Neuroscience 2610: Chapter 4.2: Electrical Activity at the Dendritic and Cell Body Membrane

  • electrical activity in neurons

    • the movement of specific ions through channels across neuronal membranes

  • semipermeability

    • cell membrane prevents the efflux of large protein anions and pumps Na+ ions out of the cell to maintain a slightly negative charge in the intracellular fluid

  • resting potential

    • electical charge across the insulating cell membrane in the absence of stimulation

    • store of potential energy produced by a greater negative charge on the intracellular side relative to the extracellular side

  • 4 charged particles take part in producing the resting potential

    • sodium(Na+)

    • potassium(K+)

    • chloride(Cl-)

    • large negatively charged protein molecules(A-)

  • more protein anions and potassium ions are found in the intracellular fluid

    • A- and K+ have a higher concentration inside the axon

  • more sodium and chloride ones are present in the extracellular fluid

    • Cl- and Na+ ions are more concentrated outside the axon

  • 3 features that contribute to the cell membrane’s resting potential

    • A- remain inside the cell because the membrane is relatively impermeable to large molecules

    • ungated K channels allows K+ ions to pass through the membrane more freely, ungated channels allow Cl- ions to pass but gates on Na+ channels keep out positively charged Na+

    • Na+ - K+ pumps eject Na+ f or the intracellular fluid and draw in K+

  • inside the cell

    • if the number of K+ ions that could accumulate on the intracellular side of the membrane were unrestricted, the positively changed K+ ions inside would exactly match the negative charged on the intracellular protein anions

      • there would be no charge across the membrane at all

  • equilibrium reversal potential

    • membrane potential of an individual ion, at which there is no net(overall) flow of that particular ion from one side of the membrane to the other

    • calculated using the Nernst equation

  • unequal distribution of different ions causes the inside of the axon to be relatively negatively charged

  • a cell membrane’s resting potential is closest to the equilibrium potential of Cl-

  • graded potentials

    • small voltage fluctuation across the cell membrane

    • stimulating a membrane electrically through a micro electrode mimics the way the membrane’s voltage changes to produce a graded potential in the living cell

  • hyperpolarization

    • increase in electrical charge due to the inward flow of Cl- ions or the outward flow of K+ ions

  • depolarization

    • decrease in electrical charge due to the inward flow of Na+

  • hyper polarization and depolarization takes place on neuronal dendrites and the soma(cell body) membrane

  • K+ channels have a role in hyper polarization because chemical TEA blocks K+ channels and blocks hyper polarization as well

  • Na+ channels in depolarization is indicated by the fact that the chemical TTX blocks Na+ channels and blocks depolarization as well

  • excitatory postsynaptic potential(EPSPs)

    • brief depolarization in response to stimulation

    • making the neuron more likely to produce an action potential

    • associated with the opeinign of Na+ channels,which allows an influx of Na+ ions

  • inhibitory postsynaptic potential(IPSPs)

    • brief hyperpolarization in response to stimulation

    • makes the neuron less likely to produce an action potential

    • associated with the opening of Cl- channels, which allows an influx of Cl-

  • action potential is not produced on the motor neuron’s cell body membrane even when an EPSP is strongly excitatory because the cell membrane of most neurons does not contain voltage activated channels

  • initial segment

    • near or overlapping the axon hillock for an action potential to begin

      • an area rich in voltage gated channels

  • temporal summation

    • addition of graded potentials to each other, when the potentials occur close in time

    • when multiple EPSPs or multiple IPSPs occurs in rapid succession, they will combine to depolarize or hyper polarize the membrane

  • spatial summation

    • addition of one graded potential to another, when the potentials occurs close in space

    • when multiple EPSPs or multiple IPSPs occur close together and combine to each other to depolarize or hyper polarize the membrane

  • if the 2 influxes are remote in time or in space or in both, no summation is possible

  • if they are widely separated in time or in space or in both, they do not interact and there is no summation

  • a neuron analyzes its inputs before deciding what to do

    • the decision is made at the initial segment, the region on the axon that initiates the action potential