Chapter 3 The Biological Bases of Behavior Biology

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 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 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 Clip. Art

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 Clip. Art

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 f. MRI scans can track brain activity.

The Brain Divided Source: Microsoft Clip. Art 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 so-called “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 Clip. Art

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.