Chapter 19: Ear

external ear

what ear is the sound-collecting organ?

middle ear

what ear is a sound conductor from the external to the internal ear?

internal ear

what ear converts sound waves into nerve impulses and registers changes in equilibrium?

otic or auditory vesicles (otocysts)

otic placodes invaginate rapidly and form what?

1. ventral component (saccule and cochlear duct)

2. dorsal component (utricle, semicircular canals, and endolymphatic duct)

During later ear development, each vesicle divides into what?

membranous labyrinth

the epithelial structures (ventral and dorsal component of the vesicle - during later ear development) form the what?

cochlear duct

penetrates the surrounding mesenchyme in a spiral fashion until the end of the eighth week

spiral organ of Corti

In the seventh week, cells of the cochlear duct differentiate into the ___ that transduces sound vibrations into electrical sig nals for hearing.

ductus reuniens

A connection between the cochlear duct and the remaining portion of the saccule is maintained but confined to a narrow pathway called the ___?

scala vestibuli and scala tympani

In the 10th week, this cartilaginous shell undergoes vacuolization. What two perilymphatic spaces are formed?

1. vestibular membrane

2. basilar membrane

The cochlear duct is separated from the scala vestibuli by the (1)___ and from the scala tympani by the (2)___

spiral ligament

The lateral wall of the cochlear duct remains attached to the surrounding cartilage by the what?

modiolus

what is the future axis of the bony cochlea?

inner ridge

what is the future spiral limbus?

outer ridge

forms one row of inner and three or four rows of outer hair cells

hair cells

what is the sensory cells of the auditory system?

tectorial membrane

what is a fibrillar gelatinous substance attached to the spiral limbus that rests with its tip on the hair cells?

organ of Corti

The sensory cells and tectorial membrane together constitute the what?

1. semi circular canals

2. crus ampullare

3. crus nonampullare

During the sixth week of development, (1) ___ appear as flattened outpocketings of the utricular part of the otic vesicle. Whereas one end of each canal dilates to form the (2) ___, the other, the (3) ___, does not widen

crista ampullaris

what contain sensory cells for maintenance of equilibrium

maculae acusticae

what develop in the walls of the utricle and saccule

vestibular fibers of cranial nerve VIII

Impulses generated in sensory cells of the cristae and maculae as a result of a change in position of the body are carried to the brain by ___.

statoacoustic ganglion

During formation of the otic vesicle, a small group of cells breaks away from its wall and forms the what?

cochlear and vestibular portions

the ganglion splits into what?

tympanic cavity

what is derived from the first pharyngeal pouch?

tubotympanic recess

what widens and gives rise to the primitive tympanic cavity?

auditory tube (eustachian tube)

where does the tympanic cavity communicates with the nasopharynx?

1. malleus and incus

2. stapes

(1)___ are derived from cartilage of the first pharyngeal arch, and the (2)___ is derived from that of the second arch

tensor tympani

what is innervated by the mandibular branch of the trigeminal nerve.

stapedius muscle

what is innervated by the facial nerve

facial nerve

the nerve to the second pharyngeal arch.

tympanic antrum

During late fetal life, the tympanic cavity ex pands dorsally by vacuolization of surrounding tissue to form the what?

external auditory meatus

what develops as an invagination of first arch tissue

auricle (external ear)

what develops from proliferation of tissues derived from the neural crest at the dorsal ends of the first and second pharyngeal arches

Hearing

what is dependent on sound waves that cause vibrations in the tympanic membrane

Congenital hearing loss

this is due to abnormalities of the hair cells or auditory nerve ganglia [sensorineural loss]

sensorineural loss and conductive hearing loss

Congenital hearing loss is due to what

Accutane [retinoids]

what can cause both types of deafness?

stapes

what is the most common ear ossicle to be involved in conductive hearing loss

Preauricular appendages and pits

what are the skin tags and shallow depressions anterior to the ear.