Hearing Disorders

HSC Biology | Study Notes

Hearing disorders are an important part of NSW Biology Stage 6, Module 8, Non-infectious Disease and Disorders. This topic matters because the syllabus specifically includes hearing loss as an example of a disorder explained through the structure and function of an organ, and links it to hearing-assistance technologies such as cochlear implants, bone conduction implants and hearing aids. HSC materials also use cases involving outer ear blockage and cochlear damage, which match the distinction between conductive and sensorineural hearing loss.   

In this lesson

• what conductive hearing loss is

• what sensorineural hearing loss is

• common causes of each type

• the effects of hearing disorders

• how hearing loss links to ear structure and function

Why hearing depends on structure and function

Normal hearing depends on sound moving through several parts of the ear and then being detected and sent to the brain.

A simple pathway is:

• sound enters the outer ear

• vibrations move through the middle ear

• the cochlea detects the vibrations

• signals are carried along the auditory nerve to the brain

If one part of this pathway is damaged or blocked, hearing can be reduced.

Conductive hearing loss

Conductive hearing loss happens when sound is not conducted efficiently through the outer ear or middle ear.

What this means

The problem is mainly with getting the sound waves to the inner ear properly.

Common causes

Possible causes include:

• blockage of the outer ear

• damage affecting sound transmission in the outer or middle ear

• problems that stop vibrations reaching the cochlea effectively

HSC-style example

A 2021 HSC question described a patient with a complete and permanent blockage of the outer ear, while the cochlea was still fully functional. The marking guideline recommended a bone conduction implant because the blocked outer ear needed to be bypassed and sound vibrations transferred directly to the cochlea. This is a clear example of conductive hearing loss.  

Effect on hearing

Because sound is not carried efficiently to the inner ear:

• hearing is reduced

• sounds may seem quieter or muffled

Sensorineural hearing loss

Sensorineural hearing loss happens when there is damage to the cochlea, the auditory nerve, or related sensory structures.

What this means

In this case, sound may still reach the inner ear, but it is not detected or transmitted properly.

Common causes

Possible causes include:

• damage to the cochlea

• damage affecting the auditory nerve

• loss of normal sensory function in the inner ear

HSC-style example

A 2024 HSC marking guideline states that cochlear implants are surgically inserted into the cochlea to improve hearing when the cochlea is damaged, and that they work by directly stimulating the auditory nerve. This is a clear example of sensorineural hearing loss. 

Effect on hearing

Because the sensory or neural part of hearing is affected:

• hearing is reduced

• clarity of sound may be poor

• even if sound enters the ear, it may not be processed normally

Conductive and sensorineural hearing loss compared

Type of hearing loss	Main problem	Main part affected
Conductive hearing loss	Sound is not carried properly to the inner ear	Outer ear or middle ear
Sensorineural hearing loss	Sound is not detected or transmitted properly	Cochlea or auditory nerve

Causes

Causes of conductive hearing loss

Conductive hearing loss is caused by problems that interfere with sound transmission.

Syllabus-level examples

Useful examples include:

• outer ear blockage

• structural problems affecting the movement of sound through the ear

• anything that prevents sound waves reaching the cochlea efficiently

The 2021 HSC example of complete and permanent blockage of the outer ear is a very clear model of this type. 

Causes of sensorineural hearing loss

Sensorineural hearing loss is caused by problems in the sensory or neural part of the hearing pathway.

Syllabus-level examples

Useful examples include:

• damage to the cochlea

• damage affecting the auditory nerve

• reduced function of structures involved in converting sound to nerve signals

The 2024 HSC material directly links cochlear damage to the need for a cochlear implant. 

Effects

Hearing disorders affect how well a person can detect and interpret sound.

Possible effects

Effects may include:

• reduced ability to hear normal sound levels

• difficulty understanding speech

• one ear hearing normally while the other has a deficit

• communication difficulties

• 
  

HSC-style example

In the 2021 HSC marking guideline for an audiology test, the sample conclusion was:

• right ear has normal hearing

• left ear has a deficit or cannot hear at a normal level 

This shows that hearing disorders may affect one ear differently from the other.

Hearing loss and everyday function

Hearing is important for:

• communication

• awareness of the environment

• learning and social interaction

If hearing is reduced, the person may find it harder to:

• detect sounds clearly

• follow conversations

• respond quickly to spoken information

This is why hearing loss is studied in Module 8 as a disorder affecting quality of life and requiring assistive technology. 

Structure and function links

A strong Module 8 answer should connect:

• the part of the ear affected

• the change in function

• the resulting hearing disorder

Conductive hearing loss

• affected structure: outer or middle ear

• functional problem: sound is not transmitted effectively

• result: reduced sound reaching the cochlea

Sensorineural hearing loss

• affected structure: cochlea or auditory nerve

• functional problem: sound is not detected or transmitted properly

• result: reduced or distorted hearing

Worked example

Exam-style question

Explain the difference between conductive hearing loss and sensorineural hearing loss.

Worked answer

Conductive hearing loss occurs when sound is not conducted efficiently through the outer or middle ear, so less sound reaches the cochlea. Sensorineural hearing loss occurs when the cochlea or auditory nerve is damaged, so sound is not detected or transmitted properly to the brain. The two disorders therefore affect different parts of the hearing pathway.  

Why this works

This answer:

• compares both disorders directly

• links each disorder to the relevant structure

• explains the functional effect clearly

Common mistakes

• Mixing up conductive and sensorineural hearing loss.

• Saying all hearing loss is caused by damage to the cochlea.

• Forgetting that outer ear blockage is a conductive problem.

• Describing the disorder without linking it to ear structure and function.

• Writing about treatment only, without first explaining the cause of the hearing loss.

Quick quiz

1. What is conductive hearing loss?

2. What is sensorineural hearing loss?

3. Which type of hearing loss is linked to outer ear blockage?

4. Which type of hearing loss is linked to cochlear damage?

5. Why is hearing loss studied in Module 8 as a disorder of structure and function?

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