Question

In some forms of otosclerosis, the stapedial foot plate, which transmits vibrations from the bones of the middle ear to the fluid within the cochlea, can become fixed in position. This limits the displacement of the stapedial foot plate during vibration. Based on this mechanism, which of the following symptoms would most likely be seen in an individual with otosclerosis? (A) \(\quad\) An increase in the perceived volume of sounds (B) \(\quad\) A decrease in the perceived volume of sounds (C) \(\quad\) An increase in the perceived pitch of sounds (D) \(\quad\) A decrease in the perceived pitch of sounds

Short answer

B) A decrease in the perceived volume of sounds

Step-by-step solution

Understand the Role of the Stapedial Foot Plate

The stapedial foot plate is a crucial part of the auditory system. It transmits vibrations from the middle ear bones to the cochlea, which is essential for the hearing process. Any limitation in its movement can affect how these vibrations are transmitted.

Identify the Effect of Limited Displacement

If the stapedial foot plate becomes fixed and cannot move properly, it won't be able to transmit vibrations efficiently. This would decrease the efficiency with which sound vibrations reach the cochlea, reducing the overall sound transmission.

Connect Limited Displacement to Hearing Symptoms

Since sound transmission to the cochlea is decreased, the volume of perceived sounds would be lower. Therefore, the individual would perceive sounds as quieter than they actually are.

Select the Corresponding Symptom

Based on the understanding that a fixed stapedial foot plate reduces sound transmission, the most likely symptom would be a decrease in the perceived volume of sounds.

Key concepts

Stapedial Foot Plate

The stapedial foot plate is an essential structure in the auditory system. Located in the middle ear, it connects to the stapes, which is one of the three tiny bones, or ossicles, that play a pivotal role in hearing. The primary function of the stapedial foot plate is to transmit vibrations from the ossicles to the fluid-filled cochlea in the inner ear.
When sound waves enter the ear, they cause vibrations that travel through the ossicles and eventually reach the stapedial foot plate. This part then acts as a bridge, transferring these vibrations into the cochlea.
In conditions like otosclerosis, the stapedial foot plate can become fixed or immobile, which disrupts this crucial transmission process. This fixation leads to a reduction in the efficiency with which vibrations are passed on to the cochlea, significantly affecting hearing.

Middle Ear

The middle ear is a small, air-filled cavity situated behind the eardrum. It houses the three ossicles: the malleus, incus, and stapes. These bones are vital for amplifying and transmitting sound vibrations from the eardrum to the inner ear. The middle ear also connects to the Eustachian tube, which helps maintain pressure equilibrium.
The ossicles form a chain with the stapes ending in the stapedial foot plate. The movement of these bones ensures that sound vibrations are properly amplified and directed towards the cochlea.
Any condition that affects the function of the middle ear, such as otosclerosis, can severely impact hearing by disrupting this transmission of sound. Proper vibration of the stapedial foot plate is essential for maintaining effective sound transmission to the cochlea.

Cochlea

The cochlea is a spiral-shaped, fluid-filled organ located in the inner ear. It is responsible for converting sound vibrations into electrical signals that the brain can interpret as sound. The cochlea contains tiny hair cells that move in response to these vibrations.
When the stapedial foot plate transmits sound vibrations into the cochlea, it creates waves in the cochlear fluid. These waves cause the hair cells to bend, leading to the generation of electrical signals that travel along the auditory nerve to the brain.
In the case of otosclerosis, if the stapedial foot plate is fixed, the transmission of vibrations to the cochlea is compromised. This leads to weaker waves in the cochlear fluid and less stimulation of hair cells, resulting in a decreased perception of sound volume.

Sound Transmission

Sound transmission refers to the process by which sound waves travel from the external environment into the brain for processing. This process starts at the outer ear, moves through the middle ear, and culminates in the inner ear.
Initially, sound waves enter the ear canal and vibrate the eardrum. These vibrations are then picked up by the ossicles in the middle ear. The stapes, through its foot plate, transmits these vibrations into the cochlea.

• From the cochlea, the vibrations are converted into electrical signals by hair cells.
• These signals are then sent to the brain via the auditory nerve.

In otosclerosis, the fixation of the stapedial foot plate disrupts this entire process, leading to muffle hearing and a decrease in the perceived volume of sounds.
This condition highlights the importance of each element in the auditory pathway for effective sound transmission and how any disruption can lead to significant auditory issues.