Human A&PBIO 304 · American River College ← Week 04 pre-work

BIO 304 · Week 04 · Interactive Workbook

Neurons & Resting Membrane Potential

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Part 1 of 4 · Recall

Fill in the blanks

Type the term that completes each statement, using the word bank. Pull it from memory first.

Word bank

HyperpolarizationEₘ (Na+)DepolarizationOutside the cellInside the cellMotor (efferent)MultipolarResting potentialSensory (afferent)K+ leak channelsBipolarPseudounipolarNet effectEₘ (K+)Na+/K+ ATPase

  1. many dendrites, one axon · most neurons
  2. one dendrite, one axon · retina, olfactory
  3. one process that splits · most sensory neurons in DRG
  4. carries signal toward CNS
  5. carries signal from CNS to effector
  6. about -70 mV (inside negative relative to outside)
  7. high K+ and high anionic protein
  8. high Na+ and Cl-
  9. pumps 3 Na+ out and 2 K+ in per ATP · primary active transport
  10. K+ leaks down its gradient toward outside
  11. inside ends up negative because K+ leaves easily and big anions cannot follow
  12. inside becomes less negative (e.g. Na+ enters)
  13. inside becomes more negative (e.g. K+ leaves or Cl- enters)
  14. ~ -90 mV · if only K+ were permeable, potential would settle here
  15. ~ +60 mV · if only Na+ were permeable

Define it: high-yield vocabulary

Write a clear definition in your own words for each term.

  1. Resting membrane potential
  2. Multipolar neuron
  3. Sensory (afferent) neuron
  4. Motor (efferent) neuron
  5. Interneuron
  6. Na+/K+ ATPase
  7. Selective permeability
  8. Depolarization
  9. Repolarization
  10. Hyperpolarization

Part 2 of 4 · Anatomy lab

Draw and label

Box A. The neuron

Directions

  1. Draw a cell body (soma) as an irregular circle. Show a nucleus inside.
  2. Add 3 to 5 short branched dendrites projecting from the soma.
  3. Extend a single long process from the opposite side. Label its base Axon hillock.
  4. Wrap the axon with discrete myelin segments. Show at least 2 unmyelinated gaps. Label one gap Node of Ranvier.
  5. Identify which cell type makes the myelin: if CNS, an oligodendrocyte; if PNS, a Schwann cell. Pick one and label it.
  6. End the axon in several axon terminals (small swellings). Label one.
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Box B. Resting membrane close-up

Directions

  1. Draw a horizontal rectangle representing a patch of plasma membrane. Label the top Outside (extracellular) and the bottom Inside (cytoplasm).
  2. Draw a Na-K ATPase pump straddling the membrane. Show arrows: 3 Na-plus leaving the cell, 2 K-plus entering, ATP being consumed.
  3. Draw at least 2 K-plus leak channels in the membrane. Show K-plus leaking OUT down its gradient.
  4. On the outside, write a large Na-plus and a small K-plus. On the inside, write a small Na-plus and a large K-plus. (Show which ion is more concentrated where.)
  5. Indicate charge: a row of minus signs lining the inside of the membrane and plus signs lining the outside.
  6. In the corner, write the resting potential value: about negative 70 millivolts.
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Structures to label

Label each on your drawing.

  1. Dendrites
  2. Cell body (soma)
  3. Nucleus
  4. Axon hillock
  5. Axon
  6. Myelin sheath
  7. Node of Ranvier
  8. Schwann cell or oligodendrocyte
  9. Axon terminal
  10. Na+/K+ ATPase
  11. K+ leak channel
  12. Na+ (high outside)
  13. K+ (high inside)
  14. Resting membrane potential (-70 mV)

Part 3 of 4 · Physiology lab

Reason it through

A. Calculation: who builds the resting potential?

1. Per ATP, the Na+/K+ ATPase moves 3 Na+ out and 2 K+ in. What is the NET charge moved across the membrane per cycle, and in which direction?
2. Does this NET pump activity make the inside more negative or more positive on its own? Explain.
3. The membrane is also leaky to K+. Which direction does K+ flow through these leak channels at rest, and why (give the gradient driving it)?
4. Of the two mechanisms (pump electrogenicity vs K+ leak), which contributes MORE to the -70 mV resting potential? Justify in one or two sentences.
5. Predict the resting potential of a cell that has lost ALL its K+ leak channels but still has a working Na+/K+ ATPase.

B. Synthesis

1. Ouabain blocks the Na+/K+ ATPase. Predict the resting membrane potential at: (a) 5 seconds, (b) 5 minutes, (c) 5 hours after exposure. Explain the trajectory.
2. Match each glial cell to one function: astrocyte, oligodendrocyte, microglia, Schwann cell, ependymal cell. Pick from: makes myelin in CNS; makes myelin in PNS; immune surveillance; blood brain barrier support; produces CSF.
3. A neuron in cold seawater has a resting potential of -90 mV instead of -70 mV. Propose one mechanistic explanation involving the Na+/K+ ATPase or the K+ leak channels.

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