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by: De Vs

Neurons BIL360

De Vs
GPA 3.6
Comparative Physiology
Dr. DuBois

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About this Document

This study guide covers the material from the Neurons chapter for Dr. Dubois' comparative physiology class. The vocabulary terms are defined and the study questions are answered.
Comparative Physiology
Dr. DuBois
Study Guide
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This 5 page Study Guide was uploaded by De Vs on Wednesday February 25, 2015. The Study Guide belongs to BIL360 at University of Miami taught by Dr. DuBois in Spring2014. Since its upload, it has received 108 views.

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Date Created: 02/25/15
CHAPTER 12 NEURONS Integration processes that produce coherency and harmonious function Combo of sensory endocrine and CNS info that promote functioning of whole organism Neuron a cell that generates electrical signals in brief self propagating impulses AP Some performs sensory functions in response to stimuli or generate nerve impulses of their own Signals are fast and addressed Dendrite where synapses are found Branching processes Cell Body Soma integration Where signal integration and impulse generation occur The cell membrane combines inhibitory and excitatory synaptic inputs If excitatory surpasses then more AP are produced d Axon conduction Propagates AP along its length Synapse ceIIceII contact points where sensory ceIIs receive input On dendrites of cell body Synapse allows for transmission of info btwn neurons thru converting a signal from electrical to chemical back to electrical Axon Hillock rst segment leaving cell body for AP initiation Axon Initial Segment where the AP is initiated Presynaptic Terminals where axon ends and divides into terminals where the output occurs Terminals form synapse with other neurons or cells An AP arriving at the terminal releases neurotransmitter across synapses to exert an excitatory or inhibitory effect on the target cell Neurotransmitter chem substance released into the synaptic cleft space btwn cells after an impulse arrives at a synapse from the presynaptic cell It binds to neurotransmitter receptors and make new electric impulse in the target neuron Afferent Neurons relay sensory signals to integrative centers of the CNS toward Efferent Neurons relay control signals instructions from the CNS to target cells like muscle or secretory lnterneurons neurons entirely within the CNS CNS central nervous system Brain and spinal cord in vertebrates PNS peripheral nervous system Myelin vertebrate large axons surrounded by myelin sheaths which are wrappings of glial cells that increase speed of impulses Increases resistance and decreases capacitance Increases conduction velocity by increasing axon length constant without increasing time constant Nodes Of Ranvier gaps where glial wrappings are absent along an axon In myelinated axons AP occur only at nodes where there are Na channels lnternodes the region btwn nodes that is covered by myelin Saltatory Conduction exhibited by myelinated axons AP jumps from node to node wo active propagations in the internode Glial Cell Neuroglia cells that surround neurons support cells of the nervous system a Schwann Cell PNS form the myelin sheath on axon b Oligodendrocyte CNS Form sheath c Astrocytes CNS Boundary btwn capillaries and neurons Take up neurotransmitters and regulate ion conc d Microglial Cells mediate immune responses in neural tissue May act as phagocytes Ion have net charge with unequal of protons and electrons Electric Current net movement of charges I Voltage separation of and charges V aka potential difference Resistance ohms limits current ow across membrane R in a membrane ions must ow thru channels Capacitance farads F ability to store electric charge A membrane has insulating properties in the biayer Passive Electrical Properties R and C passive responses are universal and the cells electrical properties don39t change Passive properties are conditions in which membrane resistance doesn39t change Resting Membrane Potential Vm inner membrane is negative Largely determined by K since membrane is more permeable to K than other ions Depolarization Iess negative inside ceII Decrease in the membrane potential Hyperpolarization more negative Increase in membrane potential Ohm39s Law deltaVIR Graded Potential deIta V change in potential Passive Spread Electrotonic Conduction voltage change will decrease with distance As a current ows along the inside of the axon some of it leaks out thru ion channel Nernst Equation relation btwn conc difference of a permeating ion across a membrane and the membrane potential at equilibrium The larger the conc difference across the membrane the larger the membrane potential at which the ion species is in equilibrium Increase conc difference increases conc gradient of the ion and increases force needed to oppose it Equilibrium Potential 58mV is equilibrium potential for K value of membrane potential at which K ions are at equilibrium and internal K conc is ten times external conc Goldman Equation membrane potential produced by several permeating ions Action Potential major electrical signal of excitable cells from voltage dependent changes in membrane permeabilites to ions Initiated by change in resting membrane potential a depolarization strong enough to open voltage gated channeIs Momentary reversal of membrane potential from 65mV to 40mV Propagate rapidIy wo degradation over