Brachial Plexus, Axillary Nerve & Musculocutaneous Nerve - Upper limb الجزء الخامس - MSS أناتومي الـ

• The brachial plexus is a network of nerves in the shoulder that carries movement and sensory signals from the spinal cord to the arms and hands

Stages of Brachial Plexus

• Roots are found in the neck region, formed by the ventral rami of C5, C6, C7, C8, and T1 spinal nerves
• Trunks are also found in the neck
• The upper trunk is formed by the union of C5 and C6 roots
• The middle trunk is formed by the C7 root
• The lower trunk is formed by the union of C8 and T1 roots
• Divisions are located behind the clavicle
• Each trunk splits into anterior and posterior divisions
• Cords are found in the axilla
• The lateral cord is the anterior division of the upper and middle trunks
• The medial cord is the anterior division of the lower trunk
• The posterior cord is the posterior division of all trunks
• Branches are located in the axilla

Branches from Roots

• The nerve to Rhomboidus, also called the dorsal scapular nerve, arises from C5 and supplies the Rhomboid group of muscles
• The nerve to serratus anterior, or long thoracic nerve, arises from C5, C6, and C7 and supplies the serratus anterior muscle

Branches from the Upper Trunk

• The suprascapular nerve supplies the supraspinatus and infraspinatus muscles
• The nerve to subclavius supplies the subclavius muscle

Branches from the Lateral Cord

• The musculocutaneous nerve supplies the coracobrachialis, biceps, and the medial half of the brachialis
• The lateral pectoral nerve supplies the pectoralis major muscle
• The lateral root of the median nerve is a branch of the lateral cord

Branches from the Medial Cord

• The medial root of the median nerve is a branch of the medial cord
• The medial pectoral nerve supplies both the pectoralis major and minor muscles
• The medial cutaneous nerve (MCN) of the arm supplies the skin of the medial side
• The medial cutaneous nerve (MCN) of the forearm supplies the skin of the medial side of the forearm
• The ulnar nerve supplies the flexor carpi ulnaris, the medial half of the flexor digitorum profundus, and the muscles of the hand that are not supplied by the median nerve
• The median nerve supplies the thenar eminence, the medial two lumbricals, and the front of the forearm, with the exception of the flexor carpi ulnaris (FCU) and the medial half of the flexor digitorum profundus (FDP)

Branches from the Posterior Cord

• The upper subscapular nerve (C5, 6) supplies the subscapularis muscle
• The lower subscapular nerve (C5, 6) supplies both the subscapularis and teres major muscles
• The nerve to latissimus dorsi (C6, 7, 8) supplies the latissimus dorsi muscle
• The axillary nerve (C5, 6) supplies the deltoid and teres minor muscles
• The radial nerve (C5, 6, 7, 8, and T1) supplies the muscles of the back of the arm and forearm

Erb's Palsy

• Erb's palsy is a type of brachial plexus injury specifically affecting the upper trunk
• It is caused by a birth injury, often due to difficult labor or shoulder dystocia
• The musculocutaneous nerve is affected, resulting in paralysis of the coracobrachialis, biceps, and medial half of the brachialis
• Axillary nerve: paralysis of teres minor & deltoid
• It also impacts the suprascapular nerve, causing paralysis of the supraspinatus and infraspinatus muscles
• Deformity results in a waiter's tip posture or policeman's tip, characterized by an adducted arm, extended elbow, and pronated forearm

Klumpke's Palsy

• Klumpke's palsy is another type of brachial plexus injury, this time affecting the lower trunk
• It is caused by overstretching of the upper limb during breech delivery
• The median and ulnar nerves that affect the lumbricals are affected
• The resulting deformity is a complete claw hand, with extension of the metacarpophalangeal joint and flexion of the interphalangeal joint

Musculocutaneous Nerve

• The origin of the musculocutaneous nerve is the lateral cord of the brachial plexus
• Its root value stems from C5, C6, and C7
• It pierces the coracobrachialis muscle
• It passes between the biceps and brachialis muscles
• It continues as the lateral antebrachial cutaneous nerve of the forearm
• It has muscular and cutaneous branches
• The muscular branches supply the coracobrachialis, biceps, and the medial half of the brachialis muscles
• The cutaneous branch forms the lateral antebrachial cutaneous nerve of the forearm, which provides sensation to the skin of the lateral side of the forearm

Axillary Nerve

• The axillary nerve originates from the posterior cord of the brachial plexus
• Root value stems from C5 and C6
• The course passes through the quadrangular space along with the posterior circumflex humeral artery
• It then passes around the surgical neck of the humerus
• Its end, it gives rise to anterior and posterior divisions
• Its muscular branches supply the deltoid and teres minor muscles
• The cutaneous branch provides sensation to the upper lateral cutaneous nerve of the arm
• Injury can result from a surgical neck fracture or shoulder dislocation
• A possible deformity is a flat shoulder