ARM
13. 03. 2014
Kaan Yücel
M.D., Ph.D.
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Dr.Kaan Yücel
http://yeditepeanatomy1.org
Arm
The arm is the region of the upper limb between the shoulder and the elbow. The superior aspect of the arm
communicates medially with the axilla. Inferiorly, a number of important structures pass between the arm and the
forearm through the cubital fossa, which is positioned anterior to the elbow joint.
The arm is divided into two compartments by medial and lateral intermuscular septa, which pass from each side of
the humerus to the outer sleeve of deep fascia that surrounds the limb.
Two types of movement occur between the arm and the forearm at the elbow joint: flexion-extension and
pronation-supination. The muscles performing these movements are clearly divided into anterior and posterior
groups, separated by the humerus and medial and lateral intermuscular septae. The anterior compartment of the arm
contains muscles that predominantly flex the elbow joint; the posterior compartment contains muscles that extend
the joint. Major nerves and vessels supply and pass through each compartment. The chief action of both groups is at
the elbow joint, but some muscles also act at the glenohumeral joint.
The skeletal support for the arm is the humerus. The anterior compartment of the arm contains three musclescoracobrachialis, brachialis, and biceps brachii muscles-which are innervated predominantly by the
musculocutaneous nerve.
The posterior compartment contains one muscle-the triceps brachii muscle-which is innervated by the radial
nerve. The flexor muscles of the anterior compartment are almost twice as strong as the extensors in all positions;
consequently, we are better pullers than pushers.
The biceps is a “three-joint muscle,” crossing and capable of effecting movement at the glenohumeral, elbow,
and radio-ulnar joints, although it primarily acts at the latter two. The biceps brachii muscle is a powerful flexor of
the forearm at the elbow joint; it is also the most powerful supinator of the forearm when the elbow joint is flexed.
The brachialis is the main flexor of the forearm. The coracobrachialis helps flex and adduct the arm and
stabilize the glenohumeral joint.
The only muscle of the posterior compartment of the arm is the triceps brachii muscle. The triceps brachii
muscle has three heads: long head, medial and lateral heads. Because its long head crosses the glenohumeral joint,
the triceps helps stabilize the adducted glenohumeral joint by serving as a shunt muscle, resisting inferior
displacement of the head of the humerus. The long head also aids in extension and adduction of the arm. The medial
head is the workhorse of forearm extension. The lateral head is strongest but is recruited into activity primarily
against resistance.
The major artery of the arm, the brachial artery, is found in the anterior compartment. Beginning as a
continuation of the axillary artery at the lower border of the teres major muscle, it terminates just distal to the elbow
joint, opposite to the neck of the radius where it divides into the radial and ulnar arteries. Branches of the brachial
artery in the arm include those to adjacent muscles and two ulnar collateral vessels (superior and inferior ulnar
collateral arteries). Additional branches are the profunda brachii artery and nutrient arteries to the humerus.The deep
artery of the arm (L. arteria profunda brachii) is the largest branch of the brachial artery.
The superficial veins are in the subcutaneous tissue, and the deep veins accompany the arteries. The two main
superficial veins of the arm, the cephalic and basilic veins. The cephalic vein ascends in the superficial fascia on the
lateral side of the biceps and drains into the axillary vein.
Four main nerves pass through the arm: median, ulnar, musculocutaneous, and radial.
The musculocutaneous nerve leaves the axilla and enters the arm by passing through the coracobrachialis
muscle. It passes diagonally down the arm in the plane between the biceps brachii and brachialis muscles. The
musculocutaneous nerve provides: motor innervation to all muscles in the anterior compartment of the arm; and
sensory innervation to skin on the lateral surface of the forearm.
The median nerve enters the arm from the axilla at the inferior margin of the teres major muscle. It passes
vertically down the medial side of the arm in the anterior compartment. The median nerve has no major branches in
the arm or in the axilla. Like the median nerve, the ulnar nerve has no branches in the arm, but it also supplies
articular branches to the elbow joint.
The radial nerve in the arm supplies all the muscles in the posterior compartment of the arm (and forearm).
The radial nerve originates from the posterior cord of the brachial plexus and enters the arm by crossing the inferior
margin of the teres major muscle. Accompanied by the profunda brachii artery, the radial nerve enters the posterior
compartment of the arm by passing through the triangular interval.
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Arm
1. INTRODUCTION
The arm is the region of the upper limb between the shoulder and the elbow. The superior aspect of
the arm communicates medially with the axilla. Inferiorly, a number of important structures pass between the
arm and the forearm through the cubital fossa, which is positioned anterior to the elbow joint.
The arm is divided into two compartments by medial and lateral intermuscular septa, which pass from
each side of the humerus to the outer sleeve of deep fascia that surrounds the limb.
