8.5 - Hearing Loss Flashcards
(15 cards)
Benefits of sound
Can hear different pitches, frequenices
- Detecting danger
- Can be used day and night
- Communication
- Travels over long distances, without needing the sender to be visible.
Outer ear
Pinna - external part of the ear
- Function: direct sound directly into the external auditory canal
- Shell shaped, mainly composed of elastic cartilage. The brain uses reflections from the twists and folds of the pinna to determine the direction of sounds. Sounds from front enhanced (directed directly into canal), background are reduced.
Auditory canal - ear canal through which the sound waves travel.
Tympanic membrane - ear drum vibrate with the same frequency of the sound wave.
- Due to its thinness, the tympanic membrae is somewhat flexible/elastic, which does not detract from the intensity of the mechanical movements.
- 22x larger and heavier than the oval window, amplification occurs - the increased surface area and likeliness to absorb soundwaves (heaviness) provides more mechanical thrust.
Note: these vibrations are through the air (auditory canal). The vibrations in the air have changed to vibrations through solid.
Middle ear
An air filled chamber with ear ossicles and the Eustachian tube.
Ear ossicles - amplifying the vibrations transmitted from the tympanic membrane to the oval window.
- The articulations between the auditory ossicles are the smallest joints in the body - highly sensitive to the most minute of vibrations. Therefore, very delicate
- Connects as a lever system: collecting the movement of the ear drum and re-directing and re-focusing this movement solely on the oval window.
Malleus - hammer, connected to the tympanic membrane.
Incus - anvil. Vibrations then pass through this bone, then the staples.
Staples - smallest bone in the human body. As the staples pushes against the oval window, the vibration are transmitted through the to fluid of the inner ear. These tiny bones magnify sound by 22 times. The stirrup is connected to the oval window of the cochlea.
Inner ear
Semicircular canals are involved in balance - fluid helps maintain balance. Whenn spinning in cirlces: As fluid stops moving, you stop feeling dizzy.
Cochlear - a sense organ of hearing, filled with fluid. Since liquid is incompressible, pressure waves are created stimulating the hair.
- The nerves respond to the vibration and firing off impulses - changing mechanical energy into electrochemical.
- It is the size of a pea and a spiral tube. Nerve cells respond to different frequences - deeper into the cochlear respond to deeper frequencies. The higher pitched nerves get damaged first (loud sound damage and old age)
- Within the cochlear is the organ of Corti, responsible for detecting different frequencies and pitch of sound.
Auditory nerve: proximity to the Cochlea makes the transmision of ions (electrochemical signals) to the brain very efficient.
- AKA cochlea nerve - transmits signals from the hair-cells to the brain, to be interpreted as sound.
Role of Eustachian tube
The tube connects the middle ear with the back of the throat. It is filled with air and respons to changes in pressure
- Maintains the internal pressure in the middle ear to equal to outside atmospheric pressure
- It also replaces air in the middle ear after it has been absorbed.
Organ of Corti
Within the cochlea
- It has sensory hair cells and stereocillia (nerve endings, which are connected with the auditory nerve). these are arranged in parallel rows along the basilar membrane.
- The basilar membrane is not uniform along its length, becoming thinner and more flexible at the other end of the membrane.
- The membrane bends in response to different frequencies. The hair cells and stereocillia will help the nerve to fire, as they are affected by the frequencies coming in.
- High frequency sound waves flex the membrane a short distance along the membrane while a low frequency sound continues to travel within the spiral.
- The volume of the sound increases the number of hair cells that are bent and results in more nerve impulses (by stereocilia) to the brain.
Pathway of sound
Outer ear - sound energy
- Sound enters the ear at the pinna as energy in the form of sound waves in a gas.
Middle ear - mechanical energy
- When the sound waves reach the tympanic membrane the energy is changed into vibrations in a solid.
- The energy is then transferred and amplified by the ossicles in the middle ear.
- At the oval window the energy is transferred to vibrations in a fluid in the cochlea of the inner ear.
Inner ear - eleco-chemical energy
- Here the energy is transformed into electro chemical energy by the stereocilia of the hair cells. The stereocilia are attached to neurones.
- The axons of the neurones join together to form the auditory nerve.
Conductive hearing loss
- Caused by problems with mechanical conductions of vibrations (preventing sound waves to pass to the inner ears)
- Malformations of ear structures, perforated eardrums, infection of outer/middle ear, ossicle trauma.
- Volume of sound is usually affected.
(outer and middle ear)
Sensorineural hearing loss
- Sensory loss in the inner ear and neural loss from the hearing nerve.
- Congential: born with it, or acquired through trauma or disease. E.g. excessive noise exposure, inherited, birth defects, trauma, tumours.
- Kinetic energy cannot be converted to electrical impulses.
- The nerves are not getting the stimulus - the brain doesn’t receive this information.
(inner ear)
Auditory processing disorder
- Problems with brain processing of the information coming from the auditory system. Although the nerves are being stimulated and impulses are being sent, this information is not being processed properly.
- Could be: Information from the nerves are not being sent properly
Hearing aids
Small electrical devices that sit behind the ear: microphone, amplifier, receiver (speaker), power supply. It is an amplifier
- Increases the volume of approaching sound waves and redirects them into the ear.
- Hearing aids detect sound waves, then transfers it to electrical energy. This is then transformed back into sound wves which are amplified into the auditory canal.
- Useful for damage to outer or middle ear (those with conductive hearing loss)
Advantages:
- Less invasive
- Compensates for the loss of volume
- Digital signal processing: smart software that improves speech understanding in noisy environment (background noise reduction), reducing feedback, customisable settings and directional capabilities.
Disadvantages:
- Sound can still distort sounds across parts of the ear.
- Can be challenging to isolate individual sounds from a noisy background.
