When hyaloplasma is said to be a viscous fluid, one gets the impression that the animal cell has a soft consistency and is deforming at all times. It's not like this.
A true "skeleton" formed by various types of protein fibers crosses the cell in various directions, giving it consistency and firmness.
This “frame” is important if we remember that the animal cell is devoid of a rigid membrane, as is the cellulosic membrane of plants.
Between the protein fibers components of this “Cytoskeleton” can be cited the actin microfilaments, the microtubules and the intermediate filamentss.
The microfilaments are the most abundant, made up of contractile protein actin and found in all eukaryotic cells. They are extremely thin and flexible, reaching 3 to 6 nm (nanometer) in diameter, crossing the cell in different directions, although they are concentrated in larger numbers on the periphery, just below the plasma membrane. Many movements performed by animal and plant cells are possible thanks to actin microfilaments.
The microtubules, in turn are thicker filaments, about 20 to 25 nm in diameter, which act as true scaffolding of all eukaryotic cells. They are, as the name implies, tubular, rigid and made up of protein molecules known as tubulineshelically arranged forming a cylinder. An example of this type of filament is what organizes the so-called cell division spindle. In this case, numerous microtubules originate and radiate from a region of the cell known as the centrosome (or cell center) and play an extremely important role in chromosome movement during division of a cell.
Another role assigned to microtubules is to serve as true 'crawlers' that allow the displacement of substances, vesicles and organoids such as mitochondria and chloroplasts within the cell. This is possible from the association of motor proteins with microtubules.
These motor proteins bind on one side to the microtubules and on the other to the substance or organoid to be transported, promoting their displacement.
For example, along the axon (extension) of a neuron, motor proteins carry along the "mat" formed by the microtubules, various substances for the axon endings that will play an important role in nerve cell function.