Development Of The Ear Flashcards
What are the otic Placodes and when do they develop?
Thickening of the ectoderm at the sides of the rhomencephalon at 22 days
What do the otic Placodes become?
Otic vesicles by invaginations into the mesenchyme
What do the otic vesicles give rose to?
The inner ear
How is the otic pit formed?
From the invagination of the otic placode that pinches from the ectoderm
What does the utricular portion of the otic vesicle give?
The semicircular canals
What does the saccular portion of the otic vesicle give?
The cochlea
What is the utriculosaccular duct?
Region of communication between utricular and saccular portions of the otic vesicle
When does development of the semicircular canals begin?
Week 6
How do the semicircular canals develop?
Flattened outpocketings of the utricular part of the otic vesicle develop. The central walls of the outgrowth appositional each other and start to breakdown. Leaves an outer canal that will form semicircular canals
What is the dilated of the semicircular canals?
Crus ampullare
What are the non-dilated ends of the semicircular canals?
Crus non-ampullare
What is within the Crista ampullaries of the ampullae?
Sensory cells for balance and vestibular fibres for CN VIII
How does the cochlear duct develop?
As an outgrowth from the saccule in weeks 6-8. Saccule grows into the surrounding mesenchyme and spirals 2.5 times. The spirals become the cochlear duct.
What does the mesenchyme surrounding the cochlear duct become?
The cartilage shell
What is the spiral ligament?
Attachment between the cochlear duct and cartilage wall
What is the modiolus?
The separation between the scala vestibuli and tympani
What separates the cochlear duct and scala tympani?
Basilar membrane
What separates the cochlear duct and scala vestibuli?
The vestibular membrane
What does the modiolus provide access for?
Auditory fibres
What do the cells adjacent to the tympani differentaite into?
Inner and outer ridge cells
What is the function of inner ridge cells?
To provide support to the tectorial membrane
What do the outer ridge cells form?
The sensory cells of hearing - hair cells
What is the function of the inner hair cell?
To associate with the auditory nerve fibres
What is the function of the outer hair cells?
To amplify sound via bending the hairs against the tectorial membrane
Where are the cells for balance found?
Utricular maccula and saccular maccula
Where are the sensory cells for hearing?
Organ of corti
Where does the middle ear develop from?
The 2nd pharyngeal pouch
What extends from the first pharyngeal arch and what will it become?
Tubotympanic recess that will form tympanic cavity
What gives the ossicle of the middle ear?
The mesenchymal condensation
What do the incus and malleus develop from?
The 1st pharyngeal arch
What does the stapes develop from?
The 2nd pharyngeal arch
What allows communication between the tympanic cavity and pharynx?
Auditory tube
How do sound waves move through the ear?
The tympanic membrane vibrates in response to sound waves. Movement passes from the malleus to th eincus to the stapes. The foot plate of the stapes is in communication with the oval window and then the bony labrynth. This creates a wave in the fluid of the bony labrynth that travels through the vestibular canal and to the scala tympani. The vibrations reach the round window where it is released.
What does the external auditory meatus extend from?
The dorsal part of the first pharyngeal cleft
When is the meatal plug formed?
Month 3
When and how does the eardrum form?
In month 7 when the meatal plug degrades
How is the auricle formed?
6 mesenchymal proliferations form around the 1st pharyngeal cleft. 3 are from arch 1 and 3 from arch 2. These form the auricular hillocks. These hillocks then fuse to form the auricle. This happens initially in lower neck and ascension occurs due to development of the mandible.
When does ear development occur?
From 22 days to 9 months
