The Auditory Sense: Hearing
The human auditory system is critical to speech perception and translation. What are the components making up the human hearing system? What role does each part of the hearing system play? How does sound reach the ear? How is sound translated to be meaningful? Each of these questions and concepts relating to the human hearing system will be answered and discussed below.
The system of human auditory allows the body to interpret and collect sound waves into meaningful messages. The ear is the primary sensory organ responsible for hearing. The ear is made up of three parts, inner, middle and outer ears. The inner part of the ear I responsible for hearing and equilibrium through the receptor cells found in it. The human ear can estimate the source of a given sound which is referred to as localization (Schnupp, Nelken & King, 2011).
In an experiment aimed at understanding how sound travels especially through solids, children are asked to sit in a circle. They are then asked if they can hear the sound and whether they can identify its source as well. For the sound to reach the eardrum, vibrations from the voice box generate tiny particles in the air that make the eardrum vibrates. In an experiment to determine if sound can move through solids, a pupil is to stand outside a wall and away from a window. The teacher is to speak some words of the class, and if the pupil hears the teacher talk, they are to move back to class.
Among the five senses in humans, hearing is considered as most significant. This is because, through hearing, humans can communicate with others by receiving and interpreting signals. Hearing originates from pressure waves hitting auditory canal which ends when the brain perceives it. Reception of sound occurs in the ears; pinna collects attenuates, reflects or amplifies the sound waves. After the reception, sound waves travel through the auditory canal into the ear drum. In the ear drum, the sound waves cause pressure variations which make the eardrum vibrate. These vibrations set the cochlea fluid into motion, and the fluid in return splits the sound to its respective place (Van Deun et al., 2009).
The hair cells as well play a critical part in making the ear fulfill its purpose. It is the hair cells in the ear that are responsible for performing transduction of the sound waves into diverse electrical insults. The auditory nerve fibers that connect to the hair cells of the spiral ganglion then transmit the electrical signals to the brain stem. It is through the hearing system that humans can detect various qualities of signals and choose the best that does not cause harm to the ear. This implies that the hearing system can identify the specific location, loudness and pitch of a sound (Tzounopoulos & Kraus, 2009).
Unlike the visual system that combines wavelengths to generate a color, the hearing system does not mix frequencies to generate a sound. Rather, the hearing system separates complex sound into their frequencies making humans able to follow different instruments when listening to music or conversation. Irrespective of the nature or intensity of sound, the vibrations are all directed to the eardrum through the auditory canal and in return makes the eardrum vibrates. It is the role of the hammer (malleus) to transmit vibrations to the anvil from where the vibration is carried to stapes or stirrup. The hammer is attached to the tympanic membrane. From the stapes, the oval window is pushed causing separation of the air-filled middle ear and inner ear. In the process, the snail-shaped cochlea of the inner ear produces waves (Ahuja & Ahuja, 2007).
The hearing system through the cochlea can separate frequencies. On one side, higher note makes one part of the cochlea basilar membrane vibrate while a lower note causes a similar effect on the diverse region of the basilar membrane. Along the basilar membrane are hair cells that generate electrical signals. These signals have the ability to excite about 30,000 auditory nerve fibers (Ahuja & Ahuja, 2007).
As noted above, the auditory nerve takes signals to the brainstem. Because the hair cells ride on various basilar membranes, they can respond to varying frequencies. Analysis of the auditory information is then done through the brain center as it flows to the superior auditory cortex. The adjacent neurons in the auditory cortex tend to respond to tones of similar frequency and normally specialize to a diverse combination of tones. Some of them respond to pure tones such as those of flute, some too complex sounds like those made by violin (Manley & Fay, 2007).
Finally, tones vary in length of response because some respond to short, some too long and others rise or fall in frequency. As a way of recognizing a word or an instrument, some neurons might use the specialized neurons to blend information that is available. Within the two sides of the brain, sounds are differently processed in the auditory cortex. This is the reason some humans have the left side is dedicated to production and perception of speech. Due to different ways the auditory cortex process sound, it is possible to see a person whose left auditory cortex has suffered stroke able to hear but cannot understand what is being said (Manley & Fay, 2007).
In conclusion, in its role to as a hearing organ, the ear has some parts that make it. Each part of the ear has a role to play and in the absence of any of the part, the complete hearing process cannot be achieved. The brain too has a contribution to make to complete the hearing cycle by translating electrical signals. The ear is therefore a very critical organ in humans.
Schnupp, J., Nelken, I., & King, A. (2011). Auditory Neuroscience: Making sense of sound. MIT Press
Van Deun, L., Van Wieringen, A., Van den Bogaert, T., Scherf, F., Officers, F. E., Van de Heyning, P. H. … & Wouters, J. (2009). Sound localization, sound lateralization, and binaural masking level differences in young children with normal hearing. Ear and Hearing, 30(2), 178-190.
Tzounopoulos, T., & Kraus, N. (2009). Learning to encode timing: mechanisms of plasticity in the auditory brainstem. Neuron, 62(4), 463-469
Manley, G. A., & Fay, R. R. (Eds.). (2007). Active processes and otoacoustic emissions in hearing (Vol. 30). Springer Science & Business Media
Ahuja, P., & Ahuja, G. C. (2007). How to Listen Better. Sterling Publishers Pvt. Ltd.