ears

Chapter 16: Ears

Objectives

  • List the anatomic landmarks of the external ear.
  • Describe the tympanic membrane and its anatomic landmarks.
  • List the functions of the middle ear.
  • State the functions of the inner ear that can be assessed.
  • Differentiate among the types of hearing loss.
  • Relate the anatomic developmental differences that alter hearing.

External Ear

Structure and Function of the External Ear
  • Auricle or Pinna
    • Definition: The external part of the ear, characterized by its movable cartilage and skin.
  • Characteristics
    • The characteristic shape of the auricle serves to funnel sound waves into its opening, which is the external auditory canal.
  • Auditory Canal
    • Description: A cul-de-sac measuring 2.5 to 3 cm in adults that leads to the eardrum (tympanic membrane).
    • Secretion: Lined with glands that secrete cerumen (a yellow waxy material) to lubricate and protect the ear.
    • Composition: The outer third of the canal consists of cartilage, while the inner two-thirds are bony, covered with thin, sensitive skin.
    • Structure: The auditory canal has a slight S-curve in adults.
  • Lymphatic Drainage
    • The lymphatic drainage of the external ear flows to the parotid, mastoid, and superficial cervical nodes.
Tympanic Membrane (TM)
  • Definition: Also known as the eardrum, it separates the outer ear from the middle ear.
  • Functions
    • Creates a barrier protecting the middle and inner ear from foreign objects.
  • Characteristics
    • Shape: Cone-shaped.
    • Size: Approximately 17.5 mm in diameter.
    • Response: The eardrum vibrates in response to sound pressure waves; the movement is incredibly small.
External Ear Abnormalities
  • Common issues include:
    • Frostbite
    • Otitis externa (swimmer's ear)
    • Brachial remnant and ear deformity
    • Sebaceous cyst
    • Tophi
    • Chondrodermatitis nodularis helicis
    • Keloid
    • Carcinoma
    • Low set ears (associated with Down syndrome).
External Ear Care Considerations
  • Hazardous Practices
    • Ear candling.
    • Using swabs.
    • Inserting foreign objects into the ear canal.

Middle Ear

Structure and Function of the Middle Ear
  • Description
    • A tiny, air-filled cavity housed in the temporal bone.
    • Contains the auditory ossicles: malleus, incus, stapes.
  • Functions
    • Conducts sound vibrations from the outer ear to the central hearing apparatus in the inner ear.
    • Protects the inner ear by reducing the amplitude of loud sounds.
    • The Eustachian tube allows for equalization of air pressure on each side of the tympanic membrane to prevent rupture.
Middle Ear Abnormalities
  • Common conditions affecting the middle ear include:
    • Acute otitis media
    • Otosclerosis
    • Mastoiditis
    • Tympanosclerosis
    • TM perforation
    • Cholesteatoma
    • Trauma
    • Neoplasms
    • Otitis Media with Effusion (OME).

Inner Ear

Structure and Function of the Inner Ear
  • Function
    • Converts mechanical sound waves to neural impulses that are recognized by the brain for:
    • Hearing
    • Balance
  • Consideration
    • Although the inner ear is not directly accessible for examination, its functions can still be assessed.
Inner Ear Abnormalities
  • Common conditions include:
    • Labyrinthitis
    • Vestibular Neuritis
    • Bacterial infections
    • Viral infections.

Hearing

Structure and Function
  • Auditory System Levels
    • Divided into three levels: Peripheral, Brainstem, and Cerebral Cortex.
  • Peripheral Level
    • The ear transmits sound and converts vibrations into electrical impulses, which the brain analyzes.
  • Key Concepts
    • Amplitude: Determines loudness of sound.
    • Frequency: Determines pitch or number of cycles per second.
  • Sound Waves
    • Generate vibrations on the tympanic membrane.
  • Binaural Interaction
    • At the brainstem level, the auditory system locates the direction of sound in space and identifies the sound source.
  • Pathways of Hearing
    • Air Conduction (AC): The normal and most efficient pathway for hearing.
    • Bone Conduction (BC): Sound vibration through cranial bones to the inner ear.
Hearing Loss
  • Conductive Hearing Loss
    • Results from mechanical dysfunction of the external or middle ear.
  • Sensorineural Hearing Loss
    • Indicates pathology within the inner ear, cranial nerve VIII (auditory nerve), or auditory areas of the cerebral cortex. Common causes include age-related nerve degeneration and ototoxic drugs.
  • Mixed Hearing Loss
    • A combination of conductive and sensorineural hearing loss in the same ear.

Equilibrium

  • Role of the Labyrinth
    • The labyrinth in the inner ear continuously provides information to the brain regarding the body's position in space.
  • Functionality
    • Similar to a plumb line to determine verticality or depth.
  • Implications of Inflammation
    • If the labyrinth becomes inflamed, incorrect information is relayed to the brain, which may result in vertigo, characterized by a staggering gait and a sensation of spinning or whirling.

Developmental Competence

Infants and Children
  • Development of the Inner Ear
    • Begins in the fifth week of gestation.
    • Initially, the ear is posteriorly rotated and low set; it ascends to its normal position at around eye level.
  • Implications of Maternal Infections
    • Maternal rubella during the first trimester can harm the organ of Corti, impairing hearing.
  • Eustachian Tube Considerations
    • Infants have a shorter, wider, and more horizontally placed Eustachian tube than adults, increasing the risk of infections migrating from the nasopharynx to the middle ear.
  • Lymphoid Tissue Around the Lumen
    • It increases during childhood and may occlude the airway, leading to higher risks of middle ear infections in infants compared to adults.
  • Auditory Canal Characteristics
    • Infants and young children possess a shorter external auditory canal with a slope opposite that of adults.
Adults
  • Otosclerosis
    • A common cause of conductive hearing loss occurring in young adults aged 20-40 years.
    • Characterized by gradual hardening leading to the fixation of the footplate of the stapes in the oval window, impeding transmission of sound and causing progressive deafness.
Aging Adults
  • Physical Changes
    • Cilia in the ear canal become coarse and stiff, potentially leading to cerumen accumulation and oxidation, greatly reducing hearing ability.
    • The cerumen also becomes drier with aging due to atrophy of the apocrine glands.
    • Impacted cerumen is a frequent and reversible cause of hearing loss in older individuals.
  • Presbycusis
    • A sensorineural type of hearing loss due to aging, begins typically in the 50s, progressively worsening over time.
    • Patients often first notice a loss in high-frequency sounds and an impairment in localizing sounds in the presence of background noise.

Culture and Genetics

Otitis Media
  • Definition: A condition involving obstruction of the Eustachian tube or the passage of nasopharyngeal secretions into the middle ear.
  • Incidence in Children: Most common illness in children, with increased severity in indigenous populations of North America, New Zealand, and northern Europe due to environmental factors.
  • Preventative Measures
    • Urge parents to hold children partly upright while feeding to mitigate risks; avoid propping bottles or letting children take bottles to bed.
    • Encouraging breastfeeding can also help prevent otitis media.
  • Consequences of Otitis Media
    • Persistent middle ear effusion post-treatment can impair hearing and pose a risk for delayed cognitive development in children.
Cerumen
  • Definition: Cerumen is genetically determined and exists in two main types:
    • Dry Cerumen: Gray and flaky; may form a mass within the ear canal.
    • Wet Cerumen: Honey brown to dark brown and moist.
  • Genetic Distribution
    • Wet cerumen occurs more frequently in Caucasians and African Americans, while dry cerumen is more common among Asians and American Indians.
  • Misconception: The presence and composition of cerumen do not correlate with poor hygiene; dry cerumen should not be mistaken for eczematous lesions.

Subjective Questions for Assessment

  • Assess for any earaches or pain in ears.
  • Inquire about infections or discharge.
  • Question the patient about their hearing troubles and environmental noise exposure.
  • Discuss any instances of tinnitus or vertigo.
  • Check when the patient's hearing was last examined and methods used for ear cleaning.
  • Note any clues during conversation that indicate possible hearing loss.

Additional History for Infants and Children

  • Inquire about ear infections and their frequency and treatment history.
  • Ask about any surgeries (e.g., ear tubes, tonsil removal).
  • Assess for any changes in infection frequency or severity.
  • Check for exposure to cigarette smoke at home.
  • Consider if the child is in group care and the number of children present.
  • Determine if the child displays any signs of hearing loss (e.g., startle response, babbling, and talking).