Pectoral Region

Draw labelled diagram to show cutaneous innervation of pectoral region.

 Enumerate the Muscles of Pectoral Region Their Nerve Supply.

    Muscle                                               Nerve Supply
Pectoralis major                   Medial (C8,T1) & lateral pectoral                                                  (C5-C7) 
Pectoralis minor                   Medial ( C8,T1) & lateral pectoral                                               (C5-C7) 
Subclavius                           Nerve to subclavius (C5,6)
Serratus anterior                  Long thoracic nerve ( C5,6,7)

Write origin, insertion, action and nerve supply of Pectoralis major and Serratus Anterior.

Pectoralis major

Origin

• Anterior surface of medial ½ of the clavicle.
• Anterior surface of sternum up to the 6th costal cartilage.
• 2nd to 6th costal cartilages.
• Aponeurosis of external oblique muscle.

Insertion

Lateral lip of bicipital groove of humerus.

Action

• When both clavicular & sternocostal parts act – adduction and  medial rotation of arm.
• Action of only clavicular part – Flexion of the arm
• Action of only sternocostal part – Extension of the flexed arm.
• When the arm is fixed – Climbing (raising the trunk)

Nerve supply: Medial & lateral pectoral nerves

Pectoralis minor

• It lies underneath pectoralis major.
• Is smaller than the pectoralis major.
• Is triangular in shape.

Attachments: 

• Originates from the 3rd-5th ribs.
• Inserts into the coracoid process of the scapula.

Action:  depresses the shoulder

Nerve supply : medial & lateral pectoral nerves.

Subclavius

• Subclavius is small muscle, which is located directly underneath the clavicle
• It protects underlying vessels and nerves especially during clavicle fractures.

Attachments:

• Originates from the junction of the 1st rib and its costal cartilage.
• Inserts into the inferior surface of the middle third of the clavicle.

Action: Anchors  and stabilizes clavicle during upper limb movements and depresses the clavicle.

Innervation: Nerve to subclavius (C5,6)

Serratus anterior

Origin: Outer surface of upper eight ribs & fascia covering the intervening intercostal muscles.

Insertion: Costal surface of the medial border of scapula.

 Action

• Protraction of upper limb i.e. pulling the scapula forwards around the chest wall during pushing & punching actions.
• Rotate the scapula laterally and upward (along with trapezius) so that glenoid cavity faces upwards and thereby help in overhead abduction.   

Nerve Supply: Long thoracic nerve (C 5,6,7).

Describe Briefly the Clavipectoral Fascia.

Clavipectoral fascia is a fibrous sheet present deep to the clavicular part of the pectoralis major muscle.

• Extent: From clavicle (margins of subclavian groove) above to the axillary fascia below.
• Muscles enclosed: Subclavius and pectoralis minor.
• Structures piercing:
  • Lateral pectoral nerve
  • Cephalic vein
  • Thoraco-acromial vessels
  • Lymphatics from mammary gland to the apical group of axillary lymph nodes.

Applied Aspect

What is the anatomical basis of ‘Winging of scapula’?
Paralysis of serratus anterior muscle due to injury to long thoracic nerve produces ‘Winging of scapula’.The medial border and inferior angle of scapula become unduly prominent specially when the patient tries to do pushing and punching actions.