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Year 1 Anatomy Revision of the Upper Limb Notes – Nerves of the Upper Limb Introduction: • This notes document will cover the information included in my presentation on the nerves of the upper limb, but with some extra information not explicitly stated in the slides • I have done my best to tailor these notes to the level of detail expected in Year 1 • You will find some additional boxes throughout this document that provide information not covered in the core text; − ‘Additional Information’ boxes contain information that is not necessarily expected in Year 1, but it may aid understanding or prove useful for those with a particular interest in this area − ‘Clinical Information’ boxes contain a little more clinical information on the relevant area, to try and integrate your learning with what you will be covering in other modules • I hope that all makes sense, but if you have any questions about my presentation or notes feel free to send me an email at fmcbride06@qub.ac.uk. Good luck! Learning Outcomes: 1. Identify the trunks, location of the divisions, cords and five main terminal branches of the brachial plexus 2. Describe the cutaneous innervation of the upper limb 3. Map out the dermatomes of the upper limb 4. Describe the origin, course and relations of the axillary nerve 5. Describe the origin, course and relations of the musculocutaneous nerve 6. Describe the origin, course and relations of the radial nerve 7. Describe the origin, course and relations of the median nerve Fionán Mac Giolla Bhríde fmcbride06@qub.ac.uk Brachial Plexus: 1. Identify the trunks, location of the divisions, cords and five main terminal branches of the brachial plexus • The brachial plexus can be divided into its roots, trunks, divisions, cords and branches • To make this somewhat easier I will discuss each section individually and add to the diagram gradually, as in my personal experience the brachial plexus can be overwhelming when you first see it • The roots arise from the ventral (anterior) rami of the C5-T1 spinal nerves • They arise in the neck and enter the axilla along with the subclavian vessels and form the brachial plexus ROOTS C5 C6 C7 C8 T1 • Once in the axilla, the C5-C6 and C8-T1 roots unite to form the superior and inferior trunks and the C7 nerve root continues as the middle trunk • At this point, the plexus runs almost horizontally, which is why the trunks are named from top to bottom ROOTS TRUNKS Superior Middle Inferior Fionán Mac Giolla Bhríde fmcbride06@qub.ac.uk• Each trunk will then give off an anterior and posterior division • The anterior divisions will innervate the anterior compartment (flexor muscles) in the upper limb • The posterior divisions will innervate the posterior compartment (extensor muscles) in the upper limb • The posterior divisions of the superior and inferior trunks unite with the posterior division of the middle trunk to form the posterior cord • The anterior division of the middle trunk units with the anterior division of the superior trunk to form the lateral cord • The anterior division of the inferior trunk continues as the medial cord ROOTS TRUNKS DIVISIONS Ant Post Ant • At this point, the plexus runs obliquely (as shown in a later image), which is why the cords are named from medial to lateral • They are also named by their relationship to the axillary artery ROOTS TRUNKS DIVISIONS CORDS Lateral Posterior Medial Fionán Mac Giolla Bhríde fmcbride06@qub.ac.uk • The cords form the five main terminal branches of the plexus • The lateral cord gives rise to the musculocutaneous nerve, and unites with fibres from the medial cord to form the median nerve • The posterior cord gives rise to the axillary and radial nerves • The medial cord gives rise to the ulnar nerve, and unites with fibres from the lateral cord to form the median nerve ROOTS TRUNKS DIVISIONS CORDS BRANCHES Musculocutaneous Axillary Median Radial Ulnar • Hopefully the brachial plexus makes a bit more sense now, and here is the full version ROOTS TRUNKS DIVISIONS CORDS BRANCHES C5 Superior Ant Lateral