2 potassium ions to the inside of the cell membrane. This results in a negative charge
inside the cell and a positive charge outside the cell, producing a potential or polarity
across the membrane.
b. Action Potential. The electrical activity that occurs in a stimulated neuron or
muscle fiber is called the action potential. This involves depolarization and subsequent
repolarization. First, sodium ions move into the cell by diffusion. This reverses the
polarity (depolarization). Second, potassium moves out of the cell by diffusion that
causes repolarization. The sodium/potassium pump then restores the ionic balance by
actively (energy required) pumping sodium back out and potassium back into the cell.
These various electrical potentials can be measured with appropriate instruments.
2-15. CELL GROWTH
a. The individual cells have the capacity to grow. They do this by acquiring
various substances from the blood and converting them into appropriate cellular
b. Sometimes, a tissue such as muscle tissue will increase in mass without an
increase in the number of units. This condition is called hypertrophy.
a. On the other hand, if an increase in tissue mass results from a greater
number of cells, we refer to this as hyperplasia.
b. Cell multiplication is accomplished through a process called mitosis. In
mitosis, the genetic material of the cell is doubled. Then, the cell divides into halves.
One-half of the genetic material goes into each of the two daughter cells. In this
manner, the two new cells each have the same genetic composition as the original cell.
Section V. EPITHELIAL CELLS AND TISSUES
Tissues are groups of like cells together performing a common function or
functions. The epithelial tissues are specialized to cover surfaces and line cavities.
They are also secretory.