Apple #541: Yawning and Stretching and Hearing

The other day, my friend Jehoshaphat came to talk to me when I was in the middle of something. The interruption made me yawn and stretch my arms above my head. I don't know why that happens, by the way, but when I'm tired that does seem to be a necessary transition when switching my attention from one thing to another.


This is the kind of yawn & stretch I'm talking about.
(Photo from Bio Break)


Anyway, he was trying to tell me something while I was yawning and stretching. I said, "Wait a second, I couldn't hear anything just then. Say that again?"

Instead of repeating what he'd just asked me, he said, "Now that's a Daily Apple right there. How come you can't hear anything while you're yawning and stretching?"

Jehoshaphat, here is that Daily Apple.

• I couldn't find any one source that explained this exactly, but my theory is that the reason you can't hear while yawning and stretching is two-fold.

• First, when you yawn, your Eustachian tube opens.

• Like how you're on an airplane and the pressure in your ear builds up, so you yawn. That opens your Eustachian tube, the pressure is equalized, and you can hear again. (Blausen Med on About.com has a really helpful video about this process.)
  

Sound normally enters the ear through the ear canal and the ear drum. The Eustachian tube beneath the middle ear opens and closes to regulate air pressure in the middle ear.
(Diagram from WebMD)

• When you yawn under regular circumstances, there's no issue related to pressure imbalance, so it's not pressure difficulties that are obstructing your hearing. It's the opening of the Eustachian tube itself.

• The top of the Eustachian tube opens into the middle ear. But the bottom end of the Eustachian tube leads to the pharynx, or the back of the throat. So when the Eustachian tube opens, you get input coming into the middle ear from two sources: from the ear canal and off the eardrum as usual, but also up from the pharynx. Having that other opening into the middle ear reduces the middle ear's ability to amplify sound and everything takes on a hollow, echoing sound.

Lots of stuff on this diagram, but I'm including it only to show you that the Eustachian tube connects to the pharynx. There are surprisingly few diagrams that depict this very well.
(Diagram from James on the CPAP forum)

• Another thing that happens when the Eustachian tube is open is that you have less of a buffer blocking out the internal sounds from your body.

• People who suffer from a rare condition called a Patulous Eustachian Tube have their Eustachian tubes open all the time. They have trouble hearing because, with the tubes open, the sounds of their own body are a lot louder: the sound of their own breathing, the sound of their own voice, even the sound of their blood flow. It can be so unbearable, they can suffer from depression and even thoughts of suicide.

• Fortunately, when we yawn, the Eustachian tube is open only briefly, so it's only temporary and not a persistent condition. But to summarize, yawning makes the sounds of our interior workings get a bit louder.

• I also noticed, though, that this can happen even if there's no yawning involved. Sometimes if I only stretch -- no yawn, just my arms above my head and stretch mainly my torso and my neck and my arms -- I experience the same thing. A deep, rushing rumbling begins in my ears and gets louder as the stretch extends. Once I drop my arms and the stretch stops, the noise in my ears stops and I can hear again.

• This is where the second part of the process comes in, and this is my theory. I'll take you through my logic step by step.

• Yawning increases blood flow to the brain.

• Stretching increases blood flow, even more than yawning.

• All kinds of huge arteries run up the neck, right along the ears.

Arteries in the head and neck, sending blood up past the ears to the brain.
(Image from The Home Cyclopedia of Health and Medicine)

• When you stretch, especially if the stretch involves the neck, a lot more blood than usual rushes up those arteries, right next to your ears.

• So I think that when you stretch, your hearing gets blocked out because what's happening is exactly what it feels and sounds like: tons more blood than usual is rushing past your ears and all you can hear is that.

Yawning and stretching like this, she really wouldn't hear a thing.
(Photo from dailybooth)

• So, putting it all together, when you yawn and stretch, you're opening the Eustachian tube which increases your ear's sensitivity to internal sound to begin with. Stretching increases the blood flow and thus the noise of the blood rushing past your ears. With the Eustachian tubes open, all that blood rushing past sounds extra-loud, and you can't hear anything else.

That's my theory and I'm sticking to it.


Sources
Science Ray, Why Can't We Hear Well When We Are Yawning?
CafeMom, Why can't your hear when you yawn or stretch?
Blausen Med, About.com, How Does Ear Pressure Work?
Mark C. Loury, MD, Eustachian Tube Patency
Finding a Solution for Patulous Eustachian Tube
Gallup & Gallup, Yawning as a Brain Cooling Mechanism, Evolutionary Psychology, 2007. 5(1): 92-101