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Neurons and Action Potentials - Anatomy & Physiology

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  • Resting membrane potential (RMP)
    The resting electrical charge of a neuron, about \(-70\,\mathrm{mV}\).
  • Why is the inside of a resting neuron negative?
    More K⁺ leaks out than Na⁺ leaks in.
  • K⁺ leak channels
    Always-open channels allowing K⁺ to diffuse out without ATP.
  • Effect of adding Na⁺ leak channels
    The resting membrane potential becomes less negative.
  • Increased membrane permeability to Na⁺ causes
    Membrane depolarization (inside becomes more positive).
  • Function of the Na⁺/K⁺ pump
    Uses ATP to pump 3 Na⁺ out and 2 K⁺ in.
  • Memory trick for Na⁺/K⁺ pump
    "3 out, 2 in, ATP to win."
  • If the Na⁺/K⁺ pump stops working
    Resting membrane potential gradually moves toward 0 mV.
  • Opening Cl⁻ channels causes
    Hyperpolarization of the neuron.
  • What maintains the resting membrane potential?
    Leak channels and the Na⁺/K⁺ pump.
  • Graded potential
    A local membrane potential with variable amplitude that fades with distance.
  • Depolarization means
    The inside of the membrane becomes less negative.
  • Channels needed for an action potential
    Voltage-gated Na⁺ and K⁺ channels.
  • Order of events in an action potential
    Rest → Threshold → Na⁺ in → K⁺ out → Hyperpolarization → Rest.
  • Unmyelinated axon conduction type
    Continuous conduction.
  • Why is an action potential self-regenerating?
    Na⁺ influx triggers the next segment to depolarize.
  • Why do action potentials travel in only one direction?
    Na⁺ channels behind the impulse are inactivated.
  • Function of myelin
    Speeds nerve impulse conduction via saltatory conduction.
  • Peak of action potential
    Na⁺ channels inactivate; K⁺ channels open causing repolarization.
  • Fastest axons
    Large-diameter myelinated axons.
  • Threshold for starting an action potential
    Approximately \(-55\,\mathrm{mV}\).
  • Factors affecting conduction speed
    Myelination and axon diameter.
  • Relative refractory period
    K⁺ channels remain open; a stronger stimulus is required to fire.
  • Synaptic cleft
    The gap between neurons at a synapse.
  • Neurotransmitter
    Chemical messenger that crosses the synapse.
  • Role of Ca²⁺ at the synapse
    Triggers vesicle fusion and neurotransmitter release.
  • Effect of neurotransmitter binding
    Opens chemically gated ion channels on the postsynaptic neuron.
  • More negative postsynaptic cell means
    Less likely to fire an action potential.
  • Na⁺ through chemically gated channels causes
    Excitatory postsynaptic potential (EPSP).
  • Opening K⁺ or Cl⁻ channels causes
    Inhibitory postsynaptic potential (IPSP).
  • Neurotransmitter at skeletal muscle
    Acetylcholine (ACh).