Question

Figure 18.8 Cochlear implants can restore hearing in people who have a nonfunctional cochlea. The implant consists of a microphone that picks up sound. A speech processor selects sounds in the range of human speech, and a transmitter converts these sounds to electrical impulses, which are then sent to the auditory nerve. Which of the following types of hearing loss would not be restored by a co chlear implant? a. Hearing loss resulting from absence or loss of hair cells in the organ of Corti. b. Hearing loss resulting from an abnormal auditory nerve. c. Hearing loss resulting from fracture of the cochlea. d. Hearing loss resulting from damage to bones of the middle ear.

Short answer

Answer: b. Hearing loss resulting from an abnormal auditory nerve.

Step-by-step solution

Option a: Hearing loss resulting from absence or loss of hair cells in the organ of Corti

A cochlear implant can restore hearing in this case. The implant bypasses the damaged hair cells in the organ of Corti and directly stimulates the auditory nerve, allowing the person to perceive sound.

Option b: Hearing loss resulting from an abnormal auditory nerve

A cochlear implant cannot restore hearing in this case. The implant relies on the auditory nerve to convey the electrical impulses from the transmitter to the brain, so if the nerve itself is abnormal or damaged, the implant will not be able to restore hearing.

Option c: Hearing loss resulting from fracture of the cochlea

A cochlear implant can restore hearing in this case. The implant does not rely on the normal functioning of the cochlea as it directly stimulates the auditory nerve. So, even if there is a fracture in the cochlea, the cochlear implant can still restore the hearing ability.

Option d: Hearing loss resulting from damage to bones of the middle ear

A cochlear implant can restore hearing in this case. The implant bypasses the damaged bones of the middle ear, taking sound information from the microphone and transmitting it to the speech processor, which then converts the sounds to electrical impulses sent directly to the auditory nerve. Based on the analysis of each option, we can conclude that: The type of hearing loss that would not be restored by a cochlear implant is:

Answer

b. Hearing loss resulting from an abnormal auditory nerve.

Key concepts

Hearing Loss

Hearing loss can happen for various reasons and affects how well sounds are heard and understood. This condition can range from mild difficulties in hearing soft sounds to total deafness.
There are primarily two types of hearing loss: conductive and sensorineural.

• Conductive Hearing Loss: This happens when sounds cannot efficiently travel through the outer or middle ear to the inner ear. Common causes include ear infections, fluid in the middle ear, or damage to the bones of the middle ear.
• Sensorineural Hearing Loss: This type results from problems in the inner ear or the auditory nerve, such as damage to the hair cells in the organ of Corti or an abnormal auditory nerve. Cochlear implants are typically used for sensorineural hearing loss because they can bypass mechanical components of hearing.

Understanding the type of hearing loss is crucial in determining the most effective treatment.

Auditory Nerve

The auditory nerve is an essential part of the hearing process. It acts as a bridge between the inner ear and the brain, carrying sound signals.
In a typical hearing process, sound waves are converted into electrical signals in the inner ear. These signals are then sent by the auditory nerve to the brain, where they are interpreted as sounds.
If the auditory nerve is abnormal or damaged, it cannot carry these signals effectively.

• This makes it a significant barrier for cochlear implants, which rely on the nerve to send electrical impulses to the brain.
• If the nerve is not functional, even a cochlear implant cannot restore hearing, as there is no pathway to transmit the sounds to the brain.

Thus, it's vital for the auditory nerve to be in good condition for hearing devices to work.

Organ of Corti

The organ of Corti is located within the cochlea in the inner ear and plays a critical role in hearing. It contains specialized cells known as hair cells.
These hair cells are responsible for converting sound vibrations into electrical signals, which are then sent to the auditory nerve. Damage or loss of these hair cells often leads to sensorineural hearing loss.
Cochlear implants are particularly beneficial for individuals with damage to the organ of Corti.

• The implant can bypass these damaged cells.
• It directly stimulates the auditory nerve, thus allowing sound signals to be transmitted to the brain, despite the nonfunctional hair cells.

This makes it possible for people with hair cell damage to hear again through technology.

Middle Ear

The middle ear consists of the eardrum and three tiny bones known as ossicles. These bones transmit sound vibrations from the eardrum to the inner ear.
When these bones are damaged, it can lead to conductive hearing loss, as the effective transmission of sound waves is impaired. Causes of damage can include infections or trauma.

• Cochlear implants can overcome problems in the middle ear by bypassing these structures entirely.
• The implant takes sound directly from the external environment and sends it straight to the auditory nerve, skipping over the middle ear entirely.

Because of this, cochlear implants can be an effective solution for hearing loss resulting from middle ear problems.