Timothy C. Hain, MD • Page last modified: July 31, 2022
While there are several other surveys of inner ear anatomy, we have diffidently here set out to put the content in our lecture on this subject on the web.
Mechanical sensors (canals and otoliths) respond to angular and linear movement. This is an artist's drawing, based on the classic drawing by Max Brodel, and some liberties were taken for clarity. For example, the length of the internal auditory canal (IAC) is very short here. See the commentary about accuracy below. We have attempted to provide some "real" images from MRI and CT scans below.
The semicircular canals are very small rings -- about 1 cm in diameter. The image above is an MRI of a normal set of inner ears, taken in the "axial" view. The snail shaped objects at the top (front of head) are the cochlea. The rings are the semicircular canals. The IAC here is, of course, anatomically accurate, and is much longer than what is shown on the artist's illustration above.
The image above is taken from a CT scan shows that the anterior canal diameter is less than 1 cm - -smaller than a dime !
There are three semicircular canals - -the anterior, superior and horizontal. Between the three canals the brain can determine rotational velocity in three dimensions.
There are also two otolith organs (click here for more). The otoliths respond to linear acceleration such as gravity or changing velocity of movement in a straight line.
The illustration of the inner ear at the top of this page, the "Master ear", is an artists redrawing of an illustration originally due to Max Brodel (1946). This small book was published posthumously, based on drawings made originally in 1939.
Jackler et al (2014) pointed out that this illustration (which has been used by many) has numerous errors -- they state "Numerous anatomic errors exist such as a 180-degree reversal of the incus and a markedly foreshortened internal auditory canal. " Some of these errors were presumably made to avoid a "cluttered image". Nevertheless, others are just anatomic errors such as the "180 degree reversal of the incus". Jackler et al (2014) provide a link to a more correct illustration here. The more accurate illustration does not reveal the structures within the ear as clearly as the Brodel drawing, but the accuracy is of course very important, especially to surgeons.