Brachial plexus Flashcards
What is the brachial plexus formed by?
The anterior rami (divisions) of spinal nerves C5, C6, C7, C8, T1.
Name the 5 parts that the brachial plexus is divided into.
Roots
Trunks
Divisions
Cords
Branches
What are the roots of the brachial plexus?
The anterior rami of the spinal nerves C5 - T1.
What structures do the nerves of the brachial plexus pass through to get to the base of the neck?
The anterior and medial scalene muscles.
How many trunks are formed at the base of the neck?
3
What roots form the superior trunk?
C5 and C6 roots.
What nerves form the middle trunk?
C7 root.
What nerves form the inferior trunk?
C8 and T1 roots.
Which triangle of the neck do the trunks traverse?
Posterior triangle.
What happens to the trunks as they pass through the posterior triangle?
Each trunk divides into 2 branches (one anterior and one posterior) to form 3 anterior and 3 posterior divisions in total.
What happens to the anterior and posterior divisions when they pass into the axilla?
They recombined into the cords of the brachial plexus.
What are the 3 cords names in relation to?
Their position relative to the axillary artery.
Which divisions form the lateral cord?
-Anterior division superior trunk
-Anterior division middle trunk
Which divisions form the posterior cord?
-Posterior division superior trunk
-Posterior division middle trunk
-Posterior division inferior trunk
Which divisions form the medial cord?
Anterior division of inferior trunk.
Which nerve roots form the musculocutaneous nerve?
C5, C6, C7
Which muscles does the musculocutnaeous nerve innervate?
Brachialis
Biceps
Coracobrachialis
Which sections of skin does the musculocutaneous nerve innervate?
Lateral half of anterior forearm
Small lateral portion of posterior forearm
Which nerve does the musculocutaneous nerve give rise to in the forearm?
Lateral cutaneous nerve of the forearm.
Which part of the skin does the lateral cutaneous nerve of the forearm innervate?
Anterolateral aspect of the forearm.
What injury most commonly damages the musculocutaneous nerve?
Penetrating injury to the axilla.
Which nerve roots form the axillary nerve?
C5 and C6.
Which muscles does the axillary nerve innervate?
Teres minor and deltoid.
Describe the sensory functions of the axillary nerve.
Gives off superior lateral cutaneous nerve of the arm = innervates inferior region of deltoid (regimental badge area).
Which type of injury can commonly damage the axillary nerve?
Fracture of humeral surgical neck
Shoulder dislocation
Iatrogenic injury during shoulder surgery
What movement will be impossible if the axillary nerve is damaged?
Abducting the shoulder >15 degrees (as deltoid will be affected)
Damage to the C5 and C6 roots of the brachial plexus can cause what?
Erb’s palsy
**Normally due to an excessive increase in the angle between the neck and the shoulder.
Which nerve roots form the median nerve?
C6 - T1 (some C5 fibres in some individuals).
Which muscles are innervated by the median nerve?
Most of flexor forearm muscles
Thenar muscles
Lateral lumbricals of index and middle fingers
Which aspects of the skin are innervated by the median nerve?
Lateral part of palm (palmar cutaneous branch)
Anterior lateral 3.5 fingers (digital cutaneous branch)
What signs are present if the median nerve is damaged at the elbow?
Thenar wasting
Hand of benediction (when making a fist only the little and ring finger flex inwards).
A supracondylar fracture of the humerus can damage which nerve?
Median.
Lacerations just proximal to the flexor retinaculum can damage which nerve?
Median.
Which signs might be present if the median nerve is damaged at the wrist?
Hand of benediction, but forearm unaffected
Which nerve roots form the radial nerve?
C5 - T1.
Which aspects of the skin are innervated by the radial nerve?
Posterior aspect of arm and forearm
Posterolateral aspect of hand
Which muscles are innervated by the radial nerve?
Triceps
Muscles in posterior compartment of forearm (mainly extensors)
Which injuries can cause damage to the radial nerve in the axilla?
Proximal humerus fracture
Shoulder dislocation
Excessive pressure on nerve in axilla (Saturday night palsy)
Which nerve is susceptible to injury in fractures of the humeral shaft?
Radial.
**Because the radial nerve is tightly bound within the spiral groove of the humerus.
Which nerve roots form the ulnar nerve?
C8 and T1.
Which aspects of the skin are innervated by the ulnar nerve?
Anterior and posterior surfaces of the medial one and a half fingers (and associated palm area)
Which muscles are innervated by the ulnar nerve?
Muscles of the hand (except thenar eminence and lateral 2 lumbricals)
Flexor carpi ulnas
Medial half of flexor digitorum profundus
How can the ulnar nerve be damaged at the elbow?
Cubital tunnel syndrome
Medial epicondyle fracture/ supracondylar fracture
What are the signs of an ulnar nerve injury?
Froment’s sign positive
Wasting of hypothenar eminence
How can the ulnar nerve be damaged at the wrist?
Lacerations to the anterior wrist
