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Human A&P BIO 304 · American River College ← Course home (Week 4)

BIO 304 . WEEK 4 . FRIDAY . LAB WORKBOOK

Action Potentials and Synaptic Transmission

Phases of the action potential, propagation, and how chemical synapses pass the signal on.

Print this page. You will draw your own diagrams from the directions below, then hand-label the structures listed. Drawing by hand is the integrity mechanism for this course.

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Part 1 of 2

Anatomy Lab

1A. What you will draw

Two drawings today. Box A is the action potential graph with channel-state bars. Box B is the chemical synapse. Be precise: the values on the y-axis matter.

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.

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.

1C. Structures to label (16)

After you finish each drawing, label every structure below directly on your sketch.

  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 2 of 2

Physiology Lab

2A. Sequence the synapse

Number the following 7 events in the correct order at a chemical synapse, starting from the action potential arriving at the axon terminal and ending with a change in the postsynaptic neuron's membrane potential.

Scrambled events:

  1. Neurotransmitter binds receptors on the postsynaptic membrane.
  2. Action potential arrives at the axon terminal.
  3. Voltage-gated calcium channels open; calcium flows in.
  4. An EPSP or IPSP is generated in the postsynaptic neuron.
  5. Synaptic vesicles fuse with the presynaptic membrane.
  6. Neurotransmitter diffuses across the synaptic cleft.
  7. Neurotransmitter is released into the synaptic cleft.

Your sequence (write the events in correct order):

2B. Synthesis questions

Answer each in 2 to 4 sentences. Use the language from this week's lecture and your drawings as evidence.

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?

3. What to submit

Complete both the Anatomy Lab (your own drawings, hand-labeled, plus the structures list) and the Physiology Lab (activity and synthesis questions). Photograph or scan every page and upload to Canvas before the deadline listed on the schedule. Hand-drawn, hand-labeled work is the integrity mechanism for this course. Typed or AI-generated diagrams are not accepted.