The muscles performing these movements are clearly divided into anterior and posterior groups,
separated by the humerus and medial and lateral intermuscular septae. The anterior compartment of the arm
contains muscles that predominantly flex the elbow joint; the posterior compartment contains muscles that
extend the joint. Major nerves and vessels supply and pass through each compartment.
Two types of movement occur between the arm and the forearm at the elbow joint: flexion-extension
and pronation-supination. The chief action of both groups is at the elbow joint, but some muscles also act at
the glenohumeral joint. The superior part of the humerus provides attachments for tendons of the shoulder
muscles.
The biceps brachii and brachialis muscles constitute the bulk of the anterior aspect of the arm, and the
triceps brachii its posterior aspect.
2. BONES
The skeletal support for the arm is the humerus. Most of the large muscles of the arm insert into the
proximal ends of the two bones of the forearm, the radius and the ulna, and flex and extend the forearm at
the elbow joint. In addition, the muscles predominantly situated in the forearm that move the hand originate
at the distal end of the humerus.
3. MUSCLES
The anterior compartment of the arm contains three muscles-coracobrachialis, brachialis, and biceps
brachii muscles-which are innervated predominantly by the musculocutaneous nerve.
The posterior compartment contains one muscle-the triceps brachii muscle-which is innervated by the radial
nerve. The flexor muscles of the anterior compartment are almost twice as strong as the extensors in all
positions; consequently, we are better pullers than pushers. It should be noted, however, that the extensors
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of the elbow are particularly important for raising oneself out of a chair and for wheelchair activity. Therefore,
conditioning of the triceps is of particular importance in elderly or disabled persons.
ANTERIOR COMPARTMENT
The coracobrachialis is an elongated muscle in the superomedial part of the arm. It is a useful
landmark for locating other structures in the arm (For example, the musculocutaneous nerve pierces it, and
the distal part of its attachment indicates the location of the nutrient foramen of the humerus).
The coracobrachialis helps flex and adduct the arm and stabilize the glenohumeral joint. With the
deltoid and long head of the triceps, it serves as a shunt muscle, resisting downward dislocation of the head of
the humerus, as when carrying a heavy suitcase. The median nerve and/or the brachial artery may run deep
to the coracobrachialis and be compressed by it. It passes through the axilla and is penetrated and innervated
by the musculocutaneous nerve.
As the term biceps brachii indicates, the proximal attachment of this fusiform muscle usually has two heads
(bi, two + L. caput, head). The two heads of the biceps arise proximally by tendinous attachments to processes
of the scapula, their fleshy bellies uniting just distal to the middle of the arm.
The tendon of the long head passes through the glenohumeral joint superior to the head of the humerus,
then passes through the intertubercular sulcus and enters the arm. In the arm, the tendon joins with its
muscle belly and, together with the muscle belly of the short head, overlies the brachialis muscle.
The long and short heads converge to form a single tendon, which inserts onto the radial tuberosity.
As the tendon enters the forearm, a flat sheet of connective tissue (the bicipital aponeurosis) fans out from
the medial side of the tendon to blend with deep fascia covering the anterior compartment of the forearm.
Approximately 10% of people have a third head to the biceps.
A broad band, the transverse humeral ligament, passes from the lesser to the greater tubercle of the
humerus and converts the intertubercular groove into a canal. The ligament holds the tendon of the long
head of the biceps in the groove. Distally, the major attachment of the biceps is to the radial tuberosity via the
biceps tendon. However, a triangular membranous band, called the bicipital aponeurosis, runs from the
biceps tendon across the cubital fossa and merges with the antebrachial (deep) fascia covering the flexor
muscles in the medial side of the forearm. The bicipital aponeurosis affords protection for these and other
structures in the cubital fossa. It also helps lessen the pressure of the biceps tendon on the radial tuberosity
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during pronation and supination of the forearm. Although the biceps is located in the anterior compartment
of the arm, it has no attachment to the humerus.
The biceps is a “three-joint muscle,” crossing and capable of effecting movement at the glenohumeral,
elbow, and radio-ulnar joints, although it primarily acts at the latter two.
The biceps brachii muscle is a powerful flexor of the forearm at the elbow joint; it is also the most
powerful supinator of the forearm when the elbow joint is flexed. Because the two heads of the biceps
brachii muscle cross the glenohumeral joint, the muscle can also flex the glenohumeral joint.
Its action and effectiveness are markedly affected by the position of the elbow and forearm. When the
elbow is extended, the biceps is a simple flexor of the forearm; however, as elbow flexion approaches 90° and
more power is needed against resistance, the biceps is capable of two powerful movements, depending on
the position of the forearm. When the elbow is flexed close to 90° and the forearm is supinated, the biceps is
most efficient in producing flexion. Alternately, when the forearm is pronated, the biceps is the primary (most
powerful) supinator of the forearm.
