1. What is the basic unit of the brain? Neurons are the nerve cells that are the major constituent of the brain. At birth the brain has the maximum number of neurons-20 billion to 200 billion neurons. Thousands are lost daily, never to be replaced and apparently not missed, until the cumulative loss builds up in very old age. return to questions

2. What two organisms (that we studied) have the most similarities within their nervous systems? The grasshopper and the earthworm have similar nervous systems, for they both a central nervous system. They both have a brain, ventral nerve cord, ganglia and peripheral nerves. return to questions

3. Chemicals produced by the ends of neurons and secreted into synaptic spaces are NEUROTRANSMITTERS. return to questions

4. What is a ganglion (gang lee un)? A ganglion is a group of cell bodies and interneurons that switch, relay and coordinate nerve impulses. For the earthworm, the so-called brain is actually a pair of ganglia joined together. Along the ventral nerve of the earthworm, each ganglion controls the nerves in its segment. If an earthworm is cut into pieces, the pieces continue to move because the ganglia function independently of the brain. If the brain is destroyed, the worm can continue to move and live. return to questions