Nerves Of The Arm And Forearm

Question 1

Musculocutaneous nerve (C5-C7)

Answer 1

• Coracobrachialis
• biceps brachii
• brachialis

Question 2

Radial nerve (C5-T1)

Answer 2

1. Triceps brachii
2. Anconeus
3. Brachioradialis
4. Extensor carpi radialis longus
5. Extensor carpi radialis brevis
6. Supinator
7. Extensor digitorum
8. Extensor digiti minimi
9. Extensor carpi ulnaris
10. Abductor pollicis longus
11. Extensor pollicis brevis
12. Extensor pollicis longus
13. Extensor indicis

Question 3

Median nerve (C5-T1) (6 - 1)

Answer 3

I. Arm and forearm:

1. Pronator teres
2. Flexor carpi radialis
3. Palmaris longus
4. Flexor digitorum superficialis

• Anterior interosseus nerve:

1. Flexor digitorum profundus (lateral/radial part)
2. Flexor pollicis longus

3.Pronator quadratus

II. Hand:

Thenar eminence:

1. Abductor pollicis brevis
2. Flexor pollicis brevis (superficial head)
3. Opponens pollicis
4. Lateral 2 Lumbricals

Question 4

Ulnar Nerve (C8-T1)

Answer 4

I. Arm and forearm:

1. Flexor carpi ulnaris
2. Flexor digitorum profundus (medial/ulnar part)

II. Hand:

Hypothenar eminence:

1. Abductor digiti minimi
2. Flexor digiti minimi
3. Opponens digiti minimi
4. Medial 2 Lumbricals
5. Interossei (3 palmar and 4 dorsal)
6. Adductor pollicis
7. Flexor pollicis brevis (deep head)

Question 5

Nerve pathways: upper extremity

Answer 5

The upper limb is supplied by a nervous network called the brachial plexus. This plexus is made by merging of the anterior rami from the lower four cervical nerves and the first thoracic nerve (C5-T1). The plexus is anatomically divided into roots, trunks, divisions, cords and finally, the terminal branches.

The roots emerge between the anterior and middle scalene muscle

Question 6

Musculocutaneous nerve (C5-C7)/ terminal branches of the brachial plexus

Answer 6

-arises at the inferior border of pectoralis minor
( push the SCM away, ask the clt sniff—> under the Clavicular → under pecminor)

-first muscle it enters is coracobrachialis and gives branches to this muscle before entering it

-runs in the flexor compartment superficial to the brachialis but deep to the biceps brachii muscle

• as it descends it innervates both of these muscles

-after giving small branch to the humerus and articular branches to the elbow joint it pierces deep fascia and emerges lateral to biceps brachii

-continues as the lateral cutaneous nerve of the forearm

-terminates as the lateral cutaneous nerve of the forearm that supplies the anterolateral skin of the forearm

• Summary: innervates the anterior compartment of the arm, including the skin of the lateral side of the forearm
• Musculocutaneous nerve palpation:

1. ask patient to sniff to engage scalenes
2. leaves axilla and travels medially, crosses laterally at mid arm
3. lateral to biceps brachii tendon at elbow
4. cutaneous: lateral aspect of anterior forearm

Question 7

Median nerve (C6-T1)

Answer 7

-arises in the axillary region ( medial to biceps, push the biceps out of the way lateral)

-descends down the centre of the arm in a superficial course

-before it enters the forearm, it passes between the tendons of biceps brachi and brachialis

-next it passes between the deep and superficial heads of the pronator teres muscle

-it then dives deeper and runs between the flexor digitorum profundus and flexor digitorum superficialis

-then passes through the carpal tunnel beneath the flexor retinaculum, and terminates by dividing into two terminal branches, the common palmar digital nerves

• Forearm:

-muscular branches to pronator teres, palmaris longus, flexor digitorum superficialis and flexor carpi radialis

-anterior interosseus nerve, which supplies the flexor pollicis longus and radial part of flexor digitorum profundus

• runs on the interosseous membrane, passes deep to pronator quadratus to supply it
• terminates by giving articular branches to the distal radioulnar, radiocarpal and carpal joints
• Hand:

-cutaneous nerve of the palm, which supplies the proximal aspect of the palm

-does not enter the carpal tunnel so is spared in carpal tunnel syndrome

-two common palmar digital nerves:

