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What is the Pinna?

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  • Written By: T.F. Johnson
  • Edited By: Jenn Walker
  • Last Modified Date: 04 November 2016
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Pinna, derived from the Latin word for feather, are what a casual observer usually refers to when they are pointing to your ears. The pinna, or auricles, as they are scientifically known, are the visible parts of the ears located on the outside of the head. The biological structure of the outer ear is composed mainly of cartilage, which provides the pinna with a great deal of flexibility and ability to be positioned for optimal listening.

The anatomy of the human pinna is split up into several major components: the helix, the antihelix, the concha, the tragus, and the lobe. The helix is the outer edge of the ear, which usually folds down and inward from the top. The antihelix is the Y-shape that is located just below the helix, and is the second-highest part of the ear. The concha is the hollow part of the ear located right next to the ear canal, and serves as the entrance to the inner ear. It is usually slightly covered by the tragus, the small flap of cartilage that faces backward. When listening to music through earbuds, the tragus is the protrusion that holds the earbuds in place. The final component, the lobe, is located at the bottom of the ear, and is the only part of the ear that is not cartilaginous, being made up primarily of fatty tissues. It serves no known biological function, and is the most common location for ear piercings.

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The entire purpose of the outer ear is to collect sonic waves, redirecting them into the aural canal so they can be interpreted and sent to the brain. This is where the pinna's unique shape comes into play, causing them to act as funnels that amplify sonic waves and redirect them straight into the ear canal. In collecting and filtering these sonic waves, the pinna also perform several important secondary functions. The most important of these secondary functions is sound localization, which is the ability to pinpoint the origin or location of a sound after hearing it. The biological architecture of the pinna allows the listener to determine the direction that a sound came from, as well as the sound's distance from the ear.

The concept of sound localization is strongly linked to the idea of head-related transfer function (HRTF) because it allows human beings to locate sounds in three dimensions. Because of HRTF, sounds can be located above, below, in front of, behind, and to either side of the human head. This is due to the fact that the pinna, along with the brain and inner ear, allow us to create a three-dimensional mental map pinpointing the source of a noise. When a sound is heard by both ears, the differences in timing and reception angle for each ear allow the listener to figure out where the sound is at relative to the body and how close the source is. Many species, humans in particular, use this biological mechanism to pick up the slack and supplement the limited range of perception that they receive from their eyes. Since the eyes only allow most species to see a small part of the world around them, the ears serve a crucial function, allowing the listeners to determine if something requires attention.

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KoiwiGal
Post 3

@Mor - I don't think it's the lumpy bits of the ear that direct sound so much as the fact that our ears are kind of shell shaped. That is the shape they use in music performance theaters as well, because it amplifies sound waves. And it is the lumpy bits that are unique to each person. Also they do a pretty good job of protecting the ear canal through cushioning. If you got hit in the side of the face and didn't have an ear there to cushion the blow, it would probably be that much worse for your inner ear.

Also, considering how much almost every culture does to ornament their ears, they will probably never go away through

evolution, because there might be a slight pressure on sexual selection that keeps them there. And even if there isn't right now, there certainly used to be.

They definitely don't qualify as vestigial organs, even though their functions aren't entirely obvious when compared to the more blatant shapes of animal ears.

Mor
Post 2

@umbra21 - I'm actually surprised that we still have flaps on the outside for ears at all. I can't imagine that pinnas do that much good for our hearing and even if they were supposed to be an ideal shape for collecting sound waves, everyone has a unique ear shape, so every single ear shape can't possibly still be ideal.

Considering how vulnerable they are to damage, and how often humans seem to get ear infections which could be prevented with a different kind of covering, I'm just not sure why the pinna isn't seen as a vestigial body part, like the appendix. Something that is left over from a time when it was once different and more useful.

umbra21
Post 1

I've always thought it was kind of cool that I could move each of my ears independently of each other. It always surprises kids anyway, and I don't think everyone can do it.

Although I guess it doesn't have much use except as a party trick. I know that animals will swivel their ears right around in order to pin point a sound, but we can't really do that except by turning our heads. And even then people are pretty hopeless at hearing things compared to most other animals.

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