Basic structure of the Nervous System

All organs and all physiological, psychological reactions are controlled by nervous system. Basically all animals besides really simple one have a nervous system. Humans nervous system stands out by its complexity. Our nervous system gives us abilities to write novels, debate, perform complex gymnastic tricks. All our actions and emotions are products of three key functions: sensory input, integration, motor output. Let say some insect is walking down your knee, the sensory receptors of your skin detect those small legs – that information is the sensory input. Then your nervous system processes the input and evaluates what should be done with input. This is the integration function, so decision might be ignore it or should I jump away . After that your hand is removing the insect, this is the motor output function or the response.
Nervous system has several levels of the organization. The two main parts are the Central and the Peripheral nervous systems. The central nervous system includes brain and spinal cord. This is the part that made decision to remove or ignore the insect and then gave order to a hand. The peripheral nervous system includes all the nerves branched off from the brain, spine that makes possible for the central system to communicate with all the parts of the body. Peripheral nervous system is working in both directions because it’s main function is the communication. It’s sensory part (afferent division) is taking sensory input like “attention insect is walking down your hand” and sends that input to the brain. The motor part (efferent division) is the part that sends commands from the brain to the muscles and glands like “hand remove the spider”.
The Motor division has two parts too. It has the Somatic nervous systems, it responsible for voluntary movements, it controls skeletal muscle movements. The second part of the Motor division is the Autonomic nervous system, it responsible for involuntary actions, it controls the heart beating, lung breathing for example. Autonomic nervous system has two parts too. It has Sympathetic part that mobilizes the body into action like “ freak out ahh Bug!!!!”. Parasympathetic part relaxes the body. So Sympathetic and Parasympathetic divisions act appositely to each other.