner's syndrome (ptosis and constriction of the pupil) which occurs as a result of traction on the cervical sympathetic chain.

Malignant infiltration of the brachial plexus may result from extension of an apical lung carcinoma (Pancoast tumor) or from metastatic spread, often from carcinoma of the breast. There is slowly progressive weakness which usually starts in the small muscles of the hand (T1) and spreads to involve the finger flexors (C8). This is usually a painful condition, and the pain may be severe. There is sensory loss on the medial aspect of the forearm (T1) extending into the medial side of the hand and the little finger (C8). A Horner's syndrome may occur if there is involvement of the cervical sympathetic ganglia. A similar syndrome may occur following radiotherapy for breast carcinoma, but this is usually painless. Thoracic surgery involving a sternal split may cause traction on the brachial plexus and usually affects the lower part of the plexus. The lower trunk of the brachial plexus (C8, T1), together with the subclavian artery, may be angulated over a cervical rib (thoracic outlet syndrome). Patients may present with vascular symptoms as a result of kinking of the subclavian artery (this is more likely to occur with large bony ribs), or they may present with neurological deficit (this is more likely in patients with small rudimentary ribs which extend into a fibrous band which joins the first rib anteriorly. Cervical ribs are quite common and are rarely associated with symptoms. There is a slow insidious onset of wasting of the small muscles of the hand, which often starts on the lateral side with involvement of the thenar eminence and first dorsal interosseous. There is pain and paresthesiae in the medial aspect of the forearm extending to the little finger, and this is often aggravated by carrying shopping or suitcases. A bruit may be heard over the subclavian artery, and the radial pulse may be easily obliterated by movements of the arm, particularly with the arm extended and abducted at the shoulder.

[Diane]

Supraclavicular nerves from the Superficial Cervical Plexus:
Here is the first in a quite long series of views of individual nerves innervating the shoulder seen in rotated views. This is of the cervical plexus. Who'd have known the superficial neck nerves covered the shoulders like a little shawl? I "learned" back in school that the skin over deltoid was innervated from C5. That info seems to have been wrong - looks like it's from C4 and up, from lateral branches of supraclavicular nerves coming off the superficial cervical plexus, according to Gray's 39th edition CD.

The skin of the shoulder region is supplied by the supraclavicular nerves from the cervical plexus. The floor of the axilla and upper medial surface of the arm is supplied by the lateral branch and upper medial surface of the arm is supplied by the lateral branch of the second intercostal nerve (the intercostobrachial nerve). The lower aspect of the medial side of the upper arm is supplied by the medial cutaneous nerve of the arm. The lateral aspect of the upper arm is supplied by the upper lateral cutaneous nerve (a branch of the axillary nerve) and the lower lateral cutaneous nerve (a branch of the radial nerve). The posterior aspect is supplied by the posterior cutaneous nerve of the arm, a branch of the radial nerve.

From p. 951, Gray's: Branches of the supraclavicular nerve, which originates from the 3rd and 4th cervical nerve roots, supply the skin in the upper pectoral region. Most of the first thoracic nerve joins the brachial plexus; it gives off a small inferior branch, which becomes the first intercostal nerve.

[Diane]

Here is the suprascapular nerve.
From p. 847, Gray's: The suprascapular nerve is a large branch of the superior trunk. It runs laterally, deep to trapezius and omohyoid and enters the supraspinous fossa through the suprascapular notch inferior to the superior transverse scapular ligament. It runs deep to supraspinatus and curves round the lateral border of the spine of the scapula with the suprascapular artery to reach the infraspinatus fossa, where it gives two branches to supraspinatus and articular rami to the shoulder and acromioclavicular joints. The suprascapular nerve rarely has a cutaneous branch. When present it pierces deltoid close to the tip of the acromion and supplies the skin of the proximal third of the arm within the territory of the axillary nerve.
Lesions of the suprascapular nerve. The commonest cause involving the suprascapular nerve is neuralgic amyotrophy. An entrapment neuropathy may occur in the scapular notch or the nerve may be damaged by trauma to the scapula and shoulder. There is no pain in the shoulder and wasting and weakness of supraspinatus and infraspinatus.

[Diane]

Dorsal Scapular Nerve
From p. 846 Gray's: The dorsal scapular nerve comes from the fifth cervical ventral ramus, pierces scalenus medius, passes behind levator scapulae, which it occasionally supplies, and runs with the deep branch of the dorsal scapular artery to the rhomboids, which it supplies.

