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Chapter 3: The Biological Bases of Behavior Central (CNS) nervous system ◦ Brain and spinal cord Peripheral (PNS) nervous system ◦ Carries messages to and from CNS Parts of the Nervous System Afferent neurons (Sensory), relay information from the senses to the brain and spinal cord. ▪ Eyes, ears, nose, mouth, and skin Efferent neurons (motor), send information from the central nervous system to the glands and muscles, ▪ enables the body to move. Interneurons carry information between neurons ▪ in the brain ▪ in the spinal cord Types of Neurons Copyright © Allyn & Bacon 2006 WWB Structures of a neuron The cell body Contains the cell’s Nucleus ◦ Round, centrally located structure ◦ Contains DNA ◦ Controls protein manufacturing ◦ Directs metabolism ◦ No role in neural signaling Dendrites Information collectors Receive inputs from neighboring neurons Inputs may number in thousands If enough inputs the cell’s AXON may generate an output Dendritic Growth Mature neurons generally can’t divide But new dendrites can grow Provides room for more connections to other neurons New connections are basis for learning Axon The cell’s output structure One axon per cell, 2 distinct parts ◦ tubelike structure branches at end that connect to dendrites of other cells Myelin sheath White fatty casing on axon Acts as an electrical insulator Not present on all cells When present increases the speed of neural signals down the axon. Myelin Sheath Hodgkin & Huxley (1952) - giant squid Fluids inside and outside neuron Electrically charged particles (ions) Neuron at rest – negative charge on inside compared to outside -70 millivolts – resting potential The Neuron at Rest Neurons communicate by means of an electrical signal called the Action Potential Action Potentials are based on movements of ions between the outside and inside of the cell When an Action Potential occurs a molecular message is sent to neighboring neurons How neurons communicate Stimulation causes cell membrane to open briefly Positively charged sodium ions flow in Shift in electrical charge travels along neuron The Action Potential All – or – none law The Action Potential Figure 3.2 The neural impulse Neuron to Neuron Axons branch out and end near dendrites of neighboring cells Axon terminals are the tips of the axon’s branches A gap separates the axon terminals from dendrites Gap is the Synapse Dendrite Axon Cell Body Synapse axon terminals contain small storage sacs called synaptic vesicles vesicles contain neurotransmitter molecules Sending Neuron Axon Terminal Synapse Neurotransmitter Release Action Potential causes vesicle to open Neurotransmitter released into synapse Locks onto receptor molecule in postsynaptic membrane Figure 3.3 The synapse Figure 3.4 Overview of synaptic transmission Locks and Keys Neurotransmitter molecules have specific shapes Receptor molecules have binding sites When NT binds to receptor, ions enter positive ions (NA+ ) depolarize the neuron negative ions (CL-) hyperpolarize Some Drugs work on receptors Some drugs are shaped like neurotransmitters Antagonists : fit the receptor but poorly and block the NT e.g. beta blockers Agonists : fit receptor well and act like the NT e.g. nicotine. When a Neurotransmitter Binds: The Postsynaptic Potential Voltage change at receptor site – postsynaptic potential (PSP) ◦ Not all-or-none ◦ Changes the probability of the postsynaptic neuron firing Positive voltage shift – excitatory PSP Negative voltage shift – inhibitory PSP Neurotransmitters and Behavior Specific neurotransmitters work at specific synapses Lock and key mechanism Agonist – mimics neurotransmitter action Antagonist – opposes action of a neurotransmitter More than 40 neurotransmitters known at present Interactions between neurotransmitter circuits Types of Neurotransmitters Acetylcholine Serotonin Norepinephrine Dopamine Endorphins GABA Glutamate Table 3.1 Common Neurotransmitters and Some of their Functions Acetylcholine Found in neuromuscular junction Involved in muscle movements Alzheimer’s Disease Deterioration of memory, reasoning and language skills Symptoms may be due to loss of ACh neurons http://www.youtube.com/ watch?v=q1BkfV2h09g Serotonin Involved in sleep Involved in depression ◦ Prozac works by keeping serotonin in the synapse longer, giving it more time to exert an effect Also involved in Obsessive Compulsive Disorder: ◦ http://www.youtube.com/watch?v=vnKZ4pdSU-s Norepinephrine Arousal “Fight or flight” response Dopamine Involved in movement, attention and learning Dopamine imbalance also involved in schizophrenia Loss of dopamine- producing neurons is cause of Parkinson’s Disease http://www.youtube.com/watch?v=ECkP VTZlfP8 Endorphins Control pain and pleasure Released in response to pain Morphine and codeine work on endorphin receptors Involved in healing effects of acupuncture Gamma-Aminobutyric Acid (GABA) Main inhibitory neurotransmitter Benzodiazepines (which include tranquilizers such as Valium) and alcohol work on GABA receptor complexes Glutamate Major excitatory neurotransmitter Too much glutamate (and too little GABA) associated with epileptic seizures Integrating Signals One neuron, signals from thousands of other neurons Neural networks Patterns of neural activity Interconnected neurons that fire together or sequentially Synaptic connections Elimination and creation Synaptic pruning Communication in the Nervous System Glia – structural support and insulation Neurons – communication ◦ ◦ ◦ ◦ ◦ Soma – cell body Dendrites – receive Axon – transmit away Myelin sheath – speeds up transmission Terminal Button – end of axon; secretes neurotransmitters ◦ Neurotransmitters – chemical messengers Central Nervous System Brain Brain and Spinal Cord Spinal Cord Central nervous system Peripheral nervous system Figure 3.5 Organization of the human nervous system Sympathetic CENTRAL NERVOUS SYSTEM SYMPATHETIC “ Fight or flight” response Release adrenaline and noradrenaline Increases heart rate and blood pressure Increases blood flow to skeletal muscles Inhibits digestive functions Brain Dilates pupil Stimulates salivation Relaxes bronchi Spinal cord Salivary glands Lungs Accelerates heartbeat Inhibits activity Heart Stomach Pancreas Stimulates glucose Secretion of adrenaline, nonadrenaline Relaxes bladder Sympathetic Stimulates ejaculation ganglia in male Liver Adrenal gland Kidney Parasympathetic CENTRAL NERVOUS SYSTEM PARASYMPATHETIC Brain “Rest and digest” system Calms body to conserve and maintain energy Lowers heartbeat, breathing rate, blood pressure Contracts pupil Stimulates salivation Spinal cord Constricts bronchi Slows heartbeat Stimulates activity Stimulates gallbladder Gallbladder Contracts bladder Stimulates erection of sex organs Summary of autonomic differences Autonomic nervous system controls physiological arousal Sympathetic division (arousing) Pupils dilate Decreases Parasympathetic division (calming) EYES Pupils contract SALVATION Increases Perspires SKIN Dries Increases RESPERATION Decreases Accelerates HEART Slows Inhibits DIGESTION Activates Secrete stress hormones ADRENAL GLANDS Decrease secretion of stress hormones Studying the Brain: Research Methods Damage studies/lesioning Studying the Brain: Research Methods Brain imaging – computerized tomography positron emission tomography magnetic resonance imaging: Transcranial magnetic stimulation (TMS) Brain has 2 Hemispheres Left & Right sides are separate Corpus Callosum : major pathway between hemispheres Some functions are ‘lateralized’ ◦ language on left ◦ math, music on right Lateralization is never 100% Corpus Callosum Right Hemisphere Left Hemisphere Figure 3.14 The cerebral hemispheres and the corpus callosum Each hemisphere is divided into 4 lobes Frontal Parietal Occipital Temporal The Cerebrum: The Seat of Complex Thought Four Lobes: Occipital – vision Parietal - somatosensory Temporal - auditory Frontal – movement, executive control systems •Cerebrum Continued •Cerebral Cortex •Higher mental processes of language, memory, and thinking. •Left Cerebral Cortex •Frontal lobe •Motor cortex •Broca’s Area •Parietal lobe •Somatosensory cortex •Occipital lobe •Visual cortex •Temporal lobe •Auditory Cortex •Wernicke’s area WWB Copyright © Allyn & Bacon 2006 Broca’s Area: speech production http://www.youtube.com/watch? v=KpkH25XVpFU Wernicke’s area: speech comprehension Figure 