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The Central Nervous System Objectives STANDARD 6.7 understand the relationship between the brain and behavior. • To identify the parts of the nervous system and explain how they work The Main Parts of the Nervous System For more information, go to http://kidshealth.org/misc/movie/bodybasics/bodybasics_brain.html The nervous system: • Has two main parts: the central nervous system and the peripheral nervous system. • BOTH are composed of neurons, or nerve cells, that transmit messages to different parts of the body. • Neurons have three main parts: cell body (produces energy), dendrites (DELIVERS info to the cell body), and axons (carries info AWAY from the cell body.) • Some neurons are several FEET long! • A neuron has many dendrites but only one axon, which tells you that your brain SENDS more messages to our bodies than it receives from our bodies. The Purpose of Neurons A neuron exists to perform three tasks: 1. To receive information (in the form of electrochemical impulses) from other neurons that feed into it 2. To carry this information down its length 3. To pass the information to the next neuron in line This transmission of an electrochemical impulse is called “firing.” They can either fire, or not. This is called the “all-or-none principle.” A neuron always fires with the same intensity regardless of the stimulation from the dendrites. The Neural Chain • The neural chain describes the path information follows as the nervous system processes it. • Your nervous system “collects” information using receptor cells, specialized cells in the sensory systems of the body. • These receptor cells convert energy into impulses (action potentials) your brain can understand. We will discuss these cells in detail when we study sensation and perception. Types of neurons • Sensory nerves carry information from the sense receptors cells to the brain and spinal cord. • Interneurons are the billions of neurons in your brain and spinal cord that process information. • Motor nerves carry information from your brain and spinal cord to your muscles and glands. The Role of the Brain • Once it receives the impulses, the brain make appropriate decisions, using its interneuron.s • The brain can make the decision, but it still has to communicate the information to the body’s muscles and glands through motor neurons. • Ex. When you have a tension headache, sensory neurons transmit a pain message to your brain. Motor neurons transmit from the brain to your muscles and glands, telling them to RELAX. They might even tell you to massage your temples or close your eyes! How does this work? • Dendrites receive information and deliver impulses to the cell body to tell the cell body (soma) how to respond. • Axons carry messages away from the cell body to other neurons, muscles, or glands. • BOTH dendrites and axons jump from neuron to neuron via synapses that connect dendrite to axon to cell body. (We will diagram this later.) • New synapses form when neurons that were not previously connected create connections. Click on the picture for a link to a Discovery Channel video explaining how neurons work. Dendrites and Axons at work How does a neuron fire? The Neural Impulse • When a neuron fires, it creates a neural impulse called an action potential, which carries the electrical charge from the dendrites to the axon terminals, referred to as firing. • After firing, each action potential is followed by a brief recharging period, known as the refractory period, when it can’t fire. • When the cell is capable of firing again, it has reached its resting potential, meaning it’s relaxed and ready to fire again. Like YOU after a nap or a vacation! Analogy of how a neuron fires • Like a neuron, a toilet has an action potential. When you flush, an “impulse” is sent down the sewer or septic pipe. • Like a neuron, a toilet has a refractory period. There is a delay after flushing when the toilet cannot be flushed again because the tank is being refilled. • Like a neuron, a toilet has a resting potential. The toilet is “charged” when the tank is filled and can be flushed again. • Like a neuron, a toilet operates on the “all-or-none principle” – it flushes with the same intensity no matter how much force you apply to the handle. Critical Thinking Activity • With one or two of your neighbors, brainstorm other analogies for the neural impulse. • Outline each step compared to the neuron just like the toilet example. • Write down each step. Synaptical Connection Synapse between axon and dendrite Neurotransmitter • Neurotransmitters travel across the synapse to carry the information from one neuron to the next. The neurotransmitter influences whether the next neuron will generate an action potential or not. Neurotransmitters can only fit in receptor sites that fit their shape, referred to as “lock and key.” The central nervous system • The central nervous system is composed of two parts: the brain and the spinal cord. • The spinal cord is a column of nerves. If you’ve ever “pinched a nerve,” then you know nerves are important. • The spinal cord is also involved in spinal reflexes (simple, automatic responses), such as touching a hot stove immediately sends a message to remove your hand. Sometimes the reflex occurs BEFORE the pain even registers! Put your dendrites & axons to work! • Line up around the room from the table next to the white board to my desk area. • The first person faces the rear of the room, and everyone else puts their back to the person behind them. • Wait for further instructions . . . Works Consulted Kasschau, Richard A. Understanding Psychology. Columbus, Ohio: Glencoe/McGraw-Hill, 2003. 6-33. Print. Rathus, Spencer A. Holt Psychology: Principles in Practice. Austin, TX: Holt, Rinehart and Winston, 2007. 2-23. Print. Blair-Broeker, Charles T., and Randal M. Ernst. Thinking about Psychology. New York: Worth Publishers, 2013. 59-92.