Pectoral Region

Question 1

What are the two heads of Pectoralis Major? Give their origins and insertions

Answer 1

The muscle has two heads – a clavicular head (attaches to the clavicle), and a sternocostal head (attaches to the sternum and ribs). Fibres from both heads attach to the edge of the intertubecular groove of the humerus.

Question 2

Describe the innervation of Pectoralis Major

Answer 2

The pectoralis major is innervated by the medial and lateral pectoral nerves, which are derived from the brachial plexus.

Question 3

What is the action of Pectoralis Major?

Answer 3

The two heads can work independently or synergistically. Together, they act to adduct and medially rotate the humerus at the shoulder. The clavicular head also performs flexion.

Question 4

Describe the origin and insertion of Pectoralis Minor

Answer 4

The muscle has a triangular shape, originating from the anterior surfaces of ribs 3 – 5. The fibres then converge to attach to the corocoid process of the scapula. Attaching to the scapula forms a ‘bridge’, which vessels passing into the upper limb must travel underneath

Question 5

How is Pectoralis Minor innervated?

Answer 5

innervated by the medial pectoral nerve

Question 6

Describe the origin and insertion of Serratus Anterior?

Answer 6

The muscle consists of several strips, which originate from ribs 2-8. They attach to the costal (rib facing) surface of the medial border of the scapula.

Question 7

What is the action of Pectoralis Minor?

Answer 7

Contraction of the pectoralis minor depresses the shoulder (an inferior motion)

Question 8

Describe the innervation of Serratus Anterior

Answer 8

It is innervated by the long thoracic nerve

Question 9

Describe the action of Serratus Anterior

Answer 9

The main action of the serratus anterior is to rotate the scapula, allowing the arm to be raised over 90 degrees. It also holds the scapula against the ribcage – this is particularly useful when upper limb reaches anteriorly (e.g punching).