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Conduction Deafness: Definition & Causes

Instructor: Sarah Phenix
In this lesson, we will explore what the conducting system of your ears is and what structures are included in that system. We will also look at what some of the causes of conduction deafness are.

Two Categories of Deafness

The auditory (hearing) aspect of your ear is actually a function of two actions: conduction and sensation.

Conducting vs. Sensory Structures of the Ear
Conducting vs. Sensory Structures of the Ear

When we refer to the conducting pathway, we mean the portion of your ear responsible for gathering sound waves into your ear as well as the route that those waves travel to reach the sensory component of your inner ear. The sensory component then translates those sound waves into the neural impulse that we interpret as sound.

Now, if you've never thought of it that way than that division of labor probably clarifies how there are two categories of deafness - one pertains to issues of the conducting system while the other deals with issues with the sensory system. In this lesson, we're specifically focusing on conduction deafness, or hearing impairments as a result of an issue with the conducting system of your ear. Let's first start by looking at the structures of the conducting system.

Conducting Structures of the Outer Ear

Conducting Structures of the Outer Ear
Outer Ear

When you hear birds chirp or a friend laugh, those 'sounds' are actually waves of reverberation in the air. Now, for you to translate those waves into sound you have to first collect them using that funnel-shaped structure that we commonly call our ears. Your pinna (ears) corral those waves of laughter or chirps into a tube called your auditory canal. Your auditory canal carries those gathered sound waves down towards the final structure of your outer ear, known as your tympanic membrane (or eardrum). The external side of your tympanic membrane marks the end of the outer region of your ear while the internal face of that membrane marks the beginning of your middle ear region.

Conducting Structures of the Middle Ear

Have you ever wondered why your tympanic membrane is commonly called an eardrum? Well, it's because both the musical drum and your eardrum have a membrane-like structure that reverberates against the air within a chamber when something is beat against it (like sound waves or drumsticks). However, while beating a musical drum produces sound waves (as the skin of the drum reverberates against the air within the drum's chamber); your eardrum reverberates in response to sound waves beating against it, kind of like drumsticks on a drum.

Conducting Structures of the Inner Ear
Conducting Structures of the Inner Ear

When sound waves beat against your tympanic membrane, those waves cause the membrane to vibrate against connecting structures, called ossicles (bony structures named the malleus, incus, and stapes). As your tympanic membrane vibrates, it pushes against those ossicles, translating those waves of sound into waves of pressure that move towards your inner ear.

The last structure of your conducting system is a tube-like canal, called the auditory tube, that connects your middle ear to your nasal passageway. This tube drains fluid as well as equalizes the pressure of your middle ear. So, why would you need to equalize pressure, you ask?

Well, remember the last time you were in a plane or driving up a tall mountain and the noises around you started to sound funny, like you were in a tin can, and then your ears 'popped' and everything sounded normal again? Well, that funny echoing noise you heard prior to the 'pop' was due to pressure building up within the chamber of your middle ear that was pressing against the back of the tympanic membrane, keeping it from naturally reverberating against the sound waves. It's basically the same idea as filling a drum's chamber with water and then beating the drum - the sound would be quite different, right?

Ok, so now that we understand the conducting 'instruments' of your ear, let's talk about all the things that can go wrong with this system and lead to hearing loss.

Causes of Conduction Deafness

Alright, since we're discussing the system that 'conducts' sound to the sensory portion of the ear, you have to keep in mind that really any type of obstruction, whether it be temporary or more serious, to the outer or middle ear can result in hearing loss. So, with that said, let's look at some common issues by region.

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