A tap on the tendon of biceps brachii at the elbow is used to test predominantly spinal cord segment
C6.
The brachialis muscle originates from the distal half of the anterior aspect of the humerus and from
adjacent parts of the intermuscular septa, particularly on the medial side. It lies beneath the biceps brachii
muscle. Its distal attachment covers the anterior part of the elbow joint.
The brachialis is the main flexor of the forearm. It is the only pure flexor, producing the greatest
amount of flexion force. It flexes the forearm in all positions, not being affected by pronation and supination;
during both slow and quick movements; and in the presence or absence of resistance. The brachialis always
contracts when the elbow is flexed and is primarily responsible for sustaining the flexed position. Because of
its important and almost constant role, it is regarded as the workhorse of the elbow flexors.
Innervation of brachialis muscle is predominantly by the musculocutaneous nerve. A small
component of the lateral part is innervated by the radial nerve.
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POSTERIOR COMPARTMENT
The triceps brachii is a large fusiform muscle in the posterior compartment of the arm. The only
muscle of the posterior compartment of the arm is the triceps brachii muscle. The triceps brachii muscle has
three heads: long head, medial and lateral heads.
The three heads converge to form a large tendon, which inserts on the proximal end of olecranon of the
ulna. Fascia of forearm is another area of insertion for the triceps brachii muscle.
Because its long head crosses the glenohumeral joint, the triceps helps stabilize the adducted
glenohumeral joint by serving as a shunt muscle, resisting inferior displacement of the head of the humerus.
The long head also aids in extension and adduction of the arm, but it is actually the least active head.
The medial head is the workhorse of forearm extension, active at all speeds and in the presence or absence of
resistance. The lateral head is strongest but is recruited into activity primarily against resistance. Pronation
and supination of the forearm do not affect triceps operation. Just proximal to the distal attachment of the
triceps is a friction-reducing subtendinous olecranon bursa, between the triceps tendon and the olecranon.
Innervation of triceps brachii is by branches of the radial nerve. A tap on the tendon of triceps brachii
tests predominantly spinal cord segment C7.
Figure 1. Muscles in the arm
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4.ARTERIES & VEINS
BRACHIAL ARTERY
The major artery of the arm, the brachial artery, is found in the anterior compartment. Beginning as a
continuation of the axillary artery at the lower border of the teres major muscle, it terminates just distal to
the elbow joint, opposite to the neck of the radius where it divides into the radial and ulnar arteries. The
brachial artery, relatively superficial and palpable throughout its course, lies anterior to the triceps and
brachialis. As it passes inferolaterally, the brachial artery accompanies the median nerve.
During its course through the arm, the brachial artery gives rise to many unnamed muscular branches.
In the proximal arm, the brachial artery lies on the medial side. In the distal arm, it moves laterally. It crosses
anteriorly to the elbow joint. In proximal regions, the brachial artery can be compressed against the medial
side of the humerus.
Branches of the brachial artery in the arm include those to adjacent muscles and two ulnar collateral
vessels (superior and inferior ulnar collateral arteries), which contribute to a network of arteries around the
elbow joint. Additional branches are the profunda brachii artery and nutrient arteries to the humerus, which
pass through a foramen in the anteromedial surface of the humeral shaft.
The deep artery of the arm (L. arteria profunda brachii) is the largest branch of the brachial artery and
has the most superior origin. It accompanies the radial nerve along the radial groove as it passes posteriorly.
The deep artery terminates by dividing into middle and radial collateral arteries, which participate in the
periarticular arterial anastomoses around the elbow.
Of the named branches of the brachial artery; the profunda brachii accompanies the radial nerve,
whereas the superior ulnar collateral artery accompanies the ulnar nerve.
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Figure 2. Brachial artery
http://en.wikipedia.org/wiki/File:Gray525.png
VEINS
Two sets of veins of the arm, superficial and deep, anastomose freely with each other. The superficial
veins are in the subcutaneous tissue, and the deep veins accompany the arteries. Both sets of veins have
valves, but they are more numerous in the deep veins than in the superficial veins. The two main superficial
veins of the arm, the cephalic and basilic veins. The cephalic vein ascends in the superficial fascia on the
lateral side of the biceps and drains into the axillary vein.
Paired deep veins, collectively constituting the brachial vein, accompany the brachial artery. Their
frequent connections encompass the artery, forming an anastomotic network within a common vascular
sheath. The pulsations of the brachial artery help move the blood through this venous network.
The brachial vein begins at the elbow by union of the accompanying veins of the ulnar and radial
arteries and ends by merging with the basilic vein to form the axillary vein. Not uncommonly, the deep veins
join to form one brachial vein during part of their course.
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Figure 3. Veins in the arm
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5. NERVES
Four main nerves pass through the arm: median, ulnar, musculocutaneous, and radial.
