Brachial Plexus Flashcards
Draw the Brachial Plexus
What are the upper/lower extremity dermatomes and myotomes
C2 Dermatome and Myotome
Dermatome: Temple, forehead, occiput
Myotome: Longus colli, SCM, rectus capitus
Reflex: none
C3 Dermatome and Myotome
Dermatome: Entire neck, posterior cheek, temporal area, prolongation forward under mandible
Myotome: Trapezius, splenius capitus
Reflex: None
C4 Dermatome and Myotome
Dermatome: Shoulder area, clavicular area, upper scapular area
Myotome: Trapezius, levator scapulae
Relex: None
C5 Dermatome and Myotome
Dermatome: Deltoid area, anterior aspect of entire arm to base of thumb
Myotome: Supraspinaturs, infraspinatus, deltoid, biceps
Reflex: BICEPS, brachioradialis
C6 Dermatome and Myotome
Dermatome: Anterior arm, radial side of hand to thumb and index finger
Myotome: Beceps, supinator, wrist extensors
Relfex: biceps, BRACHIORADIALIS
C7 Dermatome and Myotome
C8 Dermatome and Myotome
T1 Dermatome and Myotome
T4 Dermatome and Myotome
Dermatome: Nipple Line
Myotome:
T2 Dermatome and Myotome
Dermatome: Medial side of upper arm to medial elbow, pectoral and midscapular areas.
Myotome: Disk lesions at the upper two thoracic levels do not appear to give rise to root weakness. Weakness of intrinsic muscle of the hand is due to pther pathology (e.g, thoracic outlet pressure, neoplasm of ling, ulnar nerve lesion)
Draw the Brachial Plexus
Dorsal Scapular Nerve
Origin C5 nerve root of the brachial plexus
Sensory supply None
Motor supply
Levator scapulae (elevates scapula)
Rhomboid major and rhomboid minor (stabilise, retract and medially rotate scapula)
Long Thoracic Nerve
Origin: C5, C6 and C7 nerve roots of the brachial plexus
Sensory supply: None
Motor supply: Serratus anterior (protracts and stabilises scapula)
Clinical significance
The long thoracic nerve often crops up in exam questions. An injury to the long thoracic nerve, for example as a result of a sports injury or damage during axillary surgery, results in “winging” of the scapula on examination. The deformity may be visible at rest, and a classic way to elicit or exaggerate it in an OSCE is by asking the patient to push against a wall and looking for abnormal posterior protrusion of the scapula on the affected side.
Suprascapular Nerve
Origin: (C5/C6) Superior trunk of the brachial plexus
Sensory supply: Glenohumeral and acromioclavicular joints
Motor supply:
Supraspinatus (stabilises and abducts shoulder)
Infraspinatus (stabilises and externally rotates shoulder)
Nerve to Subclavius
Origin: (C6) Superior trunk of the brachial plexus
Sensory supply: None
Motor supply: Subclavius (depresses clavicle and elevates the first rib)
Lateral Pectoral Nerve
Origin: (C5/C6/C7) Lateral cord of the brachial plexus
Sensory supply: None to the skin, but it is thought to play an important role in the sensation of chest wall pain, for example after mastectomy or breast implant insertion, and is, therefore, a target for regional nerve blocks
Motor supply
Upper clavicular part of the pectoralis major (flexes, adducts and internally rotates shoulder)
Upper Subscapular Nerve
Origin: (C5/C6) Posterior cord of the brachial plexus
Sensory supply: None
Motor supply
Subscapularis (stabilises and internally rotates shoulder)
Lower Subscapular Nerve
Origin: (C5/C6) Posterior cord of the brachial plexus
Sensory supply: None
Motor supply
Subscapularis (stabilises and internally rotates shoulder)
Teres major (adducts and internally rotates shoulder, protracts and depresses scapula)
Thoracodorsal Nerve
Origin: (C6/C7/C8) Posterior cord of the brachial plexus
Sensory supply: None
Motor supply
Latissimus dorsi (extends, adducts and internally rotates shoulder, externally rotates trunk)
Clinical significance
The thoracodorsal nerve is vulnerable to injury during axillary dissection, for example during lymph node clearance for breast cancer. This results in shoulder movement weakness, which is best elicited on examination by asking the patient to place the dorsum of their hand on the opposite buttock to test extension, adduction and internal rotation. Thankfully, most patients do not suffer from significant loss of function in terms of day-to-day activities, but elderly people may struggle to pull themselves up from a sitting position, and young climbers or bodybuilders are likely to notice significantly reduced performance on the affected side.
