Ear Flashcards
How is the internal ear developed?
Via otic placodes (thickening of surface endoderm that invaginate creating otic vesicles)
How are Vesicles developed?
Cells differentiate to form ganglion cells for CN VIII
Forms membranous labyrinth where the ventral part forms saccule and cochlear duct and the dorsal part forms the utricle, semicircular ducts, and endolymphatic duct
How does the middle ear develop?
Endoderm from the 1st pharyngeal pouch
Tubotympanic recess (distal part of 1st pouch) expands to form the tympanic cavity
Proximal 1st pouch forms the auditory tube
How are ossicles developed?
1st Arch: Malleus and Incus
2nd Arch: Stapes
Stays in mesenchyme until 8th month
How does the external ear develop?
1st Pharyngeal cleft: External Acoustic Meatus
Auricle: develop from 6 auricular hillocks derived from 1/2 pharyngeal arches and 1st cleft
What does the Auricle do?
Collect sound and funnels it to the external acoustic meatus
What is the auricle made of?
elastic cartilage
What is defected in auricular abnormalities?
Neural crest defects
What is the sensory innervation of the auricle?
Auriculotemporal nerve (V3): Anterior ear
Cervical Plexus (C2-C3): Posterior Ear
Facial and Vagus Nerves: Inside the Auricle
What is Otitis Externa?
Swimmer’s Ear where the external acoustic meatus is inflamed due to bacterial infection
What does the tympanic membrane do?
- Separates external acoustic meatus from middle ear
- Vibrates in response to sound and transmits this to the ossicles
What innervates the tympanic membrane?
Outer surface: Auriculotemporal nerve and Auricular branch of the vagus nerve.
Inner surface: Glossopharyngeal nerve
What can cause a ruptured eardrum?
Otitis media, foreign bodies, trauma, and pressure
What are the ossicles?
Malleus, Incus, and Stapes
What muscles and their innervations are in the middle ear?
Tensor Tympani: V3
Stapedius: Facial Nerve
What is a stepedius reflex?
Contractions of the stapedius muscles in response to a loud noise. helps protect the inner ear from damage
What does the pharyngotympanic tube connect?
Tympanic cavity to the nasopharynx
What does the pharyngotympanic tube do?
Equalizes pressure in the middle ear with atmospheric pressure
What muscles help open the pharyngotympanic tube up and equalize pressure?
Tensor veli palatini and levator veli palatini
What is Otitis Media?
Middle Ear Infection
What is the pathway of the facial nerve?
- Enters skull via internal acoustic meatus
- Geniculate ganglion (sensory cell bodies for taste of anterior 2/3 tongue)
- Greater petrosal nerve branch: comes off of geniculate ganglion
- Nerve to stapedius branch: branches off in facial canal
- Chorda tympani branch: passes through middle ear between malleus and incus
- Exits skull via stylomastoid foramen
