Hearing

EAR ANATOMY AND PHYSIOLOGY

OUTER EAR ANATOMY

OUTER EAR PARTS

  • Pinna- the exterior of the ear

  • External canal- bridge between outer and inner ear

  • Tympanic Membrane- seperates outer ear from middle ear

(Hospital , Stanford Children's Health 2021)

OUTER EAR DISORDERS

  • Cerumen Impaction- accumulation of wax in the ear canal

  • Foreign Body Occlusion- damage to the ear canal caused by foriegn objects

  • Exotoses- benign tumors covered by skin

  • Collapsed Ear Canal

(Hearing HealthCare Centers, 2016)

MIDDLE EAR ANATOMY

  • The Eustachin Tube: a tiny tube which bridges the middle ear and the back of the nose. Equalizing the pressure, the Eustachin tube helps effective transfer of sound.

MIDDLE EAR PARTS


  • Ossiscles - Three connected, small bones which function to transmit sound wave to the inner ear. They are called:

-Malleus

-Incus

-Stapes

MIDDLE EAR DISORDERS

  • Cholesteaoma- bone loss resulting in damage of the ossicular chain

  • Otosclerosis -excess bone growth inside the ear

  • Chronic Middle Ear Inflamation- an ear infection occuring over months or ears; long term.

    (SE, 2021)

INNER EAR ANATOMY

The Vestibular System
[comprised of 5 organs: 3 semicircular canals, utricle and saccule]

  • The Vestibular System provides many functions, although, humans are usually unaware of it's helpfulness. This includes maintaining eye movements and postural reflexes.

  • Providing a sense of balance, this system supports the body in adjusting to both internal and external stimuli with regard to body position.

  • When this system is altered or damaged, individuals experience difficulty in managing head position, eye movements and physical orientation to space. Each of these issues should be of focus when completing an evaluation for brain injuries.
    (Purves, et. al 2001)

The Cochlear System:

  • Oval Window- tissue membrane between the between the innter and middle ears, responsible for taking vibrations from tympanic membrane

  • Round Window: moves vibration to inner ear

  • Scala Timpani, Reissner's Membrane, Scala Media, Basilar Membrane

  • Scala Vestibuli: producing sound to scala media

  • Stria Vascularis: produces endolymph

  • Modiolus- a porus bone containing spiral ganglion.

  • The Organ of Corti- organ responsible for hearing.

INNER EAR PARTS


  • Cochlea- full of nerve endings required for hearing.

  • Vestibule- holds receptors that help with balance.

  • Semicircular Canals- additional container of balance receptors.

  • Utricle: senses linear accelerations and and horizontal head movements.

  • Saccule: senses the body's orientation.

  • Ampulla: the opening, leading to the vestibule.

  • Perilymph: location of fluid within the inner ear, this helps

  • Endolymph: additional location of fluid in the inner ear, varying in sodium level.

    (Hospital , Stanford Children's Health 2021)

[when the two fluids mix, the result can be Meniere Disease. See below]


INNER EAR DISORDERS

  • Benign Paroxsymal Positional Vertigo- short episodes of vertigo that occur in certain positions of the head

  • Meniere Disease- results in vertigo, sensorineural hearing loss and tinnitus

  • Vestibular Schawanoma- a Schwann-Cell tumor living on the 8th cranial nerve

  • Herpes Zoster Oticus- arrival of Herpes Zoster on the 8th cranial nerve ganglia and the 7th facial cranial nerve.





(Introduction to Inner Ear Disorders By Lawrence R. Lustig et al., 2021)

Types of Pure Tone Tests:

  • Auditory Brainstem Response

  • Otoacoustic Emissions

  • Pure Tone Testing

  • Speech Testing

  • Tests of the Middle Ear

Pure Tone Speech Audiometry

  • Tests utilized to confirm a person's hearing sensitivity and to determine if it falls within the normal ranges of hearing.

  • ASHA defines four categories while delineating various speech and hearing thresholds. This includes:

      • Speech Recognition Threshold-minimum hearing level for speech

      • Spondee Threshold- speech recognition obtained with spondaic words

      • Speech Detection Threshold-minimum threshold for speech where individual can recognize it at 50% of the time

      • Speech Awareness Threshold- level at which a person can detect speech

        (ASHA, 1988)


(NYU CSD , 2021)

NYU PROTOCOLS AND FORMS:

TYPES OF TEST PERFORMED

  • Bone Conduction -Evaluates how the inner ear functions

  • Unmasked Bone Conduction

  • Air Conduction -Evaluate the entire ear's sensitivity

  • Unmasked Air Conduction

  • No response

    (eMoyo, 2021)

High vs. Low Frequency Sounds

Frequency refer to the number of vibration that occur per second or the number of cycles sound waves complete in a second. Frequency is measure in Hertz (Hz)

The Human ear perceives frequencies between 20 Hz (lowest pitch) to 20,000 Hz (highest pitch). The image is a comparison of other mammals and their range of perception.

Pujol, R. (2018)

High Frequency

Higher hertz or more vibrations produce a higher frequency sounds. 2000 hz or higher.

Examples of "high-frequency" sounds are a bird chirping, a whistle, and the "s" sound in "sun."


