Hearing

Welcome to this lesson today on hearing. Today, you will be learning about how the structures within your ear allow for you to be able to hear. Specifically, you will learn about

1. Three Main Ear Parts
2. The Process of Hearing
3. Balance & Equilibrium

1. Three Main Ear Parts

The three main parts of the ear are the outer ear, middle ear, and inner ear. 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. You can see these parts in the image below. 

2. The Process of Hearing

In the process of hearing, the first thing that needs to happen is that sound must enter the ear. Sound travels as a wave and is measured in a unit called decibels. Sound enters the ear through the auditory canal toward and is funneled toward the tympanic membrane; also commonly referred to as the eardrum. When sound waves strike the tympanic membrane, they will cause the tympanic membrane to vibrate. As the tympanic membrane vibrates, it will cause these three bones of the middle ear to vibrate as well and the three bones of the middle ear are called the anvil, the hammer, and the stirrup. From there the energy from the vibrations of the tympanic membrane, hammer, anvil, and stirrup is transferred to the cochlea. Energy from the sound waves will create pressure waves within the fluid of the cochlea. From there, the waves will be transmitted to the organ of Corti within the cochlea; the organ of Corti contains important hair cells.

Hair cells are mechanoreceptors for sound and pressure waves will push these hair cells against something called a tectorial membrane. This tectorial membrane is a jelly-like structure and very pliable. Once 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. The auditory nerve will then carry those signals to the brain for interpretation.

• Sound
• Mechanical energy that travels in the form of a wave detected by our ears.
• Decibels
• Units used to measure the intensity of sound.
• Tympanic Membrane
• A membrane located in the ear that vibrates in response to incoming sound waves. Also known as the “eardrum”.
• Round Window
• A membrane that acts as a release valve for pressure.
• Auditory Canal
• A canal that funnels sound waves from outside the ear toward the middle ear.

• Cochlea
• A coiled fluid-filled sac located in the inner ear that plays a role in sorting sound waves.
• Organ of Corti
• A structure found in the cochlea that contains hair cells, which are mechanoreceptors for sound.
• Hair Cells
• Mechanoreceptors in the ear for sound.
• Mechanoreceptors
• Sensory receptors located in the ear that aid in the process of hearing.
• Tectorial Membrane
• A structure in the cochlea with which hair cells interact to produce action potentials.
• Auditory Nerve
• A nerve that carries signals from the inner ear to the brain.

3. Balance & Equilibrium

There are 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 are semicircular canals and the vestibular apparatus.

The vestibular apparatus is actually composed of the three semicircular canals plus two fluid-filled sacs 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. As your head moves position in space, these bits of calcium will also move back and forth as well.

• Semicircular Canals
• Three structures of the inner ear that are involved with balance and equilibrium; they contain sensory receptors that detect the head's position in space.
• Vestibular Apparatus
• Composed of the three semicircular canals and two fluid-filled sacs, which monitor equilibrium.
• Otolith Organ
• A part of the vestibular apparatus that help detect changes in the position of the head in space.

This lesson has an overview on the process of hearing. Today you learned specifically about the three main parts of the ear, the steps in the process of hearing and how parts of the ear affect balance and equilibrium.

Keep up the learning and have a great day!