long distances Results from intense IocaIized increases in permeability to speci c ions Voltage Threshold AP triggered by depolarization of membrane that reaches a critical value of depolarization AllOrNone Phenomenon depolarization below threshold makes no impulse but all suprahreshold depolarizations do Absolute amp Relative Refractory Periods after AP is produced another one cant be generated for at least 1ms And it is harder to generate for a few milliseconds longer Therefore impulses cant summate Inactivation Of Na Channels when Na channels are inactivated during the falling phase to decrease permeability to Na Hodgkin Cycle produces rising phase of AP Initial depolarization and opening of Na channels increase PNa Increased Na ow into membrane further depolarization 1 Describe the anatomical structure and functional regions of a neuron Include dendrites cell bodysoma Nissl substance axon axon initial segment myelin sheath axon terminals synapse Dendriteinput Cell bodyintegration and impulse generation Axon hillock initial segment Axonconduction and propagation Axon divides into Presynaptic terminasoutput 2 What is the central nervous system Peripheral nervous system Afferent neurons Efferent neurons Interneurons Afferent neurons bring signals to the CNS Efferent neurons take signals to target cells and Interneurons are only in the CNS CNS is the brain and spinal cord PNS is nerves outside of CNS that connects organs to brain 3 What are glial cells What are the important glial cells and what is their function 0 They are nonneural cells that surround neurons 1 Microglial mediate immune responses in neurons 2 Astrocyte in the CNS Regulates ion conc supports neurons takes up neurotransmitters makes blood brain barrier and lines capillaries 3 Schwann cells form sheaths around axons in PNS 4 Oligodendrites sheaths in CNS 4 Be familiar with basic electrical concepts ions current voltage resistance capacitance What passive electrical properties are exhibited by cell membranes 0 Passive properties are resistance membranes limit current ow and capacitance ability to store charge 5 What is the resting membrane potential How might a current generated by an electrode disrupt this What is depolarization Hyperpolarization How is this related to Ohm39s law Resting potential is 65mV Inserting a current alters membrane potential it should change membrane potential by an amount proportional to the resistance and current ow ohms law Depolarization is less negative and hyperpolarization is more negative 10 11 12 13 What is passive spread Voltage change will decrease over distance How is the insidenegative resting membrane potential of living cells established What factors determine Vm Maintained by permeability to diff ions and creation of charge separation of K K diffuses down conc gradient out of cell and accumulates at outer surface All cells have more K inside and more Na outside 0 Sodium potassium pump determines Vm What is the Nernst equation How is it used What is a limitation of the Nernst equation Nerst eq tells membrane potential at equil for particular ions only for one ion 0 the larger the conc difference across a membrane the larger to equilibrium membrane potential What is the Goldman equation How is it used What is the purpose of weighting the contributions of different ion species Tells membrane potential with many ions the more permeable an ion the greater its effect What is an action potential Be able to describe the basic stages of an action potential in terms of changes in membrane potential What is the allor none aspect of action potentials What is the absolute refractory period Relative refractory period 0 AP triggered by depolarization that reaches the voltage threshold Rising phase overshoots zero gets more positive and further depolarizes Falling phase repolarization hyperpolarization Membrane remains highly permeable to K for a brief period making undershoot After AP is made there cant be another one for 1 ms refractionary period it is also hard to make another for a few seconds longer absolute refractionary period c All or none means that depolarization must meet the threshold or else it wont work Describe the changes in ion channels and membrane permeabilities to ions that occur during the stages of an action potential Note voltagedependence and timedependence of these changes 0 Increased permeability to Na caused by opening of voltagegated channels Makes polarity reversal Decreased permeability to Na caused by inactivation of Na channels Then K channels open and K ows out driving membrane to Ek Increased permeability to K caused by slower opening of voltagegated channels What is the Hodgkin cycle What phase of an action potential does the Hodgkin cycle desc be Describes the rising phase of AP in a positive feedback loop 0 Initial depolarization and opening of Na channels increase PNa Increased Na ow into membrane further depolarization more positive How are action potentials propagated down an axon in one direction via local currents They are propagated since an AP at one location can initiate an AP at a neighboring location by setting up local circuits of current ow 14What factors affect the speed of action potential propagation and how What is saltatory conduction Velocity of conduction increases with increased axon diameter Myelination increases conduction velocity Salutatory conduction is jumping from node to node which are gaps in myelin Increased temperature increases velocity


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