3.16 Language processing in the brain Brain Regions and Functions Hindbrain – vital functions – medulla, pons, and cerebellum Midbrain – sensory functions – dopaminergic projections, reticular activating system Forebrain – emotion, complex thought – thalamus, hypothalamus, limbic system, cerebrum, cerebral cortex Figure 3.12 Structures and areas in the human brain Figure 3.15 The cerebral cortex in humans The Limbic System Hypothalamus Amygdala Hippocampus Hypothalamus Contains nuclei involved in a variety of behaviors The four f’s. Feeding, fleeing, fighting, and…mating. ◦ sexual behavior ◦ hunger, thirst ◦ sleep ◦ water and salt balance ◦ body temperature regulation ◦ circadian rhythms ◦ role in hormone secretion Hypothalamus and Hormones Hypothalamus releases hormones or releasing factors which in turn cause pituitary gland to release its hormones This is a slower communication process than the chemical communication that occurs between neurons. Amygdala Inputs come from all senses Amygdala ‘reads’ emotional significance of inputs Output influences such functions as heart rate, adrenaline release Hippocampus Important in forming new memories Thalamus Relay station in brain Sensory and motor information get processed here, then sent to the higher brain centers Processes most information to and from higher brain centers Hindbrain Structures Cerebellum Brainstem ◦ medulla ◦ reticular formation ◦ pons The Endocrine System: Another Way to Communicate Hormones – chemical messengers in the bloodstream Endocrine glands Pituitary – “master gland,” growth hormone Thyroid – metabolic rate Adrenal – salt and carbohydrate metabolism Pancreas – sugar metabolism Gonads – sex hormones Endocrine System Pituitary gland—attached to the base of the brain, hormones affect the function of other glands Adrenal glands—hormones involved in human stress response Gonads—hormones regulate sexual characteristics and reproductive processes; testes in males, ovaries in females Copyright © Allyn & Bacon 2006 WWB Genes and Behavioral Genetics Genes: – segments of DNA on chromosomes transmit heredity traits Chromosomes – rod shaped and contain all genes that carry genetic information to make a human being. Dominant-recessive pattern – a set of inheritance rules for genes ◦ One dominant gene or two recessive genes required for a trait to be expressed. Multifactorial inheritance – an inheritance pattern in which a trait is influenced by both genes and environmental factors. Polygenic inheritance – many genes influence a particular characteristic like skin color. Sex linked inheritance – involves genes on the X and Y chromosomes ◦ E.g. male or female body type and red-green color blindness Behavioral Genetics – a field of research that uses twin and adoption studies to investigate the relative effects of heredity and environment on behavior. Copyright © Allyn & Bacon 2006 WWB Basic Principles of Genetics Chromosomes – strands of DNA carrying genetic information Human cells contain 46 chromosomes in pairs (sex-cells – 23 single) Each chromosome – thousands of genes, also in pairs Polygenic traits Research Methods in Behavioral Genetics Family studies – does it run in the family? Twin studies – compare resemblance of identical (monozygotic) and fraternal (dizygotic) twins on a trait Adoption studies – examine resemblance between adopted children and their biological and adoptive parents Figure 3.19 Genetic relatedness Figure 3.20 Twin studies of intelligence and personality The Evolutionary Bases of Behavior Based on Darwin’s ideas of natural selection Reproductive success key Adaptations – behavioral as well as physical The Evolutionary Bases of Behavior Adaptations – behavioral as well as physical Fight-or-flight response: helpful if a tiger is chasing you, but chronic stress causes us problems Taste preferences: fatty foods pack on calories…but if food is plentiful, this is no longer adaptive Parental investment and mating: increased survival in offspring where there is more parental investment “The effects of chronic social stress in juvenile hamsters makes sense because if they were permanently fearful of conspecifics, they would not be able to mate and have offspring.”