Unit 3

Home Up Connective Tissue Muscular Tissue Nervous Tissue

    As the summer fades into fall, I thought I should use the sunflower theme to try to keep a little bit of summer around a teeny bit longer...

    In Unit 3 we will be focusing on the remaining three tissue types:   connective, muscle, and nervous.  We have already learned about epithelial tissue in the last unit.

    Tissues contain cells, and may also contain some acellular material.   In epithelial tissue, we saw that the cells were so tightly packed that there was no room for acellular material, except for underneath it (the basement membrane).   But, you will see that in order to understand connective tissue, you will need to start paying attention to the acellular material which lies between the cells (called the extracellular matrix) as well as the cells.  Also, there may be more than one cell type within a certain tissue.  Epithelial tissue had cells of different shapes, but not typically within the same bit of epithelial tissue (so, simple squamous epithelium only had squamous cells in it, and no columnar cells were ever found).  In connective tissue you will see that cells may differ not only in shape, but also in function.

    Here are some general descriptions of the four types of tissues, to highlight their differences in features noted above.

Tissue

General Organization
Epithelial Cells are of different shapes (squamous, cuboidal, or columnar)

Acellular material only in basement membrane, but cells are too tightly packed to have room for any significant extracellular matrix material between the cells

Different types of epithelial tissue are based on cell shape and layering.
Connective Different cell types, based on their function, may all be found within the same type of connective tissue.  The main different cell types are fibroblasts, macrophages, and mast cells.

Extracellular matrix is highly prevalent in most connective tissue... in some cases, there is much more extracellular matrix material than cells!  In other cases, there are more cells than extracellular matrix.

Different types of connective tissue are based on the cell-to-extracellular matrix ratio and also on cell types found... this provides for the great number of connective tissues types and functions.
Muscular Each type of muscle tissue tends to only have one general type of cell (although there may be differences at the molecular level).  Each cell type has specific contractile capabilities.

Muscle cells tend to be highly packed (leaving no room for extracellular matrix)

Each types of muscular tissue has different cell types in general from each of the other types of muscle tissue
Nervous Two populations of cell types exist.  One of these populations has different cell types in different regions of the nervous system.

Little extracellular matrix, but it can have important functions in regeneration

Different types of nervous tissue are not really described... only one general pattern for nervous tissue is described.

      We will go through connective, muscular, and nervous tissues this week.  Then, next week, we will finish this off by finishing the skin unit... that way, we will put the dermis (connective tissue) back underneath the epidermis that we already learned about last week.  We will also finish understanding the skin as an organ by learning about how the dermis, epidermis, and even hypodermis function for our bodies.

    To keep going this week, though, connect at the top of this page to any of the unit pages.

© 2006 STCC Foundation Press
written by Dawn A. Tamarkin, Ph.D.