Trace a signal across two neurons

Trace a signal across two neurons

Separate electrical signaling within a neuron from chemical signaling across a synapse.

A question to investigate

Does doubling a stimulus necessarily double the height of each action potential?

Build a labeled signal trace and predict what changes when a receptor is blocked.

Mechanism and evidence

A neuron receives and integrates inputs. If its trigger region reaches threshold, an action potential travels along the axon. Chemical synapses use transmitter molecules released from the sending cell; binding to receptors changes activity in the receiving cell. A receiving cell can receive excitatory and inhibitory influences. The sign of an effect depends on the receptor and pathway, not only the transmitter’s name. A stronger effective input can alter firing frequency; it does not simply make each action potential proportionally taller. Glial cells support neural function, and myelin helps conduction. These distinctions are summarized in the linked introductory text.

The two records are invented, not measurements of a person’s nervous system. Treat −55 mV as this model’s threshold, not a universal biological constant. The signed number line is essential: −50 is greater than −55, while −60 is smaller. Input B reaches the threshold side; A does not. Do not add a claim about intelligence, pain, or a clinical condition to this voltage comparison.

Create two traces before inspecting the worked result. In the first, replace B’s peak input with −56 mV. In the second, keep B at −50 mV but block the receiving receptor. These changes act at different places in the causal chain. The first prevents the modeled sending spike; the second allows that spike but interrupts its usual effect on the next cell. Use the source annotation boxes to keep the two explanations separate.

A careful pathway explanation specifies both a location and a mechanism. ‘The brain stops’ is too broad. ‘The postsynaptic response in this pathway is absent although the presynaptic spike remains’ matches the invented evidence. Receptor blocking here is a conceptual intervention; this activity does not recommend substances or treatments. Real networks have feedback, many cell types and multiple interacting pathways.

Inspect the relationships

Stage	Input below threshold	Receptor blocked after sending spike
Sending spike	Absent in this model	Present
Transmitter release caused by that spike	Absent	Present
Usual receiving response	Absent	Absent

Trace task: The same final absence can have two different causes. Which intermediate observation separates them?

Worked example

For A, −60 < −55, so the simplified trigger does not fire. For B, −50 ≥ −55, so it fires. Blocking the receiving receptor changes the next cell’s response, not the already observed sending spike.

Independent application

A new trace shows normal transmitter release but no receiving response. Which observation most directly distinguishes a receptor problem from a release failure? Explain the denominator, process or rule before checking the response. Record a revision after feedback.

Reading

OpenStax Psychology 2e, cells of the nervous system. The numerical records and tasks are original fictional teaching examples; they are not findings reported by this source.