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This 3 page Class Notes was uploaded by Natasha on Saturday November 7, 2015. The Class Notes belongs to Biol 202 at St. Cloud State University taught by Schoenfuss, Heiko in Spring 2015. Since its upload, it has received 16 views. For similar materials see Human Anatomy and Physiology I in Biology at St. Cloud State University.
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Date Created: 11/07/15
Online Lecture The Nervous System The Structure of a Nerve Endoneurium surrounds each fiber the way a muscle fiber was surrounded by the epimysium The groups of fibers are bound into fascicles by perineurium The fascicles are bound together by epineurium and some blood vessels The Nervous Tissue: Neurons Neurons=nerve cells o Cells are specialized to transmit messages o There are two major regions of neurons 1. Cell body nucleus and metabolic center of the cell 2. Processes fibers that extend from the cell body The Average Neuron Dendrites that look like tree roots Synaptic terminal (axon terminal) communicates with the other cells Axon hillock is where all the information comes together The Neuron Anatomy Cell body o Nissil substancespecialized rough E.R o Neurofibrils intermediate cytoskeleton that maintains the cell shape (the cell is long and so it needs strength) o Large Nucleolus Extensions outside the cell body o Dendrites tree roots conduct impulses TOWARDS the cell body o Axons conduct impulses AWAY from the cell body (it will never go in the opposite direction) Axons and Nerve Impulses Axons end in axonal terminals Axonal terminals contain vesicles with neurotransmitters Axonal terminals are separated from the next neuron by a gap o Synaptic cleft always a small gap between adjacent neurons o Synapse junction between nerves o Synaptic terminal= axonal terminals Nerve Fiber Coverings Schwann cells produce myelin sheaths in a jellyroll like fashion or like little pieces of insulation Nodes of Ranvier gaps in the myelin sheath along the axon (small gaps between Schwann cells) Insulated copper wire copper wire = axon and the plastic around it= Schwann cell Neuron Cell Body Location Most are found in the central nervous system and have two materials o Gray matter cell bodies and unmylenated fibers o Ganglia collections of cell bodies that are outside the central nervous system Functional Properties of Neurons Irritability the ability to respond to stimuli Conductivity the ability to transmit an impulse Plasma membrane at rest is polarized o There are fewer positive ions inside the cell than outside the cell Starting a Nerve Impulse Depolarization a stimulus depolarizes the neuron’s membrane A depolarization membrane allows for the sodium to flow inside the membrane The exchange of ions initiates an action potential in the neuron The Action Potential If the action potential or nerve impulse starts, it is propagated over the entire axon It is an all or nothing response Potassium ions rush out of the neuron after sodium ions rush in and that repolarizes the membrane The sodiumpotassium pump restores the original configuration and this action requires ATP IMPORTANT CONCEPT (read in your text book) Look at the graph It takes 4 milliseconds before an action potential can fire again Threshold, stimulus, depolarization (or failed initiations), action potential, repolarization, refractory period, resting state Nerve Impulse Propagation The impulse continues to move toward the cell body Impulses travel faster when fibers have a myelinated sheath They cannot travel backwards It travels down to the synaptic end or axon terminal of the cell Schwann cells cannot exchange sodium and potassium ions that can only happen at the nodes of Ranvier Saltatory Impulse Conduction The impulse jumps (saltationLatin) from one Node of Ranvier to the next Stimulus can travel effectively and quickly down the length of the axon towards the axon terminal Continuation of the Nerve Impulse between Neurons Impulses are able to cross the synapse to another nerve o Neurotransmitter is released from a nerve’s axon terminal o The dendrite of the next neuron has receptors that are stimulated by the neurotransmitter o An action potential is started in the dendrite