Please note: This is a companion version & not the original book. Sample Book Insights: #1 The human brain contains approximately 100 billion nerve cells, which are called neurons. The proper functioning of the nervous system depends on communication between the neurons. Each neuron receives oxygen, glucose, and a host of other molecules from adjacent capillaries. #2 The human brain's 100 billion nerve cells are richly interconnected, making approximately 100 trillion synapses. In almost all instances, the nerve cells do not actually touch one another; they are separated by this tiny space. #3 The process of nerve activity begins with stimulation of the cell. The activation of excitatory receptors on the dendrites or the cell body results in a brief change in electrical potential from the cell's resting state. This change is called an action potential. #4 The effects of receptor binding vary greatly depending on which type of receptor is activated. Some neurotransmitters are excitatory, while others are inhibitory and act like a brake when turned on. The serotonin system in the brain is an exception, as the molecule serotonin is not inherently excitatory or inhibitory.