Inner Ear (Part II)

HC Cuticular Plate

A "web" of dense fibers found on top of the hair cells; made of a protein called actin; foundation for stereocilia to be securely embedded.

Stereocilia of OHCs

Three rows on top of EACH outer hair cell; embedded in HC cuticular plate and form a "W" shape; more stereocilia in basal region (150 stereocilia) than apical region (50 stereocilia); bathed in endolymph and have pores that open upon excitation.

Kinocilium

Tallest stereocilia that attaches to the tectorial membrane.

Inner HCs

Flask-shaped cells that form a single row along the basilar membrane; contain both calcium and potassium channels; have primarily afferent fibers at their base.

Function of IHCs

Transmit information to the auditory brainstem via the cochlear nerve.

Charge of IHCs

-40 mV

Stereocilia of OHCs

Three rows on top of each HC; gradually get longer in length, with kinocilium being the longest; embedded in HC cuticular plate; relatively shallow U shape; more stereocilia in apical region (100) than basal region (50-70); do not appear to be embedded in tectorial membrane; courser, thicker, stronger than OHC stereocilia; bathed in endolymph and have pores that open upon excitation.

Tip Links

Attached to pores of stereocilia; small filaments that open pores of stereocilia when a sound wave enters the IE, allowing the pores/gates to open quickly and ions to flow into the HCs, effectively exciting the system; found on IHCs and OHCs.

Cross Links

Thin filaments located on the sides of stereocilia; allow stereocilia to move in unison; found on IHCs and OHCs.

Reticular Lamina

Sealed-off upper boundary of Organ of Corti formed by various supporting cells that create tight junctions around the tops of hair cells.

Superior to RL

Stereocilia and tectorial membrane

Inferior to RL

Hair cells and other Organ of Corti support cells

Primary Purpose of RL

Separates endolymph from internal structures of Organ of Corti

Secondary Purpose of RL

Provides support for upper portion of HCs

Supporting Cells

Made of rigid cytoskeletons (microtubules and actin filaments); provide structural support for HCs; some help maintain a good ionic environment for sensory cells and create reticular lamina

Types of Supporting Cells

Phalangeal (Deiters and Inner), pillar, border, Henson, Claudius, Boettcher

Deiters Cells

Type of phalangeal cell that provides support at the base of each OUTER hair cell; cell body rests on basilar membrane; three main parts: cell body, stalk, apical plate.

Apical Plate

Helps create reticular lamina; comes in contact with adjacent outer hair cells.

Inner Phalangeal Cells

Provide support for INNER hair cells; cell body rests on basilar membrane; travels along sides of IHCs to create reticular lamina.

Pillar/Rod Cells

Rest on basilar membrane between IHCs and OHCs; help form reticular lamina; primary structures to provide support for Organ of Corti structures; create a triangular tunnel in the middle of Organ of Corti (Tunnel of Corti) that contains cortilymph.

Types of Pilar/Rod Cells

Outer (indirectly support OHCs); Inner (directly support IHCs).

Space of Nuel

Immediately lateral to outer pillar cell; filled with cortilymph.

Border Cells

Two types: inner and outer; outer cells are all cells MEDIAL to the inner border cell; inner border cell found immediately next to inner hair cells.

Hensen Cells

Supporting cells on lateral side of OHCs/Deiters Cells; medially, they help create the outer Tunnel of Corti (filled with cortilymph).

Functions of Hensen Cells

Help keep correct ion balance in inner ear by contributing to creation of reticular lamina; provide support to OHCs and tectorial membrane.

Claudian Cells

Extend from base of stria vascularis to Hensen cells; provide additional structure to lateral portion of basilar membrane.

Boettcher's Cells

Dispersed throughout Claudian cells; function relatively unknown, but they likely contribute to providing structure to lateral portion of basilar membrane; may be involved in maintaining ionic composition by creating tight junctions.

Spiral Limbus

Sits on top of upper shelf of osseous spiral lamina; attachment point for tectorial membrane; limbus and basilar/tectorial membranes create a C-shaped concavity known as spiral sulcus.

Spiral Sulcus

Contains supporting cells; afferent auditory nerves travel immediately below.

Tectorial Membrane

Gelatinous flap made of water, collagen, and various proteins; sits immediately above Organ of Corti; connected to tallest stereocilium of the OUTER hair cells (contains small notches for kinocilium to lock into); narrower at base and broadens towards apex of cochlea, mimicking the basilar membrane.

Tectorial Membrane Attachment Points

Spiral limbus and Hensen supporting cells.

Spiral Ligament

Located on outer edge of the lateral wall of scala media (covers entire lateral wall); connects membranous labyrinth to bony labyrinth; attachment point for basilar membrane; extends inferiorly into upper portion of scala tympani, providing additional support to the basilar membrane.

Stria Vascularis

Located on lateral wall (medial to spiral ligament); primary role is to produce and absorb endolymph; highly vascular and contains many capillaries; comprised of three types of cells responsible for metabolism (marginal, intermediate, basal).

Marginal Cells

Epithelial cells.

Line lateral wall of scala media.

Associated with ion channels and pumps.

Intermediate Cells

Lateral to marginal cells.

Contain melanin (when melanocytes are absent, the stria vascularis is dysfunctional).

Basal Cells

Medial to spiral ligament.

Forms tight junction with intermediate cells.

Pericytes

Cells that surround blood vessels; regulate blood flow.