Apical Pole Morphological Differentiations and Cell Junctions

Flashcards covering stereocilia structure, function, their role in the organ of Corti, and types of intercellular junctions in epithelial tissues.

What are stereocilia?

Stereocilia are long (> 2 µm), thin (0.02 µm), and immobile cytoplasmic expansions found at the apical pole of certain epithelial cells, possessing an actin filament skeleton.

Where are stereocilia notably found in the human body?

They are present on the ciliated cells of the organ of Corti in the auditory system.

How are ciliated cells arranged within the organ of Corti?

They are arranged in parallel rows from the base to the apex of the cochlea, consisting of one row of internal hair cells (CCI) and three rows of external hair cells (CCE).

What are the typical lengths and shapes of stereocilia found on external and internal hair cells?

Stereocilia on external hair cells are 6 to 7 µm long and form a 'W' shape, while those on internal hair cells are 3 to 4 µm long and form a 'U' shape.

How are stereocilia connected, and what is the functional significance of these connections?

Stereocilia are linked by protein bridges (transverse and apical) attached to the apical membrane, and their functional integrity is crucial for mechanotransduction.

Explain the mechanotransduction process involving stereocilia in the organ of Corti.

Bending of the cilia causes tension in the membrane, which opens ion channels, leading to depolarization of the plasma membrane and the release of a neurotransmitter at the nerve ending, transmitting a signal to the brain.

What are the three main groups of junctional devices found in epithelial structures?

The three groups are impermeable/tight junctions (zonula occludens), anchoring junctions (desmosomes and adherens junctions/zonula adherens), and communicating junctions (gap junctions).

What are the general functions of junctional devices in epithelial tissues?

They contribute to the cohesion, adhesiveness, support, and rigidity of epithelial structures, and facilitate the exchange of information.