Mod 3: Middle Ear and Inner Ear

The purpose of the Eustachian tube is to match the pressure of the middle ear to the pressure of the

outside world

The three middle-ear bones, known as ossicles, are the

malleus, incus, and stapes

Commissure

Nerve-fiber bundles that unite similar structures on both

sides of the brain

Ipsilateral

same side

Contralateral

opposite side

The facial nerve is contained in the

Internal Auditory Canal (IAC)

The muscles that operate in the middle ear are the ___ and the ___

tensor tympani, stapedius

Which middle-ear ossicle is embedded in the fibrous portion of the tympanic membrane?

malleus

The smallest of the middle ear bones is the

stapes

The middle-ear ossicle that rocks in the oval window to transmit the mechanical vibrations of the ossicles to the fluids of the cochlea are the

stapes

The size difference between the tympanic membrane and the oval window, along with the leverage action created by the ossicles comprise what is known as the

middle ear impedance matcher.

The muscle in the middle ear that stiffens the membrane in the oval window when it contracts in response to ____ is the ____

loud sounds, stapedius muscle

TWO WAYS for impendence matching

Size different

Ossicle Level Action

Two fluids found within the inner ear are ____ and____

perilymph, endolymph

Balance is maintained through input from the vestibular, visual, and proprioceptive systems to the

cerebellum

What part of the inner ear is responsible for equilibrium?

vestibule

The portion responsible for hearing is called the

cochlea

The three fluid-containing channels of the inner ear are the

scala tympani, scala vestibuli, and Scala media.

The scala vestibuli and scala tympani in the cochlea contain perilymph while the scala media contains

endolymph

The basilar membrane supports the _____, while Reisner’s membrane separates the scala vestibuli from the ______

organ of corti, scala media

What is the structure that overlies the stereocilia that is embedded within the outer and inner cells sheared when the basilar membrane moves up and down in response to the fluid wave created by the stapes’ movement in the oval window.

Tectorial Membrane

The organ of Corti is considered to be the

end organ of hearing

Once a neuron’s threshold has been reached, it fires with its maximum charge, a phenomenon known as the

action principle

Afferent neurons transmit impulses____ the cochlea

from (away)

Efferent neurons transmit impulses ____ the cochlea.

into

The clearest explanation of how the ear works is embodied in the ____

 Bekesy theory

The internal auditory canal contains the internal

auditory artery, facial nerve (CN7), cochlear branch, and vestibular branch

Efferent neurons carry impulses ___ the brain

from

afferent neurons carry impulses ____ the brain.

to

Fibers cross from the left cochlear nucleus to the right superior olivary complex through the

Trapezoid body

What two portions is the cochlear nucleus divided in

dorsal and ventral

 The arrangement of auditory nerve fibers from the cochlea through the central auditory structures reflects a

tonotopic organizations

Crossover points that unite symmetrical portions of the two halves of the brain are called

decussations

The reflex activity of the middle ear muscles is mediated at the level of the

Superior Olivary Complex

Within the central auditory pathways, the first point of bilateral representation of a signal presented to just one ear occurs after the

cochlear nuclues

Tonotopic Organizations

The arrangement of the cochlea where different portions respond best to different frequencies

20 hz

the apex

20,000

the base

Higher frequency =

basilar end

Where in the auditory system is the acoustic energy

Outer Ear Canal

What is the main theory that describes human hearing

Bekesy theory

Where in the auditory system is mechanical energy found?

Middle ear ossicles (malleus, incus, stapes)

Where in the auditory system is electrical/neural energy found?

inner ear specifically within the cochlea

Organ of Corti

• End organ of hearing lies on top of the basilar membrane along the scala media

• Contains the sensory hair cells which are covered by the tectorial membrane

Organ of Corti Structures

Inner Hair Cells, Outer Hair Cells, Stereocila, Basilar Membrance, Tectorial Membrane, Reissners Membrane, Stria Vascularis, Spiral Ligament, Modiolus

Inner Hair Cells

1 row of 3,000 hair cells

Outer Hair Cells

3-5 parallel rows of 12,000 to 15,000 hair cells

Stereocilia

microscopic, hair-like projections on sensory cells in the inner ear that convert sound waves and head movements into electrical signals for the brain

Basilar Membrance

a stiff, fibrous strip of tissue inside the cochlea of the inner ear that separates fluid-filled tubes and vibrates when sound enters the ear

Tectorial Membrance

• Gelatinous flap covering the tops of the stereocilia of the outer hair cells

• Hair cells are held between the basilar and tectorial

membranes

Reissner’s membrane

Separates the scala media from the scala vestibuli

Stria vascularis

Produces endolymph

Supplies oxygen and nutrients to the cochlea

Spiral Ligament

Supports the scala media

Modiolus

• Central core of the cochlea

• Where blood and nerve supply enter the cochlea

Periphery to Cortex

Ear to Brain (down going up)

Cochlear Nucleus has a ____ stimulation

ipsilateral

The trapezoid body is located within the

pods

What is the first point of decussation of the auditory system

Trapezoid Body

Superior Olivary Complex (SCO) has ___ stimulation

bilateral (both ipsi and contralateral)

Lateral Lemniscus has ___ stimulation

bilateral

Inferior Colliculus has ___ stimulation

bilateral

Medial Geniculate Body (MGB) has ____ stimulation

bilateral

What is the last subcortial relay station for auditory impulses?

(Last stop before the auditory cortex)

Medial Geniculate Body

MGB is located

in the thalamus

Auditory Cortext has ___ stimulation

bilateral

What is the highest point is within the central auditory nervous system before reaching the auditory complex:

Medial Geniculate Body (MBG)

Auditory Cortext has ____ stimulation

bilateral

Auditory Cortex

The auditory system is considered a sensory system

• Gives brain information from the cochlea