INSTANT EXPERT: EARS
Why you’re deaf and fall down a lot.
Our ears and the rest of the complex sense of hearing allow our brains to distinguish between 400,000 different sounds. But the ears also help us keep our balance, when we move. If the sensitive hair cells in the ears are harmed, the brain is advised of sounds which do not exist.
Anormal, healthy ear can distinguish between 400,000 sounds. It can also filter out sound, if you are in a room full of people and only want to listen to one conversation. It is possible due to 16,000 small hair cells that analyse the sound down to the slightest detail on its way from the external ear to the brain.
The human ear is best at capturing sound with frequencies of 1,0004,000 Hz, but it can capture sound in the entire 20-20,000 Hz interval. The ear picks up the sounds, but it is the brain that hears a sound. Basically, the ear's function is to convert pressure waves, of which a sound is made up, into nerve impulses which the brain can capture.
Our ears are made up of three parts. The external ear, which consists of connective tissue, is a type of satellite dish. The external ear captures sounds and concentrates them through the auditory canal towards the eardrum, which also makes up the border on the middle ear, where you will find the three tiniest bones of the human body. The oval window membrane marks the end of the middle ear and the entrance to the internal ear, where you will find the cochlea. When the oval window moves due to a sound, the hair cells also move, and via nerve fibres, the cells send signals towards the brain.
The signals pass through the auditory nerve to end up in the auditory cortex, i.e. the brain area responsible for sound. En route, some fibres cross over to the other side of the brain to be able to analyse where the sound came from. If the sound hits one ear first, it will reach the other about 700 microseconds later. Nerve fibres also pass from the brain stem to the hair cells to reduce their activity and so their response to particularly harmful sounds. The hair cells are very sensitive, and hefty noises such as loud rock music and plane engines could harm or destroy the cells.