Structures of the Inner EarStructures of the Inner Ear

The LabyrinthThe Labyrinth

The The inner ear,inner ear, often referred to as often referred to as the labyrinth, is composed of two the labyrinth, is composed of two separate physical parts. They are:separate physical parts. They are:

1.1. The osseous (bony) portion.The osseous (bony) portion.2.2. The membranous portion.The membranous portion.

Structures of the Inner EarStructures of the Inner Ear

Osseous portionOsseous portion Contains the:Contains the:

1.1. Perilymph fluidPerilymph fluid

2.2. CochleaCochlea

3.3. Three semicircular canalsThree semicircular canals

4.4. Vestibule Vestibule

Structures of the Inner EarStructures of the Inner Ear

Membranous portionMembranous portion Contains the:Contains the:

1.1. Endolymph fluidEndolymph fluid

2.2. SacculeSaccule

3.3. UtricleUtricle

4.4. Cochlear ductCochlear duct

Structures of the Inner EarStructures of the Inner Ear

The inner ear consists of two The inner ear consists of two major major functionalfunctional parts. They are: parts. They are:

1.1. The vestibular portion (balance)The vestibular portion (balance)

2.2. The cochlear portion (hearing)The cochlear portion (hearing)

Structures of the Inner EarStructures of the Inner Ear

The CochleaThe Cochlea

It is a fluid filled cavity which is It is a fluid filled cavity which is divided into three canals. They are:divided into three canals. They are:

1.1. The scala vestibuliThe scala vestibuli

2.2. The scala media (cochlear duct)The scala media (cochlear duct)

3.3. The scala tympaniThe scala tympani

Structures of the Inner EarStructures of the Inner Ear

For now, we will focus primarily on For now, we will focus primarily on the scala media (cochlear duct). This the scala media (cochlear duct). This is where the is where the organ of Cortiorgan of Corti is located. is located.

Structures of the Inner EarStructures of the Inner Ear

The Organ of CortiThe Organ of Corti

This is where the mechanical sound This is where the mechanical sound energy gets transduced into energy gets transduced into electrochemical energy.electrochemical energy.

Structures of the Inner EarStructures of the Inner Ear

The Organ of CortiThe Organ of Corti

It is located on top of the basilar It is located on top of the basilar membrane and consists of membrane and consists of approximately one row of approximately one row of 3500 inner 3500 inner hair cells,hair cells, and three rows of and three rows of outer hair outer hair cellscells (each row containing over 4500 (each row containing over 4500 hair cells).hair cells).

Structures of the Inner EarStructures of the Inner Ear

Inner & Outer hair cellsInner & Outer hair cells

There are some excellent photos of There are some excellent photos of both inner and outer hair cells in both inner and outer hair cells in Zemlin pages #474 and #475.Zemlin pages #474 and #475.

Structures of the Inner EarStructures of the Inner Ear

StereociliaStereocilia

Both inner and outer hairs cells have Both inner and outer hairs cells have stereocilia on top of each hair cell. stereocilia on top of each hair cell.

These stereocilia contact the tectorial These stereocilia contact the tectorial membrane.membrane.

Structures of the Inner EarStructures of the Inner Ear

StereociliaStereocilia

There are approximately 150 There are approximately 150 stereocilia on top of each outer hair stereocilia on top of each outer hair cell and 70 stereocilia on top of each cell and 70 stereocilia on top of each inner hair cell.inner hair cell.

Structures of the Inner EarStructures of the Inner Ear

Inner hair cellsInner hair cells

They contain a chemical make up They contain a chemical make up which may aid in the transduction of which may aid in the transduction of mechanical energy into mechanical energy into electrochemical energy.electrochemical energy.

Structures of the Inner EarStructures of the Inner Ear

Inner hair cellsInner hair cells

Ninety percent of the afferent VIIIth Ninety percent of the afferent VIIIth nerve fibers are innervated by the nerve fibers are innervated by the inner hair cells.inner hair cells.

Structures of the Inner EarStructures of the Inner Ear

Outer hair cellsOuter hair cells

They resemble muscle fibers, They resemble muscle fibers, complete with contractile proteins in complete with contractile proteins in cell bodies, which enables them to cell bodies, which enables them to actively change shape.actively change shape.

Structures of the Inner EarStructures of the Inner Ear

Outer hair cellsOuter hair cells

As the basilar membrane moves, it As the basilar membrane moves, it serves as an “amplifier” for inner hair serves as an “amplifier” for inner hair cell activation.cell activation.

Structures of the Inner EarStructures of the Inner Ear

The VIIIth nerveThe VIIIth nerve

It moves both afferent and efferent It moves both afferent and efferent information to the cochlear nucleus.information to the cochlear nucleus.

AfferentAfferent is neural information from the is neural information from the peripheral systems to the brain. peripheral systems to the brain. EfferentEfferent is neural information from the is neural information from the brain to the peripheral systems.brain to the peripheral systems.

Structures of the Inner EarStructures of the Inner Ear

Cochlear blood supplyCochlear blood supply Is very complex, but primary supplies are Is very complex, but primary supplies are

around in the scala media area. around in the scala media area.

The The stria vascularisstria vascularis maintains the maintains the chemical composition of the endolymph.chemical composition of the endolymph.

There are a group of There are a group of small blood vesselssmall blood vessels just below the basilar membrane which just below the basilar membrane which supply the organ of Corti with nutrients.supply the organ of Corti with nutrients.

Structures of the Inner EarStructures of the Inner Ear

Cochlear blood supplyCochlear blood supply

Please note, there is no direct contact Please note, there is no direct contact with the vascular system and the with the vascular system and the structures of the cochlea. There is an structures of the cochlea. There is an “intermediate transfer system” “intermediate transfer system” through the intracochlear fluids of through the intracochlear fluids of each site.each site.