Axillary Nerve Flashcards
What is the axillary nerve?
A major peripheral nerve of the upper limb
What are the spinal roots of the axillary nerve?
C5 and C6
What does the axillary nerve give rise to?
The superior lateral cutaneous nerve of the arm
What does the superior lateral cutaneous nerve of the arm do?
Innervates the skin over the lower deltoid (regimental badge area)
What muscles does the axillary nerve innervate?
Teres minor
Deltoid muscle
Abductors of the arm at the shoulder
Where is the axillary nerve formed?
Within the axilla region
What is the axillary nerve formed from?
Direct continuation of the posterior cord of the brachial plexus
What nerve fibres does the axillary nerve contain?
Those from the C5 and C6 nerve roots
Where does the axillary nerve lie immediately after its formation?
Posterior to the axillary artery, and anteriorly to the subscapularis muscle
What course does the axillary nerve take?
It descends to the inferior border of the subscapularis muscle, and then exits the axilla posteriorly via the quadrangular space
What is the axillary nerve accompanied by?
The posterior circumflex humeral artery
Where does the axillary nerve terminate?
In the posterior scapular region
How does the axillary nerve terminate?
By dividing into two branches
What two branches does the axillary nerve divide into?
Posterior terminal branch
Anterior terminal branch
What does the posterior terminal branch of the axillary nerve provide?
Motor innervation to teres minor muscle
Innervates skin over inferior part of deltoid
What does the anterior terminal branch of the axillary nerve provide?
Motor innervation to the deltoid muscle
What is the quadrangular space?
A gap in the muscles of the posterior scapula region
What is the purpose of the quadrangular space?
it is a pathway for neurovascular structures to move from the axilla to the posterior shoulder and arm
What is the superior boundary of the quadrangular space?
Subscapularis and teres minor
What is the inferior boundary of the quadrangular space?
Teres major
What is the lateral boundary of the quadrangular space?
Surgical neck of humerus
What is the medial border of the quadrangular space?
Long head of the triceps brachii
What passes through the quadrangular space?
The axillary nerve and posterior circumflex humeral artery
What muscles does the axillary nerve innervate?
Teres minor
Deltoid muscles
What is the teres minor part of?
The rotator cuff muscles 1
What do the rotator cuff muscles do?
Acts to stabilise the glenohumeral joint
What does the teres minor do acting individually?
Externally rotates the upper limb
What is the teres minor innervated by?
The posterior terminal branch of the axillary nerve
Where is the deltoid situated?
At the superior aspect of the shoulder
What does the deltoid perform?
Abduction of the upper limb at the glenohumeral joint
What is the deltoid innervated by?
The anterior terminal branch of the axillary nerve
What is the sensory component of the axillary nerve delivered via?
Its posterior terminal branch
What course does the posterior terminal branch take to provide sensory innervation?
After it has innervated the teres minor, it continues as the upper lateral cutaneous nerve of the arm
What does the upper lateral cutaneous nerve of the arm innervate?
The skin over the inferior portion of the deltoid
What can happen to sensation if the axillary nerve is damaged?
Sensation in the regimental badge area may be impaired or absent
May also report paraesthesia (pins and needles) in the distribution of the axillary nerve
How is the axillary nerve most commonly damaged?
By trauma to the shoulder or proximal, such as a fracture to the humerus surgical neck
How does injury to the axillary nerve affect motor functions?
Causes paralysis of the deltoid and teres minor muscles, which renders the patient unable to abduct the affected limb
How does injury to the axillary nerve affect sensory functions?
The upper lateral cutaneous nerve of the arm will be non functional, resulting in loss of sensation over the regimental badge area
What are the characteristic clinical signs of an injury to the axillary nerve?
In long standing cases, the paralysed deltoid muscle rapidly atrophies, and the greater tuberosity can be palpated in that area
