Anatomy
Head and Neck
Regarding the external ear, which of the following statements is INCORRECT:
Answer:
Sensory innervation of the external acoustic meatus is from the auriculotemporal nerve (branch of the mandibular nerve) anteriorly and superiorly and the auricular branch of the vagus nerve posteriorly and inferiorly.External Ear
Anatomy / Head and Neck / Ear
Last Updated: 23rd April 2020
The external ear consists of the auricle (pinna) and the external acoustic meatus.
![By OpenStax [CC BY 4.0], via Wikimedia Commons](https://mrcemsuccess.com/wp-content/uploads/2016/07/ear.png)
Structure of the Ear. (Image by OpenStax [CC BY 4.0], via Wikimedia Commons)
Auricle
The auricle on the side of the head is a cartilaginous folded structure.
The outer, more superficial structures of the auricle are supplied by:
- the great auricular nerve (from spinal nerves C2 - C3) inferiorly
- the lesser occipital nerve (from spinal nerves C2 - C3) posterosuperiorly
- the auriculotemporal nerve (branch of the mandibular nerve) anterosuperiorly.
The deeper parts of the auricle are supplied by the auricular branch of the vagus nerve and a branch from the facial nerve (which contributes to the auricular branch of the vagus nerve).
External Acoustic Meatus
The external acoustic meatus extends laterally from the deepest part of the concha to the tympanic membrane (about 3 cm in length). Sensory innervation of the external acoustic meatus is from the auriculotemporal nerve (branch of the mandibular nerve) anteriorly and superiorly and the auricular branch of the vagus nerve posteriorly and inferiorly.
Tympanic Membrane
The tympanic membrane separates the external acoustic meatus from the middle ear. At the periphery of the tympanic membrane, a fibrocartilaginous ring attaches it to the tympanic part of the temporal bone. At its centre, the lower end of the handle of the malleus is attached on its internal surface forming the umbo of the tympanic membrane.
Tympanic Membrane. (Image by EMAD KAYYAM [CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0)])
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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 |
