How Nerves Work 4 Flashcards
Ionic Basis of the Action Potential + Speeding up the Action Potential
What does a diagram of an action potential look like?
<p>What is the threshold to fire an action potential?</p>
<p>-55mV</p>
<p>Explain the ionic basis of the firing of an action potential?</p>
<ol> <li>Leaky K+channels bring the cell to threshold (graded potential)</li> <li>Voltage gated channels open allowing Na+to flow in and bring the cell to +40mV</li> <li>More K+channels open and bring the cell down to -90mV</li></ol>
<p>What channel is faster, and which is slower, out of Na+and K+?</p>
<p>Na+channels open faster and K+stay open for longer</p>
<p>Explain how the excitability of a cell changes?</p>
<p>The greater the membrane potential, the greater the excitability of a cell</p>
<p>What does excitability of a cell mean?</p>
<p>How easy it is to fire an action potential</p>
<p>What is the absolute refractory period?</p>
<p>When all gates are opened and the action potential fires (low excitability)</p>
<p>What is the relative refractory period?</p>
<p>Gates are closing and recovering (excitability increasing)</p>
<p>Is the size of an action potential proportional to the size of the stimulis?</p>
<p>No, they are all the same size</p>
<p>How does the size of a stimulis impact an action potential?</p>
<p>The bigger the stimulis, the more action potentials are fired (increased frequency) but the size is the same (same amplitude)</p>
<p>Are action potentials self-propogating or decremental?</p>
<p>Self propogating</p>
<p>What does self propogating mean?</p>
<p>Keep making new ones for themselves</p>
<p>How does the self propogation of action potentials work?</p>
<p>Depolarisation spreads across a membrane decrementally, opening more channels</p>
<p>Why do action potentials technically not spread backwards?</p>
<p>They do, but the gates are not opened so nothing happens and it decremenates into nothing</p>
<p>How can you increase conduction velocity?</p>
<p>Larger axons</p>
<p>Myelination</p>
<p>Why do larger axons increase conduction velocity?</p>
<p>They decrease conduction resistance</p>
<p>What two cells form myelin sheath?</p>
<p>Schann cells (PNS)</p>
<p>Oligodendrocytes (CNS)</p>
<p>Where are the voltage gates on a myelinated axon?</p>
<p>Not in the myelinated section, but in the gaps between (nodes)</p>
<p>How does depolarisation spread along a myelinated axon?</p>
<p>Spreads from node to node without decaying much to to the high insulation</p>
<p>What are some diseases that de-myelination causes?</p>
<p>Multiple scerosis</p>
<p>Gwillain-Barre syndrome</p>
<p>Why does de-myelination cause disease?</p>
<p>Signal decays quicker and doesn't reach threshold at the next node</p>
<p>What is a nerve?</p>
<p>A bundle of axons</p>
<p>What varies within the axons of a nerve?</p>
<p>The size and extent of myelination</p>
<p>What is the compound action potential?</p>
<p>Signal recorded extracellularly from large populations of axons</p>
<p>What does each bump in the graph of a compound action potential represent?</p>
<p>An action potential going past at that point in time, each one being from the same stimuli</p>
What are the different waves and speeds in a compount action potential?
A compound action potential (CAP) is a signal recorded from a nerve trunk made up of numerous axons. It is the result of summation of many action potentials from the individual axons in the nerve trunk.
<p>Which end of the spectrum of waves is most sensitive to anoxia and local anaesthetic?</p>
<p>Aa is most sensitive to anoxia</p>
<p>C is most sensitive to local anaesthetic</p>
<p>What is anoxia?</p>
<p>An absence of oxygen</p>
