Chapter 3 The Biological Bases of Behavior Communication in the Nervous System * Nervous Tissue: The Basic Hardware * Neurons are individual cells in the nervous system that receive, integrate, and transmit information. * The soma, or cell body, contains the cell nucleus and 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. * The axon ends in a cluster of terminal buttons, which are small knobs that secrete chemicals called neurotransmitters. The Neural Impulse: Using Energy to Send Information * The Neuron at Rest: A Tiny Battery * The resting potential of a neuron is its stable, negative charge when the cell is inactive. * The Action Potential * An action potential is a very brief shift in a neuron’s electrical charge that travels along an axon. * The absolute refractory period is the minimum length of time after an action potential during which another action potential cannot begin. * The All-or-None Law * The neural impulse is an all-or-none proposition. * The Synapse: Where Neurons Meet * Sending Signals: Chemicals as Couriers The synaptic cleft is a microscopic gap between the terminal button of one neuron and the cell membrane of another neuron. * Neurotransmitters are chemicals that transmit information from one neuron to another. * Receiving Signals: Postsynaptic Potentials * Postsynaptic potential is a voltage change at a receptor site on a postsynaptic cell membrane. * Reuptake is a process in which neurotransmitters are sponged up from the synaptic cleft by the presynaptic membrane. * Integrating Signals: A Balancing Act * The elimination of old synapses appears to play a larger role in the sculpting of neural networks than the creation of ney synapses. Neurotransmitters and Behavior * Acetylcholine * An agonist is a chemical that mimics the action of a neurotransmitter. * An antagonist is a chemical that opposes the action of a neurotransmitter. * Monoamines * They are three neurotransmitters: dopamine, norepinephrine, and serotonin. * Endorphins * Endorphins are internally produced chemicals that resemble opiates in structure and effects. Organization of the Nervous System * The Peripheral Nervous System * The peripheral nervous system is made up of all those nerves that lie outside the brain and spinal cord. The Somatic Nervous System * The somatic nervous system is made up of nerves that connect to voluntary skeletal muscles and to sensory receptors. * Afferent nerve fibers are axons that carry information inward to the central nervous system from the periphery of the body. * Efferent nerve fibers are axons that carry information outward from the central nervous system to the periphery of the body. * The Autonomic nervous System * The autonomic nervous system is made up of nerves that connect to the heart, blood vessels, smooth muscles, and glands. * The Central Nervous System The central nervous system consists of the brain and spinal cord. The Brain and Behavior * The Hindbrain * The hindbrain includes the cerebellum and two structures found in the lower part of the brainstem: the medulla and the pons. * The Midbrain * The midbrain is the segment of the brainstem that lies between the hindbrain and the forebrain. * The Forebrain * The forebrain is the largest and most complex region of the brain, encompassing a variety of structures, including the thalamus, hypothalamus, limbic system, and cerebrum. * The Thalamus: A Way Station The thalamus is a structure in the forebrain through which all sensory information (except smell) must pass to get to the cerebral cortex. * The Hypothalamus: A Regulator of Biological Needs * The hypothalamus is a structure found near the base of the forebrain that is involved in the regulation of basic biological needs. * The Limbic System: The Seat of Emotion * The limbic system is a loosely connected network of structures located roughly along the border between the cerebral cortex and deeper subcortical. * The Cerebrum: The Seat of Complex Thought The cerebral cortex is the convoluted outer layer of the cerebrum. * The cerebral hemispheres are the right and left halves of the cerebrum. * The corpus callosum is the major structure that connects the two cerebral hemispheres. * The Plasticity of the Brain * First, studies have shown that aspects of experience can sculpt features of brain structure. * Second, research has shown that damage to incoming sensory pathways or the destruction of brain tissue can lead to neural reorganization. * Third, recent studies indicate that the adult brain can generate new neurons.
Right Brain/Left Brain: Cerebral Specialization * Bisecting the Brain: Split-Brain Research * In split-brain surgery the bundle of fibers that connects cerebral hemispheres (the corpus callosum) is cut to reduce the severity of epileptic seizures. * Hemispheric Specialization in the Intact Brain * If you are right handed, you use your left hemisphere. * If you are left handed, you use your right hemisphere. The Endocrine System: Another Way to Communicate * The endocrine system consists of glands that secrete chemicals into the bloodstream that help control bodily functioning. Hormones are the chemical substances released by the endocrine glands. * The pituitary gland releases a great variety of hormones that fan out within the body, stimulating actions in the other endocrine glands. Heredity and Behavior: Is It All in the Genes? * Basic Principles of Genetics: * Chromosomes are threadlike strands of DNA molecules that carry genetic information. * Genes are DNA segments that serve as the key functional units in hereditary transmission. * Polygenic traits are characteristics that are influenced by more than one pair of genes. Detecting Hereditary Influence: Research Methods * Family Studies * In family studies researchers assess hereditary influence by examining blood relatives to see how much they resemble one another on a specific trait. * Twin Studies * In twin studies researchers assess hereditary influence by comparing the resemblance of identical twins and fraternal twins with respect to a trait. * Adoption Studies * Adoption studies assess hereditary influence by examining the resemblance between adopted children and both their biological and their adoptive parents. * The Interplay of Hereditary and Environment Environment can easily effect whether or not a person gets a certain disorder or personality trait, regardless of heredity. The Evolutionary Bases of Behavior * Darwin’s Insights * Fitness refers to the reproductive success (number of descendants) of an individual organism relative to the average reproductive success on the population. * Natural Selection posits that heritable characteristics that provide a survival or reproductive advantage are more likely than alternative characteristics to be passed on to subsequent generations and thus come to be “selected” over time. Subsequent Refinements to Evolutionary Theory * An adaption 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 The Key Findings on Neural Development * A critical period is a limited time span in the development of an organism when it is optimal for certain capacities to emerge because the organism is especially responsive to certain experiences.