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My approach to this is to start with the whole organ-- the brain-- and introduce the parts and what they do followed by the things that make up the brain and make it work (the neurons and neurochemicals).  Once we've established these pieces, we will then work through how emotions work in relation to these systems.  

Nervous system (SLIDE 1):

  (Click on this thumbnail to see a larger version of this picture)

As Slide 1 (above) shows, the nervous system is made up of several parts.  The greenish areas represent the Central Nervous System (CNS), which is made up of the areas encased by bone-- the brain and spinal cord.  The purplish areas represent the Peripheral Nervous System (PNS), which includes the rest of the nervous system ("peripheral" referring to the body outside the CNS).  As you can see, the PNS contains the somatic nervous system (associated with sensation and movement) and the autonomic nervous system, which is  yet broken further into the sympathetic and parasympathetic nervous systems.  

The CNS and autonomic systems will be what we will focus on the most.

Let's look at the brain-- organizing system; interpreter

             We will now take a brief tour of the brain.  Although I include pictures and diagrams, I am not interested in your being able to point out the structures on a diagram.  I will be interested in your knowing different structures' functions.  (The diagrams can help you determine functions.  You should note that more basic functions (e.g., breathing) are controlled by lower areas of the brain whereas more complex activities are governed higher up.  Also, neighboring brain structures will relate to each other.)

Overview slide:  
                                    (click to enlarge)

See the brain part descriptions in the text (pp. 85-92).

Let's work with the Autonomic Nervous System (pp. 101-102 in text).  

The two branches of the Autonomic Nervous System-- the sympathetic and parasympathetic  branches-- work in opposition to each other in order to keep the body's vital systems (e.g., cardiovascular, metabolic) working in balance.  (Another term for that internal balance is homeostasis.)

See the images below to get a sense of how the branches of the autonomic nervous system are organized and how they act on the body:

 So what does the autonomic nervous system have to do with mental states?

Strong emotions involve changes in the way the body feels.  For example, could you imagine riding a roller coaster and not feeling the heart pounding, sweating, etc.?  Or a much-anticipated date?  The emotional impact is blunted without the physical feedback.  Likewise, drugs manipulate these feelings as well as brain activity.

Several of the most-used or abused drugs are described as "sympathomimetics"-- that is, they mimic, or copy, the effects of the sympathetic nervous system.  These would include all the stimulants (cocaine, amphetamine, caffeine, nicotine).  Others work to reduce sympathetic activity, such as the antianxiety drugs (e.g., Valium).

This means, that these drugs push the body out of homeostasis (balance)-- and that people deliberately take these drugs for that reason (hence the popularity of coffee shops).

Similarly, our emotional states push our bodies out of homeostasis, in part as a way to prepare for the whatever it is that has caused the emotion (e.g., a dog barking at us leads to startle or fear responses that require the body to prepare to move!)  Stress can be seen as an emotional response of this type.  Where problems exist is when this push from homeostasis persists over time-- requiring extra work on the part of the body.

Neuotransmitters (see pp. 96-98)

The brain is made up of over a trillion nerve cells (neurons) that communicate through the release and reception of chemical messengers.  As described in the text, one type of messenger is called neurotransmitters, which are chemical substances that are stored in the terminal end of a neuron (see diagram on p. 97 and another one below), that are released when the storing neuron "fires," and have the potential to influence the activity of a receiving cell (either increasing or decreasing its likelihood of action).

While there may be over fifty neurotransmitters, up until recently only a handful have been recognized and the majority of research and focus has been on those.  The following table summarizes the main ideas about the neurotransmitters:

Summary of transmitters

PRIMARY TRANSMITTERS:

For nice interactive exercises clarifying the brain and nervous system, I recommend the  textbook's web page and their Sylvius Interactive Brain Anatomy Dictionary.  Also look at other brain links at:  Brain web links