[Diane]

Upper Lateral Cutaneous Nerve of Arm

The lateral aspect of the upper arm is supplied by the upper lateral cutaneous nerve (a branch of the axillary nerve (http://www.somasimple.com/forums/showpost.php?p=31500&postcount=9)) and the lower lateral cutaneous nerve (a branch of the radial nerve). The posterior aspect is supplied by the posterior cutaneous nerve of the arm, a branch of the radial nerve.

[Diane]

Intercostobrachial nerve:

The floor of the axilla and upper medial surface of the arm is supplied by the lateral branch and upper medial surface of the arm is supplied by the lateral branch of the second intercostal nerve (the intercostobrachial nerve).

From p. 951: The lateral cutaneous branch of the second intercostal nerve supplies the skin of the axilla and is known as the intercostobrachial nerve.

[Diane]

Subscapular Nerves, superior and inferior:

From P. 847, Gray's: Upper (superior) subscapular nerve. The superior subscapular nerve is smaller than the inferior. It arises from the posterior cord (C5 and 6), enters subscapularis at a high level, and is frequently double.

Lower (inferior) subscapular nerve. The inferior subscapular nerve arises from the posterior cord (C5 and 6). It supplies the lower part of subscapularis, and ends in teres major, which is sometimes supplied by a separate branch.

[Diane]

Axillary nerve (C5, 6): Is a branch of the posterior cord of the brachial plexus. It winds posteriorly around the neck of the humerus together with the circumflex humeral vessels and supplies deltoid and teres minor and an area of skin over the deltoid region. (From Gray's p. 804) It has an upper lateral cutaneous branch (http://www.somasimple.com/forums/showpost.php?p=31478&postcount=6).

From Gray's p. 847: The axillary nerve arises from the posterior cord (C5, 6). It is at first lateral to the radial nerve, posterior to the axillary artery and anterior to subscapularis. At the lower border of subscapularis it curves back inferior to the humeroscapular articular capsule and with the posterior circumflex humeral vessels, traverses a quadrangular space bounded above by subscapularis (anterior) and teres minor (posterior), below by teres major, medially by the long head of triceps, and laterally by the surgical neck of the humerus. It divides in the space into anterior and posterior branches. The anterior branch curves round the neck of the humerus with the posterior circumflex humeral vessels, deep to deltoid. It reaches the anterior border of the muscle and supplies it, and gives off a few small cutaneous branches which pierce deltoid and ramify in the skin over its lower part. The posterior branch courses medially and posteriorly along the attachment of the lateral head of triceps, inferior to the glenoid rim. It usually lies medial to the anterior branch in the quadrangular space. It gives off the nerve to teres minor and the upper lateral cutaneous nerve of the arm at the lateral edge of the origin of the long head of triceps. The nerve to teres minor enters the muscle on its inferior surface. The posterior branch frequently supplies the posterior aspect of deltoid, usually via a separate branch from the main stem, occasionally from the superior lateral cutaneous nerve of the arm. However, the posterior part of deltoid has a more consistent supply from the anterior branch of the axillary nerve, which should be remembered when performing a posterior deltoid-splitting approach to the shoulder. The upper lateral cutaneous nerve (http://www.somasimple.com/forums/showpost.php?p=31478&postcount=6) of the arm pierces the deep fascia at the medial border of the posterior aspect of deltoid and supplies the skin over the lower part of deltoid and the upper part of the long head of triceps. The posterior branch is intimately related to the inferior aspects of the glenoid and shoulder joint capsule, which may place it at particular risk during capsular plication or thermal shrinkage procedures. (Ball et al. 2003). There is often an enlargement or pseudoganglion on the branch to teres minor. The axillary trunk supplies a branch to the shoulder joint below subscapularis.
Lesions of the axillary nerve. The commonest causes of axillary nerve lesions are trauma (dislocation of the shoulder, fracture of the surgical neck of the humerus), and neuralgic amyotrophy. There is wasting and weakness of deltoid, which is usually clinically evident, and a patch of sensory loss on the outer aspect of the arm. This can be differentiated from a C5 root lesion by finding normal function in the distribution of the suprascapular nerve.

