5 anxiety disorders

NORMAL HUMAN NERVOUS SYSTEM 15This same loop occurs at all levels of interaction and can become exceedinglycomplex. You may have attended a professional convention or class reunion recentlyduring which you encountered an old friend whom you had not seen for some time.You caught sight of your friend, and that visual sensory information was transmittedto your brain. This image was processed by your brain, and you recognized thatwhat you were seeing was your old friend and that your friend was coming towardyou smiling. Your nervous system quickly executed the command to smile in return.Meanwhile, processing (at a more conscious level) continued as you tried to decidehow best to respond. Should you shake hands with your old friend or is a hug moreappropriate? Instantaneously, cultural rules, the intimacy of your friendship, and thesituation of the encounter were all being considered as you processed this information.You decided upon a handshake, and a command to extend your right hand wasexecuted. But more sensory input was received at that point. You noticed that yourfriend’s arms were outstretched as if to embrace you. Your brain rapidly processedthis new information, and a command was executed to extend your arms andembrace your old friend.As you can see, this loop of sensation to processing to execution can be quitesimple or very complex. In social encounters, a host of modifying interactions oftencomes into play. But in the final analysis, the purpose of the nervous system is quitesimple. It is to integrate information and coordinate your responses as you communicatewith your environment.Mechanisms of the Nervous System. We’ve talked about what the nervoussystem does. Now let’s take a look at how it does it. It does so by transmitting signalsknown as nerve impulses. The nerve cell is well suited to this task. It is a highlyexcitable cell. When a nerve cell is stimulated by incoming signals to its dendrites,it responds by opening channels (pores) in its cell membrane. When these channelsopen, charged particles called ions flood into the nerve cell. Called depolarization,this influx of ions causes a dramatic shift in the balance of electrical charges insideand outside the nerve cell. If the depolarization of the nerve cell reaches a certainthreshold, the cell “fires” an impulse, known as an action potential.Once an action potential is fired, it begins to spread. Remember, a neuron is anexcitable cell. Like fans doing “The Wave” at a football game, the excitement of theaction potential begins to travel the length of the nerve cell. The action potentialtravels up the dendrite toward the cell body, opening more channels and allowingmore ions to flood into the cell as it goes.The cell body gathers the incoming action potentials from the dendrites and sendsalong a single action potential to the axon. The action potential travels the lengthof the axon until reaching the axon terminals. At this point, the nerve cell must passthe impulse to its neighboring cells. This communication from one neuron to anotheris accomplished by neurotransmission.Neurotransmission. This is the most important part of nervous system functionfor us to understand, both because it serves as the cornerstone of nerve cell signaling,and because it is the process that is modulated by psychotropic medications and