Department of Physiology, Development and Neuroscience

Matthew J. Mason PhD

University Physiologist Tel: +44 (0)1223 333829, Fax: +44 (0)1223 333840, E-mail: mjm68@cam.ac.uk

 
 
 

My research: structure and function of the middle ear

"Consider the first and last major steps in anatomical construction of the mammalian middle ear - for we know no better or more intriguing story in the evolution of vertebrates" Stephen Jay Gould (1993).

The middle ear apparatus (Fig. 1) improves the efficiency of sound energy transfer from the air through to the fluid-filled inner ear, which contains the hair cells that will turn vibrations into electrical signals interpretable by the brain. It consists of a tympanic membrane (eardrum) which receives the sound, an air-filled middle ear cavity behind it and, within the cavity, a series of conducting elements to convey vibrations from the tympanic membrane to the oval window, the entrance to the inner ear. In mammals, these conducting elements take the form of three tiny bones, or auditory ossicles. Other terrestrial vertebrates have a different ossicular system: it is believed that a tympanic middle ear evolved several times in parallel, in different vertebrate groups.

My research involves examining a wide range of different ears (museum specimens or natural casualties), using techniques such as light microscopy, electron microscopy and micro-CT scanning. I then use models of middle ear function to investigate the likely hearing range of the animal in question, in order to answer questions about how hearing is matched to particular acoustical properties of the environment that the animal lives in, and how the ear might have evolved. For example, I have long been interested in the massive ear ossicles of golden moles (Fig. 2), which may allow these burrowing African insectivores to detect ground vibrations by means of bone conduction. I have more recently begun to investigate the enormously expanded middle ear cavities of certain elephant-shrews (Fig. 3), which improve the detection of airborne sound at the low frequencies which travel best in their desert habitat.

Here are some links for further information about what I do:

My research on the ears of mammals

My research on the ears of non-mammalian vertebrates

Podcast interview on The Naked Scientists

 

My research has been sponsored by the BBSRC and the National Institutes of Health.

Photomicrograph of the left 
middle ear apparatus of a tuco-tuco, a subterranean rodent from South 
America.

Fig. 1: Internal view of the left middle ear apparatus of a vole. The stapes footplate, projecting towards the viewer, would normally be contained within the oval window, the entrance to the inner ear.

Rotating radiograph of the skull 
of a golden mole

Fig. 2: Rotating radiograph of the skull of a golden mole, Eremitalpa granti granti. Note the enormously enlarged mallei, which appear as rounded, white masses in each ear (see Mason, 2003).

Fig. 3: Micro-CT scan of the skull of the extraordinary elephant-shrew Macroscelides. Its middle ear cavities, contained within the swollen regions of the skull which are shaded in red, have a combined volume 30% greater than brain volume! See Mason (2015).