- Needs charging/batteries replacing.
Bone conduction implant system
Air conduction is a way of hearing through sound waves travelling through the ear canal. Bone conduction is through the vibrations through the bones in the head, bypassing the eadrums and transmitting straight to the cochlea.
A bone conduction implant system can bypass damaged/blocked parts of the ear and deliver sound vibrations directly to the inner ear. Useful for those with single-sided hearing loss, conductive hearing loss or mixed hearing loss.
It consists of:
- Small titanium implant that is surgically inserted in the temporal bone behind the ear (under skin). It converts signals to mechanical vibrations, conducting to the inner ear.
- External sound processor - picks up sound waves, converting it to electrical signals. Transmitted through the skin to the implant.
- An abutment or a magnet that connects the implant to the sound processor
New technology:
- Connections to mobile phones
- Covers can be chosen for preference
- Adapts different listening environments or listening usage
Pros
- Advantages: bone conduction implants assist hearing in individuals who have reduced outer or middle ear function, as it bypasses the outer and middle ear to stimulate the inner ear directly. As the sound processor is directly in contact with the bone, sound quality from a bone conduction implant is good. This can greatly improve the quality of life for patients who have outer or middle ear issues. The lack of an earmould blocking the ear canal also helps children who have excessive ear discharge by preventing infection. Surgery is also minimally invasive, and therefore can be performed on children without a risk of further damaging hearing or severe complications (aside from soft tissue irritation)
Cons
- Disadvantages: surgery complications involve infection, if the surgical tools are not properly sterilised prior to the operation. There is also a risk that osseointegration (new bone growth around the implant) will fail to occur. This can cause the implant to fall out. Also, the site of the implant will need to be kept clean regularly, which can present a challenge for child patients if they do not have an adult to help them with this.
Cochlear implants
- External sound processor behind the ear detects sound waves with a microphone, which are broken into different frequencies and delivered to the transmitter coil.
- Transmitter coil sends this signal to the internal implant via radio waves.
- This receiver-stimulator converts the signal into electrical impulses.
- And sent down the electrode array. The array is fitted in the cochlear close to the cochlear nerve endings. These electrodes can stimulate the spiral ganglion cells electrically, sending a nerve impulse to the brain which is perceived as sound.
Cochlear implant bypasses the damaged part of the ear by stimulating the hearing nerve directly.
- Cochlear implants replace the function of damaged sensory hair cells inside the inner ear.
Advantages:
- Facilitates hearing for those with significant hearing loss; allows young children to understand and communicate through a spoken language.
- Can help regain confidence in social situations, living a fuller life.
Diasdvantages:
- Best implanted before age 5, to be helpful in language development. Speech therapy is necessary to interpret sounds they hear.
- Very expensive, surgical risks, ongoing costs to maintain external parts.
Example of a hearing disorder: Tinntus
Key causes:
- Damage to the inner ear: if the cilia of the cochlea are bent or broken, they can “leak” random electrical impulses to your brain. As the brain detects the lack of signal, it creates phantom signals as an act of neural “filling in” for missing input.
- Ear wax buildup or other foreign bodies blocking the ear canal: this creates a change in pressure that causes tinnitus.
Key impact on health:
- Phantom noises in the ear, often manifesting as ringing, buzzing or roaring. Tinnitus can be present at all times, or come and go. These sounds are due to subjective tinnitus, sounds that only the patient can hear, and can be irritating, to the extent of severely impacting the quality of life e.g. for musicians, if it interferes with ability to concentrate.
Technologies:
- Cognitive behavioural therapy - as tinnitus can also be caused by psychological issues, this targets the emotion source of tinnitus, not the sound itself.
- Tinnitus Retraining Therapy: sound therapy (wearing a masking device) and counselling to help the brain acclimate to tinnitus.
- Sound Therapy Devices: playing white noise or other repetitive comforting sounds to mask the sound of tinnitus. It is most apparent in silence.
- Removing an earwax blockage can reduce the tinnitus symptoms.
Acoustic neuroma
Overview
- An acoustic neuroma is a rare noncancerous ear tumour that develops on the vestibulocochlear nerve, which is responsible for hearing and balance
- Prevalence rate is 1 in 100,000 individuals, and people aged 65-74 are more at risk of developing it compared to young adults and children
- The tumours’ growth is caused by the overproduction of Schwann cells
- Acoustic neuromas do not spread beyond their localised region, and grow slowly over time. As they grow, they may cause unilateral tinnitus, balance issues, vertigo, facial paralysis or numbness, headaches, nausea and vomiting, as well as other symptoms
- If the tumour becomes too large, it can press against adjacent brain structures, such as the brainstem, becoming life-threatening
Microsurgery
- An incision is made in the side of the head, providing access to the inner ear. A neurosurgeon separates the nerves from the tumour and removes it
- Advantages: microsurgery is the only method that can eliminate an acoustic neuroma. Undergoing this treatment helps the patient regain normal hearing and balance, and ensures that the tumour does not continue to grow and lead to more severe consequences. Operative data from 415 patients who had undergone microsurgery between 1998-2021 was studied, and it was found that there was an age range of 15-87 year olds, although the average age at time of surgery was 51. This shows that microsurgery is compatible with adolescents as well as the elderly. A 2015 study cites data which report that long-term recurrence rate is low, ranging from 2.4-3% on average across the three different approaches of surgery
- Disadvantages: complications may arise from microsurgery. If auditory nerves are damaged during the operation, the patient may suffer hearing loss in one ear. If a facial nerve is damaged, the patient may suffer permanent facial numbness, weakeness, or paralysis. Also, the tumour may grow back, as microsurgery does not treat the root cause of acoustic neuroma, which is the overproduction of Schwann cells
Jenisha judgement: microsurgery is effective, as recurrence rates are low
