Source: Video and Images Created by Amanda Soderlind
Welcome to this lesson today on hearing. Today, we will be discussing how the structures within your ear allow for you to be able to hear. The first thing we're going to do is identify the three main parts of the ear, which are the outer ear, middle ear, and inner ear.
This part of the ear right here is considered the outer ear, most of which you can see from the outside of your body. This is the middle ear. The middle here is the location where sound waves are amplified. The outer ear is where sound waves enter, the middle here is where sound waves are amplified. And then the inner ear is where sound waves are sorted.
In the process of hearing, the first thing that needs to happen is that sound must enter the ear. Sound is a type of mechanical energy. And sound travels as a wave. And it's measured in a unit called, decibels.
Sound will enter the ear. It'll be funneled through this auditory canal towards the tympanic membrane. The tympanic membrane is also commonly referred to as the eardrum.
When these sound waves enter the tympanic membrane, it will cause the tympanic membrane to start to vibrate. And as the tympanic membrane vibrates, it will cause these three bones of the middle ear to vibrate as well.
These three bones of the middle ear are called the anvil, the hammer, and the stirrup. The vibrating of the tympanic membrane causes the three bones of the middle ear to vibrate. And then that energy is then sent to the cochlea.
The cochlea is this coiled structure right here. Energy from the sound waves will create pressure waves in a fluid of the cochlea. And those waves will then be transmitted to the organ of Corti within the cochlea.
Hair cells are mechanoreceptors for sound. These hair cells are found in the organ of Corti, which is found within the cochlea. Pressure waves will push these hair cells against something called a tectorial membrane. This tectorial membrane is a jelly-like structure. Once these hair cells get pushed against the tectorial membrane, a neurotransmitter will be released, which will then trigger an action potential in the neurons of the auditory nerve.
This here is the auditory nerve. The auditory nerve will then carry those signals to the brain for interpretation. That's the process of hearing.
We're going to talk briefly about a couple other structures of the ear that don't directly relate to the process of hearing but play more of a role in balance and equilibrium. These three structures right here, one, two, three, are called the semicircular canals. These semicircular canals contain sensory receptors that detect the head's position in space.
The vestibular apparatus also is a structure that plays a role in balance and equilibrium. The vestibular apparatus is actually composed of the three semicircular canals plus two fluid-filled sacs, which can be found within here. These two fluid filled sacs are called the saccule and the utricle. Those two fluid-filled sacs, in addition to the semicircular canals, compose the vestibular apparatus.
Now, these two fluid-filled sacs include an otolith organ. Otolith organs contain hair cells and bits of calcium. So as your head moves position in space, these bits of calcium will also move back and forth as well. So, again, it's helping to monitor your head's position in space. And it plays a role in balance and equilibrium.
This lesson has an overview on the process of hearing.