Nerves of the Superior Limb (Brachial Plexus) - Fabio Labanca

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Brachial Plexus
 
The brachial plexus seems to be a cobweb. Let us keep this concept for a little while and add information gradually. The brachial plexus indeed seems to be a cobweb, but a cobweb made by nerves (ventral rami of spinal nerves) which starts from the neck (more precisely between the vertebras C5 to T1) and spreads branches to the arm, giving, not only motor Innervation to the muscles of the upper limb, but also, sensory Innervation to the skin of the upper limb.
To categorize the different parts of the brachial plexus, we have to be aware about the “Anatomy” of the tree. The trees support themselves with their roots on the floor; if I cut off the roots, the tree will die (the same happens with the nerves, if I cut their roots off, they die). The roots converges to form the trunk, the trunk divides into divisions, the divisions into cords, the cords into terminal branches. 
 
Note: variations in the formation of the brachial plexus are common; however, the makeup of the terminal branches is unchanged
Each trunk (superior, middle and inferior) divides into two: posterior and anterior divisions. The nerves formed from the anterior division will innervate the anterior compartment of the arm and forearm and the hand (musculocutaneous, median and ulnar nerve); whereas the nerves formed from the posterior division will innervate the posterior compartment of the arm and forearm (radial and axillary nerve). 
	Axillary
	innervates deltoid, Teres Minor, Shoulder Joint
	Radial
	inervated all muscles of the posterior compartment of arm and forearm
	Musculocutaneous
	muscles of the anterior compartment of the arm
	Median
	muscles of the anterior compartment of the forearm*
	Ulnar
	muscles of the hand*
*There are few exceptions. 
	Axillary
	C5, C6
	Radial
	C5, C6, C7, C8, T1
	Musculocutaneous
	C5, C6, (C7)
	Median
	(C5), C6, C7, C8, T1
	Ulnar
	(C7), C8, T1
*The roots between branches migh not be in the terminal branches. 
The segmental innervation to the muscles of the upper limb has a proximal-distal gradient. The more proximal muscles are innervated by higher segmentals (C5,C6), whereas more distal muscles are innervated by the lower segmentals (C8,T1). 
	C5 – C6
	Shoulder muscles
	C6 – C7
	Muscles of the distal arm and proximal forearm
	C7 – C8
	Muscles of the distal forearm 
	C8 – T1
	Intrinsic muscles of the hand
If you want understand the brachial plexus deeply, you have to learn the collateral nerves. Collateral nerves are nerves which come off along the brachial plexus. We have collateral nerves on the roots, trunk and cords, as we can see on the image above. 
Roots:
	Dorsal Scapular Nerve - (C4), C5
	Rhomboid Muscle and Levator Scapulae
	Long Thoracic Nerve - C5, C6, C7
	Serratus Anterior Muscle
Superior Trunk:
	Suprascapular Nerve – (C4), C5, C6
	Supraspinatus and Infraspinatus Muscles
	Subclavian Nerve – (C4), C5, C6
	Subclavius Muscle
Cords:
Lateral Cord
	Lateral Pectoral Nerve – C5, C6, C7
	Pectoralis Major Muscle
Posterior Cord
	Upper Subscapular Nerve – C5
	Superior portion of subscapularis
	Thoracodorsal Nerve – C6, C7, C8
	Latissimus Dorsi
	Lower Subscapular Nerve – C6
	Inferior portion of Subscapularis, Teres Major
Medial Cord
	Medial Pectoral Nerve – C8, T1
	Pec Minor, Pec Major, Sternocostal 
	Medial cutaneous Nerve of Arm – C8, T1
	Skin of medial side of arm
	Medial Cutaneous Nerve of Forearm – C8, T1
	Skin of medial side of forearm
Each peripheral nerve (from the terminal branches) is a collection of nerve fibers bound together by connective tissue, like the plastic which surrounds the telephone cable.
Musculocutaneous Nerve
Axillary Nerve
Radial Nerve
Median Nerve
Ulnar Nerve
Thoracodorsal Nerve (Middle Subscapular)
Long Thoracic Nerve 
Dorsal Scapular Nerve
Dorsal scapular nerve: rhomboid major, rhomboid minor, levator scapulae. 
Lower subscapular nerve: lower portion of subscapularis and teres major
Posterior cutaneous nerve of forearm
Radial nerve
Axillary nerve: deltoid muscle and teres minor.
Suprascapular nerve: supraspinatus and infraspinatus muscle
Musculocutaneous Nerve
Radial Nerve (Deep branch; Superficial branch)
Median Nerve
Recurrent (motor) branch of median nerve to thenar muscles
Common palmar digital branches of medial nerve
Superficial branch of ulnar nerve
Median Nerve
Ulnar Nerve
Radial Nerve
Branches of median nerve to thenar muscles and to 1st and 2nd lumbricals muscles
Branches from deep branch of ulnar nerve
Deep palmar branch of ulnar artery and deep branch of ulnar nerve
Median nerve (cut)
Ulnar nerve
Sensory innervation of the brachial plexus
Nerve Injuries
Upper Trunk Injury:
Loss of intrinsic shoulder muscles (deltoid, rotator cuff, teres major). Loss of abduction and external rotation (Waiter’s tip sigh). Sensory loss on lateral side of arm. Upper trunk may be damaged by forceful separation of head from shoulder.
Lower Trunk Injury (C8-T1):
Loss of intrinsic hand muscles (thenar, hypothenar, lumbricals, interossei). Sensory loss on medial side of hand and forearm. Lower trunk may be damage by upward traction on the upper limb, cervical rib, thoracic outlet syndrome. 
Axillary: inervation of deltoid. Axillary nerve could be damaged with a fracture of the surgicak neck of the humerus or dislocation of the sholder. The clinical manifestation of this injury will be lack of strength to abduction the upper limb and deltoid atrophy.
 
Radial: inervation of the posterior compartment of the arm and forearm. The radial nerve may be damaged by sholder discolation or upward pressure in the floor of the axila (Hooneymoon palsy: when the girlfriend sleeping on your sholder and compressing your arm overnight; or Saturday night palsy: when someone sleep, usually in the chair and compress the floor of the axila). The radial nerve can also be damaged by mid-shaft fracture of the humerus and radial head fracture or dislocation. 
Median: inervation of almost all muscles of the forearm + thenar compartment. The most commum cause of damage the median nerve is carpal tunnel compression. The median nerve is the only nerve which cross the carpal tunnel. When the doctor ask to the patient make a fist, the patient with median nerve injury is not capable to do it (like in the second image). When this patient try to do it, he makes a fist like the third image below. 
Ulnar: inervation of almost all the muscle of the hand. The ulnar nerve is responsible to abduction and adduction of the digits. So, the patient who demage the ulnar nerve is not capable to do that. 
Musculocutaneous: Loss of elbow flexion and weakned supination. Sensory loss on lateral aspect of the forearm.
Long Thoracic nerve injury: injury to the long thoracic nerve causing paralysis or weakness of the serratus anterior muscle can be disabling. Patients with serratus palsy may present with pain, weakness, limitation of the shoulder elevation and scapular winging with medial translation of the scapula, rotation of the inferior angle towards the midline, and proeminence of the vertebral border.