[Diane]

Thoracodorsal nerve:
From p. 847, Gray's: The thoracodorsal nerve arises from the posterior cord (C6-8) between the subscapular nerves. It accompanies the subscapular artery along the posterior axillary wall and supplies latissimus dorsi, reaching its distal border.

[Diane]

Long Thoracic nerve: From p. 846 Gray's: The long thoracic nerve is usually formed by roots from the 5th to the 7th cervical rami, although the last ramus may be absent. The upper two roots pierce scalenus medius obliquely, uniting in or lateral to it. The nerve descends dorsal to the brachial plexus and the first part of the axillary artery and crosses the superior border of serratus anterior to reach its lateral surface. It may be joined by the root from C7, which emerges between scalenus anterior and scalenus medius, and descends on the lateral surface of medius. The nerve continues downwards to the lower border of serratus anterior and supplies branches to each of its digitations.

The long thoracic nerve is the most common nerve to be affected by neuralgic amyotrophy. Winging of the scapula may be the only clinical manifestation: it is best demonstrated by asking the patient to push against resistance with the arm extended at the elbow and flexed to 90 degrees at the shoulder.

[Diane]

Lateral Pectoral Nerve, p. 847, Gray's: The lateral pectoral nerve is larger than the medial, and may arise from the anterior divisions of the upper and middle trunks, or by a single root from the lateral cord. Its axons are from the 5th to the 7th cervical rami. It crosses anterior to the axillary artery and vein, pierces the clavipectoral fascia and supplies the deep surface of pectoralis major. It sends a branch to the medial pectoral nerve, forming a loop in front of hte first part of the axillary artery, to supply some fibres to pectoralis minor.

[Diane]

Medial pectoral nerve, from Gray's p. 847: The medial pectoral nerve is derived from the 8th cervical and 1st thoracic ventral rami and branches from the medial cord while the latter lies posterior to the axillary artery. It curves forwards between the axillary artery and vein. Anterior to the artery it joins a ramus of the lateral pectoral nerve, and enters the deep surface of pectoralis minor, which it supplies. Two or three branches pierce pectoralis minor and others may pass round its inferior border to end in pectoralis major.

[Diane]

Lower Lateral Cutaneous Nerve of the Arm, from Gray's p. 857:

The lower lateral cutaneous nerve of the arm perforates the lateral head of triceps distal to the deltoid tuberosity, passes to the front of the elbow close to the cephalic vein and supplies the skin of the lateral part of the lower half of the arm.
It is a branch of the radial nerve.

[Diane]

Medial Cutaneous Nerve of the Arm, from p. 858: The medial cutaneous nerve of the arm supplies the skin of the medial aspect of the arm. It is the smallest branch of the brachial plexus, arises from the medial cord and contains fibres from the 8th cervical and 1st thoracic ventral rami. It traverses the axilla, crossing anterior or posterior to the axillary vein, to which it is then medial, and communicates with the intercostobrachial nerve; it descends medial to the brachial artery and basilic vein to a point midway in the upper arm, where it pierces the deep fascia to supply a medial area in the distal thirds of the arm, extending on to its anterior and posterior aspects. Rami reach the skin anterior to the medial epicondyle, and over the olecranon. It connects with the posterior branch of the medial cutaneous nerve of the forearm. Sometimes the medial cutaneous nerve of the arm and the intercostobrachial nerve are connected in a plexiform manner in the axilla. The intercostobrachial nerve may be large and reinforced by part of the lateral cutaneous branch of the third intercostal nerve. It then replaces the medial cutaneous nerve of the arm and receives a connection representing the latter from the brachial plexus (occasionally this connection is absent).

[Diane]

Lateral Cutaneous nerve of the Forearm: from p. 887: The lateral cutaneous nerve of the forearm is a direct continuation of the musculocutaneous nerve (http://www.somasimple.com/forums/showpost.php?p=31544&postcount=17) as it lies lateral to the biceps tendon in the antecubital fossa. It passes deep to the cephalic vein, descending along the radial border of the forearm to the wrist. It supplies the skin of the anterolateral surface of the forearm and connects with the posterior cutaneous nerve of the forearm and the terminal branch of the radial nerve by branches which pass around its radial border. Its trunk gives rise to a slender recurrent branch which extends along the cephalic vein as far as the middle third of the upper arm, distributing filaments to the skin over the distal third of the anterolateral surface of the upper arm close to the vein. At the wrist joint the lateral cutaneous nerve of the forearm is anterior to the radial artery. Some filaments pierce the deep fascia and accompany the artery to the dorsum of the carpus. The nerve then passes to the base of the thenar eminence, where it ends in cutaneous rami. It has branches which connect with the terminal branch of the radial nerve and the palmar cutaneous branch of the median nerve. This is the one I'm getting a chance to examine these days in the anatomy lab.

