Cable Properties and Dendritic Integration · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

Fading signals that add up to a spike

Science · The Human Body · ages 18-20
Name ______________________   Date ____________

  1. What change does myelin cause in the membrane properties of an axon?

    • Higher membrane resistance and lower capacitance
    • Lower membrane resistance and lower capacitance
    • Higher membrane resistance and higher capacitance

  2. In a uniform passive dendritic cable, equal local voltage changes occur at different distances from the trigger zone. Which produces the larger depolarisation there, with other conditions unchanged?

    • The farther input: less attenuation
    • The closer input: less attenuation
    • Both inputs: equal attenuation

  3. Overlapping excitatory effects can reach threshold together even when each effect alone is too small.

    Circle one:   True   False

  4. One synapse produces repeated excitatory inputs before the earlier voltage change has faded. What is the combination of these effects called?

    • Spatial summation
    • Temporal summation
    • Passive attenuation

  5. Two passive cables have comparable membrane properties. For the same local voltage change, what does greater cable diameter predict?

    • Higher axial resistance and less passive spread
    • Unchanged axial resistance and farther passive spread
    • Lower axial resistance and farther passive spread

  6. Inputs from two different synapses have overlapping effects at the trigger zone. What is this combination called?

    • Spatial summation across synapses
    • Temporal summation at one synapse
    • Passive attenuation along a cable

  7. During the absolute refractory period, excitatory inputs that sum past the usual threshold must trigger another spike in that same membrane region.

    Circle one:   True   False

  8. In a linear model, reaching threshold requires a change of +10 mV from rest. Overlapping effects at the trigger zone are +8 mV, +5 mV and -4 mV. A student ignores inhibition and predicts firing from +13 mV. Which calculation corrects this?

    • 8 + 5 + 4 = 17 mV; above the +10 mV threshold
    • 8 - 4 = 4 mV; below the +10 mV threshold
    • 8 + 5 - 4 = 9 mV; below the +10 mV threshold
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Answer key

For grown-ups. Fold this page away before handing over the rest.

Fading signals that add up to a spike W1-mt_bbPl-eJUFF-s1

  1. Higher membrane resistance and lower capacitance · Myelin raises membrane resistance and lowers membrane capacitance. These properties support passive spread between nodes.
  2. The closer input: less attenuation · In the stated passive-cable model, the closer input undergoes less attenuation before reaching the trigger zone.
  3. True · Excitatory effects can combine while they overlap. Together they may reach threshold, although each effect alone is below it.
  4. Temporal summation · Temporal summation combines repeated inputs from one synapse when earlier effects persist as later inputs arrive.
  5. Lower axial resistance and farther passive spread · Greater diameter lowers axial resistance per unit length. With membrane properties comparable, a fixed local voltage change can spread farther.
  6. Spatial summation across synapses · Spatial summation combines effects from different synapses. Temporal summation combines repeated inputs from one synapse.
  7. False · During absolute refractoriness, sodium-channel inactivation prevents another spike in that membrane region. A threshold-only calculation cannot override that condition.
  8. 8 + 5 - 4 = 9 mV; below the +10 mV threshold · Include all three signed effects: 8 + 5 - 4 = 9 mV. This is below the required 10 mV, so these inputs do not reach threshold in the stated model.
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