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).