MAVO Year 4 · Senses · Section 11.6

The ears

Sound and vibrations

Sound travels as vibrations through a medium such as air. Frequency is the number of vibrations per second: higher frequencies generally produce higher pitch. Amplitude is the size of the vibration and is related to sound intensity.

Sound level is expressed in decibels, a logarithmic scale. A rise of 10 dB corresponds to ten times the sound intensity, not ten times the perceived loudness. Hearing-damage risk depends on both sound level and exposure time; prolonged exposure around or above 80 dB can be harmful, and very intense sounds can damage hearing quickly.

Outer and middle ear

The pinna collects sound, and the ear canal directs it towards the eardrum. Earwax helps protect and clean the canal. Sound makes the eardrum vibrate. Three small bones in the middle ear, the hammer, anvil and stirrup, transmit vibrations towards the oval window of the inner ear. Together with the eardrum, they help transfer sound efficiently from air to fluid.

The cochlea

The cochlea contains fluid and specialised sensory hair cells. Sound causes movement within it, bending structures on these cells. Their activity stimulates neurons whose impulses travel along the auditory nerve towards the brain.

The balance organs

The inner ear's balance system includes three semicircular canals and otolith organs. They detect different aspects of head movement and orientation. Movement of fluid or weighted sensory structures bends hair cells, changing signals sent to the brain.

The Eustachian tube

The Eustachian tube connects the middle ear with the upper throat. It opens during actions such as swallowing or yawning, helping equalise air pressure on both sides of the eardrum so it can move normally.