Neurobiology II

  • Net difference in electrical charge occurs at the inside and outside surfaces of the membrane

  • large potential changes caused by minuscule ionic concentrations changes

  • rate of ion movement is proportional to the difference between the membrane potential and the equilibrium potential (driving force)

Type of membrane potentials

1) resting membrane potentials

  • at rest

  • created by Na/K pumps

  • persists due to leaky channels

2) Graded potentials

  • transient changes that occur locally

  • short distance signals

  • vary in magnitude and duration

  • occur in dendrites and cell bodies

3) Action potential

  • all or none

Ligand gated ion channels cause graded changes

Goldman equation

  • describes how membrane potential is determined by ionic concentration gradients and permeabilities

Graded potentials decay over short distances

  • length constant - the distance that electronic current can spread along the membrane

    • distance to decrease to 37% of original value

Threshold potential

  • membrane potential required to initiate an action potential

  • usually around -55mV

Spatial Summation

  • integration of graded potentials occurs in space

Temporal summation

  • integration of graded potentials occur in time

Graded potentials cause depolarization or hyper polarization

  • Excitatory post-synaptic potential (EPSP)

    • a temporary depolarization of the postsynaptic membrane caused by the release of neurotransmitters from a presynaptic neuron.

    • make the postsynaptic neuron more likely to fire an action potential.

    • Neurotransmitter - glutamate and involve the opening of ligand-gated ion channels, allowing the influx of positively charged ions such as sodium (Na+) or calcium (Ca2+).

  • Inhibitory post synaptic potential (IPSP)

    • temporary hyperpolarization of the postsynaptic membrane potential caused by the opening of ion channels that allow the influx of negatively charged ions (e.g., chloride ions) or the efflux of positively charged ions (e.g., potassium ions).

    • IPSPs make it more difficult for the neuron to generate an action potential, thus inhibiting the transmission of signals between neurons.

Action Potential

  • all or none

  • long distance signals

    • maintain amplitude

  • same magnitude and duration for a given cell

  • occur in axons

  • caused by opening and closing of voltage-gated channels

Gates

  • Activation gate

    • voltage sensor

    • opens at threshold

  • Inactivation gate

    • closes from cytoplasmic side

  • Depolarization of the membrane