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The Nervous System Homework Objectives Identify the role of the nervous system. Recognize that the basic cellular unit of the nervous system is the neuron. Distinguish between sensory and motor neurons. Explain the roles of the brain, spinal cord, and peripheral nerves. The Nervous System Let’s see those hands: What is the nervous system? What does it do? Nervous System The nervous system mediates communication among different parts of the body, and mediates the body’s interactions with the environment. The nervous system is one of two major control and communication networks for the body. What are some parts of the nervous system that you know about? Nervous System The nervous system includes brain, QuickTime™ and a decompressor are needed to see this picture. spinal cord, nerves, etc. We’re going to focus today on its most basic unit, and get up to those organs tomorrow. The cells that carry messages as part of the nervous system are neurons. They are the basic unit of the system. In order to understand how they work, you need to know their basic anatomy. Neurons A neuron is a one- way communication system. Messages are received by one end, and transmitted by the other. QuickTime™ and a decompressor are needed to see this picture. Neurons The arrow indicates an electrical impulse. Neurons work like a long chain of dominoes. The dendrite is made to fire an electrical impulse when it’s hit by a chemical. The impulse travels down the axon… QuickTime™ and a decompressor are needed to see this picture. Neurons … The impulse reaches the end, where it makes the neuron release chemicals into the synapse. On the other end of the synapse are the dendrites of another neuron. That electrical impulse = an action potential. QuickTime™ and a decompressor are needed to see this picture. Neurons All action potentials are the same, there’s no actual information in the action potential. But each neuron has its own function. So the brain will be able to recognize, “if neuron #15734793 fired an action potential, that means that there was heat being applied to that section of the skin.” In this case, neuron #15734793 doesn’t fire if there’s cold or pressure being applied. Neurotransmission New vocab: Neurotransmitter: A chemical used by one neuron to signal another neuron. http://science.education.nih.gov/supple ments/nih2/addiction/activities/lesson2_ neurotransmission.htm Neurotransmission Important things to notice in order to understand how a drug works: The two neurons aren’t touching each other, there’s a space (synapse) between the end of one and the beginning of the next. The dendrite has proteins that the neurotransmitters bind to. That’s how it recognizes that it’s being signaled, and starts a new action potential. The neurotransmitters aren’t used up. They’re released to go back to the original neuron, to wait until another signal is to be transmitted. Neurons How could this neuron system be used by the body to maintain homeostasis? Neurons How could this neuron system be used by the body to maintain homeostasis? Neurons and negative feedback loops: Some neurons activate their action potentials when they detect rising body temperature. The end of their chain activates another chain of neurons, this one leading to the blood vessels of the skin. The end of this new chain signals the blood vessels to dilate, releasing excess heat. When the original heat-sensing neurons stop sensing excess heat, their action potentials stop, and the blood vessels stop being stimulated and can go back to normal. Neurons A helpful way to understanding how body systems work is to understand why things can go wrong. What is a drug? Neurons A helpful way to understanding how body systems work is to understand why things can go wrong. What is a drug? A drug is any substance which alters the body’s normal function. We’re going to look at psychoactive drugs, drugs that alter the normal functions of the nervous system. Neurons and Drug Action What could be ways that the normal action of a neuron could be changed, to produce a change in how often they send their signal? Demo Neurons and Drug Action http://science.education.nih.gov/supple ments/nih2/addiction/activities/lesson3_ cocaine.htm Neurons and Drug Action Different psychoactive drugs have different modes of action, affect different kinds of neurons and neurotransmitters, but the common thread is that they change the frequency of the action potential. Examples: Neurons and Drug Action Opiates, THC, alcohol: Increase the number of impulses by mimicking normal neurotransmitter. Methamphetamines: Release neurotransmitter from vesicles with or without an impulse. Nicotine: Release more neurotransmitter per impulse. Cocaine, amphetamine: Block reuptake. LSD, caffeine: Block postsynaptic receptor. Specific Example: THC THC is a cannabinoid, a chemical which mimics neurotransmitters called anandamide. Anandamides are the neurotransmitters of choice in the following areas of the brain, consider what interference would result in: Limbic system & hippocampus (memory and learning) Amydgala (strength/mildness of emotions, integrating emotion and action) Cerebellum (movement & coordination) Plus other areas involved in pain and hunger It makes even more sense when you consider what anandamides usually are used for: THC Anandamides are usually used during sleep. These pathways involve the calming and settling process, tuning down emotional responses, turning down pain recognition, encouraging you to eat when you get up, turning off memory and learning (a part of why you don’t remember dreams well). So, taking THC which mimics