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Message Unit 1: Biological Bases of Behavior1.1 Interaction of Heredity and Environment1.1.01 Heredity and the Environment1.1.02 The Evolutionary Perspective and Natural Selection1.1.03 Research on the Influence of Heredity and the Environment1.2 Overview of the Nervous System1.2.01 The Central Nervous System1.2.02 The Peripheral Nervous System1.3 The Neuron and Neural Firing1.3.01 Neurons and Glia1.3.02 Spinal Reflexes1.3.03 Neural Transmission1.3.04 Neurotransmitters1.3.05 Hormones1.3.06 Influence of Drugs on Neural Transmission1.3.07 Categories and Effects of Psychoactive Drugs1.3.08 Drug Tolerance, Withdrawal, and Substance Use Disorders1.4 The Brain1.4.01 The Brainstem1.4.02 The Cerebellum1.4.03 Cerebral Cortex and Limbic Structures1.4.04 Broca's and Wernicke's Areas1.4.05 Split-Brain Research1.4.06 Plasticity1.4.07 Methods Used to Examine the Brain

1.5 Sleep1.5.01 States of Consciousness1.5.02 Circadian Rhythms1.5.03 Stages of Sleep1.5.04 Theories on Sleep and Dreams1.5.05 Sleep Disorders1.6 Sensation1.6.01 Transduction and the Absolute Threshold1.6.02 The Just-Noticeable Difference and Sensory Adaptation1.6.03 Sensory Interaction and Synesthesia1.6.04 The Process of Vision1.6.05 Color Vision1.6.06 Visual Impairment1.6.07 The Process of Hearing1.6.08 Hearing Impairment1.6.09 The Process of Olfaction1.6.10 The Process of Gustation1.6.11 The Process of Touch1.6.12 The Process of Pain1.6.13 The Vestibular Process1.6.14 The Kinesthetic Process

Unit 1: Biological Bases of BehaviorTopic 1.1Interaction of Heredity and Environment1.1.01 Heredity and the Environment[ 1.1.A.1 ]Behavior is influenced by both heredity and the environment. Heredity, sometimes referred to as nature, is the transfer of genetic material from parent to offspring. Behaviors that result from genetic influences (eg, reflexes) demonstrate the effects of heredity.The environment, sometimes called nurture, comprises all nongenetic influences (eg, parenting, nutrition) on behavior. Behaviors learned from the environment (eg, how to paint) demonstrate environmental influences.Many traits and behaviors are a result of the interaction between these factors. For example, an individual's height is determined by both the genetic information passed down from their biological parents as well as the influence of their environment, such as the nutrition they received as a child.1.1.02 The Evolutionary Perspective and Natural Selection[ 1.1.A.2 ]The theory of natural selection describes how traits beneficial to a species' survival are more likely to be passed to subsequent generations.The environment determines which physical (eg, camouflage coloring) and behavioral (eg, innate fear of predators) traits promote survival and reproduction of a species. With each subsequent generation, beneficial traits (eg, camouflage coloring, innate fear of predators) become more common, allowing the species to adapt to its environment. An example of the process of natural selection is shown in Figure 1.1.

Unit 1: Biological Bases of BehaviorFigure 1.1 The theory of natural selection.The evolutionary perspective (or approach) in psychology emphasizes the impact of natural selection on behavior: traits beneficial to survival (eg, strong bonding between infants and caregivers) are more likely to be passed on to the next generation. For example, an evolutionary psychologist may investigate the role of natural selection in infant and caregiver attachment.

Unit 1: Biological Bases of BehaviorEugenicsEugenics is a controversial philosophy that aims to prevent the reproduction of individuals possessing traits seen as disadvantageous (eg, lower intelligence), while encouraging the reproduction of individuals possessing traits seen as advantageous (eg, higher intelligence). Eugenics inspired a number of harmful and discriminatory public policies in the 1900s, such as sterilization laws that targeted individuals with intellectual disabilities.1.1.03 Research on the Influence of Heredity and the Environment[ 1.1.A.3 ]Researchers investigate the influence of heredity and the environment using family studies, twin studies, and adoption studies. These studies compare siblings or parents and their children to identify the effects of genetic versus environmental factors on traits or behaviors.Adopted children share genes with biological parents but an environment with adoptive parents. Researchers can see whether adopted children resemble their biological or adoptive parents more to determine the relative role of genetic (ie, biological parents) or environmental (ie, adoptive parents) influences on behavior. For example, an adopted child resembling their biological parents more in intelligence suggests a stronger genetic influence because adopted children share genes, not an environment, with biological parents.Although they are rare, twin adoption studies can help further clarify the role of heredity and the environment for complex human traits. Identical twins raised together share the same genes and an extremely similar environment (eg, same household, same schools, similar experiences), so it is not possible to determine if similar traits are the result of genetics, environment, or a combination of the two.However, if identical twins are raised apart, traits that they share are most likely determined by genetics, whereas traits that are more similar to those of their adoptive families are most likely determined by environmental influences (see Figure 1.2).Figure 1.2 Identical twins raised together versus apart.

Unit 1: Biological Bases of BehaviorTopic 1.2Overview of the Nervous System1.2.01 The Central Nervous System[ 1.2.A.1 ]The nervous system is responsible for the regulation and integration of all body systems. Information from inside and outside the body is received and processed by the nervous system, which then coordinates purposeful reactions to this information.Cells of the nervous system include both neurons and glial cells (also called glia). Neurons are responsible for sending signals to other cells, and glial cells provide support functions to neurons and the nervous system (eg, by providing protection) (see Sub-Topic 1.3.01).The nervous system can be broadly divided into two major branches, the central and the peripheral nervous systems (Figure 1.3). The peripheral nervous system (PNS) comprises the neurons and glia located outside the brain and spinal cord (see Sub-Topic 1.2.02). Figure 1.3 Divisions of the nervous system.

Unit 1: Biological Bases of BehaviorThe central nervous system (CNS) (Figure 1.4) consists of the brain and spinal cord and is responsible for integrating information from the PNS. The PNS relays both sensory information to the CNS and motorcommands from the CNS.Figure 1.4 The central nervous system.1.2.02 The Peripheral Nervous System[ 1.2.A.2 ]The peripheral nervous system (PNS), the neurons and glia outside the brain and spinal cord, has two branches: the somatic nervous system and the autonomic nervous system (Figure 1.5). The somatic nervous system includes the sensory neurons that relay information from the body to the central nervoussystem (CNS) and the motor neurons that relay commands from the CNS to the body.

Unit 1: Biological Bases of BehaviorFigure 1.5 Divisions of the peripheral nervous system.Specifically, somatic sensory neurons transmit impulses from receptors in the skin, muscles, and joints to the spinal cord. In the context of the somatic nervous system, these sensory neurons that send signals toward the CNS are also referred to as afferent neurons.The somatic motor neurons transmit impulses from the spinal cord to the skeletal muscles, allowing individuals to consciously perform specific movements. As a result, all movements carried out on a voluntary basis (eg, walking, talking) involve the somatic nervous system. The somatic motor neurons that carry messages away from the CNS are also referred to as efferent neurons (Figure 1.6).Figure 1.6 Somatic sensory and motor neurons.

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