Problem 5 - Campbell Biology

Question

\begin{equation} \begin{array}{l}{\text { The transduction of sound waves into action potentials occurs }} \\ {\text { (A) in the tectorial membrane as it is stimulated by hair cells. }} \\ {\text { (B) when hair cells are bent against the tectorial membrane, }} \\ {\text { causing them to depolarize and release neurotransmitter }}\end{array} \end{equation}\begin{equation} \begin{array}{l}{\text { that stimulates sensory neurons. }} \\ {\text { (C) as the basilar membrane vibrates at different frequencies }} \\ {\text { in response to the varying volume of sounds. }} \\ {\text { (D) within the middle ear as the vibrations are amplified by the }} \\ {\text { malleus, incus, and stapes. }}\end{array} \end{equation}

Step-by-Step Solution

Answer

The correct answer is (B). Hair cells bent against the tectorial membrane cause depolarization and release neurotransmitter that stimulates sensory neurons.

Step 1: Understand the Question

The goal is to determine where and how sound waves are transduced into action potentials. Consider the physiological process of hearing, focusing on the roles of different parts of the ear.

Step 2: Examine Option A

Option (A) suggests the tectorial membrane is stimulated by hair cells to transduce sound. This implies the sensory transduction occurs in the tectorial membrane directly.

Step 3: Examine Option B

Option (B) states that hair cells bent against the tectorial membrane cause depolarization and neurotransmitter release, stimulating sensory neurons. Consider whether this correctly describes the transduction pathway leading to action potentials.

Step 4: Examine Option C

Option (C) claims basilar membrane vibration at different frequencies based on sound volume is responsible. Analyze whether this describes the direct transduction into action potentials within the ear.

Step 5: Examine Option D

Option (D) suggests that transduction happens in the middle ear through vibration amplification by the malleus, incus, and stapes. Explore if this accurately identifies the location and process of transduction to action potentials.

Step 6: Identify the Correct Answer

Based on the standard physiological understanding, the correct answer involves hair cells depolarizing and releasing neurotransmitters that stimulate sensory neurons. This occurs as hair cells bend against the tectorial membrane.

Step 7: Confirm the Answer

Verify if other options accurately describe any part of the process but not the key location of sound wave transduction into action potentials. Option B captures this critical step precisely.

Key Concepts

Hair Cells Function

Hair cells play a crucial role in the auditory system. They are located in the cochlea, a part of the inner ear, and their primary function is to convert sound vibrations into electrical signals. These cells have tiny projections called stereocilia that move in response to sound waves.
When sound waves enter the ear, they travel through the ear canal and cause the eardrum to vibrate. These vibrations are transmitted through the ossicles (little bones in the middle ear) to the cochlea.
Inside the cochlea, the vibrations cause the basilar membrane to move, which in turn bends the stereocilia on hair cells. This bending opens ion channels in the hair cells, leading to a change in the electrical potential of the cell and triggering the release of neurotransmitters.
These neurotransmitters then activate sensory neurons, which send electrical signals to the brain, allowing us to perceive sound. In summary, hair cells are vital for hearing because they transduce mechanical sound vibrations into electrical signals.

Tectorial Membrane

The tectorial membrane is a gel-like structure in the cochlea's sensory organ, the organ of Corti. It plays an essential role in the auditory transduction process. This membrane overlays the hair cells, and when sound vibrations cause the basilar membrane to move, the tectorial membrane shifts with it.
As the hair cells are situated between the basilar membrane and the tectorial membrane, any movement from these membranes result in the bending of the hair cell's stereocilia. This mechanical motion is pivotal for converting sound waves into electrical signals.
The interaction between the tectorial membrane and hair cells is what ensures precise and accurate detection of sound frequencies, enabling us to perceive a wide range of sounds. Therefore, the proper function and structure of the tectorial membrane are fundamental to our sense of hearing.

Sensory Neurons

Sensory neurons are specialized nerve cells responsible for converting external stimuli into internal electrical impulses. Within the context of auditory transduction, these neurons play a key role in transmitting the electrical signals generated by hair cells to the brain.
The process begins with hair cells releasing neurotransmitters when their stereocilia are bent by sound-induced movements. These neurotransmitters bind to receptors on the auditory sensory neurons, causing them to generate action potentials.
The generated action potentials travel along the auditory nerve towards the brainstem and then to the auditory cortex. This pathway allows the brain to interpret the electrical signals as different sounds.
Sensory neurons are thus indispensable for auditory perception, as they serve as the communication link between the mechanical processes in the ear and the perception of sound in the brain. Their efficient function ensures that we can react to and enjoy the sound around us.