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Chapter 3: The Biological Bases of Behavior Biology & Behavior Evidence over that past few decades has highlighted the power effects biology plays into our behavior. Much more complex than mere cause and effect, as multiple systems work simultaneously within the body. Communication in the Nervous System Your nervous system is living tissue composed of cells that fall into two major categories: glial and neurons. Neurons are individual cells in the nervous system that receive, integrate, and transmit information. The Structure and Function of Neurons Neurons process and transmit information • Two types of branches extend from the cell body: axons and dendrites Structure of Neuron Soma, or cell body, contains the cell nucleus & much of the chemical machinery common to most cells. Dendrites are the parts of a neuron that are specialized to receive information. The axon is a long, thin fiber that transmits signals away from the soma to other neurons or to muscles or glands. Structure of Neuron (con’t) The myelin sheath is insulating material that encases some axons. Axons end in a cluster of Terminal buttons, which are small knobs that secrete chemicals called neurotransmitters. Synapse is a junction where information is transmitted from one neuron to another. The Structure and Function of Neurons Neurons process and transmit information • Two types of branches extend from the cell body: axons and dendrites Glial Cells Found throughout the nervous system Glia (literally “glue”) tend to be much smaller than neurons, but are in equeal amounts. . Appear to account for over 50% of the brain’s volume. Supply nourishment, help remove waste products, & provide insulation around many axons. Glial Cells (con’t) Glia play complicated role in development of nervous system in human embryo. Myelin sheaths that encase some axons are derived from special types of glial cells. Glial Cells and the Blood-Brain Barrier Glia Form Myelin • The myelin sheath insulates axons and speeds electrical transmission along axons The Neural Impulse: Using Energy to Send Information How Neurons Work Information is received at the dendrites, is passed through the soma (cell body) to the branches ends of axon. Then transmitted to the dendrites of other cells at meeting points called synapses, where neurotransmitters are released from terminal buttons. Axons Transmit Information Neural Communication: A Two-Step Process • • Electrical signaling: action potential Chemical signaling: neurotransmitters The Neuron at Rest: A Tiny Battery Neural impulse is a complex electrochemical reaction (Hodgkin and Huxley ,1952). The neural impulse is a brief change in a neuron’s electrical charge that moves along an axon. The resting potential of a neuron is its stable, negative charge when the cell is inactive. The Action Potential Triggers the release of chemicals called neurotransmitters that diffuse across a synapse to communicate with other neurons. Like a spark traveling along a trail of gunpowder, the voltage change races down the axon. Generating an Action Potential Electrical Signaling: Propagating an Action Potential The All-or-None Law The neural impulse is an all-or-none proposition, like firing a gun. You can’t half-fire a gun. Either the neuron fires or it doesn’t, and its action potentials are all the same size ( Kandel, 2000). Weaker stimuli do not produce smaller action potentials and stronger stimuli do not evoke larger action potentials. Sending Signals: Chemicals as Couriers Neuron that sends a signal = presynaptic neuron neuron that receives = postsynaptic neuron. Arrival of action potential triggers the release of neurotransmitters—chemicals that transmit information from one neuron to another. Chemical Signaling: Releasing Neurotransmitters Receiving Signals: Postsynaptic Potentials When a neurotransmitter & receptor molecule combine, reactions in cell membrane cause a postsynaptic potential (PSP), a voltage change at a receptor site on a postsynaptic cell membrane. Receiving Signals: Postsynaptic Potentials Two types of messages can be sent from cell to cell: excitatory and inhibitory. An excitatory PSP is a positive voltage shift that increases the likelihood that the postsynaptic neuron will fire action potentials. An inhibitory PSP is a negative voltage shift that decreases the likelihood that the postsynaptic neuron will fire action potentials. Receiving Signals: Postsynaptic Potentials (con’t) Once synaptic activity is complete, reuptake occurs when neurotransmitters are sponged up from the synaptic cleft by the presynaptic membrane. Communicating Through the Synapse Overview of Synaptic Transmission Synapses & Neural Pathways Neurotransmitters and Behavior NEUROTRANSMITTERS ARE FUNDAMENTAL TO BEHAVIOR, PLAYING A KEY ROLE IN EVERYTHING FROM MUSCLE MOVEMENTS TO MOODS AND MENTAL HEALTH. Acetylcholine (ACh) Plays a key role in muscular movement. Contributes to the regulation of attention, arousal, and memory. Disoder associated with imbalance of Ach = Alzheimer’s. Source: Microsoft ClipArt Monoamines: Dopamine (DA) Dopamine (DA) contributes to control of voluntary movement. Cocaine and amphetamines elevate activity at DA synapses Dopamine circuits in medial forebrain bundle characterized as “reward pathway” Disorders from imbalance of DA: Parkinson's, schizophrenic disorders & addictive disorders Monoamines: Norepinephrine (NE) Contributes to modulation of mood and arousal. Cocaine and amphetamines elevate activity at NE synapses. Disorders from imbalance = Depressive disorders Monoamines: Serotonin Involved in regulation of sleep and wakefulness, eating, aggression Antidepressant drugs affect serotonin circuits Disorders from imbalance = depressive, obsessive- compulsive & eating disorders. GABA Serves as widely distributed inhibitory transmitter, contributing to regulation of anxiety & sleep/arousal Valium and similar antianxiety drugs work at GABA synapses Disorder from imbalance = Anxiety disorders Endorphins Resemble opiate drugs in structure and effects Play role in pain relief and response to stress Contribute to regulation of eating behavior May underlie the experience of the “runner’s high.” Source: Microsoft ClipArt Organization of the Nervous System The Organization of the Nervous System The Spinal Cord The Spinal Nerves and Reflexes The Central Nervous System CNS is bathed in cerebrospinal fluid, which provides a protective cushion. The Peripheral Nervous System Consists of the nerves that lie outside the brain and spinal cord. Subdivided into: somatic nervous system = connects to muscles and sensory receptors autonomic nervous system = connects to blood vessels, smooth muscles, and glands. The Somatic Nervous System and the Cranial Nerves The Peripheral Nervous System (con’t) autonomic nervous system controls the largely automatic arousal that accompanies emotion & is divided into sympathetic parasympathetic Cannon (1932) called it the fight-or-flight response = organisms generally respond to threat by preparing physically for attacking (fight) or fleeing (flight) the enemy. Fight or Flight Response Redefined Human stress response is an elaborate and complex psychobiological series of reactions designed for coping, adaptation, & survival of both the individual and the species. Theory has expanded to include fight, flight, freeze, or faint as the most likely behaviors induced in the stress response (Bracha, 2004). Human Stress Response Taylor (2000) addressed gender imbalances in research by exploring how women react to stress. She suggested “tend and befriend” is more accurate description of how, when women see another person in distress, they will circle the wagons using friendship to tend to the person. More recent studies show this is not gender specific. The Autonomic Nervous System and Homeostasis The Brain and Behavior Looking Inside the Brain: Research Methods Lesioning involves destroying a piece of the brain to see the effect on behavior. CT scans and MRI scans provide images of brain structure. PET scans and fMRI scans can track brain activity. The Brain Divided Source: Microsoft ClipArt The Brain Divided The Hindbrain The medulla regulates functions such as breathing and circulation The cerebellum is involved in movement and balance The pons contributes to sleep and arousal. The Midbrain Segment of the brainstem that lies between the hindbrain and the forebrain. Contains an area that is concerned with integrating sensory processes, such as vision and hearing ( Stein, Wallace, & Stanford, 2000). The Forebrain The largest & most complex region of the brain. Houses a variety of structures including the thalamus, hypothalamus, limbic system, and cerebrum All three structures are located near the top of the brainstem. The Thalamus: A Relay Station A structure in the forebrain through which all sensory information (except smell) must pass to get to the cerebral cortex. Appears to play an active role in integrating information from various senses. The Hypothalamus: A Regulator of Biological Needs A structure found near the base of the forebrain that is involved in the regulation of basic biological needs Plays a major role in the regulation of basic biological drives related to survival, including the socalled “four F’s”: fighting, fleeing, feeding, and fornicating. The Limbic System: The Seat of Emotion A loosely connected network of structures located roughly along the border between the cerebral cortex and deeper subcortical areas. Includes parts of the thalamus & hypothalamus, the hippocampus, the amygdala, and other nearby structures. The Limbic System (con’t) hippocampus & adjacent structures clearly play a role in memory processes In essence, this is the part of the brain that processes our experiences through our inner storyline. The Limbic System (con’t) Amygdala may play a central role in the learning of fear responses and the processing of other basic emotional responses. The limbic system also appears to contain emotion- tinged “pleasure centers.” The Cerebrum: The Seat of Complex Thought Cerebrum = largest and most complex part of the brain. Includes brain areas responsible for our most complex mental activities, including learning, remembering, thinking, and consciousness itself. The Cerebrum: The Seat of Complex Thought The cerebral cortex is the convoluted outer layer of the cerebrum. The cortex is folded and bent, so that its large surface area—about 1.5 square feet—can be packed into the limited volume of the skull. The cerebrum is divided into two halves called hemispheres. The Cerebrum: The Seat of Complex Thought The corpus callosum is the major structure that connects the two cerebral hemispheres The Cerebrum: The Seat of Complex Thought Each cerebral hemisphere is divided by deep fissures into four parts called