MUSCULOCUTANEOUS NERVE
The musculocutaneous nerve leaves the axilla and enters the arm by passing through the
coracobrachialis muscle. It passes diagonally down the arm in the plane between the biceps brachii and
brachialis muscles. After giving rise to motor branches in the arm, it emerges laterally to the tendon of the
biceps brachii muscle at the elbow, penetrates deep fascia proximal to the cubital fossa, and becomes truly
subcutaneous as lateral cutaneous nerve of forearm to course initially with the cephalic vein in the
subcutaneous tissue.
The musculocutaneous nerve provides:
 motor innervation to all muscles in the anterior compartment of the arm;
 sensory innervation to skin on the lateral surface of the forearm.
MEDIAN NERVE
The median nerve enters the arm from the axilla at the inferior margin of the teres major muscle. It
passes vertically down the medial side of the arm in the anterior compartment and is related to the brachial
artery throughout its course. The median nerve has no major branches in the arm or in the axilla.
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ULNAR NERVE
The ulnar nerve enters the arm with the median nerve and axillary artery. The ulnar nerve in the arm
passes distally from the axilla anterior to the insertion of the teres major and to the long head of the triceps,
on the medial side of the brachial artery. In the middle of the arm, the ulnar nerve penetrates the medial
intermuscular septum and enters the posterior compartment. It then passes into the anterior compartment of
the forearm. Posterior to the medial epicondyle, where the ulnar nerve is referred to in lay terms as the
“funny bone,” it is superficial, easily palpable, and vulnerable to injury. Like the median nerve, the ulnar nerve
has no branches in the arm, but it also supplies articular branches to the elbow joint.
RADIAL NERVE
The radial nerve in the arm supplies all the muscles in the posterior compartment of the arm (and
forearm). The radial nerve originates from the posterior cord of the brachial plexus and enters the arm by
crossing the inferior margin of the teres major muscle. Accompanied by the profunda brachii artery, the radial
nerve enters the posterior compartment of the arm by passing through the triangular interval.
As the radial nerve passes diagonally, from medial to lateral, through the posterior compartment, it
lies in the radial groove directly on bone. On the lateral side of the arm, it enters the anterior compartment
where it lies between the brachialis muscle and a muscle of the posterior compartment of the forearm-the
brachioradialis muscle. The radial nerve enters the forearm just deep to the brachioradialis muscle. In the
arm, the radial nerve has muscular and cutaneous branches.
Muscular branches include those to the triceps brachii, brachioradialis, and extensor carpi radialis
longus muscles. In addition, the radial nerve contributes to the innervation of the lateral part of the brachialis
muscle. Cutaneous branches of the radial nerve that originate in the posterior compartment of the arm are
the inferior lateral cutaneous nerve of arm and the posterior cutaneous nerve of forearm, both of which
penetrate through the lateral head of the triceps brachii muscle and the overlying deep fascia to become
subcutaneous.
The inferior lateral cutaneous nerve of the arm supplies the skin over the lateral and anterior aspects
of the lower part of the arm. The posterior cutaneous nerve of the forearm runs down the middle of the back
of the forearm as far as the wrist.
Anterior to the lateral epicondyle, the radial nerve then divides into deep and superficial branches.
The deep branch of the radial nerve is entirely muscular and articular in its distribution. The superficial branch
of the radial nerve is entirely cutaneous in its distribution, supplying sensation to the dorsum of the hand and
fingers.
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Figure 4. Nerves in the arm
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Table. Muscles of the arm
Muscle
Proximal
Attachment
(Origin)
Biceps brachii
Short head: tip of
coracoid process of
scapula
Long head:
supraglenoid tubercle
of scapula
Coracobrachialis Tip of coracoid
process of scapula
Distal Attachment
(Insertion)
Innervationa
Function
Tuberosity of radius
and fascia of forearm
via bicipital
aponeurosis
Musculocutaneous
nerve (C5, C6, C7)
Supinates forearm and,
when it is supine. flexes
forearm; short head resists
dislocation of shoulder
Middle third of medial
surface of humerus
Musculocutaneous
nerve (C5, C6, C7)
Helps flex and adduct arm;
resists dislocation of
shoulder
Brachialis
Distal half of anterior
surface of humerus
Coronoid process and
tuberosity ulna
Flexes forearm in all
positions
Triceps brachii
Long head:
infraglenoid tubercle
of scapula
Lateral head:
posterior surface of
humerus, superior to
radial groove
Medial head:
posterior surface of
humerus, inferior to
radial groove
Proximal end of
olecranon of ulna and
fascia of forearm
Musculocutaneous
nerve (C5, C6, C7)
and small
contribution by the
radial nerve at the
lateral part
Radial nerve
(C6, C7, C8)
Chief extensor of forearm;
long head resists
dislocation of humerus;
especially important during
adduction
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