NERVE: Whales have wildly stretchy cheek-nerves.

Fin Whale (painting) from science writer Darren Naish

Suppose you arrive at a fancy pool party, and everyone is casually filling their mouths with whole bottle of wine before taking a gulp.

After a silent prayer for their livers, you can't help but wondering "Could I accomplish the same depraved feat?" To engulf so much wine, you guess that you'd need supremely elastic jowls.  And after swallowing, you’d ideally like your face to return to its original shape.  

Thankfully such parties are rare among humans, but amongst whales it's downright polite to balloon your mouth with each gargantuan swig – and worse, to spit most of it back into the pool!

This is the famous lunge-feed of the Rorqual whales – the manner in which they filter krill by the ton from surrounding seawater.  But expanding their cheeks to more than twice their resting size requires more than a rowdy attitude – they need very extensible nerves to make it happen.

All nerves can stretch. But usually we're talking  5-10%-of resting length.  When most nerves go beyond this, they quickly become dysfunctional, defensive, and (with enough force or time) degraded.

But whale cheeks are different -- their nerves can stretch up to 150%! The way they extend themselves might offer some clues on how nerves relate to different surrounding tissues, and how to care for more stretch-sensitive nerves in the rest of us.

'Bungee cord' nerves within whale cheeks. (Stanford report)

So how do Whale-cheek nerves stretch so much? Same way that all nerves do it, only moreso. 

Nerves are composed of many nested collagen layers – each stiff in itself – but loosely linked to each other with elastic fibers and constrained by fluid pressure. 

During movement of the surrounding body, a nerve will slide passively within its larger interface. Then if the nerve's container lengthens further, the nerve's rippled collagen unripples (see Bands of fontana) and its circumferential fibers narrow to 'squeeze' the internal volume, and thus re-distribute pressure.

Outer collagen layers of a nerve provide a hard stop at the end of a nerve's stretch. (Lillie et al 2017)

The exterior sheath is the last to run out of slack, thus acting like a 'check ligament' on the whole system.  In this way, the delicate conducting fibers at the center of this arrangement bear the least force, and are able to maintain a calm inner ocean of homeostasis.

So what could this teach us for the mechanical health of our own nerves? 

(c) Hamm 2025, from recent video How do Nerves Get Injured, and How can they Heal?

A few implications occur to me:

• All ‘Neurodynamic’ tests and movements, like sliders and tensioners, should first carefully take the inherent slack out of the nerve before commencing the glide/stretch.  Otherwise, the movement cannot reliably engage the nested tube in question.

• Time is an important component of nerve glides/stretching.  As long as we're not creating pain or other contraindications, we should give nerves at least a breath or two in one position, to fully re-distributed their internal fluids and membranes, before moving to the next position.

• That said, we shouldn't linger too long -- even whale nerves do best with brief (often < 30 second) intervals of stretch, followed by a return to relative slack. Any sustained stretch to nerves tends to ligate their blood supply, and make them take protective action -- altered muscle behavior and neurogenic inflammation.

• What we call a neurodynamic ‘tensioner’ or a nerve stretch is actually a slider -- just for internal layers of the nerve.  So it may help to visualize this internal sliding, and perhaps to palpate along the length of a tensioned nerve in search of places where its circumference feels stiff.  This may indicate a place where fluid pressure is greater, or internal fascicles can’t glide along each other.

From Shah, 2017. Nerve architecture enables mechanical load-bearing.

"Movement of organisms imposes mechanical loads on peripheral nerves. Schematics of nerves observed to stretch during (A) Caenorhabditis elegans (nematode) crawling (touch receptor nerves) and (B) human elbow flexion (ulnar nerve) are shown in red 4, 18. An extreme version of nerve stretch occurs during rorqual whale feeding, as described in this issue [1]. (C) Undulations in axons and fascicles, first described by Fontana in 1781 [5], provide strain relief, thereby protecting neural elements from deformation-induced damage. In mammals, this waviness creates an optical effect known as the 'bands of Fontana' [19]. (D) A well-organized extracellular matrix, consisting of endoneurium (surrounding individual nerve fibers), perineurium (surrounding fascicles), and epineurium (ensheathing the entire nerve), bears mechanical loads in peripheral nerves. (E) Lillie et al. observed that superposed waviness of the nerve core and of fascicles within the core enable the dramatic extension of ventral groove blubber (VGB) nerves during rorqual whale lunge feeding 1, 8."

Lastly, may the whale inspire our sense of resilience -- nerves are incredibly robust!  Much of peripheral nerve pathology is about sensitization and autonomic dysfunction – to be respected for sure – but we should instill in ourselves and our patients a sense that nerves can learn to handle incredible forces and feats.  After all, I'm not not swilling Krill by the truckload! Are you?

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If you're interested in further whale nerdness, check out this gray whale cranial base I encountered on the Washington Coast:

And if you're a healthcare provider interested in Jaw Nerves, you might like my online/in-person class Neurofascial Approach to Jaw Pain.