Microvilli and stereocilia are both cell surface protrusions, but they differ significantly in their structure, function, and composition.
Structural Differences
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Microvilli: These are bristle-like protrusions, much shorter than stereocilia. Their core is composed of a bundle of actin filaments arranged in a parallel manner. They lack the branching seen in stereocilia. They are found on various cell surfaces, increasing surface area for absorption.
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Stereocilia: These are longer and often branched protrusions. They are also composed of actin filaments, but unlike microvilli, their actin filaments are cross-linked and organized into bundles, sometimes with branching. They are found in specialized sensory cells of the inner ear (hearing and balance) and the epididymis (sperm maturation).
Functional Differences
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Microvilli: Primarily function to increase surface area for absorption of nutrients and other substances. Think of the lining of the small intestine.
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Stereocilia: Primarily involved in sensory transduction. In the inner ear, they detect sound vibrations and head movements. In the epididymis, they may assist in sperm maturation.
Compositional Differences
- Both are primarily composed of actin filaments, but the organization and cross-linking differ significantly impacting their structure and function. Stereocilia are characterized by a more complex internal organization that provides the structural basis for their mechanosensory function. Microvilli have a simpler actin filament arrangement.
In summary: While both are finger-like projections from cells, stereocilia are longer, often branched, and specialized for sensory function, whereas microvilli are shorter, unbranched, and primarily function to increase surface area. The core difference lies in their internal structural organization of actin filaments. One can consider stereocilia as modified, more complex versions of microvilli.
