Anatomy
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Upper Limb
Question 10 of 30
You are performing a neurological examination on a patient who complains of weakness of the left arm. You note muscle wasting in the posterior forearm. The muscles of the posterior compartment of the forearm are all innervated by which of the following nerves:
Answer:
The muscles of the posterior forearm are all innervated by the radial nerve.Posterior Forearm Muscles
Anatomy / Upper Limb / Posterior Forearm
Last Updated: 10th April 2019
The posterior forearm is divided into the superficial and deep groups:
- The superficial group is made up of:
- the brachioradialis
- the extensor carpi radialis longus and brevis
- the extensor digitorum
- the extensor digiti mini
- the anconeus
- the extensor carpi ulnaris
- The deep group is made up of:
- the supinator
- the abductor pollicis longus
- the extensor pollicis longus and brevis
- the extensor indicis
The muscles of the posterior forearm are all innervated by the radial nerve.
Muscles of the Posterior Forearm (Superficial). (Image by Henry Vandyke Carter [Public domain], via Wikimedia Commons)
![By Henry Vandyke Carter [Public domain], via Wikimedia Commons](https://mrcemsuccess.com/wp-content/uploads/2016/12/Posterior-Compartment-Forearm-2.png)
Muscles of the Posterior Forearm (Deep). (Image by Henry Vandyke Carter [Public domain], via Wikimedia Commons)
Function
Table: Function and Innervation of the Posterior Forearm Muscles
| Muscle | Function | Innervation |
|---|---|---|
| Brachioradialis | Flexion of elbow | Radial nerve |
| Extensor carpi radialis longus | Extension and abduction of wrist | Radial nerve |
| Extensor carpi radialis brevis | Extension and abduction of wrist | Radial nerve |
| Extensor digitorum | Extension of all four fingers, extension of wrist | Radial nerve |
| Extensor digiti minimi | Extension of little finger | Radial nerve |
| Extensor carpi ulnaris | Extension and adduction of wrist | Radial nerve |
| Supinator | Supination of forearm | Radial nerve |
| Abductor pollicis longus | Abduction and extension of thumb | Radial nerve |
| Extensor pollicis longus | Extension of thumb (CMCJ, MCPJ, IPJ) | Radial nerve |
| Extensor pollicis brevis | Extension of thumb (CMCJ and MCPJ) | Radial nerve |
| Extensor indicis | Extension of index finger | Radial nerve |
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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 |