[Diane]

Musculocutaneous Nerve: from p. 857 Gray's: The musculocutaneous nerve is the nerve of the anterior compartment of the arm. It gives a branch to the shoulder joint and then passes through coracobrachialis, which it supplies, emerging to pass between biceps and brachialis. It sends branches to both these muscles. In the cubital fossa it lies at the lateral margin of the biceps tendon where it continues as the lateral cutaneous branch of the forearm (http://www.somasimple.com/forums/showpost.php?p=31542&postcount=16).

The musculocutaneous nerve has frequent variations. It may run behind coracobrachialis or adhere for some distance to the median nerve and pass behind biceps. Some fibres of the median nerve may run in the musculocutaneous nerve, leaving it to join their proper trunk; frequently the reverse occurs, and the median nerve sends a branch to the musculocutaneous. Occasionally it supplies pronator teres and may replace radial branches to the dorsal surface of the thumb.

[Diane]

Medial Cutaneous Nerve of the Forearm: From p. 858: The medial cutaneous nerve of the forearm comes from the medial cord. It is derived from the 8th cervical and 1st thoracic ventral rami. At first it is between the axillary artery and vein, and gives off a ramus which pierces the deep fascia to supply the skin over the biceps, almost to the elbow. The nerve descends medial to the brachial artery, pierces the deep fascia with the basilic vein midway in the arm and divides into anterior and posterior branches. The larger, anterior branch usually passes in front of, occasionally behind, the median cubital vein, descending anteromedial in the forearm to supply the skin as far as the wrist and connecting with the palmar cutaneous branch of the ulnar nerve. The posterior branch descends obliquely medial to the basilic vein, anterior to the medial epicondyle, and curves round to the back of the forearm, descending on its medial border to the wrist, supplying the skin. It connects with the medial cutaneous nerve of the arm, the posterior cutaneous nerve of the forearm, and the dorsal branch of the ulnar.

It is depicted in bright pink in the forearm images.

[Diane]

Posterior Cutaneous Nerve of the Forearm branch of radial nerve: from p. 858: The posterior cutaneous nerve of the forearm arises with the lower lateral cutaneous nerve of the arm. Perforating the lateral head of triceps, it descends first lateral in the arm, then along the dorsum of the forearm to the wrist, supplying the skin in its course and joining, near its end, with dorsal branches of the lateral cutaneous nerve of the forearm.
From p. 887: The posterior cutaneous nerve of the forearm passes along the dorsum of the forearm to the wrist. It supplies the skin along its course and near its end joins the dorsal branches of the lateral cutaneous nerve of the forearm.

[Diane]

At last, the Big Three we all learned in school. I saved them for the end, to create "families" of cutaneous neural innervation by popping in links to all the appropriate posts above and from elsewhere.

Starting with the Radial Nerve: From Gray's, p. 886:
RADIAL NERVE
There is some variation in the level at which branches of the radial nerve arise from the main trunk in different subjects. Branches to extensor radialis brevis and supinator may arise from the main trunk of the radial nerve or from the proximal part of the posterior interosseous nerve, but almost invariably above the arcade of Frohse.

Radial Tunnel Syndrome
Radial tunnel syndrome is an entrapment neuropathy of the radial nerve near the elbow, where four structures can potentially cause compression of the nerve. These are fibrous bands (which can tether the radial nerve to the radiohumeral joint); the sharp tendinous medial border of extensor carpi radialis brevis; a leash of vessels from the radial recurrent artery as it passes to supply brachioradialis and extensor carpi radialis longus; the arcade of Frohse, which is the free aponeurotic proximal edge of he superficial part of supinator.

Usually the only presenting symptom is pain over the extensor mass just distal to the elbow. There is no sensory disturbance or motor loss, but there is frequently tenderness along the course of the radial nerve near the radial head. The pain is exacerbated when the elbow is extended and the wrist is passively flexed and pronated, or extended and supinated against resistance. Extension of the middle finger against resistance when the elbow is fully extended also may lead to increased pain. These manoeuvres tighten the anatomical structures which cause compression.

