INTRODUCTION

A. Excitable Tissue: able to generate Action Potentials (APs)

B. Types of Excitable Tissues

1. Neurons (nerve cells)

a. components

1) soma (cell body): metabolic center (vital, always present), information integration (note axoplasmic flow in both directions along axon)
2) dendrites (branches from the soma): receive information, generally but not always present
3) axons (one or two long branches from the soma): transmit information

b. organization

1) Central Nervous System (CNS): neurons of the brain and spinal cord
2) Peripheral Nervous System (PNS): neurons outside the brain and spinal cord

Note: Sometimes the neurons within the alimentary tract are considered a separate division, the enteric nervous system

3) axon groups: axons running together in the PNS are termed nerves; axon groups running together and of similar function are in the CNS generally called tracts, although other terms are frequently used (column, lemniscus, etc.)

e.g. vagus nerve, sciatic nerve; spinothalamic tract, corticospinal tract, but also dorsal columns, medial lemniscus

4) a group of somas of similar function in the PNS is called a ganglion; in the CNS, it is generally called a nucleus

e.g. dorsal root ganglion, celiac ganglion, red nucleus, cuneate nucleus