Anatomy
Upper Limb
A 38 year old man is brought into the ED following an altercation with another male, during which he has suffered a laceration to the right pectoral region. He is complaining of difficulty moving his shoulder and you suspect a nerve injury. The pectoralis major muscle is innervated by which of the following nerves:
Answer:
The pectoralis major is innervated by the medial and lateral pectoral nerves which originate from the brachial plexus in the axilla.Pectoralis Major Muscle
Anatomy / Upper Limb / Pectoral Region
Last Updated: 8th April 2019
The pectoralis major is the largest and most superficial muscle of the anterior wall. Its inferior margin underlies the anterior axillary fold, which marks the anteroinferior border of the axilla.
Table: Function and Innervation of the Pectoralis Major Muscle
| Muscle | Pectoralis Major |
|---|---|
| Origin | Clavicular head: Medial half of clavicle
Sternocostal head: Medial part of anterior thoracic wall (anterior surface of sternum, first seven costal cartilages, sternal end of sixth rib, aponeurosis of external oblique) |
| Insertion | Lateral lip of intertubercular sulcus of humerus |
| Function | Flexion, adduction and medial rotation of arm at glenohumeral joint |
| Innervation | Medial and lateral pectoral nerves |
Origin
The muscle has two heads:
- the clavicular head originates from the anterior surface of the medial half of the clavicle
- the sternocostal head originates from the medial part of the anterior thoracic wall (the anterior surface of the sternum, the first seven costal cartilages, the sternal end of sixth rib and the aponeurosis of the external oblique)
Insertion
The muscle inserts into the lateral lip of the intertubercular sulcus of the humerus.
Function
Acting together, the two heads of the pectoralis major flex, adduct and medially rotate the arm at the glenohumeral joint.
Innervation
The pectoralis major is innervated by the medial and lateral pectoral nerves which originate from the brachial plexus in the axilla.
![Fig 1.1 Pectoralis Major Muscle Image modified by FRCEM Success. Original by Henry Vandyke Carter [Public domain], via Wikimedia Commons](https://mrcemsuccess.com/wp-content/uploads/2016/12/Pectoralis-Major.png)
Pectoralis Major Muscle. (Image modified by FRCEM Success. Original by Henry Vandyke Carter [Public domain], via Wikimedia Commons)
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- Biochemistry
- Blood Gases
- Haematology
| Biochemistry | Normal Value |
|---|---|
| Sodium | 135 – 145 mmol/l |
| Potassium | 3.0 – 4.5 mmol/l |
| Urea | 2.5 – 7.5 mmol/l |
| Glucose | 3.5 – 5.0 mmol/l |
| Creatinine | 35 – 135 μmol/l |
| Alanine Aminotransferase (ALT) | 5 – 35 U/l |
| Gamma-glutamyl Transferase (GGT) | < 65 U/l |
| Alkaline Phosphatase (ALP) | 30 – 135 U/l |
| Aspartate Aminotransferase (AST) | < 40 U/l |
| Total Protein | 60 – 80 g/l |
| Albumin | 35 – 50 g/l |
| Globulin | 2.4 – 3.5 g/dl |
| Amylase | < 70 U/l |
| Total Bilirubin | 3 – 17 μmol/l |
| Calcium | 2.1 – 2.5 mmol/l |
| Chloride | 95 – 105 mmol/l |
| Phosphate | 0.8 – 1.4 mmol/l |
| Haematology | Normal Value |
|---|---|
| Haemoglobin | 11.5 – 16.6 g/dl |
| White Blood Cells | 4.0 – 11.0 x 109/l |
| Platelets | 150 – 450 x 109/l |
| MCV | 80 – 96 fl |
| MCHC | 32 – 36 g/dl |
| Neutrophils | 2.0 – 7.5 x 109/l |
| Lymphocytes | 1.5 – 4.0 x 109/l |
| Monocytes | 0.3 – 1.0 x 109/l |
| Eosinophils | 0.1 – 0.5 x 109/l |
| Basophils | < 0.2 x 109/l |
| Reticulocytes | < 2% |
| Haematocrit | 0.35 – 0.49 |
| Red Cell Distribution Width | 11 – 15% |
| Blood Gases | Normal Value |
|---|---|
| pH | 7.35 – 7.45 |
| pO2 | 11 – 14 kPa |
| pCO2 | 4.5 – 6.0 kPa |
| Base Excess | -2 – +2 mmol/l |
| Bicarbonate | 24 – 30 mmol/l |
| Lactate | < 2 mmol/l |
