The Ear

Ear anatomy is primarily a lab topic... but without a good foundation in ear anatomy, it is difficult to understand the senses it supports. So, some of this will repeat what you are learning in lab. In fact, I have simplified my description of ear anatomy to avoid too much repetition.

ear.jpg (35886 bytes) Here is a drawing from a textbook showing the general layout of the ear... Basically, the three main regions (outer, middle, and inner ear) can be seen. We will be spending much of our time in this unit on the inner ear.

The main regions of the inner ear are shown in blue here. They include the cochlea (for hearing), the vestibule (for static* balance sense) and the semicircular canals (for dynamic** balance sense).

*static: remaining the same (static balance sense-- knowing your body position at a given time)
**dynamic: changing over time (dynamic balance sense-- knowing how your body position changes over time)

Another very good website on ear anatomy, that also clearly presents information on the ear fluids (endolymph and perilymph) is this Washington University website.

I want to remind you here, while you can see a picture of the entire ear anatomy, of the role of the auditory (or Eustachian) tube of the middle ear. The middle ear consists of bones within an air-filled space. The outer ear has air in it, too, air that is continuous with the atmospheric air. The inner ear is not filled with air-- it is filled with fluid.

Different altitudes have different natural air pressures. The higher you ascend, the lower the air pressure, and the lower you descend, the higher the air pressure. Therefore, if you hike up a mountain, when you near the top, the atmospheric air pressure is lower than what it had been at the bottom.

Before you started your hike, the air pressures on either side of the tympanic membrane (both outer and middle ear sides) were the same. As you hiked up to the top, the outer ear air pressure dropped. With less pressure inside, the tympanic membrane should buckle out, from the excess pressure in the middle ear. Any buckling of the tympanic membrane decreases your hearing ability and can be painful. The balance in pressures between the outer and middle ears must be restored. That's what the auditory tube is for. When a discrepancy in pressure arises, the auditory tube can open for a short interval to allow air at the atmospheric pressure in your throat to enter and replace the middle ear air.

What I would like you to be able to do at this point, is to understand how the anatomy of the ear can allow for both hearing and vestibular senses. That basically means that you need to remember that outer and middle ear regions really only function in audition, while the inner ear does both audtion and vestibular senses. Also, you should review inner ear anatomy to ensure that you understand how each portion of the inner ear takes care of a specific function (either auditory or vestibular). Some of that will also be done on the following pages.

Some other ear websites earpenny.gif (58624 bytes) that cover either ear anatomy or do an overall job on hearing AND the vestibular system are:

*another Washington University website (some of the images I use on these pages are from here).

*A set of web pages on the ear from Eastern Virginia Medical School provides a nice, detailed anatomical description.

*The Ear Surgery Information Center has a really neat site. It shows ear anatomy, and also discusses ear disorders and surgeries. In addition, this neat picture of the inner ear over a penny is from that page.