Nerves of the Upper limb Flashcards
What is the anatomy of the brachial plexus?
SUMMARY: 5 Roots (formed by ANTERIOR RAMI) –> 3 trunks –> 6 divisions –> 3 cords –> 5 terminal branches (peripheral nerves).
BREAKDOWN: Anterior rami from C5 and C6 form the UPPER TRUNK; C7 continues as the MIDDLE TRUNK; C8 and T1 unite to form the LOWER TRUNK.
Each trunk branches to form an ANTERIOR and POSTERIOR division. Divisions have no terminal branches.
Upper and middle anterior divisions combine to form the LATERAL CORD; lower anterior divisions continue as the MEDIAL CORD; all three posterior divisions unite to form the POSTERIOR CORD.
It is from the cords that most of the terminal nerves emerge.
What are the main terminal branches of the brachial plexus CORDS? (x5)
LATERAL CORD: gives the musculocutaneous nerve.
POSTERIOR CORD: gives the axillary and radial nerve.
MEDIAL CORD: gives the ulnar nerve.
LATERAL AND MEDIAL CORDS: unite to form the median nerve.
How are the cords of the brachial plexus named?
Named in relation to their position to the axillary artery e.g. posterior cord is posterior to the artery.
Cords: which cords give rise to which type of muscle in the upper limb? !!!
POSTERIOR cord gives rise to EXTENSOR MUSCLES; LATERAL and MEDIAL cords give rise to FLEXORS.
What are collateral branches of the brachial plexus? Two types?
There are a number of ‘collateral’ branches that come off the brachial plexus ‘prematurely’. These branch before the terminal branches in the brachial plexus – SUPRACLAVICULAR BRANCHES emerge above the clavicle (from a trunk or root), and INFRACLAVICULAR emerge below the clavicle (from a cord).
List the main supraclavicular branches of the brachial plexus. (x4) Brief action?
Dorsal scapular: innervate rhomboid.
Long thoracic: serratus anterior.
Suprascapular: supraspinatus and infraspinatus muscles; glenohumeral joint.
Subclavian nerve: subclavis and sternoclavicular joint – connected to accessory phrenic nerve.
List the main infraclavicular branches of the brachial plexus. (x7) Brief action?
Lateral pectoral: pectoralis major and some pectoralis minor.
Medial pectoral: pectoralis minor and sternocostal part of major.
Upper subscapular: superior portion of subscapularis.
Lower subscapular: inferior portion of subscapularis and teres major.
Thoracodorsal: latissimus dorsi.
Medial cutaneous nerve of the arm: sensory to front and medial skin of arm.
Medial cutaneous nerve of the forearm: sensory to medial skin of forearm.
SUMMARY: What are the roots of the motor nerves of the upper limb? (x5)
C3-C7 (some not even in brachial plexus): shoulder girdle muscles.
C5-C6: supply shoulder joint muscles and elbow flexors.
C7-C8: supply elbow joint extensors.
C6-C8: supply wrist and coarse hand muscles – rough movements.
C8-T1: supply intrinsic muscles of hand – fine movements.
SUMMARY: What are the roots of the five main terminal branches of the brachial plexus? !!!
• Axillary – C5,6. • Radial – C5-T1. • Median – C6- T1. • Ulnar – C8-T1 (and C7 supplies flexor carpi ulnaris). • Musculocutaneous – C5-7.
What are the dermatomes of the upper limb?
Note how the dermatomes are cyclic i.e. the nerve roots cycle round the arm. Pretty easy to remember.
What is the pattern of sensory nerve distribution in the upper limb?
Look at photo.
Why is the dermatome and sensory nerve distribution of the upper limb different?
The dermatome maps out individual SPINAL NERVE ROOTS in the arm; sensory nerve distribution maps out individual TERMINAL BRANCH NERVES which are made up of multiple, condensed spinal nerve roots from recombination in the brachial plexus e.g. the ulnar nerve passes sensory innervation to the C8 and T1 spinal nerves.
What is the course and function of the axillary nerve?
Exits the posterior fossa posteriorly, then passes laterally, winding around the surgical neck of the humerus under the glenohumeral joint, deep to the deltoid. It supplies the teres minor and DELTOID muscles and is sensory to skin of superolateral arm (via superior lateral cutaneous nerve of arm).
How may the axillary nerve become damaged? Result of damage? (x3)
Where it passes under the shoulder joint and close to the surgical neck of the humerus, it is vulnerable to damage in dislocations and damage to the surgical neck of the humerus. Damage to the axillary nerve would result in area of anaesthesia to superolateral area of skin of arm, wasting of the deltoid muscle and loss of ability to ABDUCT arm.
What is the course and function of the radial nerve?
Exits axillary fossa posterior to axillary artery, passing posterior to the humerus in the radial groove between the lateral and medial heads of the triceps. Enters the cubital fossa, dividing into superficial, cutaneous (sensory) and deep, motor radial nerves. Supplies all muscles of the posterior compartments of the forearm and arm, and skin of the posterior and inferolateral arm, posterior forearm and dorsum of hand lateral to axial line of ring finger.
