KIN 292 1st Edition Lecture 16These 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 - continuedII. 21.7 Hormonal Regulation of GrowthIII. 21.8 Thyroid HormonesIV. 21.9 GlucocorticoidsOutline of Current Lecture I. 7.1 Overview of the Nervous SystemII. 7.2 Cells of the Nervous SystemIII. 7.3 Establishment of the Resting Membrane PotentialIV. 7.4 Electrical Signaling Through Changes in Membrane PotentialV. 7.5 Maintaining Neural StabilityCurrent LectureStructure of a neuron:1. Dendrites – receive incoming information, usually lots of them2. Cell body (soma) houses nucleus ,etc3. Axon hillock -AP generated here4. Axon-could be short or long5. Axon Terminals – store & releases neurotransmitter that diffuses across synapse- An example of a multipolar neuron - multiple projections from Cell body(soma), Most common neuronThese 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 axonVery 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 PNSGlial 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 axon7.3 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 mVEquilibrium 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 themembrane•Electrochemical force = 0•EK = 61 mV × log 4 mM = –94 mV140 mM•ENa = 61 mV × log 145 mM = +60 mV 15 mMResting 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 KIon•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 anionsFigure 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 diffusiono 2. Permeability difference in K & Nao 3. Na+/K+ pumpResting 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 potential7.4 Electrical Signaling Through Changes in Membrane Potential•Describing changes in membrane potential•Graded potentials•Action potentials•Propagation of action potentialsFigure 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 pointElectrical 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 receptorsFigure 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