Study Notes on Ear Anatomy and Hearing

Chapter 15: Ears

Structure and Function

  • Auricle (Pinna): The visible part of the ear, collects sound.

  • External Auditory Canal: Tube running from the outer ear to the eardrum.

  • Eardrum (Tympanic Membrane): Vibrates in response to sound waves, transmitting sound to the middle ear.

  • Malleus, Incus, and Stapes: The three ossicles in the middle ear that transmit sound to the inner ear.

  • Eustachian Tube: Connects the middle ear to the nasopharynx, helping to equalize pressure.

  • Labyrinth: Inner ear structure consisting of the vestibular system (balance) and cochlea (hearing).

  • Vestibular and Semicircular Canals: Help maintain balance by detecting head movement.

  • Cochlea: Spiral-shaped organ responsible for converting sound vibrations into electrical impulses.

Structure and Function: Hearing

  • The auditory system is divided into three levels:

    • Peripheral Level: Ear transmits sound and converts vibrations into electrical impulses for the brain.

    • Brainstem Level: Involved in processing the auditory information.

    • Cerebral Cortex Level: Higher-level processing of sound information.

  • Amplitude: Refers to loudness, meaning a higher amplitude equals a louder sound.

  • Frequency: Refers to pitch, or the number of cycles per second; measured in Hertz (Hz).

  • Sound waves produce vibrations on the tympanic membrane, leading to auditory processing.

Structure and Function: Pathways of Hearing

  • Air Conduction (AC): Normal pathway of hearing where sound waves travel through air; this is the most efficient method of hearing.

  • Bone Conduction (BC): Alternate route where sound is transmitted through vibrations of the skull bones directly to the inner ear and cranial nerve VIII.

Structure and Function: Hearing Loss

  • Hearing loss can result from anything that obstructs sound transmission:

    • Conductive Hearing Loss: Mechanical dysfunction of the external or middle ear that impairs sound transfer.

    • Sensorineural Hearing Loss (Perceptive Hearing Loss): Indicates pathology within the inner ear, cranial nerve VIII, or auditory areas of the cerebral cortex.

    • Mixed Hearing Loss: A combination of conductive and sensorineural hearing loss in the same ear.

Equilibrium

  • The labyrinth in the inner ear provides constant information to the brain about body position and balance.

  • Functions like a plumb line to determine the position (verticality or depth) of the head relative to gravity.

  • Inflammation of the labyrinth can lead to inaccurate information being sent to the brain, resulting in a staggering gait and sensation known as Vertigo.

Developmental Competence: Infants and Children

  • In early development, the ear is posteriorly rotated and low set, eventually ascending to its normal placement around eye level.

  • An infant's Eustachian tube is relatively shorter, wider, and more horizontal than in adults, making them more susceptible to middle ear infections.

  • The auditory canal is shorter and has an opposite slope compared to adults, increasing the risks of various ear issues during early childhood.

Developmental Competence: Adults

  • Otosclerosis: A common cause of conductive hearing loss in young adults aged 20 to 40 years; gradual hardening of the stapes footplate that impedes sound transmission.

Developmental Competence: Aging Adults

  • Cilia lining the ear canal become coarse and stiff with age.

  • Presbycusis: A type of hearing loss that occurs gradually with aging, even in quiet environments.

Cerumen

  • Cerumen (Ear Wax): Genetically determined and comes in two major types:

    • Dry Cerumen: Gray, flaky, can form a thin mass in the ear canal.

    • Wet Cerumen: Honey brown to dark brown and moist.

Subjective Questions Regarding Ear Health

  • Ask about symptoms:

    • Earache: Any pain or discomfort in the ears?

    • Infections: History of ear infections?

    • Drainage: Any discharge from the ears?

    • Hearing Trouble: Any issues with hearing?

  • Efforts to treat: Use of hearing aids or devices? What helps with hearing?

  • Coping Strategies: How does hearing loss impact daily life? Job issues? Family support?

Subjective Questions Regarding Noise Exposure

  • Exposure to Loud Noises:

    • Living near a noise-polluted area, heavy machinery, or loud music?

    • Protective measures taken, such as use of headphones or earplugs?

Subjective Questions on Tinnitus and Vertigo

  • Tinnitus:

    • Experiences of ringing, crackling, or buzzing in ears? Frequency and timing?

  • Vertigo:

    • Feelings of spinning or lack of balance? Differentiate between subjective and objective vertigo.

Ear Cleaning and Hearing Check History

  • Procedures: How does the individual clean ears?

  • Hearing Check: Last hearing evaluation? Use of hearing aids and device maintenance?

Inspection and Palpation of External Ear

  • Inspect External Ear:

    • Size and shape: should be symmetrical and of equal size.

    • Skin condition: should match facial skin tone, with no lesions or abnormalities.

    • Tenderness: Check for pain when moving the pinna or pushing on the tragus.

    • External Auditory Meatus: Assess size and condition, presence of cerumen, redness, or swelling.

Abnormal Findings: External Ear

  • Frostbite: Damage to the skin and underlying tissues due to freezing.

  • Otitis Externa: Known as swimmer's ear, an outer ear canal infection.

  • Brachial Remnant: A deformity found on the ear.

Lumps and Lesions on External Ear

  • Abnormal growths can include:

    • Sebaceous Cyst: A noncancerous bump under the skin.

    • Tophi: A characteristic of gout; white nodules formed on the ear.

    • Chondrodermatitis Nodularis Helicis: Irritation on the ear.

    • Keloid: Raised scar; abnormal growth of scar tissue.

    • Carcinoma: Skin cancer that can develop on the ear.

Inspect with Otoscope

  • Preparation for Inspection:

    • Adjust the speculum size according to auditory meatus; tilt the head to improve visibility.

    • Insertion Technique: Insert slowly to avoid pain; inspect the tympanic membrane (TM) for any irregularities.

Ear Canal Abnormalities

  • Abnormal findings during otoscopic examination may include:

    • Excessive Cerumen: Blockage due to wax buildup.

    • Ototitis Externa: Symptoms include redness and swelling of the ear canal.

    • Osteoma: Bony growth within the ear canal.

    • Other findings include foreign bodies, exostosis, and furuncles (infected hair follicles).

Tympanic Membrane Inspection

  • Color and Characteristics: Normal TM is shiny, translucent, and pearl-gray.

  • Integrity of Membrane: Check for perforations; the normal TM should remain intact.

    • Scarring: May appear as a dense white patch as a result of previous infections.

Abnormal Findings: Tympanic Membrane

  • Retracted Drum: Indication of negative pressure in the middle ear.

  • Otitis Media with Effusion (OME): Fluid accumulation behind the TM.

  • Acute (Purulent) Otitis Media: Presence of pus behind the TM.

  • Other conditions include perforation, cholesteatoma, and visual signs like hemotympanum (blood behind TM).

Hearing Tests

  • Hearing Assessment: Begins during history taking; assess how well the person hears conversational speech.

  • Tuning Fork Tests: Used for quick assessment.

    • Rinne Test: Compares air conduction to bone conduction.

    • Weber Test: Helps determine where hearing loss is located (conductive vs. sensorineural).

    • Whispered Voice Test: A quick screening measure.

  • Romberg Test: Assesses balance using the vestibular apparatus of the inner ear by standing with closed eyes.

Summary Checklist: Ear Examination

  • Inspect External Ear: Look at size, shape, position, skin condition, and tenderness.

  • Otoscopic Examination: Check for redness, swelling, and cerumen in the external canal.

  • Inspect Tympanic Membrane: Evaluate color, characteristics, position, and integrity to assess overall function and health of the ear.