CH48 - Chapter 48: The Nervous System Nervous Systems in...

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Chapter 48: The Nervous System Nervous Systems in General Simple animals like hydra have a nervous system arranged in a diffuse network called nerve nets There is no centralization (no part of the network is any more important than any other part) More complex animals have nerve nets as well as nerves , which are bundles of fiberlike extensions of neurons. Sea stars, for example, have a central nerve ring tat has nerves that extend out to nerve nets in each arm The most complex animals have a Central Nervous System (CNS) usually located at the anterior. The development of this primary, controlling part of the nervous system is called cephalization Nerves that connect the CNS with the rest of the body are part of the peripheral nervous system (PNS) The Brain and Spinal Cord in humans is an example of a CNS Information Processing In general there are three stages of information processing by nervous systems 1. Sensory Input : sensory neurons transmit information from external stimuli (light, sound, touch, heat, smell, and taste) and internal conditions (blood pressure, blood CO 2 level, and muscle tension, for example). This info is sent to the CNS for processing. 2. Integration : In the CNS, interneuron analyze and interpret the sensory input taking into account the immediate context and what happened in the past. The CNS the decides how to respond. 3. Motor Output : leaves the CNS via motor neurons to effector cells which can be either muscle cells or endocrine glands, which then do something (move or release hormones, for example) Neuron Structure The ability of neurons to receive and transmit information depends on their elaborate
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CH48 - Chapter 48: The Nervous System Nervous Systems in...

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