Lecture+17+-+Neuronal+Structure%2C+Function+and+Diversity+II (1)

Lecture+17+-+Neuronal+Structure%2C+Function+and+Diversity+II (1)

Info icon This preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: Wednesday’s Class NEURONAL STRUCTURE, FUNCTION & DIVERSITY II Chapter 5 pp. 162-­‐174 Chapter 4 pp. 142-­‐160 Important Deadlines Problem Set #2 – Available 5pm Today April 20th •  Closes Wednesday April 27th, 11:59PM •  ONE SUBMISSION ONLY (save and don’t submit unWl ready) •  Answers will only be revealed aZer quiz closes •  4% of total grade/ Problem Set •  BE SURE TO SUBMIT YOUR ANSWERS BY DEADLINE! What you should be able to do by the end of today’s lecture •  Explain the nature of the membrane potenWal and the factors that influence it. •  Sketch and label a typical nerve, discuss the funcWon of each region, and appreciate the nature of diversity in neuron structure. •  DisWnguish between graded potenWals and acWon potenWals. •  Understand how ligand-­‐gated channels and voltage-­‐gated affect electrical events and ion movements, recognizing the importance of electrochemcial gradients. Neural Zones (e.g. Motor neuron) •  Four funcWonal zones •  1. Signal recep.on –  Dendrites and the cell body (soma) –  Incoming signal received and converted to change in membrane poten.al •  2. Signal integra.on –  Axon hillock –  Strong signal is converted to an ac.on poten.al (AP) •  3. Signal conduc.on –  Axon (some wrapped in myelin sheath) –  AP travels down axon •  4. Signal transmission –  Axon terminals –  Release of neurotransmi=er Principles in Animal Physiology, Figure 5.2 Signals in the Dendrites & Cell Body •  Incoming signal –  Example: neurotransmiher •  Membrane-­‐bound receptors bind to neurotransmiher –  Receptors transduce the chemical signal to an electrical signal by changing ion permeability of membrane –  Change in ion permeability causes change in membrane potenWal (graded poten.al) Changes in membrane potenWal •  Graded: –  Amount of voltage change is proporWonal to current applied –  DepolarizaWon •  Two sides of membrane become more equally charged (MP becomes less –ve) –  HyperpolarizaWon •  Two sides of membrane become less equally charged (MP becomes more –ve) –  Sub-­‐threshold to elicit all-­‐or-­‐none response •  All-­‐or-­‐none: –  Membrane potenWal change above a threshold elicits a massive depolarizaWon (acWon potenWal) Graded PotenWals •  Vary in magnitude (graded) depending on strength of sWmulus –  More neurotransmiher à more ion channels open à larger magnitude of graded potenWal •  DepolarizaWon –  Na+ or Ca2+ channels open •  HyperpolarizaWon –  K+ and Cl– channels open Principles in Animal Physiology, Figure 5.7 Graded PotenWals Graded PotenWals Travel Short Distances •  Conduc.on with decrement – ↓ strength with ↑ distance from opened ion channel •  Due to –  Leakage of charged ions across the membrane –  Electrical resistance of the cytoplasm –  Electrical properWes of the membrane •  Electrotonic current spread –charge spreads through the cytoplasm causing changes in membrane potenWal •  Can be excitatory or inhibitory Graded PotenWals Travel Short Distances Principles in Animal Physiology, Figure 5.8 AcWon PotenWals travel Long Distances •  CharacterisWcs of AcWon PotenWals: –  Triggered by net graded potenWal at axon hillock (trigger zone) –  Do not degrade over Wme or distance –  Travel long distances along membrane –  “All-­‐or-­‐none” •  Occurs or does not occur •  All APs of the same magnitude –  Must reach threshold poten.al to fire •  DepolarizaWons below threshold will not iniWate an acWon potenWal Neural Zones (e.g. Motor neuron) •  Four funcWonal zones •  1. Signal recep.on –  Dendrites and the cell body (soma) –  Incoming signal received