1. Chapter 55 Disorders of Hearing and Vestibular Function

2. Structure of the Ears External and middle ear
Function in capturing, transmitting, and amplifying sound
Inner ear
Contains the receptive organs that are stimulated by sound waves (hearing) or head position and movement (vestibular function)

3. Causes of Disorders of the External Ear
Impacted cerumen
Inflammation (otitis externa)
Drainage from the external ear (otorrhea)

4. Three Basic Functions of the Eustachian Tube
Ventilation of the middle ear, along with equalization of middle ear and ambient pressures
Protection of the middle ear from unwanted nasopharyngeal sound waves and secretions
Drainage of middle ear secretions into the nasopharynx

5. Disorders of the Middle Ear and Eustachian Tube
Acute otitis media in children
The eustachian tube is shorter, more horizontal, and wider
Infection can spread more easily through the eustachian canal of infants who spend most of their day in the supine position.
Otitis media (OM)
An infection of the middle ear associated with a collection of fluid
Otitis media with effusion
The presence of fluid in the middle ear without signs and symptoms of acute ear infection

6. Disorders of the Middle Ear and Eustachian Tube (cont.)
Otosclerosis
The formation of new spongy bone around the stapes and oval window, which results in progressive deafness
Bone increasingly immobilizes the stapes, reducing the transmission of sound
Pressure on middle ear structures or the vestibulocochlear nerve may contribute to the development of tinnitus, sensorineural hearing loss, and vertigo.

7. Disorders of the Inner Ear
Tinnitus
The perception of abnormal ear or head noises, not produced by an external stimulus
Hearing loss (qualified as mild, moderate, severe, or profound)
Conductive hearing loss 
Stimuli are not adequately transmitted
Sensorineural hearing loss  
Disorders that affect the inner ear, auditory nerve, or auditory pathways of the brain
Mixed hearing loss

8. Treatment of Hearing Loss
Simple removal of impacted cerumen
Hearing aids
Cochlear implants
Reconstruction of the tympanic membrane
Special consideration for children

9. Question
Which of the following explains why infants are more susceptible to acute otitis media?
Poor hygiene
Kids will usually put things in their ears
The infant ear canal is smaller
The eustachian tube is shorter

10. Answer Poor hygiene Kids will usually put things in their ears
The infant ear canal is smaller
The eustachian tube is shorter: It is also more horizontal and wider, and with infants lying on their back most of the time, it is easy for the infection to spread.

11. Balance Reflexes Vestibular nuclei Integrative center for balance
Receive input from visual and somatic receptors
CN III, IV, and VI
Reflex movements of the neck, limb
Vestibulo-ocular reflexes
Trunk muscles

12. Nystagmus
The involuntary rhythmic and oscillatory eye movements that preserve eye fixation on stable objects in the visual field during angular and rotational movements of the head
Initiated by impulses generated by the movement of the endolymph in the semicircular ducts
Transmitted to the vestibular nuclei and relayed to the appropriate extraocular motor nuclei for controlling conjugate eye movement

13. Disorders of Vestibular Function
CNS lesions involving the cerebellum and lower brain stem
Vertigo
An illusion of motion occurs
The person may be stationary and the environment in motion (objective vertigo) or the person may be in motion and the environment stationary (subjective vertigo)
Motion sickness
A form of normal physiologic vertigo
Caused by repeated rhythmic stimulation of the vestibular system, such as is encountered in car, air, or boat travel

14. Disorders of Peripheral Vestibular Function
The peripheral vestibular system consists of a set of paired inner ear sensory organs, each sending messages to brain centers that interpret signals related to the body’s position in space and control eye movement.
Benign paroxysmal positional vertigo: these signals are distorted
Sudden onset of dizziness or vertigo provoked by certain changes in head position
Ménière’s disease: these signals are unbalanced by unilateral involvement of one of the vestibular organs
Fluctuating episodes of tinnitus, feelings of ear fullness, and violent rotary vertigo that often renders the person unable to sit or walk

15. Possible Causes of Ménière’s Disease
Trauma
Infection (e.g., syphilis)
Immunologic
Endocrine (adrenal-pituitary insufficiency and hypothyroidism)
Vascular disorders have been proposed as possible causes of Ménière’s disease.

16. Central Causes of Vertigo
Abnormal nystagmus and vertigo can occur as a result of CNS lesions involving the cerebellum and lower brain stem
Brain stem ischemia
Tumors
Multiple sclerosis

17. Basis for Diagnosis of Vestibular Disorders
A description of the symptoms
A history of trauma or exposure to agents that are destructive to vestibular structures
Physical examination
Tests of eye movements (e.g., nystagmus) and muscle control of balance and equilibrium often are used.

18. Question Is the following statement true or false?
Nystagmus is an abnormal condition.

19. Answer
False: Normal eye adjustments are considered nystagmus, but some pathological nystagmus does occur.