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

BIO 304 · Week 04 · Interactive Workbook

Action Potentials & Synaptic Transmission

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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

Acetylcholine (ACh)All-or-noneRestingAbsolute refractory periodGABADepolarizationHyperpolarizationSerotoninEPSP (excitatory)ReuptakeSaltatory conductionConduction speed scales withNT crosses synaptic cleftSummation (spatial)Voltage-gated Ca²⁺ channels open

  1. about -70 mV; Na+ and K+ voltage gates closed
  2. Na+ voltage-gated channels open; Na+ rushes in; rises to +30 mV
  3. K+ channels close slowly; briefly dips below -70 mV
  4. either fires fully or not at all
  5. no AP possible; Na+ channels inactivated
  6. myelinated; AP jumps node to node; fast
  7. myelination and axon diameter
  8. Ca²⁺ enters terminal
  9. binds receptor on postsynaptic membrane
  10. partial depolarization; ligand opens Na+ channel
  11. EPSPs from many inputs add together
  12. NMJ, parasympathetic; CNS arousal
  13. main CNS inhibitory; targets of benzodiazepines
  14. mood, sleep, appetite
  15. transporters pull NT back into presynaptic neuron (SSRIs block this)

Define it: high-yield vocabulary

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

  1. Threshold
  2. Depolarization
  3. Repolarization
  4. All-or-none principle
  5. Absolute refractory period
  6. Saltatory conduction
  7. Nodes of Ranvier
  8. Neurotransmitter
  9. EPSP
  10. IPSP
  11. Temporal summation
  12. Spatial summation
  13. Acetylcholine
  14. Reuptake

Part 2 of 4 · Anatomy lab

Draw and label

Box A. Action potential graph

Directions

  1. Draw an x-axis (time, in milliseconds) and a y-axis (membrane voltage, mV, from -90 to +40).
  2. Plot a single action potential. Start at the resting potential (-70 mV). Rise to threshold (-55 mV). Spike up to about +30 mV. Fall through 0 back down. Dip slightly below -70 mV (afterhyperpolarization) before returning to rest.
  3. Label each phase on the curve: Resting, Threshold, Depolarization, Peak, Repolarization, Hyperpolarization, Return to rest.
  4. Below the graph, draw 3 horizontal bars showing when these channels are OPEN, aligned with the curve above: Voltage-gated Na+ (activation gate), Voltage-gated Na+ (inactivation gate closes during peak), Voltage-gated K+.
  5. Mark the absolute refractory period and the relative refractory period on the time axis.
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Box B. Chemical synapse

Directions

  1. Draw an axon terminal (presynaptic) at the top. Inside it, sketch a cluster of synaptic vesicles. Label them.
  2. Show voltage-gated Ca-squared-plus channels in the presynaptic membrane, with arrows of Ca-squared-plus entering when an AP arrives.
  3. Draw the synaptic cleft as a small gap below.
  4. Draw the postsynaptic membrane below the cleft. Show ligand-gated receptors embedded in it.
  5. Show neurotransmitter molecules being released into the cleft and binding the postsynaptic receptors.
  6. Label: Action potential arriving, Voltage-gated Ca2+ channel, Synaptic vesicle, Neurotransmitter, Synaptic cleft, Postsynaptic receptor.
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Structures to label

Label each on your drawing.

  1. Resting potential (-70 mV)
  2. Threshold (-55 mV)
  3. Peak (+30 mV)
  4. Depolarization
  5. Repolarization
  6. Hyperpolarization
  7. Absolute refractory period
  8. Relative refractory period
  9. Voltage-gated Na+ channel
  10. Voltage-gated K+ channel
  11. Axon terminal
  12. Voltage-gated Ca2+ channel
  13. Synaptic vesicle
  14. Neurotransmitter
  15. Synaptic cleft
  16. Postsynaptic receptor

Part 3 of 4 · Physiology lab

Reason it through

A. Sequence the synapse

Explain the main structure-function relationship for this topic.

B. Synthesis

1. Saltatory conduction is much faster than continuous conduction. Explain the structural reason in terms of where voltage-gated channels cluster and what the action potential actually does between nodes.
2. Why does a neuron need an inactivation gate on its voltage-gated Na+ channel? Predict what propagation would look like if this gate did not exist. Why is unidirectional conduction important?
3. SSRIs immediately block serotonin reuptake (within minutes), yet clinical relief from depression takes 4 to 6 weeks. Propose a mechanism for this lag. What downstream changes might account for it?

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