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UVM NSCI 110 - Conduction Down the Axon
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NSCI 110 1st Edition Lecture 10 Outline of Last Lecture I. Hyperpolarization and depolarization both involve changes in membrane potentialII. An electrochemical gradient in a neuron is formed by contributions from ion diffusion and electrical gradientsIII. There are four key ions involved in giving a neurons its resting membrane potentialIV. Ion channels consist of membrane-spanning proteinsa. Cause the membrane to be porous and selectiveV. There are passive and active factors that contribute to generating an action potential down an axonVI. Each ion has a different permeability to the membraneVII. Equilibrium potential is the voltage at which the flow of a specific ion through a membrane is equal or balanced in both directionsOutline of Current Lecture I. Current and voltage clamps allow you to measure changes in membrane potential or current flow, respectivelyII. Self-propagation is a key property of neurons a. Once the action potential is initiated, it is able to move down the axon in an all-or-none fashionIII. Axon hillocks have the highest concentration of voltage-gated sodium channelsa. Conduction normally begins here and travels toward the terminal endb. Orthodromic vs. antidromic conductionIV. Saltatory conduction allows action potentials to travel rapidly down an axonV. Electrical properties at the synapsea. No electrical thresholdb. Graded (summation)c. Decremental responseCurrent LectureI. In the absolute refractory period, another action potential cannot occura. When it reaches the relatively refractory period, a second action potential can occur but it takes a stronger voltage than the initial amountII. Relating ion current flow to the parts of the action potentiala. Current clamp: allows you to measure changes in voltagei. Current being held constant (experimentally)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.ii. Allows you to measure changes in membrane potential (Vm)b. Voltage clamp: allows you to measure changes in ion currenti. Vm being held constantii. Allows you to measure the changes in current flowIII. Property of self-propagationa. Once the action potential is initiated, it is able to move down the axon in an all-or-none fashionb. As the action potential moves down the axon, the absolute refractory period switches to the tail end of the conductioni. After first threshold is reached the inside of the cell becomes positively charged and spreads down the membraneii. This causes adjacent sodium channels to open and become depolarized as well1. Basis for cell propagationiii. The potassium channels help repolarize and “reset” the membrane so it may conduct another action potentialc. An advantage of an inactivation gate is limiting activityi. Stops current flow within a specific period of time (in sodium channels)IV. Orthodromic conduction travels toward the terminal buttons (i.e. when inducing the action potential)a. Sodium ions flow around point of depolarization, causing the action potential to flow toward the soma as well (antidromic conduction)b. Axon hillock has highest concentration of voltage-gated sodium channels, so conduction usually begins here and travels toward the terminal endi. However, when the action potential is induced in the middle of the axon, it may travel both directions V. Salutatory conduction (in myelinated axons)a. Allows rapid conduction of action potential down the axoni. Leaps from one Node of Ranvier to the next (so opening all channels in the axon is not necessary)1. There are no voltage-gated channels underneath these myelin segmentsb. Ions flow down the axon underneath the membrane to the next area that contains voltage-gated channelsi. Positive charge travels from node to nodeii. Channels at nodes densely populated at the edges of the myelinated segmentsc. Different myelinated fibers categorized by axon diameteri. Larger diameter conducts action potential more quicklyVI. Electrical properties at the synapsea. No electrical threshold because they are ligand-gated (not voltage-gated)i. Molecule generates a change in membrane potentialb. Graded (summation)i. Potentials may sum together (no need for all-or-none)ii. Occurs where there is overlap on the post-synaptic membraneiii. May sum over space or timec. Decremental responsei. Greatest change in membrane potential occurs at initial binding but decreases in strength over time 1. Becomes weaker further away from point of stimulation (space and time)ii. Limits an action potential from traveling from the post-synaptic membrane to the axon hillockd. EPSPs are produced at the same time close together and sum to form a larger EPSPi. IPSPs behave similarly e. PSE (pre-synaptic excitation)i. PSI (pre-synaptic


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UVM NSCI 110 - Conduction Down the Axon

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