Ear Development Flashcards
(27 cards)
What are the two main functions of the inner ear? Which structures are responsible for each?
1) HEARING - in the cochlea; sound waves transduced into electric signals by hair cells in the Organ of Corti
2) BALANCE - controlled by vestibular system; semicircular canals & otolith organs detect directional movements
inner ear also consists of otic capsule - bony structure surrounding and protecting the inner ear
what is the cochlea? function, organisation to detect different sound frequencies?
cochlea = spiral-shaped fluid-filled structure that transforms sound waves into electrical signals through sensory hair cells
- signals transmitted via auditory nerve to brain regions
tonotopically organisation - allows detailed pitch perception:
- stiffer hair cells at base of cochlea = high-freq sounds
- more flexible hair cells at apex of cochlea = low-freq sounds
What is the Organ of Corti? What does it consist of, what is its role?
Organ of Corti = main sensory organ of hearing inside cochlea duct
- inner and outer hair cells (sensory receptors, transmit sound info, amplify sound vibrations)
- supporting cells (structural and functional support)
What structures are found in the vestibular system? what is their function?
utricle & saccule
three semicircular canals
- send balance and spatial orientation information to the brain
How do hair cells function in the inner ear sensory organs?
hair cells have stereocilia on apical surface - movement of surrounding fluid bends stereocilia = opens ion channels = mechanical stimulation converted to electrical signals - to brain via auditory nerve/ sensory neurons
What is the embryonic origin of the inner ear?
inner ear originates from otic placodes - specialised thickened area of ectodermal cells
otic placode invaginates > forms the otic vesicle (otocyst) > develops into inner ear structures (cochlea, vestibular system, neurons)
What are the main structures that arise from the otic vesicle?
otic vesicle gives rise to structures of the inner ear:
- cochlea = for hearing
- vestibular system = for balance
- associated neurons connecting to vestibulo- auditory areas of the brain
Where is the Organ of Corti located? What is its function?
Organ of Corti = inside cochlear duct within cochlea
- transduces sound vibrations into electrical signals
- sent to the brain via the auditory nerve
- hair cells (sensory) - important in sound detection
What is the role of inner hair cells and outer hair cells in the cochlea?
inner hair cells
- primary sensory receptors
- convert vibrations caused by sound into electrical impulses
- transmitted to the brain via the auditory nerve
outer hair cells
- act as a cochlear amplifier
- amplify sound vibrations by changing shape when stimulated
- enhance sound detection; fine-tuning auditory sensitivity
What is the function of the basilar membrane in the cochlea, and how does it contribute to hearing?
basilar membrane is located inside the cochlea
- vibrates in response to sound waves
tonotopic organisation allows it to detect different sound frequencies
- stiffer base of membrane = higher freq sounds; apex more flexible = lower freq
- helps in the precise detection of sound pitch
What signaling pathways are involved in the development of the inner ear?
FGF Signalling: Plays a crucial role in the formation and patterning of the otic placode and inner ear structures.
Wnt Signalling: Involved in patterning the inner ear, including otic placode induction.
BMP Signalling: Regulates epibranchial placode formation and helps with dorsoventral patterning in the otic vesicle.
Notch Signalling: Governs hair cell differentiation by controlling lateral inhibition in the cochlea.
Atoh1: A proneural gene required for hair cell differentiation and formation in the cochlea.
what is the otic placode? its developmental origin?
specialised region originating from the pre-placodal region of ectodermal cells - gives rise to otic vesicle > develops into structures of the inner ear (cochlea for hearing; vestibular system for balance)
inductive signals from the underlying mesoderm & other tissues pattern PPR - specify otic placode
How do Wnt8a, FGFs, BMPs and Cerberus collaborate to induce the otic placode as inductive signals?
Wnt8a, FGFs, and BMPs work in a tightly regulated network to induce the otic placode:
Wnt8a promotes otic placode formation in the posterior PPR.
FGFs from the hindbrain signal to the ectodermal cells to form the otic placode in the posterior region of the PPR.
BMPs act to suppress otic placode fate in certain regions and help define the dorsoventral pattern of the developing otic vesicle.
Cerberus (Wnt/BMP antagonist) helps promote the formation of the otic placode by blocking the effects of Wnt and BMP in specific regions
summary:
Wnt and BMPs are critical in defining the boundaries between the otic placode and other placodes, like the epibranchial placode.
Cerberus, a molecule that blocks Wnt and BMP signals, helps ensure the correct development of the otic placode in the posterior part of the head.
What is the role of Pax2 in inner ear development?
Pax2 = ke TF; essential for otic placode formation and the inner ear
- induction and maintenance of the otic vesicle
- early patterning of the inner ear
loss of Pax2 = severe inner ear defects
What is the role of Gbx2 and Otx1 in placode development?
Gbx2 = expressed in posterior region of PPR, marks area otic placode will form
- establishes AP axis of inner ear structures
- Gbx2 mutations = otic placode formation defects
Otx2 = specifies anterior PPR regions (olfactory/ lens/ trigeminal placodes)
- defines anterior boundary of PPR
inductive signals of ear development?
Wnts (Wnt8a) = promotes otic placode formation in posterior PPR
FGFs = promotes otic placode formation in posterior PPR
BMPs = suppress otic placode fate in certain regions; DV pattern specification of otic vesicle
Cerberus = Wnt/BMP antagonist; suppresses otic placode formation in certain ectodermal regions
key transcription factors for otic placode formation?
Otx1 = anterior PPR specification & sensory placodes
Gbx2 = optic placode formation in posterior PPR
Pax2 = TF for early otic placode induction and inner ear development
What is the role of molecular signalling in otic vesicle patterning?
molecular signalling defines: AP/ DV/ ML axes
- FGF, Wnt, BMP, and Notch establish these axes and guide the formation of cochlea (for hearing) and vestibular structures (for balance)
What are the key signalling pathways involved in otic vesicle patterning?
FGF signalling: specifies anterior region, contributing to cochlear development.
Wnt signalling (Wnt8a): posterior patterning and vestibular structure formation.
BMP signalling: defines DV patterning, particularly for vestibular structures.
Notch signalling: regulates lateral inhibition, ensuring proper differentiation of sensory cells like hair cells and supporting cells.
What are the restricted domains of gene expression in the otic vesicle?
distinct regions of otic vesicle gene expression:
Posterior domain: Gbx2 - contributes to vestibular system development.
Anterior domain: Otx1 - develops into the cochlea.
Dorsal domain: Expresses BMPs and forms vestibular structures such as semicircular canals.
Ventral domain: Expresses FGF8 and is crucial for cochlear development.
What is the importance of the restricted domains in otic vesicle patterning?
ensure the proper formation of different components of the inner ear - each domain specifies cochlear & vestibular system development, and sensory organs
What is the role of Sox2 in sensory organ formation?
Sox2 = TF for sensory organ formation in the inner ear
- marks the prosensory domain = where sensory organs (e.g. hair cells, supporting cells) differentiate
- loss of Sox2 = absence of sensory organs
What is the function of Lmx1 in sensory organ development?
Lmx1 = TF for DV patterning of otic vesicle
- specifies dorsal region = forms vestibular system & other sensory organs
- differentiation of cochlea hair cells
How does the maturation of the Organ of Corti occur?
organ of corti undergoes cellular maturation in the cochlea as sensory cells differentiate
- transition from proliferating to differentiating cells controlled by the upregulation of p27Kip1, a cell cycle inhibitor
- sensory cells in cochlea begin expressing proneural gene Atoh1 = undergo differentiation into hair cells & supporting cells
