Anatomy
Upper Limb
An 18 year old man presents to the Emergency Department following a rugby match. He is complaining of pain over his left shoulder and is unable to depress the tip of his shoulder, you suspect an injury to his pectoralis minor or the nerve supplying it. The pectoralis minor muscle is innervated by which of the following nerves:
Answer:
The pectoralis minor muscle is innervated by the medial pectoral nerve, which originates from the brachial plexus in the axilla.Pectoralis Minor Muscle
Anatomy / Upper Limb / Pectoral Region
Last Updated: 8th April 2019
The pectoralis minor is a small triangular-shaped muscle that lies deep to the pectoralis major muscle and passes from the thoracic wall to the coracoid process of the scapula.
Table: Function and Innervation of the Pectoralis Minor Muscle
| Muscle | Pectoralis Minor |
|---|---|
| Origin | Anterior surfaces and superior borders of ribs 3 – 5 and from deep fascia overlying related intercostal spaces |
| Distal Attachment | Medial border and upper surface of coracoid process of scapula |
| Actions | Depresses tip of shoulder, protracts scapula |
| Innervation | Medial pectoral nerve |
Origin
The muscle originates as three muscular slips from the anterior surfaces and upper margins of ribs 3 - 5 and from the fascia overlying muscles of the related intercostal spaces.
Insertion
The muscle fibres pass superiorly and laterally to insert into the medial and upper aspects of the coracoid process.
Function
The muscle protracts the scapula (by pulling the scapula anteriorly on the thoracic wall) and depresses the lateral angle of the scapula.
Innervation
The muscle is innervated by the medial pectoral nerve, which originates from the brachial plexus in the axilla.
![Modified by FRCEM Success. Original by Henry Vandyke Carter [Public domain], via Wikimedia Commons](https://primary-cdn.frcemsuccess.com/wp-content/uploads/2016/12/Pectoralis-Minor.jpg)
Pectoralis Minor 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 |
