Median Nerve Flashcards
What is the median nerve?
A major peripheral nerve of the upper limb
What are the nerve roots of the median nerve?
C6-T1 (also contains fibres from C5 in some individuals)
What muscles does the median nerve innervate?
The flexor muscles in the anterior compartment of the forearm (except flexor carpi ulnaris, and part of the flexor digitorum profundus)
Thenar muscles and lateral two lumbricals in the hand
What are the sensory functions of the median nerve?
Gives rise to the palmar cutaneous branch and the digital cutaneous branch
What does the palmar cutaneous branch innervate?
The lateral part of the palm
What does the digital cutaneous branch innervate?
The lateral three and a half fingers on the anterior (palmar) surface of the hand
What is the median nerve derived from?
The medial and lateral cords of the brachial plexus, and so contains fibres from all five roots (C5-T1)
What course does the median nerve take?
After originating from the brachial plexus in the axilla, the median nerve descends down the arm, initially lateral to the brachial artery. Halfway down the arm, the nerve crosses over the brachial artery, and becomes situated medially.
How does the median nerve enter the anterior compartment of the forearm?
Via the cubital fossa
Where does the median nerve travel in the forearm?
Between the flexor digitorum profundus and flexor digitorum superficialis muscles
What does the median nerve give rise to in the forearm?
Two major branches, the anterior interosseous nerve, and the palmar cutaneous nerve
What does the anterior interosseous nerve do?
Supplies the deep muscles in the anterior forearm
What does the palmar cutaneous nerve do?
Innervates the skin of the lateral palm
How does the median nerve enter the hand?
Via the carpal tunnel
What happens to the median nerve in the hand?
It terminates by dividing into two branches, the recurrent branch and the palmar digital branch
What does the recurrent branch do?
Innervates the thenar muscles
What does the palmar digital branch do?
Innervates the palmar surface and fingertips of lateral three and a half digits
Innervates the two lateral lubrical muscles
What is the most common mononeuropathy?
Carpal tunnel syndrome
What causes carpal tunnel syndome (CTS)
Compression of the median nerve within the carpal tunnel
What can CTS be due to?
Thickened ligaments and tendon sheath
What is the aetiology of CTS?
Most often idiopathic
What happens if CTS if left untreated?
Can cause weakness and atrophy of thenar muscles
What will patients with CTS comment on?
Numbness, tingling and pain in the distribution of the median nerve. The pain will usually radiate to the forearm
What are the symptoms of CTS often associated with?
Waking the patient from their sleep
Being worse in the mornings
How are tests for CTS carried out?
Tinel’s Sign
Phalen’s manoeuvre
How is Tinel’s sign tested for?
Tapping the nerve in the carpal tunnel to elicit pain in median nerve distribution
What is Phalen’s manoeuvre?
Holding the wrist in flexion for 60 seconds to elicit numbness/pain in median nerve distribution
What does treatment of CTS involve?
Use of a splint, holding the wrist in dorsiflexion overnight to relieve symptoms.
If this is unsuccessful, corticosteroid injections into the carpal tunnel can be used
In severe case, surgical decompression of the carpal tunnel may be required
What muscles does the median nerve innervate in the superficial layer of the anterior forearm?
Pronator teres, flexor carpi radialis and palmaris longus
What muscles does the median nerve innervate in the intermediate layer of the anterior forearm?
Flexor digitorum superficialis
What does the median nerve give rise to?
The anterior interosseous nerve
What does the anterior interosseous nerve supply?
The deep flexors- the flexor pollicis longus, pronator quadratus, and the lateral half of the flexor digitorum profundus
What do the muscles supplied by the median nerve do?
In general, performs flexion of the wrist, and flexion of the digits of the hand
How does the median nerve innervate some of the muscles in the hand?
Via two branches, the recurrent branch of the median nerve, and the palmar digital branch of the median nerve
What does the recurrent branch of the median nerve innervate?
Thenar muscles
What are thenar muscles?
Muscles associated with movements of the thumb
What does the palmar digital branch innervate?
The lateral two lumbricals
Wha to the lateral two lumbricals perform?
Flexion at the metacarpophalangeal joints of the index and middle fingers
What sensory functions is the median nerve responsible for?
Cutaneous innervation of part of the hand
How is cutaneous innervation of the hand by the median nerve achieved?
Via two branches, the palmar cutaneous branch and the palmar digital cutaneous branch
Where does the palmar cutaneous branch arise?
In the forearm
Where does the palmar cutaneous branch innervate?
The lateral aspect of the palm
Does the palmar cutaneous branch pass through the carpal tunnel?
No
Where does the palmar digital cutaneous branch?
In the hand
Where does the palmar digital cutaneous branch innervate?
The palmar surface and the fingertips of the lateral three and a half digits
Where is the median nerve particularly vulnerable to damage?
At the elbow and wrist
How does damage to the median nerve at the elbow commonly occur?
Supracondylar fracture of the humerus
How does damage to the median nerve at the elbow affect motor functions?
The flexors and pronators in the forearm are paralysed, with the exception of the flexor carpi ulnaris and medial half of the flexor digitorum profundus
The forearm is constantly supinated, and flexion is weak and often accompanied by adduction
Flexion at the thumb is prevented, as both the longus and brevis muscles are paralysed
The lateral two lumbrical muscles are paralysed, and the patient will not be able to flex at the MCP joints or extend at the IP joints of the index and middle fingers
Why is forearm flexion often accompanied by adduction when there is median nerve damage at the elbow?
Because of the pull of the flexor carpi ulnaris
How are sensory functions affected when there is median nerve damage at the elbow?
Lack of sensation over the area that the median nerve innervates
What are the characteristic signs of median nerve damage at the elbow?
Thenar eminence is wasted
If patient tries to make a fist, only little and ring fingers can flex completely, resulting in ‘hand of benediction’
Why is the thenar eminence wasted when there is median nerve damage at the elbow?
Due to atrophy of the thenar muscles
How does median nerve damage at the wrist commonly occur?
Lacerations just proximal to the flexor retinaculum
How are motor functions affected by median nerve damage at the wrist?
Thenar muscles and lateral two lumbrical muscles paralysed, affecting opposition of the thumb and flexion of the index and middle fingers
How are sensory functions affected by median nerve damage at the wrist?
Same as at elbow
What are the characteristic signs of median nerve damage at the wrist?
Same as at elbow
