The Brain and Nervous SystemThe nervous system is broken down into two major systems: Central Nervous System and Peripheral Nervous System. Well discuss the Central Nervous System first.TheCentral Nervous Systemconsists of the brain and the spinal cord. TheCerebralCortex, which is involved in a variety of higher cognitive, emotional, sensory, and motor functions is more developed in humans than any other animal. It is what we see when we picture a human brain, the gray matter with a multitude of folds covering thecerebrum. The brain is divided into two symmetrical hemispheres:left(language, the rational half of the brain, associated with analytical thinking and logical abilities) andright(more involved with musical and artistic abilities). The brain is also divided into four lobes:oFrontal (motor cortex) motor behavior, expressive language, higher level cognitive processes, and orientation to person, place, time, and situationoParietal (somatosensory Cortex) involved in the processing of touch, pressure, temperature, and painoOccipital (visual cortex) interpretation of visual informationoTemporal (auditory cortex) receptive language (understanding language), as well as memory and emotionTypically the brain and spinal cord act together, but there are some actions, such as those associated with pain, where the spinal cord acts even before the information enters the brain for processing. The spinal cord consists of theBrainstemwhich is involved in life sustaining functions. Damage to the brainstem is very often fatal. Other parts of the brainstem include theMedullaOblongata, which controls heartbeat, breathing, blood pressure, digestion;ReticularActivatingSystem(ReticularFormation), involved in arousal and attention, sleep and wakefulness, and control of reflexes;Pons regulates states of arousal, including sleep and dreaming.Cerebellum balance, smooth movement, and postureThalamus "central switching station" relays incoming sensory information (except olfactory) to the brainHypothalamus controls the autonomic nervous system, and therefore maintains the bodys homeostasis, which we will discuss later (controls body temperature, metabolism, and appetite. Translates extreme emotions into physical responses.LimbicSystem emotional expression, particularly the emotional component of behavior, memory, and motivationAmygdala attaches emotional significance to information and mediates both defensive and aggressive behaviorHippocampus involved more in memory, and the transfer of information from short-term to long-term memoryThePeripheral Nervous Systemis divided into two sub-systems. TheSomatic Nervous System primary function is to regulate the actions of the skeletal muscles. Often thought of as mediating voluntary activity. The other sub-system, called theAutonomic Nervous System,regulates primarily involuntary activity such as heart rate, breathing, blood pressure, and digestion. Although these activities are considered involuntary, they can be altered either through specific events or through changing our perceptions about a specific experience. This system is further broken down into two complimentary systems: Sympathetic and Parasympathetic Nervous Systems.TheSympathetic Nervous Systemcontrols what has been called the "Fight or Flight" phenomenon because of its control over the necessary bodily changes needed when we are faced with a situation where we may need to defend ourselves or escape. Imagine walking down a dark street at night by yourself. Suddenly you hear what you suspect are footsteps approaching you rapidly. What happens?Your Sympathetic Nervous System kicks in to prepare your body: your heart rate quickens to get more blood to the muscles, your breathing becomes faster and deeper to increase your oxygen, blood flow is diverted from the organs so digestion is reduced and the skin gets cold and clammy and rerouted so to speak to the muscles, and your pupils dilate for better vision. In an instant, your body is prepared to either defend or escape.Now imagine that the footsteps belong to a good friend who catches up to you and offers to walk you home. You feel relief instantly, but your body takes longer to adjust. In order to return everything to normal, theParasympathetic Nervous Systemkicks in. This system is slow acting, unlike its counterpart, and may take several minutes or even longer to get your body back to where it was before the scare.These two subsystems are at work constantly shifting your body to more prepared states and more relaxed states. Every time a potentially threatening experience occurs (e.g., someone slams on their breaks in front of you, you hear a noise in your house at night, you hear a loud bang, a stranger taps you on the shoulder unexpectedly), your body reacts. The constant shifting of control between these two systems keeps your body ready for your current situation.

