Study Guide for Chapter 44

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University of Toronto Scarborough
Biological Sciences
Mary Olaveson

Chapter 44 Neurons and Nervous System -Nervous system is composed of two unique categories of cells: nerve cells or neurons and glial cells or glia -Neurons are excitable: they can generate and propagate electrical signals, which are known as nerve impulses, or action potentials -Most neurons have long extensions called axons that enable them to conduct action potentials over long distances. -Glial cells do not conduct action potentials: rather, they support neurons physically, immunologically, and metabolically Nerve- is a bundle of axons that come from many different neurons -Networks include three functional categories of called which can be though of as being involved with sensory input, integration and motor output: 1) Afferent neurons carry sensory information into the nervous system. That system comes from specialized sensory neurons that transduce (convert) various kind of sensory input into action potentials 2) Efferent neurons carry commands to physiological and behavioral effectors such as muscles and glands 3) Third category of cells called interneurons integrate and store information and facilitate communication between sensory and effectors CNS- brain and spinal cord - Information is transmitted from the sensory cells to the CNS and from the CNS to effectors via neurons that extend or reside outside of the brain and the spinal cord; these neurons and their supporting cells are called the PNS Figure 44.1 Nervous system Vary in Size and Complexity Nerve Net- serves simple behaviors such as contraction and relaxation Sea anemone Ganglia- in each segment coordinate movement and an anterior brain controls more complex behavior earthworm Specialized ganglia- in squid, more complex behaviors are served by collections of Neurons Synapses- information is passed from one neuron to another where they come into close proximity at structures called synapses Presynaptic neuron-the cell that sends the message Postsynaptic neuron- the cell that receives information from 1000 or more synapses -Most neurons have four regions: - A cell body contains the nucleus and most of the cells organelles - Dendrites many projections may sprout form the cell body, where these projections are shrub like dendrites, which bring information from other neurons or sensory cells to the cell body - Axons the longest projection that usually carries information away from the cell body
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