NewThe Purist Q is open. Ten questions on the anatomy of skin, free.Try it
AnatomyM8
The Purist QNew

Series 1: The Skin · Episode 5, not yet released

Innervation

Block It, Spare It, Reconstruct It

25 minutes. 19 references, each checked at source.

Follow the podcast
Listen on SpotifyListen on Apple Podcasts

Block the A fibres in your own forearm with a pressure cuff, and cold stops feeling cold, it starts feeling like burning. That single experiment tells you the fibre you were taught carries cold does not carry cold.

Episode 5 of The Anatomy Purist, Series 1: The Skin. Dev opens with a block that failed in an abscess and works back through the innervation of the skin: the four cutaneous mechanoreceptors, including the one that is *not* encapsulated; the real two-point discrimination bands and Lundborg and Rosén's case against trusting them; why innocuous cold travels on A-delta and not C fibres; the dermatome map problem almost nobody teaches; why local anaesthetic really fails in infected tissue, which is not simply pH; Seddon versus Sunderland; and what nerve coaptation in a sensate flap actually buys you.

Tiered Foundation to Purist. Every reference verified, every unverifiable claim flagged as unverifiable.

Themes from this episode

Practice what you just heard

Two questions on the themes of this episode, free, marked as you go. Then one from the Vault on the same ground.

Question 1 · Applied

Why is a superficial partial-thickness burn more painful than a full-thickness burn?

Answer to see the explanation and the source.

Question 2 · Foundation

Which mechanoreceptor lies in the dermal papillae of glabrous skin and mediates light touch and texture discrimination?

Answer to see the explanation and the source.

From the Vault, on the same theme

Thorax: Thoracic Wall, Diaphragm & Thoracic Inlet · Purist Locked

Local anaesthetic deposited deep to erector spinae on the tip of a thoracic transverse process produces anaesthesia over several chest wall dermatomes, front and back. Which pathway best explains this spread?

  • ADiffusion into the epidural space through the intervertebral foramina at every anaesthetised level
  • BBlockade of dorsal rami alone, with dermatomal overlap accounting for the anterior chest changes
  • CSpread in the plane superficial to erector spinae to the lateral cutaneous branches
  • DDirect intraneural uptake and centripetal spread along the nearest spinal nerve
  • EAnterior passage around the costotransverse ligaments into the paravertebral space

Unlock to see the answer

Unlock the Vault, £49
Try ten free questions from the seriesWhat the Vault is

References

  1. Standring S, editor. Gray's Anatomy: The Anatomical Basis of Clinical Practice. 42nd ed. London: Elsevier; 2020. [Textbook, no PMID.]
  2. Johnson KO. The roles and functions of cutaneous mechanoreceptors. Curr Opin Neurobiol. 2001;11(4):455-61. PMID: 11502392. doi:10.1016/s0959-4388(00)00234-8
  3. Johansson RS, Flanagan JR. Coding and use of tactile signals from the fingertips in object manipulation tasks. Nat Rev Neurosci. 2009;10(5):345-59. PMID: 19352402. doi:10.1038/nrn2621
  4. Purves D, Augustine GJ, Fitzpatrick D, et al., editors. Neuroscience. 2nd ed. Sunderland (MA): Sinauer Associates; 2001. Chapter: Mechanoreceptors Specialized to Receive Tactile Information. NCBI Bookshelf ID: NBK10895. [Textbook, no PMID.]
  5. Treede RD, Meyer RA, Campbell JN. Evidence for two different heat transduction mechanisms in nociceptive primary afferents innervating monkey skin. J Physiol. 1995;483(Pt 3):747-58. PMID: 7776255.
  6. Yarnitsky D, Ochoa JL. Release of cold-induced burning pain by block of cold-specific afferent input. Brain. 1990;113(Pt 4):893-902. PMID: 2397391. doi:10.1093/brain/113.4.893
  7. McKemy DD. The molecular and cellular basis of cold sensation. ACS Chem Neurosci. 2013;4(2):238-47. PMID: 23421674.
  8. Lee MWL, McPhee RW, Stringer MD. An evidence-based approach to human dermatomes. Clin Anat. 2008;21(5):363-73. PMID: 18470936. doi:10.1002/ca.20636
  9. Seddon HJ. Three types of nerve injury. Brain. 1943;66(4):237-88. doi:10.1093/brain/66.4.237 [Predates PubMed indexing, which begins in 1946; verified at the publisher.]
  10. Sunderland S. A classification of peripheral nerve injuries producing loss of function. Brain. 1951;74(4):491-516. PMID: 14895767. doi:10.1093/brain/74.4.491
  11. Mackinnon SE, Dellon AL. Surgery of the Peripheral Nerve. New York: Thieme; 1988. [Textbook, no PMID.]
  12. Dellon AL. Evaluation of Sensibility and Re-education of Sensation in the Hand. Baltimore: Williams & Wilkins; 1981. [Textbook, no PMID.]
  13. Lundborg G, Rosén B. The two-point discrimination test, time for a re-appraisal? J Hand Surg Br. 2004;29(5):418-22. PMID: 15336741. doi:10.1016/j.jhsb.2004.02.008
  14. Punnia-Moorthy A. Evaluation of pH changes in inflammation of the subcutaneous air pouch lining in the rat, induced by carrageenan, dextran and Staphylococcus aureus. J Oral Pathol. 1987;16(1):36-44. PMID: 2435877. doi:10.1111/j.1600-0714.1987.tb00674.x
  15. Punnia-Moorthy A. Buffering capacity of normal and inflamed tissues following the injection of local anaesthetic solutions. Br J Anaesth. 1988;61(2):154-9. PMID: 3415887. doi:10.1093/bja/61.2.154
  16. Ueno T, Tsuchiya H, Mizogami M, Takakura K. Local anesthetic failure associated with inflammation: verification of the acidosis mechanism and the hypothetic participation of inflammatory peroxynitrite. J Inflamm Res. 2008;1:41-8. PMID: 22096346. doi:10.2147/jir.s3982
  17. Kabakcı AG, Bozkır MG. Dimension, location and clinical importance of supraorbital foramen and notch: a combined cadaveric and dry skull study. Aesthetic Plast Surg. 2025;49(1):322-33. Epub 2024 Jul 1. PMID: 38951229. doi:10.1007/s00266-024-04196-7
  18. Santanelli F, Tenna S, Pace A, Scuderi N. Free flap reconstruction of the sole of the foot with or without sensory nerve coaptation. Plast Reconstr Surg. 2002;109(7):2314-22. PMID: 12045556. doi:10.1097/00006534-200206000-00023
  19. Neurapraxia. In: StatPearls. Treasure Island (FL): StatPearls Publishing. NCBI Bookshelf ID: NBK560501.
Episode 4: Blood SupplyEpisode 6: Skin Appendages
All episodes

Before you go

Tell us how this one landed

What worked, what you had to replay, and what you would like covered next. Requests are the main way the running order gets decided.

Send feedbackReport an error in this episode