Microtubules have many features that distinguish them from microfilaments and intermediate filaments. To begin with, the outside diameter of a microtubule (usually about 25 nm) is much greater than that of microfilaments. Furthermore, microtubules are hollow, containing a central lumen about 15 nm in diameter. Microtubule length is quite variable. Some microtubules are less than 200 nm long, but in [...]
Some of the most important functions of nerve cells are as follows: 1. Conduction of Nerve Impulses 2. Ion Gradients across the Membrane 3. Initiation of the Action Potential 4. Conduction of the Action Potential 5. Synaptic Transmission. The tissues of the nervous system contain a variety of cells, but one of the most highly differentiated and specialized is the [...]
A dramatic example of the degree of specialization that can accompany cellular differentiation is provided by a family of white blood cells called lymphocytes. There are two major types of lymphocytes T lymphocytes and B lymphocytes. Both originate from pluripotent stem cells in the hemopoietic tissues of the embryo (i.e., the liver and bone marrow). From there the stem cells [...]