Low Frequency

Lower hertz or the fewer vibrations produce a low frequency sounds. 500 hz or lower.

Examples of "low-frequency" sounds are a rumble of thunder, a tuba, and sounds like the "oo" in "who."


Hearing loss (2017); The Audiogram (Asha)

Types of Hearing Loss

Classification of hearing loss may be dependent on: the type of loss, the dB (decibels) level and frequencies affected, age of onset, general health.


Shipley, K. G., & McAfee, J. G. (2016)

Conductive Hearing Loss

  • Occurs when the transmission of sound is interrupted in the outer or middle ear.

  • Is usually a temporary loss or may be repairable with medicine or surgery

COMMON CAUSES

  • In Children- Middle ear Infection or Otitis Media

  • In Adults- Otosclerosis, a disease in the middle ear ossicles

  • Both Children and Adults- a hole in the ear drum, physical obstructions such as a tumor, object enlarge in the ear, infection of the ear canal (external Otitis), poor function of the eustachian tube, or congential malformation.

Sensorineural Hearing Loss

  • Occurs when the hair cells of the cochlea or the acoustic nerve (CN VIII) in the inner ear are damaged

  • Is usually permanent and treated by prescribing hearing aids

  • Cochlear implants may be an option

COMMON CAUSES

  • Loss of hearing through bone conduction

  • illness or infections

  • trama to the head

  • damage from drugs

  • exposure to excessively loud noises

  • age (prebycusis)

  • genetic hearing loss

  • congenital malformation of the inner ear.

Mixed Hearing Loss

  • Co-occuring with conductive and sensorineural loss in the same ear or both ears

  • Both air and bone conduction pathways are involved

  • Sensorineural = the amount of speech sound distortion present

  • Common causes for both conductive and sensorineural hearing loss are the same for mixed hearing loss

  • Treatment may include a combination of medicine, surgery, and presciption of hearing aids.







Shipley, K. G., & McAfee, J. G. (2016)

Other Hearing pathologies

  • Central Auditory Processing disorders: Neurlogical condition that stems from problems in the auitory center of the brain.

  • Retrocochlear hearing loss: Damage to the auditory nerve or central auditory system.

  • Tinnitus: A chronic or temporary ringing in one or both ears. Commonly people may experience at least once in their live.

Shipley, K. G., & McAfee, J. G. (2016)

Hearing Screening Form: https://2nyu.speech.steinhardt.nyu.edu/content/files-api/files/04e51af8-256c-46df-b8bb-4dbc6872e0bf

References

Audiometric symbols. American Speech-Language-Hearing Association. Retreived on September 17, 2021 from https://www.asha.org/policy/gl1990-00006/

ASHA. (1988, January 1). Determining threshold level for speech. American Speech-Language-Hearing Association. Retrieved September 16, 2021, from https://www.asha.org/policy/gl1988-00008/.

eMoyo. (2021). How to read an Audiogram. eMoyo Technologies. Retrieved September 18, 2021, from https://emoyo.net/post-kudu/how-to-read-an-audiogram/#intro.

Hearing HealthCare Centers. (2016, December 28). Disorders of the outer ear and hearing loss. Hearing HealthCare Centers. Retrieved September 17, 2021, from https://www.hearinghealthcarecenters.com/hearing-loss-articles/disorders-of-the-outer-ear-and-hearing-loss/.

Hearing Loss - Understanding the Audiogram. (May 2017). Washington Self-Insurers Association. Retrieved on September 17, 2021 from https://www.wsiassn.org/news-and-media/blog/hearing-loss-understanding-audiogram/

Introduction to Inner Ear Disorders By Lawrence R. Lustig, By, Lustig, L. R., & Last full review/revision Jun 2021| Content last modified Jun 2021. (2021, June). Introduction to inner ear disorders - ear, nose, and throat disorders. Merck Manuals Professional Edition. Retrieved September 19, 2021, from https://www.merckmanuals.com/professional/ear,-nose,-and-throat-disorders/inner-ear-disorders/introduction-to-inner-ear-disorders.


Pujol, R. (June 2018) Human auditory range. Journey in the world of hearing. Retrieved on September 17, 2021 from http://www.cochlea.org/en/hear/human-auditory-range

Purves D, Augustine GJ, Fitzpatrick D, et al., editors. Neuroscience. 2nd edition. Sunderland (MA): Sinauer Associates; 2001. Chapter 14, The Vestibular System. Available from: https://www.ncbi.nlm.nih.gov/books/NBK10819/

Shipley, K. G., & McAfee, J. G. (2016). Assessment in speech-language pathology: A resource manual (6th ed.). Boston, MA: Cengage.

SE, S. K. (2021). Middle ear diseases: Causes, symptoms & diagnostics. Schoen Clinic. Retrieved September 19, 2021, from https://www.schoen-clinic.com/middle-ear-diseases.


Hospital , S. (2021). Stanford Children's Health. Stanford Children's Health - Lucile Packard Children's Hospital Stanford. Retrieved September 17, 2021, from https://www.stanfordchildrens.org/en/topic/default?id=anatomy-and-physiology-of-the-ear-90-P02025.


The Audiogram. American Speech-Language-Hearing Association. Retreived on September 17, 2021 from https://www.asha.org/public/hearing/audiogram/