The Nervous System


Ok, so we kind of understand what a neuron is and how it works (at least pretend you understand, it will make me feel good). 

Now neurons don’t hang out all alone (like my friend Rob on a Saturday night), they party hardy together in what scientists call our nervous system.

There are basically three types of neurons that you should know about for the AP Exam.

  • Sensory (sometimes called Afferent) Neurons: Sensory (Afferent) neurons take information from our senses (touch, vision, hearing etc…) to our brain.  When you have one of those infected zits and you try to pop it but the pain is just too much to bear; it is sensory (afferent) neurons that are telling your brain about the pain.
  • Motor (sometimes called Efferent) Neurons: Motor (Efferent) neurons take information from the brain and send in out to the rest of the body.  If you have your heart set on popping that zit, you use motor (efferent) neurons to move your fingers into the proper pinching to pop position.
  • Interneurons: These are the middlemen neurons.  You see, sensory and motor neurons hate talking to each other (they had a bad break up a few years back) and interneurons help them communicate with each other (you know that guy who sends messages back and forth between you and your best friend when you are fighting- that is the interneuron).  Interneurons are located in the brain and spinal cord while motor and sensory neurons are located throughout the body.

Think of it this way.  You are in sitting in math class and that really annoying guy sneezes on the back of your head.  Sensory (afferent) neurons send the feeling of sticky wetness up your spinal cord to your brain.  The sensory neurons pass the information off to the interneurons.  The interneurons hanging out in the brain decide what to do.  They then tell the motor (efferent) neurons the plan.  The motor (efferent) neurons then travel down your body and help your hand reach around and smack the guy upside the head.

Organization of the Nervous System



As you can see from the diagram above, the nervous system is broken down just like my man Stephan Marbury breaks down opposing defenses.  The two major categories of our nervous system are the Central and Peripheral Nervous Systems.

Central Nervous System (CNS)

An easy way to think about the CNS is all nerve encased in bone.  In the case of human that includes just the brain and spinal cord.  We will talk WAY more about the brain in the next chapter.

Peripheral Nervous System (PNS)

The PNS consists of all the other nerves in our body or all nerves that are not encased in bone.  The PNS is divided into two categories, the Somatic and Autonomic Nervous Systems.

The Somatic Nervous System controls all of our voluntary muscle movements.  Everything from choosing to kick a ball to scratching an itch.  Every time you choose to move your body you are using motor neurons in the somatic nervous system.

The Autonomic Nervous System controls all of the automatic functions of our body.  Our heart rate, lungs, internal organs, etc…  Think about it for a second.  Lets day you eat a Hostess Cream filled cupcake.  The cupcake goes into your stomach.  Do you think about squirting stomach acid on the food? No!  Do you turn the food into glucose and fat your body can use? No!  Do you turn the leftover food into poop? No!  Although it would be really cool if we could control that.  All of these things happen automatically in our bodies, thus the name autonomic nervous system.  Now to make things even more complicated, the autonomic system is broken down into two more nervous systems; the sympathetic and parasympathetic.

  • Sympathetic Nervous System: Whether it is the morning before the AP Exam, the night of a big date or you just pissed off a guy named Bubba, you are going to be nervous.  Whenever our body feels stress, the sympathetic nervous system automatically does some things to attempt to make things better.  It will speed up your heart rate, dilate your pupils, move alot of blood into your arms and legs and away from your stomach and genitals.  Why does your body do this?  It thinks that when you are stressed, there is a good chance you might die, so it gets ready to fight or run; you may have heard this called the fight or flight response.  The sympathetic nervous system was really important when we were stressed because dinosaurs were chasing us (of course I know that humans were not around when dinosaurs were, but the thought of a T-Rex chasing a caveman is just really neat). 

But in today’s world when being stressed means a test the next day, the changes in our body do not necessarily help (be thankful that school is your biggest stressor- it could be alot worse).

  • Parasympathetic Nervous System:  This part of the autonomic nervous system relaxes us (the opposite of the sympathetic).  think of the parasympathetic nervous system as what happens to you after a big Thanksgiving dinner.  You are tired, your pupils constrict,  the blood hangs out in your stomach and genitals- life is good.