Theperipheral nervous system, or PNS, consists of the nerves andgangliaoutside of thebrainandspinal cord.[1]The main function of the PNS is to connect thecentral nervous system(CNS) to the limbs and organs. Unlike the CNS, the PNS is not protected by theboneof spine and skull, or by theblood-brain barrier, leaving it exposed totoxinsand mechanical injuries. The peripheral nervous system is divided into thesomatic nervous systemand theautonomic nervous system; some textbooks also includesensory systems.[2]Thecranial nervesare part of the PNS.[3]General classificationBy directionThere are two types ofneurons, carryingnerve impulsesin different directions. These two groups of neurons are: Thesensory neuronsareafferentneurons which relay nerve impulses toward thecentral nervous system. Themotor neuronsareefferentneurons which relay nerve impulses away from the central nervous system.By functionThe peripheral nervous system is functionally as well as structurally divided into thesomatic nervous systemandautonomic nervous system. Thesomatic nervous systemis responsible for coordinating the body movements, and also for receiving external stimuli. It is the system that regulates activities that are under conscious control. Theautonomic nervous systemis then split into thesympathetic division,parasympathetic division, andenteric division. Thesympatheticnervous systemresponds to impending danger, and is responsible for the increase of one's heartbeat and blood pressure, among other physiological changes, along with the sense of excitement one feels due to the increase of adrenaline in the system. ("fight or flight" responses). Theparasympatheticnervous system, on the other hand, is evident when a person is resting and feels relaxed, and is responsible for such things as the constriction of the pupil, the slowing of the heart, the dilation of the blood vessels, and the stimulation of the digestive andgenitourinarysystems. ("rest and digest" responses). The role of theentericnervous systemis to manage every aspect of digestion, from the esophagus to the stomach, small intestine and colon.

Question:What Is the Somatic Nervous System?Answer:The somatic system is the part of theperipheral nervous systemthat is responsible for carrying motor and sensory information both to and from thecentral nervous system. This system is made up of nerves that connect to the skin, sensory organs and all skeletal muscles. The system is responsible for nearly all voluntary muscle movements as well as for processing sensory information that arrives via external stimuli including hearing, touch and sight.Parts of the Somatic Nervous SystemThe somatic nervous system derives its name from the Greek wordsoma, which means "body." The somatic nervous system contains two major types of neurons: sensory neurons (or afferent neurons) that carry information from the nerves to the central nervous system, and motor neurons (or efferent neurons) that carry information from the brain and spinal cord to muscle fibers throughout the body.The neurons of the somatic nervous system project from the central nervous system directly into the muscles and sensory organs. The system is a direct path with synapses to connect nearby neurons. The body of the neuron is located in the CNS, and the axon then projects and terminates in the skin, sense organs or muscles. Electrochemical impulses then travel along the axon to the brain or spinal cord.Reflex Arcs and the Somatic Nervous SystemIn addition to controlling voluntary muscles movements, the somatic nervous system is also associated with involuntary movements known as reflex arcs. During a reflex arc, muscles move involuntarily without input from the brain. This occurs when a nerve pathway connects directly to the spinal cord. Some examples of reflex arcs include jerking your hand back after accidentally touching a hot pan or an involuntary knee jerk when your doctor taps on your knee.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) neuronssend the feeling of sticky wetness up your spinal cord to your brain. Thesensory neuronspass the information off to theinterneurons. Theinterneuronshanging out in the brain decide what to do. They then tell themotor (efferent)neurons the plan. Themotor (efferent) neuronsthen travel down your body and help your hand reach around and smack the guy upside the head.Organization of the Nervous SystemAs 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 theCentralandPeripheral Nervous Systems.Central Nervous System (CNS)An easy way to think about theCNSisall 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)ThePNSconsists of all the other nerves in our body orall nerves that are not encased in bone. The PNS is divided into two categories, theSomatic and Autonomic Nervous Systems.The Somatic Nervous Systemcontrols 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 Systemcontrols 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 nameautonomicnervous system. Now to make things even more complicated, the autonomic system is broken down into two more nervous systems; thesympatheticandparasympathetic. 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 systemautomaticallydoes 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 thefight 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.