PSY 2012 0004 Katie s Notes Chapter 3 Biological Psychology 3 1 Neurons and Behavior Physiological explanation describes the mechanisms that produce a behavior Example A bird may know how to fly South for the winter due to the position of the Sun hormones or the magnetic field Evolutionary explanation relates behavior to the evolutionary history of the species Individuals with less successful behaviors are less likely to pass on their genes Developmental explanation ontogenetic deals with changes over age No animal or person is literally born with a behavior We are born with the capacity to develop a behavior Nervous system cells Your brain consists of an enormous number of separate cells called neurons Neurons receive and transmit information electrochemically Sensory neurons carry information from sense organs to the central nervous system Neurons in the central nervous system process and interpret information and send commands to muscles glands and organs Neurons do not have a fixed anatomy Neurons constantly grow and shed dendrites and axons Usually this occurs in response to experience and learning Gila support the neurons in many different ways Provide insulation Synchronize activity among neighboring neurons Remove waste products They are 1 10th the size of the neurons but about 10 times as numerous 1 PSY 2012 0004 Katie s Notes A neuron consists of three parts a cell body dendrites and an axon Cell body contains the nucleus of the cell Dendrites widely branching structures that receive input from other neurons Axon a single long thin straight fiber with branches near its tip An axon transmits information to other cells Some vertebrate axons are covered in myelin an insulating sheath that speeds up the transmission of impulses along an axon Concept Check Which part of a neuron receives input from other neurons Which part sends messages to other cells Dendrites receive input from other neurons An axon sends messages Action potential an excitation that travels along an axon at a constant strength no matter how far it must travel The all or none law An action potential is either happening or not there s no sort of action potential It reaches the brain at full strength but more slowly than regular electrical conduction would 2 PSY 2012 0004 Katie s Notes How action potential works An unstimulated axon has resting potential an electrical polarization across the membrane or covering of an axon An action potential starts in either of two ways o Many axons produce spontaneous activity o An input from other neurons can excite a neuron s membrane A polarized axon is charged negatively 70 millivolts relative to its outside Sodium is concentrated outside the neuron and potassium mostly inside o They are held in place by the pump s special gates During an action potential sodium gates open and sodium ions enter the axon bearing a positive charge o This depolarization makes the charge inside the cell positive After an action potential occurs the sodium gates close at that point and open at the next point along the axon As the sodium gates close potassium gates open and potassium ions flow out of the axon 3 PSY 2012 0004 Katie s Notes Concept Check If a mouse and a giraffe both get pinched on the toes at the same time which will respond faster The mouse will react faster because the action potentials have a shorter distance to travel in the mouse s nervous system that in the giraffe s Fill in these blanks When the axon membrane is at rest the inside has a charge relative to the outside When the membrane reaches its threshold ions enter from outside to inside bringing with them a charge That flow of ions constitutes the of the axon negative sodium positive action potential Synapses The specialized junction between one neuron and another a neuron releases a chemical that either excites or inhibits the next neuron Excitatory messages cause the next cell to fire continue to carry the action potential Inhibitory messages decrease the likelihood the action potential will continue to travel Synaptic communication Each axon bulges into a terminal bouton or presynaptic ending When the action potential reaches it neurotransmitters are released A neurotransmitter is a chemical stored in the neuron It activates special receptors of other neurons When released they diffuse to the surface of the postsynaptic neuron They attach to receptors on the dendrite cell body exciting or inhibiting the cell After the message is sent the neurotransmitter detaches from the receptors It may be reabsorbed by the axon that released it reuptake diffuse away be removed as a waste product metabolized or remain in the synapse 4 PSY 2012 0004 Katie s Notes 5 PSY 2012 0004 Katie s Notes Concept Check What is the difference between the presynaptic neuron and the postsynaptic neuron The presynaptic neuron releases a neurotransmitter that travels to the postsynaptic neuron where it activates an excitatory or inhibitory receptor Learning and environmental challenges sometimes produce branching in axons and dendrites of an organism s neurons How would that affect the number of synapses It would increase the number of synapses Dopamine is a neurotransmitter that excites postsynaptic neurons If a drug were injected into an animal that blocked dopamine from attaching to its receptors what would happen to the postsynaptic neurons They would be less likely to produce further action potential Neurotransmitters and Behavior There is a helpful chart on page 69 of the textbook Table 3 1 Some of the Most Important Neurotransmitters New understanding of the role of neurotransmitters has revolutionized the health sciences Drugs that act on specific receptors in the nervous effect an organism s functioning and Unusual behaviors or dysfunctions may be due to lack or excess of particular Example Parkinson s disease a condition that affects about 1 of people over the age of 50 The main symptoms are difficulty initiating voluntary movement slow movement tremors rigidity and depressed mood Gradual decay in a system of axons that release dopamine produces these behavior neurotransmitters symptoms movement Dopamine is a neurotransmitter that promotes activity levels and facilitates Symptoms can be managed in mild cases with the drug L dopa It is synthesized into dopamine by the neurons 6 PSY 2012 0004 Katie s Notes 3 2 Drugs and Their Effects The biological basis of drug abuse and dependence Nearly all abused and addictive drugs increase