Phrenic Nerve Flashcards

Explore the phrenic nerve's cervical roots, neck and thoracic course, diaphragmatic innervation, sensory distribution, and clinical anatomy.

Card 1 of 30Question

What is the phrenic nerve?

A mixed peripheral nerve that provides the principal motor supply to the diaphragm and sensory innervation to nearby structures.

In This Section

1. What is the phrenic nerve?

A mixed peripheral nerve that provides the principal motor supply to the diaphragm and sensory innervation to nearby structures.

2. Which spinal nerve roots form the phrenic nerve?

The anterior rami of C3, C4, and C5, with C4 usually providing the largest contribution.

3. From which nerve plexus does the phrenic nerve principally arise?

The cervical plexus, with an additional contribution commonly arising from C5.

4. Where does the phrenic nerve form in the neck?

Near the lateral border of the anterior scalene muscle in the upper cervical region.

5. Which muscle does the phrenic nerve cross as it descends through the neck?

The anterior surface of the anterior scalene muscle.

6. Which fascial layer covers the phrenic nerve as it descends over the anterior scalene?

The prevertebral layer of deep cervical fascia.

7. What is the relationship of the phrenic nerve to the internal jugular vein in the lower neck?

The phrenic nerve generally descends posterior to the internal jugular vein.

8. What is the usual relationship of the phrenic nerve to the subclavian artery?

It typically crosses anterior to the first part of the subclavian artery near the thoracic inlet.

9. How does the phrenic nerve usually pass relative to the subclavian vein?

It typically passes posterior to the subclavian vein as it enters the thorax.

10. What is the relationship of the phrenic nerve to the lung root?

It passes anterior to the root of the lung on each side.

11. How does the course of the phrenic nerve differ from that of the vagus nerve near the lung root?

The phrenic nerve passes anterior to the lung root, while the vagus nerve passes posterior to it.

12. Along which structure does the phrenic nerve descend through the mediastinum?

The fibrous pericardium, between the pericardium and mediastinal pleura.

13. Which major vein is closely related to the right phrenic nerve in the superior mediastinum?

The superior vena cava.

14. Which cardiac surface is closely related to the descending left phrenic nerve?

The lateral surface of the pericardium over the left ventricle.

15. Through which diaphragmatic opening does the right phrenic nerve commonly pass?

The caval opening at approximately the T8 vertebral level, alongside the inferior vena cava.

16. How does the left phrenic nerve typically reach the abdominal surface of the diaphragm?

By piercing the muscular portion of the left hemidiaphragm separately from the major diaphragmatic openings.

17. What is the primary motor function of the phrenic nerve?

Innervation of the diaphragm, the principal muscle of inspiration.

18. What happens to the diaphragm during phrenic nerve stimulation?

The diaphragm contracts and descends, increasing thoracic volume during inspiration.

19. Which portion of the diaphragmatic pleura receives sensory innervation from the phrenic nerve?

The central portion of the diaphragmatic pleura.

20. Which part of the diaphragmatic peritoneum receives sensory fibers from the phrenic nerve?

The central diaphragmatic peritoneum.

21. Which layers of the pericardium receive sensory innervation from the phrenic nerve?

The fibrous pericardium and parietal layer of the serous pericardium.

22. Which arteries accompany the phrenic nerves along the pericardium?

The pericardiacophrenic arteries, branches of the internal thoracic arteries.

23. What is an accessory phrenic nerve?

A variable additional nerve, often arising from C5 through the nerve to subclavius, that joins the main phrenic nerve.

24. What is the typical consequence of complete unilateral phrenic nerve injury?

Paralysis of the ipsilateral hemidiaphragm.

25. What abnormal diaphragmatic movement may occur during inspiration after unilateral phrenic nerve paralysis?

Paradoxical upward movement of the affected hemidiaphragm.

26. What is the anatomical basis of referred shoulder pain from diaphragmatic irritation?

Phrenic sensory fibers enter C3 to C5 spinal segments, overlapping cervical sensory pathways supplying the shoulder region.

27. Why is the phrenic nerve vulnerable during surgery involving the pericardium?

It descends directly along the lateral fibrous pericardium and may be injured during dissection.

28. Why can an interscalene brachial plexus block temporarily impair diaphragmatic function?

Local anesthetic may spread to the phrenic nerve on the anterior scalene, causing ipsilateral hemidiaphragmatic weakness.

29. What is the respiratory consequence of complete bilateral phrenic nerve paralysis?

Severe diaphragmatic weakness with impaired ventilation, particularly when lying supine.

30. Which imaging test can demonstrate paradoxical diaphragmatic movement in phrenic nerve palsy?

Dynamic diaphragm ultrasonography or fluoroscopic sniff testing.