Medial Pectoral Nerve
Origin: (C8/T1) Medial cord of the brachial plexus
Sensory supply: None to the skin, but may have a role in the sensation of chest wall pain following breast surgery
Motor supply
Pectoralis minor (stabilises scapula, raises ribs during inspiration)
Lower sternocostal part of the pectoralis major (extends, adducts and internally rotates shoulder)
Medial Cutaenous Nerve of the Arm
Origin: (T1) Medial cord of the brachial plexus
Sensory supply: Skin of the lower third the of the medial arm
Motor supply
None
Medial Cutaneous Nerve of the Forearm
Origin: (C8) Medial cord of the brachial plexus
Sensory supply: Skin over biceps muscle, antecubital fossa and medial forearm
Motor supply: None
Musculocutaneous Nerve
Origin: (C5/C6/C7) Lateral cord of the brachial plexus
Sensory supply: Lateral forearm
Motor supply:
Anterior compartment of the arm:
Biceps (flexes elbow, supinates forearm)
Brachialis (flexes elbow)
Coracobrachialis (adducts shoulder, flexes elbow)
Clinical significance
Musculocutaneous nerve injuries are rare, but result in very weak elbow flexion and weak forearm supination which can be very disabling.
CLINICAL FEATURES OF MUSCULOCUTANEOUS NERVE PALSY
SENSORY LOSS
numbness over lateral forearm
MOTOR DEFICIT
paralysis of anterior compartment of arm – very weak elbow flexion and weak forearm supination
absent biceps reflex
DEFORMITY
wasting of anterior compartment of arm
elbow usually held in extension with forearm pronated
Axillary Nerve
Origin: (C5/C6) Posterior cord of the brachial plexus
Sensory supply: “Sergeant’s patch” over the lower deltoid
Motor supply
Deltoid (abducts, flexes and extends shoulder)
Teres minor (stabilises and externally rotates shoulder)
Clinical significance
The axillary nerve may be injured by shoulder dislocations or proximal humeral fractures, resulting in numbness over the sergeant’s patch and profound weakness of shoulder abduction from 15-90°. Other examination findings include deltoid wasting and weakness of shoulder flexion, extension and external rotation.
COMMON INJURIES
fracture of surgical neck of humerus
stab wounds to posterior shoulder
anterior shoulder dislocation
pressure of crutches on armpits (“crutch palsy”)
CLINICAL FEATURES OF AXILLARY NERVE PALSY
SENSORY LOSS
numbness over “sergeant’s patch”
MOTOR DEFICIT
paralysis of deltoid – very weak shoulder abduction from 15-90°; weak shoulder flexion and extension
paralysis of teres minor – weak shoulder external rotation
DEFORMITY
wasting of deltoid muscle, making the bones of the shoulder joint very prominent and obvious
shoulder may appear adducted and internally rotated
Radial Nerve
Origin: (C5/C6/C7/C8/T1) Posterior cord of the brachial plexus
Sensory supply
Posterior arm and forearm
Lateral ⅔ of the dorsum of the hand
Proximal dorsal aspect of lateral 3½ fingers
Motor supply
The radial nerve supplies the posterior compartment of the arm, which contains triceps (extends and adducts shoulder, extends elbow).
It also supplies the entirety of the posterior compartment of the forearm. This consists of:
Brachioradialis (flexes elbow)
Anconeus (extends elbow, stabilises elbow joint)
Supinator (supinates forearm)
Extensor carpi radialis longus and brevis (extend and abduct wrist)
Extensor carpi ulnaris (extend and adduct wrist)
Extensor digitorum
Extensor pollicis longus and brevis
Extensor indicis
Extensor digiti minimi
Abductor pollicis longus (abducts thumb)
Clinical significance
Radial nerve injuries are commonly due to compression, for example by leaning or lying on the arm for extended periods, excessively tight plaster casts or prolonged tourniquet use. It can also be damaged by fractures of the humerus or radius, or by stab wounds. Radial nerve injury results in loss of innervation to the muscles of the posterior compartments of the arm and forearm. This manifests as numbness in the radial nerve distribution and a “wrist drop” deformity with very weak extension of the elbow, wrist and fingers.
