Anatomy
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Upper Limb
A 34 year old presents to the ED following a road traffic collision. His primary survey is unremarkable. During secondary survey you note the patient has signs of weakness to the left serratus anterior muscle. The serratus anterior muscle is innervated by which of the following nerves:
Answer:
The serratus anterior is innervated by the long thoracic nerve, which is derived from the roots of the brachial plexus, passes through the axilla along the medial and passes vertically down the serratus anterior muscle on its external surface, just deep to skin and superficial fascia.Serratus Anterior Muscle
Anatomy / Upper Limb / Pectoral Region
Last Updated: 16th November 2020
Table: Function and Innervation of the Serratus Anterior Muscle
| Muscle | Serratus Anterior |
|---|---|
| Origin | Lateral surfaces of ribs 1 – 8/9 and deep fascia overlying the related intercostal spaces |
| Distal Attachment | Costal surface of medial border of scapula |
| Function | Protraction and rotation of scapula; keeps medial border and inferior angle of scapula opposed to thoracic wall |
| Innervation | Long thoracic nerve |
Origin
The serratus anterior muscle originates as a number of muscular slips from the lateral surfaces of ribs 1 - 8/9 and the intervening deep fascia overlying the related intercostal spaces.
Insertion
The muscle forms a flattened sheet, which passes posteriorly around the thoracic wall to insert primarily on the costal surface of the medial border of the scapula.
Function
The serratus anterior pulls the scapula forward over the thoracic wall and facilitates scapular rotation. It also keeps the costal surface of the scapula closely opposed to the thoracic wall.
Innervation
The serratus anterior is innervated by the long thoracic nerve, which is derived from the roots of the brachial plexus, passes through the axilla along the medial and passes vertically down the serratus anterior muscle on its external surface, just deep to skin and superficial fascia.
![Modified by FRCEM Success. Original by Henry Vandyke Carter [Public domain], via Wikimedia Commons](https://primary-cdn.frcemsuccess.com/wp-content/uploads/2016/12/Serratus-Anterior.jpg)
Serratus Anterior 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 |
