KIN 292 1st Edition Lecture 16 These come from the slideshows provided by the professor and include extra notes and explanations Highlighted or bolded information are things that I believe to be information that is important to look over multiple times The notes in red are my personal additions and quotes of Professor Starnes from the class lecture Outline of Last Lecture I 21 6 Thermoregulation continued II 21 7 Hormonal Regulation of Growth III 21 8 Thyroid Hormones IV 21 9 Glucocorticoids Outline of Current Lecture I 7 1 Overview of the Nervous System II 7 2 Cells of the Nervous System III 7 3 Establishment of the Resting Membrane Potential IV 7 4 Electrical Signaling Through Changes in Membrane Potential V 7 5 Maintaining Neural Stability Current Lecture Structure of a neuron 1 Dendrites receive incoming information usually lots of them 2 Cell body soma houses nucleus etc 3 Axon hillock AP generated here 4 Axon could be short or long 5 Axon Terminals store releases neurotransmitter that diffuses across synapse An example of a multipolar neuron multiple projections from Cell body soma Most common neuron These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute Transport in Neurons Enzymes vesicles etc are synthesized in cell body and transported to axon terminals through microtubules and neurofilaments Kinesins name origin shared with kinesiology Anterograde transport soma to axon terminal Retrograde transport axon to soma Fast transport shown moves vesicles at 100 400 mm day Slow transport moves smaller molecules 0 5 40 mm day Specialized transport systemsneeded due to length of axon Very Tidy Arrangement of Neurons those with similar functions tend to be grouped together Nuclei Grouping of cell bodies in CNS Pathways tracts commissures Bundle of axons traveling together in CNS Ganglia Grouping or cluster of cell bodies in PNS Nerves Bundle of axons traveling together in PNS Glial Cells 90 of all cells in the nervous system Glia Latin meaning glue Four types Astrocytes ch 9 location CNS Microglia ch 9 location CNS Oligodendrocytes form myelin on CNS axons Schwann cells form myelin on PNS axons only glial cell located inPNS Formation and origins of myelin sheaths Myelin sheath greatly enhances velocity of AP but limits ion movement across the cell membrane Most ion movement occurs within Nodes of Ranvier CNS one oligodendrocyte sends out projections providing myelin segments for several axons PNS each Schwann cell provides myelin for only a single axon 7 3 Resting Membrane Potential Establishment Why do we care Because electrical signaling occurs through changes in membrane potential Vm and resting potential is the base cell is not sending or receiving signals The resting Vm depends on the concentration gradients of all ions across the plasma membrane and the permeability of the membrane for those ions All cells have a resting membrane potential 5 mV to 100 mV More negative charges inside than outside Resting membrane potential of neurons excitable cells Approximately 70 mV Equilibrium Potential for a cell freely permeable to a single ion Nernst Eq ch 4 Equilibrium exists when there is no net force to move ion across the membrane Electrochemical force 0 EK 61 mV log 4 mM 94 mV 140 mM ENa 61 mV log 145 mM 60 mV 15 mM Resting Membrane Potential of Typical Neuron Neurons have sodium and potassium Leak channels that are always open and selectively permeable to their respective ion Many more K leak channels than Na channels making cell about 25 times more permeable to K Ion Let s see what happens when we have 2 ions freely permeable instead of just one Nernst Eq does not apply when more than one ion freely diffusing Outside cell high sodium and chloride Inside cell high potassium and organic anions Figure 7 10 Establishing a steady state resting membrane potential Due to membrane being more permeable to K K flows out faster than Na flows in membrane potential develops Electrical forceopposesoutflow of K and favorsinflow of Na K outflow slows down Na inflow speeds up Eventuallymembranepotential stabilizes Na K pump counteracts leakage flows maintains Na and K gradients steady state At this point K outflow and Na inflow are equal They are still moving because 70 mV is different from their equilibrium constants Resting Vm Contributors o 1 K and Na diffusion o 2 Permeability difference in K Na o 3 Na K pump Resting Membrane Potential The resting membrane potential is closer to the potassium equilibrium potential Why Under what condition would resting Vm be midway between EK andENa A Neuron at Rest Small Na leak at rest high force because Vm far away from ENa low permeability Small K leak at rest low force high permeability Sodium pump returns Na and K to maintain gradients The strength of the net force increases the farther away the membrane potential is from the equilibrium potential 7 4 Electrical Signaling Through Changes in Membrane Potential Describing changes in membrane potential Graded potentials Action potentials Propagation of action potentials Figure 7 11 Changes in membrane potential Electrical signals occur due to Vm moving away from resting Vm when certain gated channels open or close in response to particular stimuli Resting Vm is the reference point Electrical Signals Neurons Types of gated channels Voltage gated Open or close in response to changes in membrane potential Ligand chemically gated Open or close in response to ligand binding Mechanically gated Open or close in response to mechanical force Associated with some sensory and visceral receptors Figure 7 13 Decremental property of graded potentials Small temporary change in membrane potential Magnitude varies graded with stimulus strength and weakens as distance away from stimulus increases Can be excitatory depoloarization shown or inhibitory hyperpolarization Graded Potentials Ligand or mechanical stimulus Examples neurotransmitter touch Action Potentials generated when voltage gated Na channels open at threshold voltage Action potential of excitable membranes Rapid large depolarization is used for communication All or none It either occurs or does not if graded potentials do not reach threshold Stronger stimuli increase frequency of APs but not magnitude of an individual AP Action potentials travel along axons from the cell body to the axon terminal or if an afferent neuron from the receptor to the terminal