The Arm

Question 1

Identify the surface landmarks of the arm.

Answer 1

1. Greater tubercle of the humerus
2. Shaft of the humerus
3. Medial epicondyle of the humerus
4. Lateral epicondyle of the humerus
5. Medial and lateral supracondylar ridges
6. Deltoid muscle
7. Biceps muscle
8. Brachial artery pulsations
9. Ulnar nerve
10. The superficial veins in front of elbow (i.e., cephalic,
    basilic, and median cubital veins)
11. Head of radius
12. Olecranon process of ulna

Question 2

Identify the contents of the anterior compartment of the arm.

Answer 2

Muscles: Biceps brachii, coracobrachialis, and brachialis.
Nerve: Musculocutaneous nerve.
Artery: Brachial artery.
In addition to the above structures, the following large nerves
also pass through the anterior compartment of arm:
Median nerve.
Ulnar nerve.
Radial nerve.

Question 3

Identify the origin, insertion, nerve supply, blood supply and actions of the biceps brachii muscle.

Answer 3

Origin: 1. Long head arises from supraglenoid tubercle of the scapula
2. Short head arises from the tip of the coracoid process
(along side coracobrachialis muscle)
Insertion: 1. By a tendon into the posterior part of the radial
tuberosity.
2. By its aponeurosis (bicipital aponeurosis) into the deep
fascia on the medial aspect of the forearm.
Nerve supply: By musculocutaneous nerve (C5, C6, and C7).
Actions: 1. It is strong supinator of the forearm, when elbow is
flexed.
2. It is a powerful flexor of the forearm, when elbow is
extended.
3. It is also a weak flexor of the shoulder joint.

Question 4

What is biceps reflex?

Answer 4

It is tested during physical examination by tapping the tendon of biceps brachii by reflex hammer with forearm pronated and partially extended at elbow. The normal reflex is brief jerk-like flexion of the elbow. The normal reflex confirms the integrity of musculocutaneous
nerve and C5 and C6 spinal segments.

Question 5

Identify the origin, insertion, nerve supply, blood supply and actions of the coracobrachialis muscle.

Answer 5

Origin: From the tip of coracoid process of the scapula (along with
short head of the biceps brachii).
Insertion: Into the middle of the medial border of the shaft of the
humerus.
Nerve supply: By musculocutaneous nerve.
Actions: It is a weak flexor and adductor of the arm.

Question 6

Identify the important anatomical events that occur at the insertion of the coracobrachialis muscle.

Answer 6

1. Circular shaft of the humerus becomes triangular below this level.
2. Brachial artery passes from medial side of the arm to its anterior
   aspect.
3. Basilic vein pierces the deep fascia.
4. Median nerve crosses in front of the brachial artery from the
   lateral to medial side.
5. Radial nerve pierces the lateral intermuscular septum to pass from
   the posterior compartment to the anterior compartment.
6. Ulnar nerve pierces the medial intermuscular septum to pass from
   the anterior compartment to the posterior compartment.
7. Medial cutaneous nerve of the arm and forearm pierces the deep
   fascia.
8. Nutrient artery pierces the humerus.

Question 7

Identify the origin, insertion, nerve supply, blood supply and actions of the brachialis muscle.

Answer 7

Origin: Lower half of the shaft of humerus (front side)
Insertion: Coronoid process of ulnar (anterior surface)
Nerve supply: It has dual innervation;
1. Medial two third by musculocutaneous
2. Lateral one third by radial nerve.
Action: strong flexor of the elbow joint.

Question 8

Which muscle is also known as the work-horse of the elbow joint.

Answer 8

brachialis muscle.

Question 9

Identify the origin, course, branches and distribution of the musculocutaneous nerve.

Answer 9

Origin and course: It is the nerve of the front of the arm. it arises from the lateral cord of the brachial plexus in the axilla. it runs downward and laterally, pierces the coracobrachialis which it supplies, then passes between the biceps and brachialis muscles. It appears at the lateral margin of the biceps tendon and pierces deep fascia just above the elbow and descends over the lateral aspect of the forearm as the lateral cutaneous nerve of the forearm.
Branches and distribution:
1. Muscular branches - to biceps brachii, coracobrachialis and
brachialis muscles.
2. Cutaneous branch - Lateral cutaneous nerve of the forearm;
supplies the skin on the front and lateral aspect of the forearm.
3. Articular branch - to elbow joint (through its branch to brachialis
muscle)

Question 10

What are the signs and symptoms when injury to the musculocutaneous nerve occur.

Answer 10

1. Loss of strong flexion and supination
2. Loss of biceps tendon reflex.
3. Loss of sensation along the lateral aspect of the forearm.

Question 11

Identify the origin, course and branches of the brachial artery.

Answer 11

Origin and Course: It is the main artery of the arm. it begins at the lower border of the teres major muscle as a continuation of the axillary artery and terminates in front of the elbow by dividing into radial and ulnar arteries.
Branches:
1. Muscular branches to the muscles of the anterior compartment of
the arm.
2. Profunda brachii artery
3. Nutrient artery to humerus
4. Superior ulnar collateral artery
5. Inferior ulnar collateral (or supratrochlear artery)
6. Radial and ulnar arteries (terminal branches)

Question 12

Identify 5 arterial anastomosis around the elbow joint.

Answer 12

1. In front of the medial epicondyle:
   (a) Inferior ulnar collateral artery and branch from the superior ulnar collateral artery (branches of the brachial artery), anastomose with
   (b) Anterior ulnar recurrent artery (branch of the ulnar artery).
2. Behind the medial epicondyle:
   (a) Superior ulnar collateral artery and a branch from the inferior ulnar collateral artery (branches of brachial artery), anastomose with
   (b) Posterior ulnar recurrent artery (branch of the ulnar artery).
3. In front of lateral epicondyle:
   (a) Radial collateral artery (branch of the profunda brachii artery), anastomose with
   (b) Radial recurrent artery (branch of the radial artery).
4. Behind the lateral epicondyle:
   (a) Posterior descending artery (branch of the profunda brachii artery), anastomose with
   (b) Interosseous recurrent artery (branch of the posterior interosseous artery); and a branch of common interosseous artery (a branch of the ulnar artery).
5. Above the olecranon fossa:
   (a) Middle collateral artery (branch of the profunda brachii artery), anastomose with
   (b) Transverse branch from the posterior division of the inferior ulnar collateral artery.

Question 13

Identify the origin, course, branches and distribution of the median nerve.

Answer 13

Origin and course: The median nerve arises from the lateral and medial cords of the brachial plexus in axilla. It begins at the lower border of the teres major muscle passing through the anterior compartment of the arm. it is crossed by the bicipital aponeurosis at the elbow joint. (It is closely related to the brachial artery throughout its course in the arm)
Branches:
1. Nerve to pronator teres just above the elbow.
2. Vasomotor nerve to the brachial artery.
3. Articular branch to the elbow joint at or just below the elbow.

Question 14

Identify the origin and course of the ulnar nerve.

Answer 14

Origin and course: arises from medial cord of the brachial plexus in the axilla. It then runs downwards on the medial side of the arm medial to the brachial artery up to the insertion of coracobrachialis. Here it pierces the medial intermuscular septum to enter the posterior compartment of the arm. At the elbow, the ulnar nerve passes behind the medial epicondyle of humerus where it can be easily palpated. The ulnar nerve does not give any branch in the arm.

Question 15

Identify the origin, course, branches and distribution of the radial nerve.

Answer 15

Origin and course: The radial nerve arises from the posterior cord of the brachial plexus in the axilla. In the arm the nerve first lies posterior to the brachial artery. Then it winds around the back of the arm to enter the radial/spiral groove of humerus between the lateral
and medial heads of the triceps; where it is accompanied by profunda brachii artery. At the lower end of the spiral groove, it pierces lateral intermuscular septum and enters the anterior compartment of the arm. Here it continues downward in front of the elbow in the cubital fossa, between the brachialis and brachioradialis muscles. It divides into two terminal branches: (a) a sensory branch, the superficial radial nerve, and (b) a motor branch, the deep radial nerve. The latter disappears into the substance of supinator muscle just below the elbow.
Branches:
1. In the axilla:
(a) Nerves to long and medial heads of triceps.
(b) Posterior cutaneous nerve of the arm.
2. In the spiral groove:
(a) Nerves to lateral and medial heads of triceps.
(b) Nerve to anconeus.
(c) Lower lateral cutaneous nerve of the arm.
(d) Posterior cutaneous nerve of forearm.
3. In the anterior compartment of the arm:
(a) Nerves to brachialis, brachioradialis, and extensor carpi radialis longus.
(b) Articular branches to the elbow joint.
(c) Deep radial nerve.
(d) Superficial radial nerve.

Question 16

State the boundaries of the cubital fossa.

Answer 16

Lateral: Medial border of brachioradialis muscle.
Medial: Lateral border of pronator teres muscle.
Base: An imaginary horizontal line, joining the front of two epicondyles of the humerus.
Apex: Meeting point of the lateral and medial boundaries.
Here brachioradialis overlaps the pronator teres.
Floor: It is formed by two muscles, brachialis in the upper
part and supinator in the lower part
Roof: It is formed from superficial to deep by;
1. skin
2. superficial fascia
3. deep fascia

Question 17

State the contents of the cubital fossa.

Answer 17

1. Median nerve
2. Brachial artery
3. Biceps tendon
4. Radial nerve
   Contents of cubital fossa mnemonic from medial to lateral MBBS: (M= median nerve, B=brachial artery, B= Biceps tendon, S= superficial radial nerve)

Question 18

Identify the contents of the posterior compartment of the arm.

Answer 18

Muscle: Triceps brachii
Nerve: Radial nerve
Artery: Profunda brachii artery
The following structures also pass through the posterior compartment;
1. Ulnar nerve
2. Ulnar collateral arteries

Question 19

Identify the origin, insertion, nerve supply, blood supply and actions of the triceps brachii muscle.

Answer 19

Origin:
1. Long head: Infraglenoid tubercle of the humerus
2. Lateral head: oblique ridge above the spiral groove on the upper part of the posterior surface of the humerus
3. Medial head: Posterior surface of the lower half of the shaft of humerus below the spiral groove
Insertion:
The common tendon is inserted into the posterior part of the superior surface of the olecranon process of ulna.
Nerve supply
By radial nerve (C7, C8). Each head receives a separate branch from radial nerve in the following manner:
Nerve to long head arises from the radial nerve in axilla.
Nerve to lateral head arises from the radial nerve in the radial groove.
Nerve to medial head arises from the radial nerve in the radial groove.
Actions
The triceps brachii is the powerful extensor of the elbow joint.
The long head supports the head of humerus during hyperabduction of the arm.

Question 20

Identify the origin, course and branches of the profunda brachii artery.

Answer 20

Origin and Course: The profunda brachii artery is the largest branch of the brachial artery. It arises from the posterolateral aspect of the brachial artery just below the teres major. It accompanies the radial nerve through the radial groove and then terminates by dividing into anterior and posterior descending branches, which take part in the arterial anastomosis around the elbow joint.
Branches:
1. Deltoid (ascending) branch
2. Nutrient artery to humerus
3. Anterior descending (radial collateral) artery