This is where the streams of nerve impulses are converted into meaningful sound.Īll of this happens within a tiny fraction of a second….almost instantaneously after sound waves first enter our ear canals. These nerve impulses follow a complicated pathway in the brainstem before arriving at the hearing centres of the brain, the auditory cortex. What happens next is even more remarkable because, when each ‘hair cell’ detects the pitch or frequency of sound to which it’s tuned to respond, it generates nerve impulses which travel instantaneously along the auditory nerve. High-pitched sounds will stimulate ‘hair cells’ in the lower part of the cochlea and low-pitched sounds in the upper part of the cochlea. Remarkably, the ‘hair cells’ in the cochlea are tuned to respond to different sounds based on their pitch or frequency of sounds. As the stapes vibrates, it makes the fluids in the cochlea move in a wave-like manner, stimulating the microscopically small ‘hair cells’. This happens because the last of the three bones in this chain, the stapes, sits in a membrane-covered window in the bony wall which separates the middle ear from the cochlea of the inner ear. The eardrum vibrations caused by sound waves move the chain of tiny bones (the ossicles – malleus, incus and stapes) in the middle ear transferring the sound vibrations into the cochlea of the inner ear. The eardrum is so sensitive to sound vibrations in the ear canal that it can detect even the faintest sound as well as replicating even the most complex of sound vibration patterns. These sound waves make the eardrum vibrate. Sound waves, which are really vibrations in the air around us, are collected by the pinna on each side of our head and are funnelled into the ear canals. The physiology of hearing, just like its anatomy, is very complex indeed and is best understood by looking at the role played by each part of our hearing system described above. Diagram of the main parts of the peripheral hearing system The central hearing system consists of the auditory nerve and an incredibly complex pathway through the brain stem and onward to the auditory cortex of the brain. The cochlea is filled with special fluids which are important to the process of hearing. The cochlea, which contains many thousands of sensory cells (called ‘hair cells’), is connected to the central hearing system by the hearing or auditory nerve. The hearing part of the inner ear and is called the cochlea which comes from the Greek word for ‘snail’ because of its distinctive coiled shape. The inner ear has both hearing and balance organs.The malleus connects to the eardrum linking it to the outer ear and the stapes (smallest bone in the body) connects to the inner ear.
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