Musculocutaneous C6 Axillary Middle Posterior Median C7 Post Radial C8 Inferior Medial Ulnar Ant T1 Fionán Mac Giolla Bhríde fmcbride06@qub.ac.uk• For completion, I have included a schematic with the smaller branches that arise from the plexus to innervate the scapulohumeral muscles and skin of the arm/forearm • However, I don’t feel that intricate knowledge of where these branches arise is necessary for year 1 anatomy • Just to note, the middle subscapular nerve is also known as the thoracodorsal nerve (innervating the latissimus dorsi muscle) Dorsal Scapular Suprascapular Lateral Nerve to subclavius pectoral Upper, middle & lower subscapular Medial pectoral Medial cutaneous nerve Long thoracic of arm & forearm • Here is a more anatomical diagram illustrating the location of each part of the plexus in the arm Moore KL, Dalley AF, Agur AMR. Clinically Orientated Anatomy. Page 722 Fionán Mac Giolla Bhríde fmcbride06@qub.ac.ukCutaneous Innervation of the Upper Limb: 2. Describe the cutaneous innervation of the upper limb 3. Map out the dermatomes of the upper limb • The cutaneous innervation of the upper limb arises primarily from cutaneous branches of the brachial plexus or the nerves that arise from it • I have included two diagrams of the cutaneous innervation below; one highlights the areas innervated by the five main nerves of the brachial plexus, and the other provides the specific cutaneous branches ANTERIOR POSTERIOR Axillary nerve Radial nerve Radial nerve Musculocutaneous nerve Ulnar nerve Median nerve • The medial cutaneous nerve of the arm and forearm arise from the medial cord of the brachial plexus • The posterior cutaneous nerve of the arm and forearm are branches of the radial nerve • The lateral cutaneous nerve of the forearm is the direct continuation of the musculocutaneous nerve ANTERIOR POSTERIOR Axillary nerve Axillary nerve Posterior cutaneous Medial cutaneous nerve of arm & forearm nerve of arm Posterior cutaneous nerve of arm & forearm Lateral cutaneous Medial cutaneous Lateral cutaneous nerve of forearm nerve of forearm nerve of forearm Superficial branch of radial nerve Ulnar nerve Superficial branch of radial nerve Median nerve Fionán Mac Giolla Bhríde fmcbride06@qub.ac.uk• Dermatome – area of skin innervated by the sensory fibres from a single spinal nerve • Spinal nerve – mixed nerve (containing motor, sensory and autonomic fibres) originating from a single spinal cord level • The most superior portion of the shoulder is innervated by the C3-C4 dermatomes (via supraclavicular nerves) but these are rarely tested in upper limb examination • Beginning with C5 at the superolateral aspect of the arm, the dermatomes follow sequentially around the forearm, hand and back up into the axilla with T2 • The dermatomes do not match the areas supplied by the peripheral cutaneous nerves because multiple spinal nerves contribute to each peripheral nerve so there is an overlap of fibres ANTERIOR POSTERIOR Drake RL, Vogl W, Mitchell AWM, Gray H. Gray’s anatomy for students. Page 697 CLINICAL INFORMATION During neurological examination of the DERMATOME LANDMARK upper limb, sensation is tested in each dermatome. C5 Lateral aspect of the elbow C6 Tip of the thumb In order to ensure every dermatome is assessed, it is helpful to use landmarks C7 Tip of the middle finger that are easy to remember. C8 Tip of the little finger These are summarised in the table T1 Medial aspect of the elbow opposite. Fionán Mac Giolla Bhríde fmcbride06@qub.ac.ukAxillary Nerve: 4. Describe the origin, course and relations of the axillary nerve • The axillary nerve has C5-C6 nerve roots and arises from the posterior cord of the brachial plexus (posterior to the axillary artery) • It travels through the quadrangular space, along with the posterior circumflex humeral artery, and winds around the humerus (A) • It innervates the deltoid and teres minor muscles, and the ‘regimental badge’ area of skin in the upper arm A NERVE ROOT MUSCULAR INNERVATION CUTANEOUS INNERVATION deltoid Axillary C5-C6 ‘regimental badge’ area teres minor CLINICAL INFORMATION The axillary nerve can