EDAIC Anatomy — Questions and Answers
Question 1: At which vertebral level does the conus medullaris (tip of the spinal cord) typically terminate in a healthy adult?
- T10–T11
- L1–L2 (Correct answer)
- L3–L4
- L4–L5
Correct answer: L1–L2
In adults the spinal cord ends at approximately the L1–L2 level. This is why lumbar puncture and spinal anaesthesia are performed below L2 (typically L3–L4 or L4–L5) to avoid direct cord trauma. In neonates the cord ends lower (around L3) and ascends with growth.
Question 2: The brachial plexus is formed by the anterior primary rami of which spinal nerve roots?
- C4–C8
- C5–T1 (Correct answer)
- C4–T1
- C5–C8
Correct answer: C5–T1
The brachial plexus arises from C5, C6, C7, C8, and T1. C4 may contribute a small branch (pre-fixed variant) and T2 a small contribution (post-fixed variant), but the classic five roots are C5–T1. This is essential knowledge for interscalene, supraclavicular, infraclavicular, and axillary block planning.
Question 3: The cricothyroid membrane, the target for emergency surgical airway access, connects which two cartilaginous structures?
- Thyroid and arytenoid cartilage
- Cricoid and arytenoid cartilage
- Thyroid and cricoid cartilage (Correct answer)
- Epiglottis and thyroid cartilage
Correct answer: Thyroid and cricoid cartilage
The cricothyroid membrane spans between the inferior border of the thyroid cartilage and the superior border of the cricoid cartilage. It lies in the midline, is relatively avascular, and is the preferred site for needle or surgical cricothyroidotomy in a 'can't intubate, can't oxygenate' scenario.
Question 4: In the antecubital fossa, what is the positional relationship of the median nerve to the brachial artery?
- Lateral to the artery
- Posterior to the artery
- Medial to the artery (Correct answer)
- Anterior to the artery
Correct answer: Medial to the artery
The median nerve lies medial to the brachial artery in the antecubital fossa. The mnemonic VAN (Vein–Artery–Nerve, medial to lateral) helps recall that the median nerve is the most medial structure. Awareness of this relationship is important during antecubital IV placement and brachial artery cannulation.
Question 5: The phrenic nerve descends through the thorax. Which statement best describes its intrathoracic course?
- It travels posterior to the lung root alongside the vagus nerve
- It passes through the aortic hiatus with the aorta
- It descends along the internal thoracic vessels
- It descends anterior to the lung root along the lateral surface of the fibrous pericardium (Correct answer)
Correct answer: It descends anterior to the lung root along the lateral surface of the fibrous pericardium
The phrenic nerve (C3, C4, C5) descends anterior to the lung root (hilum) and travels along the lateral surface of the fibrous pericardium to reach the diaphragm. The vagus nerve, by contrast, descends posterior to the lung root. This anatomy explains why pericardial surgery or mediastinal tumours can injure the phrenic nerve, causing diaphragmatic paralysis.
Question 6: Which bony landmark defines the superior boundary of the 'safe triangle' for intercostal chest drain insertion in the midaxillary line?
- The clavicle
- The upper border of the rib below the target intercostal space (Correct answer)
- The lower border of the rib above the target intercostal space
- The manubriosternal angle (angle of Louis)
Correct answer: The upper border of the rib below the target intercostal space
Intercostal neurovascular bundles (vein, artery, nerve — VAN order, superior to inferior) run in the groove on the inferior surface of each rib. Inserting a chest drain over the upper border of the lower rib avoids the bundle. The 'safe triangle' for a drain is bounded by pectoralis major anteriorly, latissimus dorsi posteriorly, and the 5th intercostal space inferiorly, with entry over the superior rib border.
EDAIC Anatomy
At which vertebral level does the conus medullaris (tip of the spinal cord) typically terminate in a healthy adult?