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INTRODUCTION TO THE NERVOUS SYSTEM Functions of the Nervous System Organization of the Nervous System Nervous Tissue: Support Cells & Neurons Support cells in the CNS are grouped together as “neuroglia” Function: to support, insulate, and protect neurons 1. Astrocyte 2. Microglial Cells 3. Ependymal Cells 4. Oligodendrocytes Anatomy of a Neuron Structure of Schwann Cells Where are the Neuron Cell Bodies? Most neuron cell bodies are found in the central nervous system Gray matter—cell bodies in clusters called “nuclei” White matter – dense collections of myelinated fibers called “tracts” Ganglia—collections of cell bodies in the peripheral nervous system Neuron Classification Functional Classification of Neurons Free nerve endings Meissner’s corpuscles Proprioceptors Golgi tendon Lamellar corpuscles Muscle spindle Structural Classification of Neurons Multipolar neurons—many extensions from the cell body Structural Classification of Neurons Bipolar neurons—one axon and one dendrite Structural Classification of Neurons Unipolar neurons—have a short single process leaving the cell body Nerve Impulses Also known as “Action Potentials” All-or-Nothing If the action potential starts, it is propagated (carried) over the entire axon Impulses travel faster when fibers have a myelin sheath What is an “Action Potential”? It starts with a neuron at “resting potential” What is an “Action Potential”? A stimulus causes Na+ to come in through a small patch of membrane What is an “Action Potential”? The action potential “propagates” What Happens at the End of the Neuron? There is transmission of a signal across the synapse Axon Axon of transmitting terminal neuron Vesicles Action potential arrives Synaptic cleft Receiving neuron Synapse What Happens at the End of the Neuron? How Does the Neuron Get Back to “Normal”? Through the process of “repolarization”