How may the radial nerve become damaged? Result of damage? (x4)
Radial nerve runs closely apposed to the shaft of the humerus, so can be damaged in humeral fractures. Damage would result in anaesthesia to the lateral dorsum of the hand, posterior forearm and posterior arm, muscle wasting of the posterior arm and forearm muscles, loss of extension of forearm/hand/fingers –> e.g. wrist drop, and LOSS OF POWER GRIP. Result depends on how distal the damage was to the nerve!
Why do we lose the ability of the power grip in radial nerve damage when power grip involves flexion of digits?
Efficient power grip requires an extended wrist. Being unable to extend wrist from radial nerve damage makes it harder to do the power grip.
How may the ulnar nerve become damaged? (x2) Result of damage? (x3)
Injuries to the medial epicondyle of the humerus causes injury to the ulnar nerve at the elbow; AND self-harm injuries when people cut their wrists.
Damage causes CLAW DEFORMITY at rest from (i) weakened extension of the interphalangeal joints, from lost innervation to the third and fourth lumbricals (see photo), and (ii) loss of third and fourth lumbrical-mediated flexion of the metacarpophalangeal joints; Many small muscles of the hand affected, but thumb, index and middle finger largely spared; Loss of sensation in ulnar half of palm, dorsum of hand and medial 1 and a half digits.
What is the course and function of the median nerve?
Emerges lateral to axillary artery (despite forming from lateral and medial cords). It descends through the arm adjacent to the brachial artery, becoming more anterior to lie medial to the brachial artery beneath the bicipital aponeurosis in the cubital fossa. Travels down the forearm and through the carpal tunnel between the tendons of the FDS and palmaris longus.
Supplies muscles of the anterior forearm compartment (except for flexor carpi ulnaris and ulnar half of the flexor digitorum profundus). It also supplies intrinsic muscles of the hand in thenar palm, and sensory to lateral part of the hand.
What are the signs of Carpal Tunnel Syndrome? (x3) !!!
- Wasting of thenar eminence and abductor pollicis brevis is revealed in its place as this is supplied by the ulnar nerve.
- Clawing: unlike in ulnar injury, the clawing affects lateral three digits. Here, MCP joints of the index and middle fingers are hyperextended from lack of functioning 1st and 2nd lumbricals, and loss of flexion in IP joints from defective FDP and FDS – all supplied by median nerve. There is also loss of thenar muscles so thumb cannot oppose. Patient will therefore form a HAND OF BENEDICTION – when forming a tight fist, there is partially extended index and middle fingers. Makes FINE MOVEMENTS INCREDIBLY DIFFICULT e.g. writing.
- Anaesthesia in lateral 3 and a half digits. HOWEVER, the palmar cutaneous branch of the median nerve runs above the flexor retinaculum, so sensation of the thenar eminence is not lost!
What is the course and function of the long thoracic nerve?
- Emerges from the root of the neck and runs over the serratus anterior muscle posteriorly.
- Supplies the serratus anterior muscle.
What happens when the long thoracic nerve is damaged?
Damage is easy from trauma or stretch because it is long and relatively superficial. Damage paralyses the serratus anterior to produce a WINGED SCAPULA which is most prominent when the arm is lifted forward, and patient pushes outstretched arm against a wall.
How might Erb-Duchenne Palsy arise? (x2)
- Stretching the shoulder away from the neck from fall – see photo (1).
- Stretching neck during birth – see photo (2).
What are the signs of Erb-Duchenne Palsy?
- Includes loss of sensation in the arm.
- WAITER’S TIP: Wasting of the muscles of mainly in the shoulder and anterior arm – resulting in issue with flexion of the arm in particular; Forearm pronates by lack of biceps supination.
How might Klumpke’s palsy arise? (x2)
Over-abduction due to gripping overhead to beak a fall, OR pulling on the arm during childbirth.
What are the signs of Klumpke’s palsy? (x3)
- Intrinsic minus hand deformity – T1 mainly supplies small muscles of the hand via the ulnar and median nerves –> CLAWED HAND. Paralysis of all intrinsic muscles of the hand when both C8 and T1 are damaged.
- C8/T1 dermatome numbness.
- Horner’s syndrome.
What is clawed hand? Two types of clawed hand – describe aetiologies? !!!
- Clawing is hyperextension at MCP joints and flexion at IP joints.
- CAUSE 1: ulnar nerve lesion - the IP joints of little and ring fingers cannot straighten completely like the other three fingers which gives a claw-like hand. It is worth remembering that in a lesion of this nerve, if the subject attempts to make a fist, the little and ring fingers cannot flex completely (to form a tight fist) while the other three fingers form a tight fist. This gives a claw-like hand.
- CAUSE 2: median nerve lesion – subject is asked to form a tight fist with all fingers. This results in partially extended index and middle fingers (“hand of Benediction”). Here, MCP joints of index & middle fingers are hyperextended (1st & 2nd lumbricals) and loss of flexion in the proximal IP joints (flexor digitorum superficialis) and in the distal IP joints (FDP). Also, the loss of thenar muscles function the thumb cannot oppose.
What is the triceps tendon reflex? How is it tested? What does it test?
- HOW: Ask the subject to rest comfortably (sitting or lying supine), with elbow semi-flexed and hand pronated. The examiner should support the elbow with one hand. Tap the triceps tendon directly with the tendon hammer. If the reflex arc is intact there will be a brisk contraction of the triceps causing extension of the forearm. Compare with that of the contralateral limb.
- Tests integrity of the radial nerve – C7, C8.
