Introduction
How do we hear sounds from the atmosphere? Every living organism has a way of hearing sound. Some of the animals do not have ears but can still respond to sound. The auditory canal might be different from one organism to the other. Dogs can hear sounds that are of high frequencies that the human ear cannot perceive. Snakes might not have ears, but they still have a way of sensing the movement of sound through vibrations. The human ear works the same way as those of the other primates. It is no wonder that experiments regarding the human auditory system are carried out on primates. The auditory system in humans is very important in relaying pieces of information from one person to another (Abbas, 1993). This facilitates communication amongst humans. Apart from this function, the human ear can act as a warning mechanism when there is danger. One can hear a siren and or a horn and will react in a way to avoid an accident. The auditory system not only serves as an earring aid but also acts as a balancing mechanism that allows humans to walk upright. Damage to the inner ear would cause one to lose a sense of balance. These elements of the ear show how important the auditory system is to humans.
Parts of the ear and their functions
Listening to soft music can be soothing to the ear but how does the ear decode the sound wave from the stereo into music? In trying to understand this, we must look at the components that constitute the human auditory system (the ear). It is important to understand that a system consists of different parts that perform different functions; that is targeted to achieve a certain goal. The human auditory system is complex and to understand it you have to look at the various parts of the ear and understand the various functions they perform.
The outer part of the ear is the pinna also referred to as concha. This directs all the sounds into another part of the ear called the canal. The pinna is the flap of cartilage covered by skin, found on either side of the head. It acts as a satellite, capturing sound waves from all corners. It can locate the direction the sound is coming from; that is why one can tell where a certain sound is coming from. Sounds reach the ear at different times; if a sound comes from the left side of the ear, the left ear will pick it first before the right ear. The delay in picking up the signal is referred to as a phase. When the sound signal is loud on the right side, the left ear will receive a slightly lower level of sound. The sound waves are channeled down the ear canal as compressed waves. Decoding of this sound takes place at different levels within the ear.
The ear canal follows immediately after the pinna. It is a cavity that resonates with the sound waves from the pinna to the middle ear. From the ear canal, the sound travels to the eardrum also called the timpanic membrane. Adjacent to the eardrum is the malleus and incus which vibrate at intervals to transmit the sound wave to the cochlea. The cochlea nucleus is used to clarify the signal of the sound produced.
The cochlea is a coil-like structure within the ear. The cochlea contains fluid that vibrates with the sound waves as it receives it. Within the cochlea is another membrane called the basilar, which acts as an analyzer breaking down the sound into frequencies. The membrane is tapered and has variations in its thickness (Gardner, 1973). The basilar membrane will vibrate at different points within its thickness to give different frequencies depending on. Introducing new sounds while the first sound is still resonating will cause a phenomenon called spectral masking; this makes it difficult to hear the subsequent sounds. On the other hand, the superior olivary is used to measure the sources of sound and measures the inter-aural time delays between the two ears (Billow, 2003).
The basilar membrane does not detect the sound waves on its own; it gets help from the countless hair cells lining the membrane. Although there are different kinds of hair cells the most important ones are the inner and outer cells. The inner cells convert the sound waves they receive into neural impulses, transmitted to the brain via the auditory nerve. The response of each cell is random and depends on the movement of the basilar membrane. The inner hair cells will continue working even if there is no sound wave coming in (Graff, 2009).
The outer cells are also found within the basilar membrane. Their work is to receive the signal from the brain. The outer and inner hairs work together in unison to make sense of the sound and also to detect the loudness of the sound being transmitted.
Conclusion
Even though we have some information about how the ear works, more studies need to be carried out to give more information as to what goes on in the ears.
References
Abbas, P. J. (1993). “Physiology of the auditory system.” Otolaryngology-Head and neck surgery. St.Louis, Mosby: Journal of the acoustic society of America.
Billow, O. K. (2003). The Auditory System: The Internal Functions of the Ear. New York, NY: Craft medical Learning.
Gardner, M. B. (1973). Problems of localization in the Medium plane: Effects of the Pinnae Cavity Occlusion. Illinois: Professional Educational International.
Graff, N. L. (2009). The Human Ear: How Do We Hear? Maryland: Jones & Barlett Learning.