COMMON INJURIES
fractures of proximal humerus, shaft of humerus or radius
stab wounds to antecubital fossa, forearm or wrist
this includes blood tests and venflons!
pressure of crutches on armpits (“crutch palsy“)
the patient falling asleep with arm hanging over the back of a chair, classically whilst drunk (“Saturday night palsy“)
somebody else falling asleep with their head lying on the patient’s arm (“honeymoon palsy“)
excessively tight plaster casts, wristbands or handcuffs
prolonged tourniquet use on upper arm, for example during orthopaedic or plastics procedures
Median Nerve
(C5/C6/C7/C8/T1)
Origin
Lateral and medial cords of the brachial plexus
Sensory supply
Thenar eminence, the lateral ⅔ of the palm of the hand
Palmar aspect of lateral 3½ fingers
Dorsal fingertips of lateral 3½ fingers
Motor supply
All muscles of the anterior compartment of forearm EXCEPT flexor carpi ulnaris and the medial two parts of flexor digitorum profundus.
The median nerve, therefore, supplies pronator teres, flexor carpi radialis, palmaris longus, flexor digitorum superficialis, the lateral two parts of flexor digitorum profundus, flexor pollicis longus and pronator quadratus.
These forearm muscles flex the wrist, the proximal interphalangeal joints of all four fingers and the distal interphalangeal joints of the index and middle fingers. They also pronate the forearm and abduct the wrist.
The median nerve also supplies the LOAF muscles of the hand:
The lateral two lumbricals
Opponens pollicis
Abductor pollicis brevis
Flexor pollicis brevis
The lumbricals flex the MCPJs and extend the IPJs of the index and middle finger.
The muscles of the thenar eminence flex, abduct and oppose the thumb.
Clinical significance
The median nerve is most commonly damaged by compression within the carpal tunnel at the wrist, resulting in numbness of the median nerve distribution to the hand, wasting of the thenar eminence, weak grip strength and a “hand of benediction” deformity due to an inability to flex the index or middle fingers. It can also be injured by supracondylar fractures of the humerus and stab wounds or lacerations to the forearm or wrist.
Ulnar Nerve
Origin: (C8/T1)
Medial cord of the brachial plexus
Sensory supply
Hypothenar eminence
Medial ⅓ of the palm of the hand
Palmar aspect of the lateral 1½ fingers
Medial ⅓ of the dorsum of the hand
Dorsal aspect of the medial 1½ fingers
Motor supply
The ulnar nerve supplies just two muscles in the anterior compartment of the forearm
Flexor carpi ulnaris, which flexes and adducts the wrist
The medial two parts of flexor digitorum profundus, which flex the distal interphalangeal joints (DIPJs) of the ring and little fingers.
It also supplies all of the intrinsic muscles of the hand EXCEPT the LOAF muscles supplied by the median nerve. These can be remembered as the HILA muscles:
Hypothenar eminence
Interossei
Medial two lumbricals
Adductor pollicis
The hypothenar eminence consists of opponens digiti minimi, flexor digiti minimi brevis and abductor digiti minimi, which oppose, flex and abduct the little finger respectively.
The palmar interossei adduct the fingers, whilst the dorsal interossei abduct them.
The medial two lumbricals flex the MCPJs and extend the IPJs of the ring and little fingers.
Adductor pollicis adducts the thumb – it is worth noting that this muscle does not form part of the thenar eminence and actually lies deep beneath it as a separate structure.
Clinical significance
The ulnar nerve may be injured by supracondylar fractures of the humerus, medial epicondylar fractures, stab wounds to the forearm or wrist, or compression at either the cubital tunnel in the elbow or Guyon’s canal in the wrist. This results in numbness in the ulnar distribution to the hand, wasting of the hypothenar eminence and intrinsic muscles of the hand, a “claw hand” deformity due to an inability to extend the ring and little fingers, and weak finger abduction and adduction.
Cutaneous Nerve supply of hand