lobes. Lobes & their primary known functions: occipital lobe (vision), parietal lobe (touch), temporal lobe (hearing), frontal lobe (movement of the body) The Cerebrum: Mirror Neurons Neurons activated by performing an action or by seeing another monkey or person perform the same action. Mirror neurons appear to provide a new model for understanding complex social cognition at a neural level. New findings suggest mirror neurons may play a fundamental role in the acquisition of new motor skills The Cerebrum: Prefrontal Cortex disproportionately large in humans, accounting for about one-third of the cerebral cortex. Contributes to certain types of decision making as some sort of “executive control system,” which is thought to monitor, organize, and direct thought processes. Affected functions include problem solving, delaying gratification, planning, compassion & higher order reasoning. Plasticity of the Brain Neuroplasticity - anatomical structure and functional organization of the brain are more flexible or “plastic” than widely assumed. Neurogenesis—the formation of new neuron Neuroplasticity Right Brain/Left Brain CEREBRAL SPECIALIZATION Hemispheric Specialization in the Intact Brain Two sides of the brain are in constant communication. Newer brain imaging methods map fluid communication networks in the brain Revealing a highly dynamic interhemispheric communication & coordination (Doron, Bassett, & Gassaniga, 2012). Images of Einstein’s brain reveal exceptional degree of connectivity btwn right & left hemispheres. The Endocrine System: Another Way to Communicate Endocrine system = system of glands that secrete hormones into the blood stream that help control bodily functioning. Hormone release tends to be pulsatile (released several times per day in brief bursts that last only a few minutes). The Endocrine System Oxytocin—a hormone released by pituitary, that regulates reproductive behaviors. Fosters bonding, empathy, and trust. The Endocrine System Much of the endocrine system is controlled by the nervous system through the hypothalamus connected to the pituitary gland. Pituitary gland releases variety of hormones that fan out within the body, stimulating actions in the other endocrine glands. Pituitary is the “master gland” of the endocrine system. The Pituitary Gland The Endocrine Glands Heredity and Behavior IS IT ALL IN THE GENES? Basic Principles of Genetics Chromosomes are threadlike strands of DNA (deoxyribonucleic acid) molecules that carry genetic information. Genes are DNA segments that serve as the key functional units in hereditary transmission. Genes, Chromosomes, and DNA Basic Principles of Genetics The basic units of genetic transmission are pairs of genes housed on chromosomes, which can be scrambled in an endless variety of ways. The key to the concept of genetic relatedness is that closer relatives share a larger proportion of genes than more-distant relatives. Basic Principles of Genetics Like chromosomes, genes operate in pairs, with one gene of each pair coming from each parent. Most behavioral qualities appear to involve polygenic inheritance, which means that many pairs of genes play a role in influencing the traits. Detecting Hereditary Influence: Research Methods Family studies evaluate hereditary influence by examining blood relatives to see how much they resemble one another on a specific trait. Adoption studies assess hereditary influence by examining the resemblance between adopted children and both their biological and their adoptive parents. Detecting Hereditary Influence: Research Methods Twin studies estimate hereditary influence by comparing the resemblance of identical twins and fraternal twins with respect to a trait. Twin studies generally can provide the strongest evidence. The Interplay of Heredity and Environment Epigenetics = study of heritable changes in gene expression that do not involve modifications to the DNA sequence. New work in epigenetics has further demonstrated that genetic and environmental factors are deeply intertwined. The Evolutionary Bases of Behavior Evolutionary psychology = theory that analyzes behavioral processes in terms of their adaptive significance. Darwin’s Insights Darwin argued that if a heritable trait contributes to an organism’s survival or reproductive success, organisms with that trait should produce more offspring than those without the trait & the prevalence of that trait should gradually increase over generations-thanks to natural selection. Darwin’s Insights Fitness refers to organisms’ reproductive success. Variations in reproductive success are what really fuels evolutionary change. Source: Microsoft ClipArt Later Refinements to Evolutionary Theory An adaptation is an inherited characteristic that increased in a population (through natural selection) because it helped solve a problem of survival or reproduction during the time it emerged. Later Refinements to Evolutionary Theory Because of the incremental nature of evolution, adaptations sometimes linger in a population even though they no longer provide a survival or reproductive advantage. Examples of behaviors sculpted by evolution include eating behavior, the avoidance of predators, and mating strategies. Behaviors as Adaptive Traits Modern evolutionary psychology is based on the well-documented assumption that a species’ typical patterns of behavior often reflect evolutionary solutions to adaptive problems.