Lecture 13- The Inner ear Flashcards
Inner ear
Consists of 2 important structures
*
- Vestibular apparatus
- Cochlea
both the cochleae and vestibular apparatus are
- fluid filled tubes
- Involved in hearing (cochlea) and balance (vestibular
Cochlea
- Fluid movement (generated by footplate of stapes)
- Converted into AP (in the CN VIII- vestibulocochlear nerve) perceived as sound in the temporal lobe for perception of sound
Vestibular apparatus
*
- Fluid movement (generated by position and rotation of head)
- Converted into APs (CNVIII) –> perceived as position sense and balance
Inner ear pathology presents with a combination of
- Hearing loss
- Tinnitus
- Disturbances in balance and vertigo (specific to inner ear)
where is the cochlea housed
Arranged in a spiral housed within the petrous part of the temporous bone.
how does the cochlear allow us to hear
- Movement at the oval window (by the movement of the ossicles causing movement on the footplate onto the oval window) causes movement of fluid in the cochlear duct
- Waves of fluid cause movement of special sensory cells (stereocilia)–> generates AP via CN VIII (vestibulocochlear) –> temporal region of brain
Outline how we hear
- Auricle and external auditory canal focuses and funnels sound waves towards the tympanic membrane which vibrates
- Vibration of TM causes vibration across chain of ossicles (amplifies) and ends in vibration of the foot of the stapes on the oval window
- Fluid filled cochlea duct
- Within the duct is the organ of corti – where we found the stereocilia
- Vibration created by ossicles leads to waves in the channels of fluid which lead to movement of stereocilia (nerve cells) AND TRIGGERS AP IN COCHLEAR PART OF CN VIII
- Generate sound
- PRIMARY AUTITORY CORTEX= TEMPORAL LOBE
Vestibular apparatus (position and balance)
x
Fluid filled tubes (endolymph)with specialised hair cells that generate action potential when moved
vestibulocochlear apapratus is made up of
- 3 semi-circular canals
- Anterior
- Posterior
- Lateral
- Includes semi-circular ducts, saccules and utricle also contain stereocilia
how does the vestibulocochlear apparatus give us balance
- Moving position of rotation of head moves fluid bends stereocilia generates AP via CN VIII (vestibular part) Brain
- Perceive and maintain sense of balance
Conditions which affect inner ear cochlea or vestibular apparatus (symptoms will depend on inner ear structure involved)
- Presbycusis
- Benign paroxysmal positional vertigo
Conditions can affect both cochlea and vestibular apparatus
- Meniere’s disease
- Infections (upper resp tract infection)
-
Presbycusis
- x
- Sensorineural (arises due to cochlear or vestibulocochlear nerve problem) hearing loss associated with old age
- Bilateral and gradual
- Corrected with hearing aids
- Sensorineural (arises due to cochlear or vestibulocochlear nerve problem) hearing loss associated with old age
- Benign paroxysmal positional vertigo
- Vertigo only (most common cause)
* Only upsets vestibular apparatus)- Short lived episodes (seconds): triggered by movement of head e.g. turning over in bed, bending down
- Caused by crystals that forms within the tubes of the vestibular apparatus–> crystal dislodge –>create movement in the fluid –>movement of stereocilia –> signals via AP when we are still
- Vertigo only (most common cause)
diagnosis of benign paroxysmal positional vertigo
Dix- Hallpike and Epley manoeuvres –>dislodging crystals
