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In order to fully appreciate social neuroscience, you need an understanding of the core components of the brain and nervous system. Let’s start at the neuronal level. A neuron is the basic building block of the brain and nervous system. Although some variation exists in the structure of neurons, they typically have three major sections: the soma, dendrites, and the axon (see Figure 2.4). Within the soma or cell body is the nucleus, which houses DNA, mitochondria, and other elements that are heavily involved in the production of electricity and various metabolic processes. Dendrites are branching structures that extend from the soma and receive messages or information from adjacent axons. Finally, axons are relatively long and narrow structures that transmit the messages or information to the dendrites of other neurons via the terminals located at their ends.

Neurons generally do not touch one another; rather, information that is communicated between them must pass through the fluid in the synapse or synaptic gap. The messages themselves are specialized chemicals or neurotransmitters that are released by axon terminals and are, to varying degrees, “taken up” by the receiving dendrites. Neurotransmitters typically either excite (turn on) or inhibit (turn off) other neurons, and many of them are particularly critical to normal mental functioning. You have no doubt heard of neurotransmitters such as dopamine and serotonin, and perhaps norepinephrine, GABA, and acetylcholine (see Table 2.2). Dopamine, for instance, is released when we engage in enjoyable activities, such as eating chocolate, or receiving social rewards, such as a compliment. Serotonin, as you may know, helps in the regulation of emotion: Low levels of serotonin have been associated with social isolation and depression.

Neurons come in many shapes and sizes and serve a variety of functions in the nervous system. For our purposes, the most important ones are motor, sensory, interneurons, and mirror neurons. Motor neurons send information to the muscles to create movement, whereas sensory neurons transmit sensations received at various points of the body to the central nervous system. Interneurons connect motor and sensory neurons. Mirror neurons, only recently discovered in 1990s, have a very specific function: to allow one organism to imitate the actions—and perhaps emotions—of another organism (Iacoboni, 2008). These neurons are activated when we observe the actions of another person and essentially “mirror” that action. For instance, seeing the angry face of another person activates the muscles in your own face that are involved in displaying anger, and consequently, you are better able to put yourself in that person’s shoes (Pfeifer & Dapretto, 2009). Similarly, your cringe reaction to watching a girl stub her toe suggests you come close to feeling her pain. More generally, researchers have argued that this mirror system provides the physiological basis for empathy (Iacoboni, 2009).

Table 2.2

Figure 2.4 The Parts of a Neuron

Source: Barnes, J. (2013). Essential Biological Psychology. Thousand Oaks, SAGE.