Lecture_Notes_Chapter_48 - Chapter 48 Nervous Systems The...

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Chapter 48: Nervous Systems The human brain contains an estimated 100 billion nerve cells, or neurons Each neuron may communicate with thousands of other neurons Functional magnetic resonance imaging is a technology that can reconstruct a three- dimensional map of brain activity The results of brain imaging and other research methods reveal that groups of neurons function in specialized circuits dedicated to different tasks Unlike a computer hard drive, where information belonging to the same file of program can be dispersed over the entire data carrier Nervous systems consist of circuits of neurons and supporting cells All animals except sponges have some type of nervous system What distinguishes the nervous systems of different animal groups is how the neurons are organized into circuits Organization of Nervous Systems The simplest animals with nervous systems, the cnidarians have neurons arranged in nerve nets Sea stars have a nerve net in each arm connected by radial nerves to a central nerve ring in simple cephalized animals, such as flatworms a central nervous system (CNS) is evident Annelids and arthropods have segmentally arranged clusters of neurons called ganglia These ganglia connect to the CNS and make up a peripheral nervous system (PNS) Nervous systems in molluscs correlate with the animals’ lifestyles Sessile molluscs have simple systems while more complex molluscs have more sophisticated systems In vertebrates the central nervous system (CNS) consists of a brain and dorsal spinal cord The peripheral nervous system (PNS) connects to the CNS Information Processing Nervous systems process information in three stages: o Sensory input, integration, and motor output Sensory neurons transmit information from sensors that detect external stimuli and internal conditions Sensory information is sent to the CNS where interneurons integrate the information Motor output leaves the CNS via motor neurons which communicate with effector cells
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The three stages of information processing are illustrated in the knee-jerk reflex Neuron Structure Most of a neuron’s organelles are located in the cell body. The neuronal cell bodies may be distant from nerve terminals (=synapses) Concentrations of nerve cell bodies near the spinal cord of mammals are called ganglia Most neurons have dendrites o Highly branched extensions that receive signals from other neurons The axon is typically a much longer extension that transmits signals to other cells at synapses o That may be covered with a myelin sheath Neurons have a wide variety of shapes that reflect their input and output interactions Supporting Cells (Glia) Glia are supporting cells that are essential for the structural integrity of the nervous system and for the normal functioning of neurons In the CNS, astrocytes provide structural support for neurons and regulate the extracellular concentrations of ions and neurotransmitters
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This note was uploaded on 09/28/2009 for the course BIOL 172 taught by Professor Staff during the Spring '08 term at Hawaii.

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Lecture_Notes_Chapter_48 - Chapter 48 Nervous Systems The...

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