+ the first supplies the radial two lumbricals

+ the second runs between the ring and middle finger, and divides to give the proper digital nerves that provide sensation to the hand *

-recurrent branch to the muscles of the thenar eminence (flexor pollicis brevis, abductor pollicis brevis, opponens pollicis)

*skin of the palmar and distal dorsal aspects of the lateral three-and-the-half digits and adjacent palm

-skin of the palmar and distal dorsal aspects of the thumb and radial half of 2nd digit

-skin of palmar and distal dorsal aspects of the adjacent sides of 2nd-4th digits

-skin of the central palm

• Summary: innervates the anterior compartment of the forearm (except for the flexor carpi ulnaris and medial half of the flexor digitorum profundus), the thenar eminence (opponens pollicis, abductor pollicis brevis, flexor pollicis brevis), lateral lumbricals, and the skin of the lateral hand
• Median nerve palpation:

1. ask patient to sniff to engage scalenes
2. under clavicle and pectoralis major
3. anterior medial aspect of axilla
4. medial to biceps brachii
5. medial cubital fossa
6. central/medial aspect of forearm
7. through carpal tunnel at wrist
8. cutaneous: thumb, index, middle and 1/2 of ring finger (palm); tips of same fingers on dorsal side

Question 8

Axillary (Circumflex) nerve (C5-6)

Answer 8

-descends in the axilla anterior to the subscapularis

-emerges from the axilla at the level of the lower border of the subscapularis, by traversing the quadrangular space

-superior margin of the teres major inferiorly, the inferior margin of the teres minor superiorly, the lateral margin of the long head of the triceps brachii medially and the surgical neck of the humerus laterally. - supplies a branch to the shoulder joint

-then passes medial to the surgical neck of the humerus before dividing into three terminal branches:

+ anterior branch winds around the surgical neck of the humerus, posteriorly, supplies the anterior aspect of deltoid

+ posterior branch supplies the posterior aspect of the deltoid and teres minor;
it passes around the lower border of the deltoid (now referred to as the superior/upper lateral cutaneous nerve of the arm); supplies skin over the lower part of deltoid and over upper part of the long head of triceps (anteriorly and posteriorly)

+ articular branch supplies the glenohumeral joint.

Summary: innervates the deltoid, long head of the triceps brachii and teres minor muscles

-sensory innervation for the shoulder joint and the skin covering region of the deltoid muscle

• Axillary nerve palpation:

1. ask patient to sniff to engage scalenes
2. lateral part of subscapularis
3. exits axilla at quadrangular space
4. cutaneous: anterior, lateral and posterior aspect of deltoid

Question 9

Radial nerve (C5-T1)

Answer 9

-arises in the axilla between coracobrachialis and teres major muscles

-descends obliquely downwards through the posterior aspect of the arm, between the bellies of medial and lateral head of triceps, through a shallow depression on the posterior surface of the humerus (radial groove)

-provides muscular branches that innervate triceps brachii, anconeus, and brachioradialis

-in the distal part of the arm, it wraps around the distal humerus and courses anterior to the lateral condyle of humerus, where it penetrates the lateral inter muscular septum

-once it crosses the cubital fossa, it terminates by dividing into two terminal branches: superficial (sensory) and deep (motor)

-superficial (sensory) branches: skin of the posterior and inferior lateral aspect of the arm

-posterior brachial cutaneous nerve

-lateral inferior cutaneous brachial nerve

-once it enters the cubital region, and before its division, it provides one more sensory branch called the posterior antebrachial cutaneous nerve

-innervates a strip of skin down the middle of the posterior forearm

-deep (motor) branch: innervation to the posterior compartment of the forearm

-descends inferiorly through the posterior aspect of the forearm where it penetrates the supinator and emerges as the posterior interosseous nerve

-supply muscles in the posterior compartment of the forearm (the wrist extensors and the long

• extensor carpi radialis longus, extensor carpi radialis brevis, extensor carpi ulnaris, extensor digitorum, extensor indicis, extensor digiti minimi, extensor pollicis longus, extensor pollicis brevis and abductor pollicis longus

-superficial branch enters the hand from the radial side

-provides sensation to the thenar eminence and dorsal aspect of the radial 3 and a half digits of the

• Summary: innervates the posterior compartments of the arm and forearm, skin of posterior arm, forearm and the dorsolateral part of the hand.
• Radial nerve palpation:

