CoursesPhysiologyIntroductionThe cell and its functionsCytoskeleton

Cytoskeleton

Learning objectives

After completing this study unit, you will be able to:

Compare the types of cytoskeletal filaments and their functions.
Describe the structure and function of microvilli, cilia, and flagella.

Introduction

The cytoskeleton is a complex thread-like network of fibrous proteins that spans the cytoplasm. It provides an internal scaffolding and is responsible for maintaining cell structure, resisting mechanical forces, and anchoring organelles. The cytoskeleton also forms tracks for substance transport within the cell, guides cell division and is essential for cell motion.

The cytoskeleton is made up of three main types of filaments:

Microfilaments are the thinnest filaments. They are made of actin and are located below the cell membrane and throughout the cytoplasm.
Intermediate filaments can be made of keratin, lamin or other proteins. They are found in the cytoplasm and inside the nuclear envelope.
Microtubules are the thickest filaments and are made of tubulin. Most microtubules originate from the centrosome and span the entire cell, while others originate from the basal bodies and form the axoneme, which is the core of cilia and flagella.

Cytoskeletal filaments form the core of cellular extensions, which are appendages that protrude from the surface of the cell. They include microvilli (short fingerlike non-motile projections), cilia (non-motile and motile hairlike structures) and flagella (long motile structures with whiplike movements). Cell extensions are primarily useful for nutrient absorption and cell motion.

Explore concepts

Cytoskeleton and associated structures

The cytoskeleton is a complex thread-like network of fibrous proteins that spans the cytoplasm.

Types of cytoskeletal filaments

The cytoskeleton is made up of microfilaments, intermediate filaments and microtubules.

Cellular extensions

Cellular extensions can expand the cell surface area (microvilli) and create motion (cilia, flagella).

Take a quiz

Build a solid foundational knowledge of the cytoskeleton with the quiz below!

Summary

Key points about the cytoskeleton
Definition	Thread-like network of fibrous proteins that spans the cytoplasm
Functions	Maintains cell structure, resists mechanical forces, anchors organelles, and assists with substance transport, cell division and cell motion
Main filaments	Microfilaments Made of actin, 5-9 nm Support the cell membrane, allow muscle contraction, split the cytoplasm during cell division Intermediate filaments Made of keratin, lamin and other proteins, 8-12 nm Anchor organelles, provide mechanical resistance, support the nuclear envelope Microtubules Made of tubulin; originate from centrosome and span entire cell, 25 nm Provide structural support, act as support for the transport of substances within the cell, organize the mitotic spindle
Cellular extensions	Microvilli Core of actin microfilaments; expand the surface of cells to improve absorption Cilia Core of microtubules; can be non-motile (often receptors) or motile (sweeping motion to move substances along the cell surface) Flagella Core of microtubules; whip-like motion allows free-floating cells like sperm to move
Cellular motion	Microfilaments: crawling motion Microtubules: ciliary sweeping motion, flagellar whip-like motion
Cellular division	Microfilaments: formation of contractile ring to divide cytoplasm Microtubules: formation of mitotic spindle, separation of sister chromatids