How We Hear                                    

Outer Ear

•         The outer ear consists of the external ear, the ear canal and the ear drum. The outer ear gathers sound waves from the surrounding air and funnels them through the ear canal to the eardrum. When these sound vibrations reach the eardrum the eardrum begins to vibrate.

   Middle Ear

•         The middle ear includes the eardrum and the three smallest bones in the body. The eardrum is a thin, flexible barrier between the outer and middle ear. When sound waves reach the eardrum, it begins to vibrate and sets off a chain reaction causing the three ear bones in the middle ear to vibrate. The three bones are the hammer, anvil, and stirrup. The stirrup, the smallest bone in the human body, fits into the oval window which is the opening to the fluid-filled inner ear. When the stirrup moves, fluid in the inner ear carries the vibrations into the canal of the cochlea.

   Inner Ear

•         The inner ear consists of both the cochlea and the vestibular system that works to keep the body balanced. The cochlea is a delicate snail-shaped structure containing the sensory organs for both balance and hearing. More than 20,000 individual hair cells (cillia) are inside the cochlea. Movement of the cochlear fluid bends these hair cells, stimulating them to generate electrical impulses in the auditory nerve where they are transported to the brain.

   Sensory or Auditory Nerve

•          The stimulating of the sensory cells in the inner ear causes impulses to be sent beyond the cochlea to the auditory nerve. In the auditory nerve sound messages are sent to the brain where they are interpreted as sound. If these parts of the brain are damaged or not stimulated for long periods of time, a person may not be able to hear speech even at high levels.

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