1. ask patient to sniff to engage scalenes
2. posterior aspect of arm: proximal-medial curving to distal-lateral aspect of the arm as it descends
3. distal lateral arm then moves anterior to lateral epicondyle
4. anterior-lateral forearm curves over radius to dorsal wrist
5. cutaneous: posterior-middle of arm and forearm, lateral palm, thumb, index, middle and 1/2 or ring finger

Question 10

Ulnar nerve (C8-T1)

Answer 10

-passes distally through the axilla
-descends on the medial aspect of the arm, medial to biceps brachii
-in the mid-portion of the arm, it pierces the medial inter muscular septum to enter the posterior
-runs anterior to the medial head of triceps brachii muscle and passes under the arcade of Struthers
-a thin, aponeurotic band, that extends from the medial head of triceps to the medial inter muscular septum
-then passes between the medial epicondyle and olecranon in the cubital tunnel to enter the anterior compartment of the forearm
-posterior to the medial epicondyle, it is subcutaneous and easily palpable
-here, the nerve gives off articular branches to the elbow joint
-continues into the anterior compartment of the forearm by passing between the humeral and ulnar heads of the flexor carpi ulnaris
-descends on the medial aspect of the forearm, over flexor digitorum profundus and deep to flexor
-close to the wrist, it emerges lateral to flexor carpi ulnaris
-it runs superficial to the flexor retinaculum (transverse carpal ligament) to enter the hand just lateral to
-gives rise to two cutaneous branches in the forearm:
+ palmar cutaneous nerve
+ dorsal cutaneous nerve
-these nerves pass into the hand to provide sensory innervation
-at the wrist, it enters the hand by coursing through the Guyon’s canal (ulnar canal), a groove between the pisiform and the hook of the hamate, bridged by the palmar carpal ligament
-it divides into superficial and deep branches to provide both sensory and motor innervation to the hand

• Summary: innervates the flexor carpi ulnaris and medial half of the flexor digitorum profundus, the hypothenar eminence (opponens digiti minimi, abductor digiti minimi, flexor digiti minimi brevis, palmaris brevis), medial lumbricals, dorsal and palmar interossei, adductor pollicis, and the skin of the medial hand (anterior and posterior aspect of little finger and half of ring finger and medial palmar and dorsal skin).
• Ulnar nerve palpation:

1. ask patient to sniff to engage scalenes
2. medial aspect of triceps brachii in posterior compartment
3. medial side of arm to elbow
4. posterior to medial epicondyle
5. through flexor carpi ulnaris to travel on anterior and then medial part of forearm
6. medial aspect of wrist
7. cutaneous: 5th finger and 1/2 of 4th finger palmar and dorsal

Question 11

Axillary or Posterior Circumflex Nerve

Answer 11

• An axillary nerve injury is characterized by trauma to the axillary nerve: from either a compressive force, a traction injury following anterior dislocation of the shoulder, or a forced Abduction movement of the shoulder joint. An axillary nerve injury can cause signs and symptoms of a localized neuropathy.
• Sensory functions: Gives rise to the upper lateral cutaneous nerve of arm, which innervates the skin over the lower deltoid (‘regimental badge area’).
• Motor functions: Innervates the Teres minor and Deltoid muscles.
• Anatomical Course:

+ The axillary nerve is formed within the axilla area of the upper limb. It is a direct continuation of the posterior cord from the brachial plexus - and therefore contains fibres from the C5 and C6 nerve roots.

+ In the axilla, the axillary nerve is located posterior to the axillary artery and anterior to the subscapularis muscle. It exits the axilla at the inferior border of subscapularis via the quadrangular space, often accompanied by the posterior circumflex humeral artery and vein.

+ The axillary nerve then passes medially to the surgical neck of the humerus, where it divides into three terminal branches:

• Posterior terminal branch - provides motor innervation to the posterior aspect of the deltoid muscle and teres minor. It also innervates the skin over the inferior part of the deltoid as the upper lateral cutaneous nerve of the arm.

• Anterior terminal branch - winds around the surgical neck of the humerus and provides motor innervation to the anterior aspect of the deltoid muscle. It terminates with cutaneous branches to the anterior and anterolateral shoulder.

• Articular branch - supplies the glenohumeral joint