Anatomy
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Upper Limb
You are examining the shoulder of a 43 year old woman who complains of progressive weakness in her left arm. You note wasting of the left trapezius muscle in comparison with the right. The trapezius muscle is innervated by which of the following nerves:
Answer:
The trapezius is innervated by the spinal part of the accessory nerve (motor supply) and the anterior rami of C3 and C4 (sensory supply). These nerves pass vertically along the deep surface of the muscle. The accessory nerve can be evaluated by testing the function of the trapezius muscle, most easily done by asking the patient to shrug their shoulders against resistance.Trapezius Muscle
Anatomy / Upper Limb / Pectoral Region
Last Updated: 8th April 2019
The trapezius muscle is responsible for the smooth contour of the lateral side of the neck and over the superior aspect of the shoulder.
Table: Function and Innervation of the Trapezius Muscle
| Muscle | Trapezius |
|---|---|
| Origin | Superior nuchal line, external occipital protuberance, medial margin of ligamentum nuchae, spinous processes of C7 – T12 and the related supraspinous ligaments |
| Insertion | Superior edge of crest of the spine of the scapula, acromion and posterior border of lateral one-third of clavicle |
| Function | Elevation of scapula, rotation of scapula during abduction of humerus above horizontal, retraction and depression of scapula |
| Innervation | Spinal accessory nerve |
Origin
The trapezius muscle has an extensive origin from the axial skeleton, originating from the superior nuchal line, the external occipital protuberance, the medial margin of the ligamentum nuchae, the spinous processes of C7 - T12 and the related supraspinous ligaments.
Insertion
The muscle inserts onto the skeletal framework of the shoulder (to the superior edge of the crest of the spine of the scapula, the acromion and the posterior border of the lateral one-third of the clavicle) along the inner margins of a continuous U-shaped line of attachment orientated in the horizontal plane, with the bottom of the U directed laterally.
Function
The trapezius is a powerful elevator of the shoulder and also rotates the scapula to extend the reach superiorly (during abduction of the humerus above horizontal). The middle fibres retract the scapula and the lower fibres depress the scapula.
Innervation
The trapezius is innervated by the spinal part of the accessory nerve (motor supply) and the anterior rami of C3 and C4 (sensory supply). These nerves pass vertically along the deep surface of the muscle. The accessory nerve can be evaluated by testing the function of the trapezius muscle, most easily done by asking the patient to shrug their shoulders against resistance.
![By Mikael Häggström, used with permission. (Image:Gray409.png) [Public domain or Public domain], via Wikimedia Commons](https://mrcemsuccess.com/wp-content/uploads/2016/12/Trapezius-649x1024.png)
Trapezius Muscle. (Image by Mikael Häggström, used with permission. (Image:Gray409.png) [Public domain or 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 |