be damagedby shoulder dislocation or fracture of the surgical neck of the humerus. If damaged, the deltoid and teres minor muscles willno longer receive innervation. There will be an inability to fully abduct the arm at the shoulder (deltoid) and a weakness in lateral rotationof the shoulder (teres minor), along with loss of sensation in the regimental badge area. Deltoid atrophy may occur if the injury is left untreated. Fionán Mac Giolla Bhríde fmcbride06@qub.ac.ukMusculocutaneous Nerve: 5. Describe the origin, course and relations of the musculocutaneous nerve • The musculocutaneous nerve has C5-C7 nerve roots and arises from the lateral cord of the brachial plexus • It pierces coracobrachialis and travels between biceps brachii and brachialis (B), innervating these three muscles • At the elbow, the nerve travels superficially and continues as the lateral cutaneous nerve of the forearm (C), innervating the skin on the lateral aspect of the forearm B C NERVE ROOT MUSCULAR INNERVATION CUTANEOUS INNERVATION biceps brachii Musculocutaneous C5-C7 brachialis lateral forearm coracobrachialis CLINICAL INFORMATION The musculocutaneous nerve can be damaged byshoulder dislocation or trauma to the arm, but this injury is uncommon. If damaged, the biceps brachii and coracobrachialis muscles will no longer receive innervation. Brachialis receives some dual innervation from the radial nerve so it may beunaffected. There will be a weakness in elbow flexion (biceps brachii & corachobrachialis) and forearm supination (biceps brachii), but these movements are not lost completely because other muscles that perform these actions are innervated by other nerves. There will also be a loss of sensation in the lateral forearm. Fionán Mac Giolla Bhríde fmcbride06@qub.ac.ukRadial Nerve: 6. Describe the origin, course and relations of the radial nerve • The radial nerve has C5-T1 nerve roots and arises from the posterior cord of the brachial plexus • It has a long course with many branches, but its primarily role is to innervate the muscles (extensors) and skin of the posterior compartment of the upper limb (as shown in the table below) • It leaves the axilla by travelling posteriorly into the triangular interval along with the profunda brachii artery in the spiral groove of the humerus (D) • It continues posteriorly in the arm before travelling anterior to the lateral epicondyle of the humerus between the brachialis and brachioradialis (E) • Technically, the radial nerve lies lateral to the cubital fossa in the elbow, but some sources consider it a content of the cubital fossa – so either definition should be fine in an exam • It divides at the elbow into a superficial (F) and deep (G) branches • The deep branch is motor and innervates the extensor muscles of the posterior compartment of the forearm • The superficial branch is sensory and travels deep to brachioradialis in the forearm and becomes superficial at the wrist, extending into the hand and innervating the skin on the lateral dorsal aspect of the hand and the dorsal aspect of the lateral 3 ½ digits (except the nailbeds) D E F G Fionán Mac Giolla Bhríde fmcbride06@qub.ac.uk NERVE ROOT MUSCULAR INNERVATION CUTANEOUS INNERVATION triceps brachii anconeus brachialis brachioradialis extensor carpi radialis longus extensor carpi radialis brevis posterior arm extensor digitorum posterior forearm Radial C5-T1 extensor digiti minimi lateral dorsal aspect of hand extensor carpi ulnaris dorsal aspect of lateral 3 ½ digits supinator extensor indicis abductor pollicis longus extensor pollicis longus extensor pollicis brevis ADDITIONAL INFORMATION The radial nerve gives off the posterior cutaneous nerves of the arm and forearm when it travels in the spiral groove. These nerves travel inferiorly into the posterior arm and forearm to provide sensory innervation to the skin inthese regions. The deep branch of the radial nerve travels between the superficial and deep heads of supinator at the elbow, and once it emerges from supinator it is known as the posterior interosseus nerve (although it is technically the exact same nerve,just