Transcript Neurons
Biological Bases of Behavior Everything psychological is simultaneously _________ Every idea, mood, urge is a biological happening Love, laugh, and cry with your body Many people talk separately about biological and psychological influences on behavior “To think, feel, or act without a body would be like running without legs” Biological Psychologists Biological Psychologists: branch of psychology concerned with the links between _________ & __________ Each system is composed of subsystems that are in turn composed of even smaller subsystems Structure and Communication Neurons – What are they? The basic building block of the nervous system -- a nerve _____ Neurons perform three basic tasks Receive Carry Pass on to the next neuron electrochemical information The brain is made up of approximately ________ 100 billion neurons. Kinds of Neurons Sensory Neurons (a.k.a. Afferent Neurons) carry incoming information from the sense receptors to the CNS. Motor Neurons (a.k.a. Efferent Neurons) carry outgoing information from the CNS to muscles and glands. Interneurons connect the two neurons. Sensory Neuron Interneuron Neuron Motor Neuron • Sensory neurons take info. from the senses to the brain. • Interneurons take messages from sensory neurons to other parts of the brain or to motor neurons. • Motor neurons take info. from the brain to the rest of the body. Structure of a Neuron Structure of a Neuron – Dendrites Structure of a Neuron – Soma Structure of a Neuron – Axon Structure of a Neuron – Neural Impulse Structure of a Neuron – Myelin Sheath Structure of a Neuron – Terminals Neurons come in a variety of shapes and sizes, but they all have the same basic structure Neurons – magnified view Neuron – another view Neurons – How do they work? Neurons send messages to other neurons – this is what keeps every part of our body in communication with every other part. Neurons “fire” – send an impulse (message) down their length – or they don’t “fire” http://brainu.org/files/movies /action_potential_cartoon.swf Action Potentials This “firing” of impulse messages is called the action potential. Action potential: is a brief electrical charge that travels down the axon of the neuron. What causes an impulse to fire or not fire? Resting Potential: when a neuron is at rest and capable of generating an action potential There are fluids inside and outside of the neuron, filled with electrically charged particles (ions) When the neuron is at rest, there is a negative charge on the inside of the neuron compared to the outside. Action Potentials, cont. Stimulation from inputs to dendrites causes the cell membrane to open briefly Positively charged sodium ions flow in through the cell membrane If resting potential rises above threshold, an action potential starts to travel from the cell body down the axon Threshold - Each neuron receives excitatory and inhibitory signals from many neurons. When the excitatory signals minus the inhibitory signals exceed a minimum intensity (threshold) the neuron fires an action potential. Action Potential, cont. Refractory period - The “recharging phase” when a neuron, after firing, cannot generate another action potential Neuron Communication All-or-None Principle: if a neuron fires it will always fire at the same intensity A strong stimulus can trigger more neurons to fire, and to fire more often, but all action potentials are of the same strength and speed. A neuron does NOT fire at 30%, 45% or 90% but at 100% each time it fires. Just like a gun, there is no “part-way” firing Action Potential PowerPoint® 2000 or better with Flash® plug-in required to view animations. Right-click on animation for playback controls. Instructor’s Notes Copyright © Houghton Mifflin Company. All rights reserved. So what, exactly, are neurotransmitters and what do they do? Neurotransmitters Neurotransmitters: chemical messenger that travels across the synapse from one neuron to the next Can influence whether the second neuron will generate an action potential or not Select Neurotransmitters Neurotransmitter Acetylcholine (ACh) Dopamine (DA) Function Released by motor neurons controlling skeletal muscles. Enables muscle action, attention, arousal, and memory Influences voluntary movement, learning, attention, and pleasurable emotions Affects mood, hunger, sleep, and arousal Examples • • • • • Serotonin • With Alzheimer’s disease, ACh-producing neurons deteriorate. Some ACh receptors stimulated by nicotine. Excess dopamine receptor activity linked to schizophrenia. Decreased levels produce the decreased mobility and tremors of Parkinson’s disease. Undersupply linked to depression and obsessive-compulsive disorder. Prozac and some other antidepressant drugs raise serotonin levels. • How Neurotransmitters Influence Us Serotonin • pathways are involved with mood regulation. Dopamine pathways are involved with diseases such as: • Schizophrenia (too much DA) • Parkinson’s disease (not enough DA). Select Neurotransmitters (cont.) Neurotransmitter Function Examples Norepinephrine (NE) Helps control alertness, mood, and arousal Undersupply can depress mood. A major inhibitory neurotransmitter Undersupply linked to seizures, tremors, and insomnia. Endorphins Contribute to pain relief and perhaps to some pleasurable emotions (“Runner’s High”) Resemble opiate drugs in structure and effects Glutamate A major excitatory neurotransmitter; involved in memory Oversupply can overstimulate brain, producing migraines or seizures (which is why some people avoid MSG, monosodium glutamate, in food) GABA (gammaaminobutyric acid)