Brachial Plexus - Advanced

Brachial Plexus - Advanced

Innervation Patterns from the Brachial Plexus

See: Brachial Plexus

I. The axillary nerve (C5, C6)

• Innervates the deltoid muscle, most notably, which is responsible for the latter 70 to 80 degrees of arm abduction. Whereas supraspinatus is responsible for the first 20 to 30 degrees of arm abduction.
• Innervates teres minor, which assists in shoulder external rotation, which makes sense along with the deltoid's role in shoulder abduction.

II. The musculocutaneous nerve (C5, C6)

• Innervates the biceps brachii (most notably) it is superficial and flex the forearm in supination The role of the biceps brachii in supination explains why supination is at least partially preserved in radial nerve injury (when the radial-innervated supinator muscle, itself, is weak).
• Brachialis muscle, which is deep and flexes the elbow with the forearm in any position.
• Coracobrachialis, which is an important anatomical landmark because the axillary nerve penetrates it to run underneath the biceps brachii; it assists the clavicular head of the pectoralis major muscle in shoulder flexion.

III. The long thoracic nerve (C5, C6, C7)

• Innervates serratus anterior
• Injury causes scapular winging

IV. Dorsal scapular nerve (C4 (not shown), C5)

• Innervates the rhomboid muscles, which pull the scapula toward midline and downward

V. The nerve to the subclavius muscle (C5, C6)

• Exists where the C5 and C6 roots join together.
• The subclavius provides clavicle depression

VI. The suprascapular nerve (C5, C6) originates from the upper trunk

• Innervates the supraspinatus muscle (C5, C6), which is responsible for the first 20 to 30 degrees of arm abduction.
• Innervates the infraspinatus muscle (C5, C6), which is the primary external rotator of the arm (the other is… teres minor).

VII. The pectoral nerves:

• Lateral pectoral nerve (C5, C6, C7)
• Medial pectoral nerve (C8, T1)
  • Both innervate the pectoralis major muscle, which provides shoulder adduction and shoulder internal rotation.
  • Lateral pectoral nerveinnervates the clavicular head of pectoralis major, which additionally provides shoulder flexion.
  • Medial pectoral nerveinnervates the sternal head of the pectoralis major muscle, which additionally provides shoulder extension.
  • The pectoral nerves (mostly the medial pectoral nerve) also innervate pectoralis minor, which provides scapula depression.

VIII. The thoracodorsal nerve (C6, C7, C8)

• Lies along posterior cord interspersed between the upper and lower subscapular nerves
  • Innervates latissimus dorsi, which provides shoulder adduction.

IX. The subscapular nerves:

• Upper subscapular nerve (C5, C6)
• Lower subscapular nerve (C5, C6)
  • Innervate the subscapularis muscle, which assists in shoulder internal rotation.
  • Lower subscapular nerve also innervates teres major, which assists in shoulder internal rotation (compare this to teres minor, which assists in shoulder external rotation and is innervated by the axillary nerve).

Plexus Anomalies

• Prefixed plexus is the term for when the brachial plexus is shifted up one level and receives substantial innervation from C4
• Postfixed plexus refers to when the plexus is shifted down one level and receives substantial innervation from T2.