with a different name). This nerve innervates the deepest muscles of the posterior compartment of the forearm. The superficial radial nervedivides into dorsal digital branches that innervate the skin over the lateral 3 ½ digits, excluding the nailbeds (which are innervated by the median nerve). The nailbeds are not innervated by the radial nerve because embryologically they develop on the palmar aspect of the fingers and then migrate dorsally over time. CLINICAL INFORMATION The radial nerve can be injured by humeral shaft fractures, trauma to the elbow or fracture of the distal radius (eg. Colle’s fracture). If damaged, the extensor muscles of the arm and forearm will no longer receive innervation.This will lead to ‘wrist drop’ characterised by the inability to extend the wrist (ERCL, ECRB & ECU) and metacarpophalangeal joints (ED, EDM, EI) of the digits. The interphalangeal joints will be extendable due to the lumbricals and interossei (innervated by themedian/ulnar nerve). If the lesion is very proximal (eg. trauma to axilla), there may be loss of elbow extension as well due to denervation of the triceps brachii. Fionán Mac Giolla Bhríde fmcbride06@qub.ac.ukMedian Nerve: 7. Describe the origin, course and relations of the median nerve • The median nerve has C5-T1 nerve roots and arises from the medial and lateral cords of the brachial plexus • Like the radial nerve, it has a long course and multiple branches, but its primary role is to innervate most muscles (flexors) of the anterior compartment of the forearm and lateral skin of the hand (as shown in the table below) • In the arm, it travels lateral to the brachial (H) artery before crossing medial to it as it enters the cubital fossa (I) • In the forearm (J), it innervates the muscles of the anterior compartment (except flexor carpi ulnaris and the medial ½ flexor digitorum profundus) • At the wrist it gives off the palmar cutaneous branch (which innervates the palmar skin of the lateral hand) before continuing into the hand • In the hand, it passes through the carpal tunnel innervates the muscles of the thenar eminence and lateral two (1 and 2 ) lumbricals H I J NERVE ROOT MUSCULAR INNERVATION CUTANEOUS INNERVATION pronator teres flexor carpi radialis palmaris longus flexor digitorum superficialis lateral ½ flexor digitorum profundus lateral palmar aspect of hand Median C5-T1 flexor pollicis longus palmar aspect of lateral 3 ½ digits pronator quadratus nailbeds of lateral 3 ½ digits abductor pollicis brevis flexor pollicis brevis opponens pollicis 1 & 2 lumbricals Fionán Mac Giolla Bhríde fmcbride06@qub.ac.uk ADDITIONAL INFORMATION At the elbow, the median nerve gives off the anterior interosseus branch. This branchis purely motor and travels along the interosseus membrane and innervates the deeper muscles of the anterior compartment (lateral ½ FDP, FPL and PQ). Just proximal to the wrist the palmar cutaneous branch arises from the median nerve and travels superificial to the flexor retinaculum to innervate the skin . This is the reason why sensation is often preserved in carpal tunnel syndrome. In the hand, the median nerve divides intothree branches; recurrent, lateral and medial. The recurrent st brancndinnervates the thenar muscles (AP, FPB & OP). The lateral and medial branches innervate the 1 and 2 lumbricals, respectively, and the palmar skin and nailbeds of the lateral 3 ½ digits. CLINICAL INFORMATION Carpal tunnel syndrome involves compression of the median nerve in the carpal tunnel at the wrist. The exact cause is often unknown, but this pathology is associated with diabetes, female sex and pregnancy. The main symptoms are pain (but not sensory loss) over the lateral palmar skin of the hand (innervated by palmar cutaneous branch of median nerve) and weakness in thumb movements. This is due to loss of the thenar muscles which are innervated by the median nerve. If left untreated, thenar muscle wastingmay occur. Flexion of the other digits is not affected as the muscles producing these movements arise in the forearm, proximal to the injury. Fionán Mac Giolla Bhríde fmcbride06@qub.ac.uk