Inner Ear Flashcards
What is the inner ear?
- Cavity within the petrous temporal bone filled with fluid-perilymph
- Within cavity is membranous labyrinth
What is the membranous labyrinth?
Epithelial sac filled with fluid- endolymph within inner ear
What are the types of sensory receptors in the walls of the membranous labyrinth?
- Maculae= vestibular receptors
- Christae Ampullaris= vestibular receptors
- Spiral organ of Corti= auditory receptors
In which region of the membranous labyrinth are the maculae located? What type of sensory information do they pick up?
Utricle & Saccule- balance
U= Centrifugal & vertical acceleration
S= Linear acceleration
In which region of the membranous labyrinth is the christie ampullaris located? What type of sensory information do they pick up?
Semicircularis canal
Dynamic equilibrium related to angular acceleration
Define vertigo & nystagmus and what type of injury can lead to them
-Injury to peripheral vestibular system
N= Continuous, involuntary movement of the eyes
V= Person/surroundings are spinning
What is the Organ of Corti?
-Specialised region in wall of cochlear duct
Describe the structure of the bony cochlear
- Encloses cochlear duct
- Duct spirals around central axis of bone
- Central region encloses spiral ganglion made up of cell bodies of first order auditory neurons
How does fluid in the inner ear move?
Vibration of basilar membrane caused by sound waves
How does vibration of basilar membrane lead action potentials in sensory nerves?
1) Causes hairs (steroecilia) to deform against overlying gelatinous tectorial membrane
2) Leading to depolarisiation/hyperpolarisation of sensory hair cells
3) Generates action potentials in sensory nerve fibres synapsing at the base of the cells
Which region of the basilar membrane vibrates maximally with:
- High frequency
- Low frequency
- High= Vibrates near base, stiff, deep part of Heschl’s
- Low= Vibrates near apex, more flexible, anterolateral Heschl’s
What is sensorineural & conduction deafness?
S= Damage to hair cells within cochlear/ neural pathway of hearing C= Problem conducting sound waves along the route of the ear
What is the location of the inner ear?
Petrous part of temporal bone
What are the cavities? What do they contain
- Vestibule
- SSC
- Cochlea
- All contain perilymph
What are perilymph & endolymph made up of? Why is this important?
P= High Na & Low K conc
E= Low Na & High K conc
Important as creates electrical potential across membrane
What is the cochlea made up of?
- Cochlea duct
- Scala tympani
- Scala vestibuli
What is the Scala Vestibule continuous with?
Scala tympani
What is the function of the round window?
Outlet to allow fluid movement
How is the cochlea duct distorted?
Perilymph pushes round scala vestibuli and against cochlea duct (fluid filled so distorted)
What happens when hair cells move?
- Cilia move opening ion channels
- Depolarisation of cells
- Fibres run down through cochlea nerve
How does sound reach the thalamus?
- From inner ear neurons carry impulse to auditory centres in the brainstem
- This is sent superiorly to the superior olivary nucleus
- Next sent to the inferior colliculi via the lateral lemniscus
- To (inferior brachium) medial geniculate nucleus of thalamus
- Finally to Heschl’s gyrus at temporal gyrus
What is the function of Stapedius & Tensor tympani?
Dampen down sound to prevent damage to hair cells of specific frequency (inability to hear certain frequencies)
What do motor fibres of the auditory pathway project to and where?
- Inferior colliculus= Reflex head &eye movement, CN 3, 4,6
- Superior olivary= to stapedius (CN7), tensor tympani (CN v3)
- Cochlea nuclei= cochlea
