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chap48studyguide - Chapter 48 Nervous Systems Study Guide...

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Chapter 48 Nervous Systems Study Guide Overview: Command and Control Center The human brain contains an estimated 10 11 (100 billion) neurons. ° Each neuron may communicate with thousands of other neurons in complex information- processing circuits. Recently developed technologies can record brain activity from outside the skull. ° One technique is functional magnetic resonance imaging (fMRI), which reconstructs a 3- D map of the subject’s brain activity. ° The results of brain imaging and other research methods show that groups of neurons function in specialized circuits dedicated to different tasks. The ability of cells to respond to the environment has evolved over billions of years. The ability to sense and react originated billions of years ago with prokaryotes that could detect changes in their environment and respond in ways that enhanced their survival and reproductive success. ° Such cells could locate food sources by chemotaxis. Later, modification of this simple process provided multicellular organisms with a mechanism for communication between cells of the body. By the time of the Cambrian explosion, systems of neurons that allowed animals to sense and move rapidly had evolved in essentially modern form. Concept 48.1 Nervous systems consist of circuits of neurons and supporting cells Nervous systems show diverse patterns of organization. All animals except sponges have some type of nervous system. What distinguishes nervous systems of different animal groups is how the neurons are organized into circuits. Cnidarians have radially symmetrical bodies organized around a gastrovascular cavity. ° In hydras, neurons controlling the contraction and expansion of the gastrovascular cavity are arranged in diffuse nerve nets. The nervous systems of more complex animals contain nerve nets, as well as nerves, which are bundles of fiberlike extensions of neurons. With cephalization come more complex nervous systems.
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° Neurons are clustered in a brain near the anterior end in animals with elongated, bilaterally symmetrical bodies. In simple cephalized animals such as the planarian, a small brain and longitudinal nerve cords form a simple central nervous system (CNS). In more complex invertebrates, such as annelids and arthropods, behavior is regulated by more complicated brains and ventral nerve cords containing segmentally arranged clusters of neurons called ganglia. ° Nerves that connect the CNS with the rest of the animal’s body make up the peripheral nervous system (PNS). Nervous systems consist of circuits of neurons and supporting cells. In general, there are three stages in the processing of information by nervous systems: sensory input, integration, and motor output.
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