35.2.1  How does acute otitis media affect hearing?

In normal situations, the middle ear is filled with air, which transmits sounds from the outside world to tiny bones (called the ossicles, see Figure 35.3), causing them to vibrate. The vibration generates signals which the auditory nerve transmits to the brain. This process enables us to hear the sounds. If infection reaches the middle ear, the lining becomes red and inflamed, and it leaks sticky tissue fluid (mucus) into the ear. As the infection builds up, white blood cells crowd into the area to fight the infectious agents and the middle ear becomes filled by pus – a thick whitish-yellowish fluid, formed by mucus packed with living and dead bacterial cells and debris from damaged tissue in the ear.

  • What effect do you think pus in the middle ear will have on normal hearing, and why?

  • It is likely to impair hearing, because the thick, sticky pus stops the ossicles from vibrating properly, so sounds are not transmitted to the brain in the normal way.

35.2  Acute otitis media

35.2.2  Causes, transmission and risk factors for acute otitis media