an anandamide activates these pathways while the person is awake. Hence, calmness/stupor, lack of pain, hunger, lack of integration between emotion and action, lack of coordination, not feeling emotions strongly, and difficulty with forming memories and learning. THC withdrawal then makes sense in context: irrationality and outbursts, difficulty re-coordinating the learning processes, etc. The withdrawal symptoms take time to dissipate as neurons try to return to normal activity, though truly chronic use can prevent that. Neurons and Drug Action Understanding how psychoactive drugs are related to neurons and neurotransmitters also lets you understand dependence and withdrawal. Consider that, to maintain homeostasis, neurons have mechanisms by which they can reduce their sensitivity to neurotransmitters. Neurons and Drug Action Understanding how psychoactive drugs are related to neurons and neurotransmitters also lets you understand dependence and withdrawal. Consider that, to maintain homeostasis, neurons have mechanisms by which they can reduce their sensitivity to neurotransmitters. Now, what will neurons probably do when exposed to those different drugs repeatedly? Neurons and Drug Action And why do you think it is that, after giving up a drug that had effect A on the user, they tend to have the opposite of effect A during withdrawal? A can be a lot of things. Happiness, concentration, elevated heart rate, etc. Neurons and Drug Action So, psychoactive drugs can have a variety of effects. It depends on dosage and route of administration, among other things, but effects include: Influence on neuronal action, as we just discussed Altering the brain’s ability to metabolize glucose (cocaine and others do this) - what would be the result? Even neuron death (alcohol, meth, ecstasy among others) - why might that happen? Neurons and Drugs Knowing what they do about drugs and their effect on neurotransmission, though, has also allowed scientists to develop psychoactive drug regimes for treatment purposes. How could a psychoactive drug like morphine reduce pain? In people with chronic clinical depression, who don’t release enough of the neurotransmitter serotonin, how could a drug treat that condition? Neurons and Drugs Neurons and neurotransmission are at the center of research on: ADHD: http://videos.howstuffworks.com/discoveryhealth/14425-human-atlas-adhd-video.htm Chronic depression Alcoholism & Addiction Schizophrenia Acute life events: can you use neurotransmission to explain why people often remain depressed after an acute event, like death or torture, even if they’re not thinking about it anymore or don’t “feel” bothered? Neurons So you know that neurons communicate axon-to-dendrite. This means that what you get is a long chain of neurons, like an extended game of telephone or dominoes. A long bundle of neurons is called a nerve. QuickTime™ and a decompressor are needed to see this picture. Nerves The body is riddled with a huge network of nerves, all with different functions. Sensory nerves send information to the brain: they detect and inform the command center of stimuli, like pressure, heat, moisture, damage… Your tongue is equipped with sensory nerves to QuickTime™ and a decompressor are needed to see this picture. carry messages that they’ve detected tastes like salt or sweet. Your optic nerve sends messages that its photoreceptors have sensed light. Nerves Then, there are motor nerves send information from the brain to the body: nerves whose signal is a command, like “dilate this blood vessel,” “contract this muscle,” “relax that muscle.” QuickTime™ and a decompressor are needed to see this picture. Nerves This network of sensory and motor nerves woven throughout the body is called the peripheral nervous system. What does peripheral mean? QuickTime™ and a decompressor are needed to see this picture. Nervous System But of course, those sensory nerves send their message somewhere, and the motor nerves get their message from somewhere. You know where, right? CNS The central nervous system receives and processes stimuli and issues responses. It’s comprised of the brain and the spinal cord. QuickTime™ and a decompressor are needed to see this picture. QuickTime™ and a decompressor are needed to see this picture. CNS The brain is the major command center. It’s a huge complicated bundle of neurons (for everyone but this guy), and each area has a different function. QuickTime™ and a decompressor are needed to see this picture. Brain There are areas which control breathing, body temperature, etc. The higher cognitive functions - memory, emotion, learning - are also there. Why can’t I just read definitions of things? Why do Ms. Stang and our teachers make us read and listen and write and do problems and activities and homework and labs with them? Because what learning actually is is a new connection. You don’t make a new neuron, you connect existing dendrites & axons. So the more different ways that you encounter or do QuickTime™ and a decompressor are needed to see this picture. something, the more new connections you make, the more learning, the more likely it is that you will be able to access the memory. Spinal Cord The spinal cord carries messages to and from the brain, and it also has some control functions, like reflexes. QuickTime™ and a decompressor are needed to see this picture. Sense Organs Other organs generally considered to be part of the nervous system are certain sensory functions, like your eyes and aspects of your ears and chemical senses. QuickTime™ and a decompressor are needed to see this picture. QuickTime™ and a decompressor are needed to see this picture.