Basilar Membrane: Lining & Function

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  • 0:04 Definition
  • 1:18 The Organ of Corti
  • 2:37 Distinguishing Volume & Pitch
  • 3:27 Lesson Summary
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Lesson Transcript
Instructor
Katie Chamberlain

Katie has a PhD in Microbiology and has experience preparing online education content in Biology and Earth Science.

Expert Contributor
Christianlly Cena

Christianlly has taught college physics and facilitated laboratory courses. He has a master's degree in Physics and is pursuing his doctorate study.

The basilar membrane is a key player in the process of hearing. To 'hear' more about it, we think that completing this lesson 'sounds' like a good idea. We have also 'heard' good things about the quiz.

Definition of Basilar Membrane

The basilar membrane is a structure within the inner ear that is moved by incoming sound waves and is essential for the sense of hearing. The ear as we see it is only the outer ear (or pinna). If we shrank and travelled into the ear canal we would soon have to cross the eardrum (or the tympanic membrane), and then we would enter the middle ear. Here, we would find three tiny bones (malleus, incus, and stapes).

Sound waves enter the ear through the air and then transmit movement to these little bones. One of those bones, the stapes, acts like a door knocker, tapping on another membrane called the oval window which separates the middle ear and the inner ear. The oval window is the start of a coiled structure (like a snail) called the cochlea, where a fluid called perilymph moves when the oval window is struck by the stapes.

As the sound waves enter the perilymph of the cochlea at the oval window, they travel all the way to the apex. They then zip around a hairpin turn and travel back through the coiled cochlea. You can imagine that their return-tunnel is parallel to the tunnel they took towards the apex. Along the length of this return-tunnel is the basilar membrane.

The Organ of Corti

The basilar membrane has hair cells attached to its surface (on the side that does not face the perilymph). We don't mean hairs like the kind on your head. Hair cells are just the name of a type of mechanoreceptor, which means that they are stimulated by movement. Deep in the ear, surrounded by a fluid called endolymph (similar to the perilymph) they do not move except by sound waves. As a sound wave moves through the perilymph, the basilar membrane moves, too. Check out this diagram:

cochlea

The coiled cochlea is shown here as if it were unrolled. It also shows how the basilar membrane differs in width and the different frequencies detected at each end.

At the top of the hair cells are teensy tiny little cilia. These tiny little hair-like extensions gently touch against a sturdy ceiling-like structure called the tectorial membrane. Together, the basilar membrane, the hair cells/cilia, and the tectorial membrane make a structure called the Organ of Corti.

As the basilar membrane moves, the hair cell's cilia are brushed gently against the surface of the tectorial membrane. This bending movement triggers the hair cells to fire a neural impulse, which means that a sound wave was detected. Voila, hearing!

Distinguishing Volume and Pitch

The basilar membrane moves in accordance with the size of the sound wave. A louder sound will make the membrane move more. A quieter sound wave will make it move less. This is how the body senses volume, which is determined by the height of the sound waves.

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Additional Activities

Basilar Membrane True or False Activity

In this activity, you will check your knowledge regarding the lining and function of the basilar membrane, as presented from the lesson.

Directions

Determine whether the following statements are true or false. To do this, print or copy this page on a blank paper and underline or round the answer.

1. The oval window is a membrane-covered opening that leads from the middle ear to the outer ear.

True | False

2. In the labyrinth of the inner ear is a fluid that moves by sound waves known as perilymph.

True | False

3. Movement of the basilar membrane in response to sound waves causes the depolarization of hair cells in the Organ of Corti.

True | False

4. Hair cells are the sensory receptors of the auditory system that are stimulated by movement.

True | False

5. The sound waves enter the endolymph of the cochlea at the oval window and move all the way to the apex.

True | False

6. A sound wave is detected when hair cells fire a neural impulse.

True | False

7. Sound waves enter the ear canal and then transmit movement to these little bones known as Organ of Corti.

True | False

8. Pitch refers to the strength of sound waves and is characterized by its height or amplitude.

True | False

9. The cochlea is the complex, spirally-coiled, and tapered cavity of the inner ear in which sound vibrations are converted into nerve impulses.

True | False

10. Cilia are structures that serve either for locomotion by moving or as sensors.

True | False


Answer Key

1. False, because the correct statement is, The oval window is a membrane-covered opening that leads from the middle ear to the inner ear.

2. False, because the correct statement is, In the labyrinth of the inner ear is a fluid that moves by sound waves known as endolymph.

3. True

4. True

5. False, because the correct statement is, The sound waves enter the perilymph of the cochlea at the oval window and move all the way to the apex.

6. True

7. False, because the correct statement is, Sound waves enter the ear canal and then transmit movement to these little bones known as stapes.

8. False, because the correct statement is, Pitch refers to the strength of sound waves and is characterized by its height or amplitude.

9. True

10. True

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