and converted to change in membrane poten.al •  2. Signal integra.on –  Axon hillock –  Strong signal is converted to an ac.on poten.al (AP) •  3. Signal conduc.on –  Axon (some wrapped in myelin sheath) –  AP travels down axon •  4. Signal transmission –  Axon terminals –  Release of neurotransmi=er Principles in Animal Physiology, Figure 5.2 AcWon PotenWals are generated when net graded potenWals surpass threshold potenWal ResWng membrane potenWal of most neurons is -­‐70mV & threshold potenWal is -­‐55mV Subthreshold graded potenWals (less than +15mV) do not trigger an AP Graded potenWals that are at or above threshold potenWal (greater than +15mV) Principles in Animal Physiology, Figure 5.9 IntegraWon of Graded Signals No AcWon PotenWal Generated Axon hillock is the decision point Principles in Animal Physiology, Figure 4.8 IntegraWon of Graded Signals Threshold surpassed & AcWon PotenWal Generated Axon hillock is the decision point Principles in Animal Physiology, Figure 5.10 IntegraWon of Graded Signals •  Many graded potenWals can be generated simultaneously •  Many receptor sites •  Many kinds of receptors •  Temporal summa.on – graded potenWals that occur at slightly different Wmes can influence the net change •  Spa.al summa.on – graded potenWals from different sites can influence the net change Principles in Animal Physiology, Figure 5.11 AcWon PotenWals •  Occur only when membrane potenWal at axon hillock reaches threshold •  Three phases: –  DepolarizaWon –  RepolarizaWon –  HyperpolarizaWon •  Absolute refractory period –  Cell incapable of generaWng a new AP •  Rela.ve refractory period –  More difficult to generate new AP Principles in Animal Physiology, Figure 5.12 Voltage Gated Ion Channels •  Change shape due to changes in membrane potenWal –  Closed at resWng potenWal •  PosiWve feedback –  Influx of Na+ à local depolarizaWon à more Na+ channels open à more depolarizaWon •  Na+ channels open first (depolarizaWon) •  K+ channels open more slowly (repolarizaWon) •  Na+ channels close •  K+ channels close slowly –  relaWve refractory period caused by open K+ channels Principles in Animal Physiology, Figure 5.12 Na+ Channels have two gates •  AcWvaWon gate –  Voltage dependent –  Opens when membrane reaches threshold •  InacWvaWon gate –  Time-­‐dependent –  Closes aZer brief Wme Principles in Animal Physiology, Figure 5.14 RelaWonship between voltage-­‐ gated Na+ and K+ channels during an AP Principles in Animal Physiology, Figure 5.16 Neural Zones (e.g. Motor neuron) •  Four funcWonal zones •  1. Signal recep.on –  Dendrites and the cell body (soma) –  Incoming signal received and converted to change in membrane poten.al •  2. Signal integra.on –  Axon hillock –  Strong signal is converted to an ac.on poten.al (AP) •  3. Signal conduc.on –  Axon (some wrapped in myelin sheath) –  AP travels down axon •  4. Signal transmission –  Axon terminals –  Release of neurotransmi=er Principles in Animal Physiology, Figure 5.2 AcWon PotenWals are “Self PropagaWng” Principles in Animal Physiology, Figure 5.17 AcWon PotenWals are “UnidirecWonal” •  AcWon potenWals start at the axon hillock and travel towards the axon terminal •  “Up-­‐stream” Na+ channels (just behind the region of depolarizaWon) are in the absolute refractory period Principles in Animal Physiology, Figure 5.17 •  The absolute refractory period prevents backward (retrograde) transmission and summaWon of APs •  Rela.vely refractory period also contributes by requiring a very strong sWmulus to cause another AP Thursday’s Class NEURONAL STRUCTURE, FUNCTION & DIVERSITY III Chapter 5 pp. 174-­‐195 Chapter 4 pp. 160-­‐191 ...
View Full Document

{[ snackBarMessage ]}

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern