Cutaneous Innervation and Shoulder Anatomy

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Questions and Answers

Which nerve is responsible for the cutaneous innervation of the anterior aspect of the shoulder?

Axillary nerve

Supraclavicular nerve (correct)

Intercostobrachial nerve

Musculocutaneous nerve

What structure separates the upper border of pectoralis major from deltoid muscle?

Infraclavicular fossa (correct)

Pectoral fascia

Clavipectoral fascia

Inferior border of the clavicle

Which fascia is continuous inferiorly with the fascia of the abdomen?

Axillary fascia

Clavipectoral fascia

Superficial fascia (correct)

Pectoral fascia

What is the primary role of the clavipectoral fascia?

To fill the gap between pectoralis minor and subclavius Signup and view all the answers

What are the origins of the pectoralis major muscle?

Clavicle and sternum Signup and view all the answers

Which of the following is NOT a cutaneous nerve innervating the arm?

Radial nerve Signup and view all the answers

What is a key feature of the pectoral fascia?

Covers the pectoralis major muscle Signup and view all the answers

The axillary fascia splits into two layers at which muscle?

Latissimus dorsi Signup and view all the answers

Which of the following correctly describes the pectoralis major muscle?

Thick and fan-shaped Signup and view all the answers

Which structure is NOT associated with the clavipectoral fascia?

Long thoracic nerve Signup and view all the answers

What is the primary function of the pectoralis major muscle?

Adduction and medial rotation of the humerus Signup and view all the answers

Which muscle is primarily responsible for protracting the scapula?

Serratus anterior Signup and view all the answers

What is the innervation for the coracobrachialis muscle?

Musculocutaneous nerve Signup and view all the answers

Which artery gives rise to both the anterior and posterior circumflex humeral arteries?

Axillary artery Signup and view all the answers

What is the outcome of an injury to the long thoracic nerve?

Winged scapula appearance Signup and view all the answers

Which vein forms the axillary vein at the lower border of teres major?

Basilic vein Signup and view all the answers

What is the main action of the biceps brachii muscle?

Flexion and supination of the forearm Signup and view all the answers

Which muscle helps to flex the humerus at the shoulder joint?

Coracobrachialis Signup and view all the answers

What is the function of the subclavius muscle?

Stabilizes the shoulder girdle Signup and view all the answers

Where does the brachial artery typically run?

Deep to the biceps brachii Signup and view all the answers

Study Notes

Cutaneous Innervation of the Shoulder and Arm

The anterior aspect of the shoulder and arm is innervated by ventral branches of spinal nerves T1-T6, supplying the intercostal nerves
These nerves send branches to the anterior and lateral surfaces of the shoulder and arm.

Superficial Structures of the Anterior Shoulder

The superficial fascia of the anterior shoulder is continuous with the fascia of the neck, upper limb, and abdomen.
It contains the mammary gland.
The deep fascia covers the pectoralis major muscle.
The pectoral fascia extends between the fasciculi of the pectoralis major, attaching medially to the sternum, superiorly to the clavicle, and inferolaterally to the fascia of the shoulder, axilla, and thorax.

Infraclavicular Fossa

The infraclavicular fossa separates the upper border of the pectoralis major from the deltoid muscle.
It contains the cephalic vein and the deltoid branch of the thoracoacromial artery.
The lower border of the pectoralis major forms the anterior axillary fold.

Clavipectoral Fascia

The clavipectoral fascia is a strong fibrous sheath located behind the clavicular part of the pectoralis major
It fills the gap between the pectoralis minor and subclavius muscles.
It covers the axillary vessels and nerves.
The fascia splits around the subclavius muscle, attaching to the clavicle both anteriorly and posteriorly to the groove for the subclavius.
The clavipectoral fascia is pierced by the cephalic vein, thoracoacromial artery, lateral pectoral nerve, and lymph vessels.

Pectoralis Major Muscle

The pectoralis major is a thick, fan-shaped muscle.
It originates from the clavicle, sternum, costal cartilages of ribs 2-6/7, and the aponeurosis of the external oblique abdominal muscle.
Clavicular and sternal fibers are separated by a slight cleft.
It inserts into the lateral lip of the intertubercular sulcus of the humerus.
It is innervated by the medial and lateral pectoral nerves.
Its functions include adduction and medial rotation of the humerus.
The clavicular head helps to flex the humerus.
The sternocostal head extends the humerus from a flexed position.

Pectoralis Minor Muscle

The pectoralis minor is a thin, triangular muscle located posterior to the pectoralis major.
It originates from the upper margins and outer surfaces of ribs 3-5.
Its fibers ascend laterally, converging in a flat tendon that inserts into the coracoid process.
It is innervated by the medial and lateral pectoral nerves.
Its functions include assisting the serratus anterior in drawing the scapula forward around the chest wall, rotating the scapula with the levator scapulae and rhomboids to depress the point of the shoulder, and assisting in forced inspiration.

Subclavius Muscle

The subclavius is a small, triangular muscle located between the clavicle and the first rib.
It originates from the junction of the first rib and its costal cartilage.
It passes upwards and laterally, inserting into the groove on the inferior surface of the middle third of the clavicle.
It is innervated by the subclavian nerve of the brachial plexus.
Its function is to pull the point of the shoulder down and forward, stabilizing the clavicle during shoulder movements.

Serratus Anterior Muscle

The serratus anterior originates from the outer surfaces of the first eight ribs.
Its lower three slips interdigitate with the upper five slips of the external oblique abdominis muscle.
It passes anterior to the scapula and inserts into the medial border of the scapula.
It is innervated by the long thoracic nerve.
Its functions include protracting the scapula and holding it against the thoracic wall.
By fixing the scapula to the thorax, it acts as an anchor for the bone, allowing other muscles to use it as a fixed point for movements of the humerus.
Its inferior fibers help to raise the glenoid cavity when the arm is raised above the head.
Injury to the long thoracic nerve can lead to winged scapula, where the medial border of the scapula moves posterolaterally away from the thoracic wall on the affected side.

Superficial Fascia of the Arm

The superficial fascia of the arm contains cutaneous nerves, superficial vessels, and the following veins:
- Cephalic: drains to axillary vein
- Basilic: forms axillary vein at the lower border of teres major
- Median cubital: connects the cephalic and basilic veins.

Brachial Fascia

The brachial fascia is the deep fascia of the arm.
It is continuous with the fascia covering the deltoid and pectoralis major muscles.
It forms medial and lateral intermuscular septa on each side of the humerus, dividing the arm into anterior and posterior compartments.

Coracobrachialis Muscle

The coracobrachialis muscle originates from the apex of the coracoid process, along with the tendon of the short head of the biceps muscle.
It inserts into the middle third of the medial surface of the body of the humerus.
It is innervated by the musculocutaneous nerve, which pierces the muscle.
Its function is adduction and flexion of the arm.

Biceps Brachii Muscle

The biceps brachii is a large, fusiform muscle with two heads.
The short head originates from the apex of the coracoid process.
The long head originates from the supraglenoid tubercle.
The tendon of the long head crosses the head of the humerus within the capsule of the shoulder joint and descends in the intertubercular groove.
It inserts into the tuberosity of the radius and the bicipital aponeurosis.
Its function is flexion and supination of the forearm.
The long head also helps to flex the arm.

Brachialis Muscle

The brachialis muscle lies posterior to the biceps brachii.
It is the main flexor of the forearm.
It originates from the distal half of the anterior surface of the humerus and the intermuscular septum.
It inserts into the coronoid process and tuberosity of the ulna.
It is innervated by the musculocutaneous nerve.

Arteries of the Shoulder and Arm

The subclavian artery becomes the axillary artery, which then becomes the brachial artery.
The axillary artery is divided into three parts based on its position relative to the pectoralis minor muscle: proximal, posterior, and distal.

Branches of the Axillary Artery

Superior thoracic artery
Thoracoacromial artery: pierces the clavipectoral fascia and has the following branches:
- Pectoral
- Acromial
- Clavicular
- Deltoid
Lateral thoracic artery
Subscapular artery: the largest branch with the following branches:
- Circumflex scapular artery
- Thoracodorsal artery
Anterior circumflex humeral artery
Posterior circumflex humeral artery: passes through the quadrangular space with the axillary nerve.

Brachial Artery

The brachial artery runs between the tendon of the teres major and 1 cm distal to the elbow joint (neck of the radius).
Its terminal branches are the radial and ulnar arteries.
The brachial artery is accompanied by venae comitantes, which are connected by transverse and oblique branches.

Branches of the Brachial Artery

Deep brachial artery: the largest branch, accompanies the radial nerve in the radial groove
- Anterior descending branch
- Posterior descending branch
Nutrient humeral artery
Superior and inferior ulnar collateral arteries

Superficial Veins of the Arm

Cephalic vein: located in the superficial fascia along the anterolateral surface of biceps brachii.
Basilic vein: located in the superficial fascia on the medial side of the inferior part of the arm.
Median cubital vein: connects the basilic and cephalic veins, located anterior to the bicipital aponeurosis. This vein is commonly used for venipuncture.

Nerves of the Arm

Median nerve
Ulnar nerve
Musculocutaneous nerve
Radial nerve
Axillary nerve

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Description

This quiz explores the cutaneous innervation of the shoulder and arm, detailing the spinal nerves involved along with the anatomical aspects of the anterior shoulder. It also covers the infrastructure of the infraclavicular fossa and its relation to surrounding structures. Test your understanding of these essential concepts!