From p. 857: The radial nerve descends behind the third part of the axillary artery and the upper part of the brachial artery, anterior to subscapularis and the tendons of latissimus dorsi and teres major. With the profunda brachii artery it inclines dorsally, passing through the triangular space below the lower border of teres major, between the long head of triceps and the humerus. Here it supplies the long head of triceps, and gives rise to the posterior cutaneous nerve of the arm which supplies the skin along the posterior surface of the upper arm. It then spirals obliquely across the back of the humerus, lying posterior to the uppermost fibres of the medial head of triceps which separate the nerve from the bone in the first part of the spiral groove. Here it gives off a muscular branch to the lateral head of triceps and a branch which passes through the medial head of triceps to anconeus. On reaching the lateral side of the humerus it pierces the lateral intermuscular septum to enter the anterior compartment; it then descends deep in a furrow between brachialis and proximally brachioradialis, then more distally extensor carpi radialis. Anterior to the lateral epicondyle it divides into superficial and deep terminal rami.

The branches of the radial nerve in the upper arm are: muscular, cutaneous, articular; in the forearm superficial terminal (http://www.somasimple.com/forums/showpost.php?p=31596&postcount=23) and posterior interosseus (http://www.somasimple.com/forums/showpost.php?p=31596&postcount=23).

Muscular branches supply triceps, anconeus, brachioradialis, extensor carpi radialis longus and brachialis in medial, posterior and lateral groups. Medial muscular branches arise from the radial nerve on the medial side of the arm. They supply the medial and long heads of triceps; the branch to the medial head is a long slender filament which, lying close to the ulnar nerve as far as the distal third of the arm, is often termed the ulnar collateral nerve. A large posterior muscular branch arises from the nerve as it lies in the humeral groove. It divides to supply the medial and lateral heads of triceps and anconeus, that for the latter being a long nerve which descends in the medial head of triceps and partially supplies it; it is accompanied by the middle collateral branch of the profunda brachii artery and passes behind the elbow joint to end in anconeus. Lateral muscular branches arise in front of the lateral intermuscular septum; they supply the lateral part of brachialis, brachioradialis, and extensor carpi radialis longus.

Cutaneous branches are the posterior cutaneous nerve of the arm (http://www.somasimple.com/forums/showpost.php?p=31601&postcount=24) and lower lateral cutaneous (http://www.somasimple.com/forums/showpost.php?p=31540&postcount=14) (not to be confused with plain "lateral cutaneous" which is from musculocutaneous) nerve of the arm, and the posterior cutaneous nerve of the forearm (see posterior cutaneous nerve of the arm sketch).


The radial nerve is green, others are yellow.
At the elbow, on the forearm view, the posterior interosseous branch of the radial is in purple, while the rest of the radial is red.

[Diane]

Ulnar nerve: From p. 857 Gray's: The ulnar nerve gives no branches in the arm. It runs distally through the axilla medial to the axillary artery and between it and the vein, continuing distally medial to the brachial artery as far as the mid arm. Here it pierces the medial intermuscular septum, inclining medially as it descends anterior to the medial head of triceps to the interval between the medial epicondyle and the olecranon, with the superior ulnar collateral artery.

[Diane]

Median nerve: from p. 857, Gray's: The median nerve enters the arm lateral to the brachial artery. Near the insertion of coracobrachialis it crosses in front of (rarely behind) the artery, descending medial to it to the cubital fossa where it is posterior to the bicipital aponeurosis and anterior to brachialis, separated from the latter by the elbow joint. It gives off vascular branches to the brachial artery and usually a branch to pronator teres, a variable distance proximal to the elbow joint.

[Diane]

Here are a couple views of color-coded nerves in forearms.

[Diane]

Posterior Cutaneous Nerve of the Arm: from p. 857, Gray's: The small posterior cutaneous nerve of the arm arises in the axilla and passes medially to supply the skin on the dorsal surface of the arm nearly as far as the olecranon. It crosses posterior to and communicates with the intercostobrachial nerve.
I have a few views of it below. Note how there is a real starburst of interconnected neural structure on the medial side of the arm. I've shown the radial nerve in red and some of its cutaneous branches in green, including the posterior cutaneous nerve of the forearm.