The Mystery of the Human Ear

The human ear consists of mainly three parts they are:

-The outer ear

-The middle ear and

-The inner ear

Each other these have a function to what we perceive sound as (How the ear works, n.d.).

However, what is sound?

A Sound is a phenomenon that is produced when an object vibrates. It moves through a medium (typically air) and reaches the auditory system of a person or an animal, and thus one can perceive it as sound (Sound, n.d.).

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How Sound Waves Work (Designua, n.d.)

The hearing is, however, a process of converting these external environmental sounds into nerve impulses which are then perceived by our brain (Hawkins, 2018a, para. 1). The human ear is an organ that detects these sounds and offers the sense of balance (equilibrium) (Hawkins, 2018b, para. 1).

The human ear anatomically speaking has three parts as previously mentioned. The outer ear that is visible in all humans and mammals is called the auricle or piNna, and through a narrow spaced canal called the auditory canal, it ends with the tympanic membrane also known as the eardrum (Hawkins, 2018b, para. 2).

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The Human Ear Canal – I (Staab, 2014)

The very process of hearing starts from the outer ear as sound waves are captured through a uniquely shaped pinna and travel to the eardrum which is 10mm wide (javitzproductions, 2012).

Furthermore, the middle ear is made up of three bones called the malleus (hammer), incus (anvil), and stapes (stirrup). Together these three bones are called the auditory ossicles (Hawkins, 2018b, para. 2).

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(Ossicles of middle ear, n.d.)

The small air-filled cavity in the temporal bone is where this three chain of bones are located (Hawkins, 2018b, para. 2).

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Styloid process of temporal bone (Volker, 2018)

As one receives the sound waves from the eardrum, the middle ear transfers this energy to the three bones previously stated, and the three bones start motion. The fig. 3 shows that the hammer is attached to the eardrum and as sound travels the force is increased all the way to the stirrup (javitzproductions, 2012). At the end of the of this chain, there is a footplate or the oval window that creates motion of the fluid in the inner ear (CrashCourse, 2015).

This is, however, a little more complicated. The reason is that of the size difference between the stirrup and the eardrum. The footplate is 3.2mm² while the eardrum is 55mm². As the sound waves hit every inch of the eardrum this transfer of energy is much more significant in pressure as it reaches a smaller surface area which is the stirrup (Harris, 2001, para. 7). The pressure now applied to the cochlear fluid by the footplate is 22 times greater than when the sound had first arrived (Harris, 2001, para. 9).

Moving further into the more complicated part of the ear is the inner ear where the main components are the vestibular apparatus, and the cochlea is located (Hawkins, 2018b, para. 2).

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Inner ear (Somso, n.d.)

Among these two, the sense of hearing is controlled by the cochlea while the movement and balance of our head are executed by the vestibular apparatus (CrashCourse, 2015).

There are three various chambers given in the image below. The most important one is the basilar membrane (CrashCourse, 2015). As sound waves travel from the stirrup to this membrane the fibers move (there are approximate 20,000 to 30,000 fibers along this membrane) with the correct frequency of sound, one would hear, and energy is released. While this takes place, the fibers also move the hair cells next to it, these hair cells are what sends electric impulses to the cochlea nerve and straight to our brain, and various intricate sounds are then memorized (javitzproductions, 2012).

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Cochlea unrolled and in cross-section (Lasbury, 2011)

The Cochlea can be considered the part that enables one to sense various frequencies as each of the fibers have a specific frequency range (Forinash, n.d.).

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Uncoiled cochlea with basilar membrane (Forinash, n.d.)

Thus, this process happens at a blistering rate allowing us to perceive sound from all around our surroundings.

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(Ear diagram, n.d.)

REFERENCES:

CrashCourse. (2015, May 4th). Hearing & Balance: Crash Course A&P #17 [Video File]. Retrieved from https://www.youtube.com/watch?v=Ie2j7GpC4JU&t

Designua. (n.d.). How Sound Waves Work [Image]. Retrieved from https://www.dreamstime.com/stock-illustration-how-sound-waves-work-object-vibrates-air-will-vibrate-air-molecules-around-air-molecules-will-vibrate-other-image42512242

Ear diagram [Image]. (n.d.). Retrieved from http://www.amplifon.ie/hearing-loss/understanding-hearing-loss/how-our-hearing-works/

Forinash, K. (n.d.). Uncoiled cochlea with basilar membrane [Image]. Retrieved from https://soundphysics.ius.edu/?page_id=992

Harris, T. (2001). How Hearing Works. Retrieved from https://health.howstuffworks.com/mental-health/human-nature/perception/hearing3.htm

Hawkins, J. E. (2018)a. Human Ear. Retrieved from https://www.britannica.com/science/ear/The-physiology-of-hearing

Hawkins, J. E. (2018)b. Human Ear. Retrieved from https://www.britannica.com/science/ear

How the ear works. (n.d.). Retrieved from https://www.hearinglink.org/your-hearing/how-the-ear-works/

javitzproductions. (2012, June 15th). How the ear works [Video File]. Retrieved from https://www.youtube.com/watch?v=qgdqp-oPb1Q

Lasbury, M. (2011) Cochlea unrolled and in cross section [Image]. Retrieved from http://biologicalexceptions.blogspot.com/2011/09/yours-ears-hear-but-can-you-hear-your.html

Ossicles of middle ear [Image]. (n.d.). Retrieved from http://www.emedmd.com/content/middle-ear-anatomy

Somso. (n.d.). Inner ear [Image]. Retrieved from https://mesa-anatomy.weebly.com/ear.html

Sound. (n.d.). Retrieved from http://www.physics-and-radio-electronics.com/physics/sound.html

Staab, W. (2014). The Human Ear Canal – I [Image]. Retrieved from http://hearinghealthmatters.org/waynesworld/2014/human-ear-canal/

Volker, J. H. (2018). Styloid process of temporal bone [Image]. Retrieved from https://www.earthslab.com/anatomy/styloid-process-of-temporal-bone/

APPENDIX:

More detailed video can be viewed below,

https://www.youtube.com/watch?v=PeTriGTENoc

Impedance matching calculates this,

The surface area of the eardrum is 55mm² which is 17 times larger than 3.2mm² of the footplate.

3.2 x 17 = 54.4 an approximation that later is 55mm² (varied by human beings).

The chain of bones in the middle ear (Ossicles) act as a lever system. The bones are connected in a way that if the hammer moves at a particular speed, say 1; the speed is increased so very slightly by the time the sound waves reaches the footplate which is 1.3.

Thus the final pressure being 17 x 1.3 = 22 times. The sound we perceive from our eardrum is later perceived 22 times which is enough pressure to create motion in the fluid of the inner ear (Joshi, Mendhurwar, 2018, p. 222).

Joshi, V. D., & Mendhurwar, S. J. (2018). Physiology: Prep Manual for Undergraduates 6th edition. New Delhi, India: Reed Elsevier India Pvt Ltd