It's not quite accurate to say there are only four functional categories of eukaryotic cells. It's more helpful to think about them as a spectrum with many different functions. However, we can group them into four major categories based on their primary roles in the body:

1. Epithelial Cells: These cells form sheets that cover the surfaces of the body, both internal and external. They act as barriers and regulators of what enters and exits the body, and are found in skin, lining of organs, and glands.

2. Connective Tissue Cells: This category is incredibly diverse and includes cells responsible for support, structure, and connection within the body. Examples include:

* Fibroblasts: Produce the fibers of connective tissue like collagen and elastin

* Chondrocytes: Found in cartilage, providing cushioning and support

* Osteoblasts: Build bone tissue

* Blood cells: Transport oxygen, fight infections, and help with clotting

3. Muscle Cells: These cells are specialized for contraction and allow movement. There are three main types:

* Skeletal muscle: Attached to bones, responsible for voluntary movement

* Smooth muscle: Found in the walls of internal organs, responsible for involuntary movement

* Cardiac muscle: Found in the heart, responsible for pumping blood

4. Nervous Cells: These cells are responsible for communication throughout the body. They include:

* Neurons: Transmit electrical signals

* Glial cells: Support and protect neurons

It's important to remember that these categories are not absolute. Many cells have overlapping functions, and there are many specialized subtypes within each category.