7.1.4 Inner Ear Anatomy Flashcards
What are the two parts of the inner ear?
Vestibular appartatus (balance)
Cochlea (Hearing)
Both fluid filled with endolymph
How do we percieve sound?
Footplate of stapes hits the oval window, this causes fluid movement
Fluid movement converted into action potentials in CNVIII, percieved as sound
How fluid movement generated in the vestibular apparatus?
Position and rotation of head cause fluid movement, converted into action potentials, percieved as position sense and balance
How are action potentials generated from fluid movement?
Sterocilia move as fluid moves this generates action potentials
Where are stereocilia found?
Cochlear duct in the organ of corti
How does inner ear pathology present?
Hearing loss (sensorineural)
Tinnitus
Disturbances of balance and vertigo
What two windows separate the inner ear from the middle ear?
Oval window (stapes hits this)
Round window
How do we hear?
- Auricle and external auditory canal focuses and funnels sound waves towards
tympanic membrane which vibrates - Vibration of the ossicles (stapes at the oval window) sets up vibrations/movement in cochlear fluid
- Sensed by stereocilia (nerve cells) in the cochlear duct (part called the spiral organ of Corti)
- Movement of the stereocilia in organ of Corti trigger action potentials in cochlear part of CN VIII
- Primary auditory cortex (make sense of the input)
What makes up the vestibular apparatus?
- Semicircular ducts (anterior, posterior and lateral, therefore cilia able to respond to 3 different planes)
- Saccule
- Utricle
Also contain stereocilia
What occurs in the vestibular apparatus?
Moving position or rotation of head moves fluid
Stereocilia bend in response to rotational acceleration and pull of gravity
Action potentials generated via CNVIII
APs sent to brain which percieves and maintains our sense of balance
What condition can affect the cochlea only?
Presbycusis
-Sensorineural hearing loss associated with old age
-Bilateral and gradual
What condition affects the vestibular apparatus only?
Benign Paroxysmal Positional Vertigo
-Vertigo only
-Short-lived episodes (seconds); triggered by movement of head e.g. bending over
Crystals form within vestibular apparatus, they are able to move so when you move your head the crystals move fluid, sterocilia are movement and aps are generated causing the brain to percieve movement
What conditions affect both the cochlea and VA?
Menieres disease
Acute labrynthitis
Acute vestibular neuronitis
What is menieres disease?
Vertigo, hearing loss and tinnitius (typically unilateral)
Aural fullness, nausea and vomiting
Symptoms last for 30 mins to 24 hours
Recovery between episodes
Hearing may deteriorate over time (dips during episodes)
What causes menieres disease?
Due to endolymph, may have over production or reduced drainage
