Question
Wed December 28, 2011 By: Yogesh Punetha

Explain the structure and working of human ear with labelled diagram

Expert Reply
Wed December 28, 2011
Hearing allows humans to perceive sounds and noises. The auditory organ is responsible for hearing, but the inner ear also accommodates the sensory organs for the sense of balance. In anatomic terms, both organs constitute one unit. The VIII cranial nerve  is responsible for the ear.
 
 
 
 
The outer ear, middle ear and cochlea of the inner ear constitute the organ for perceiving sound.  


The outer ear includes the auricle (concha auriculae) and the external auditory canal (meatus acusticus externs) together the eardrum (membrana tympani) as boundary between the outer ear and middle ear (cavum tympani).
The middle ear is also called the tympanic cavity (cavum tympani), which is continued in the Eustachian tube (tuba auditiva) as connection to the upper part of the throat.


The inner ear has a highly complex system of passages and cavities called the bony labyrinth. It is filled with a liquid, the perilymph. In this liquid there is a membranous labyrinth similarly filled with liquid (endolymph). This is the organ for auditory sensation but also the organ of balance (vestibular system).
The hearing organ is a particularly important sensory organ since, apart from the ability to hear, it is a prerequisite for developing speech. This is why it is more important than the eye.


The hearing organ can detect sound waves, which enter through the outer ear to the ear drum (membrana tympani) and make this vibrate. Because of the connection between the ear drum and the malleus (manubrium mallei), the vibrations are transferred by the chain of auditory ossicles and then on to the stapes in the fenestra ovalis, which is surrounded by the skin labyrinth of the inner ear. The organ of Corti in the cochlea is stimulated by this and the impulse is carried by nerves to the core of cranial nerve VIII within the rhomboid cavity. The hearing sense is triggered here.


The sounds which we hear are based on sound waves. These are longitudinal waves of molecules which result from regularly repeating changes in air pressure. The frequency and length of the vibrations are called frequency. (Vibration per second = 1 Hertz). With increasing frequency, the pitch of the sound gets higher. Short waves, i.e. higher frequencies, are perceived as high-pitches sounds. Long waves, i.e. lower frequencies, are perceived as low-pitched sounds.

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