Biology & life sciences · 12 / 12
Nerve signals: pathway and coding
Final-year concepts · Worked example and 4 exercises with solutions, at your pace.
The principle, simply
A neuron transmits electrical signals along its membrane. Propagated action potentials have a stereotyped amplitude; intensity can be encoded by frequency and recruited neurons. At a chemical synapse, neurotransmitter acts on receptors in the next cell. Connections can be excitatory or inhibitory.
- 01Receptor
- 02Electrical signal
- 03Synapse and integration
- 04Muscle response
WORKED EXAMPLE
From principle to reasoning
A stretch reflex links muscle receptor → sensory neuron → spinal circuit → motor neuron → muscle. The brain also receives information; the reflex can begin without a prior conscious decision.
Solve a problem in this subject
- Frame a question
State the relationship to explain and its scale: molecule, cell, organism, population or geological time.
- Describe evidence
Give a measurable observation, unit, comparison and conditions before explaining it. Observation and inference do different jobs.
- Connect a mechanism
Use a precise concept and label arrows as production, transfer, action or transformation. Sequence alone does not prove causation.
- Answer with a limit
Connect evidence and knowledge to the question. Distinguish the simplified model from living systems and identify a missing condition.
YOUR TURN
01 · Try before checking
Does a stronger stimulus necessarily create a taller action potential?
One hint
Separate amplitude from frequency.
Reveal and understand the solution
No. In the same axon, action potential amplitude is stereotyped; frequency can increase and neuron recruitment also matters.
Compare method, conditions and answer; identify the exact part to revisit.
IMPROVE THROUGH PRACTICE
Three additional challenges with solutions
Start with the first challenge. Write your method before opening a hint; use the solution to find the first step that needs work.
Does a stronger stimulus necessarily increase action-potential amplitude?
A hint to get started
An action potential is all-or-none.
Step-by-step solution
- Within one axon, amplitude is approximately stereotyped.
- Intensity can be encoded by firing frequency.
- Separate single-event amplitude from event count.
Which step did you miss? Retry without help, then explain why the method works.
Order neurotransmitter release, action-potential arrival and receptor binding.
A hint to get started
The electrical event precedes chemical transmission.
Step-by-step solution
- The action potential reaches the presynaptic terminal.
- Neurotransmitter is released into the cleft.
- It binds postsynaptic receptors and may alter target-cell activity.
Which step did you miss? Retry without help, then explain why the method works.
Must a simple spinal reflex wait for a conscious decision?
A hint to get started
Separate reflex circuitry from conscious perception.
Step-by-step solution
- A spinal circuit can initiate the response without a prior conscious decision.
- Sensory information can also reach the brain.
- Higher centres can still modulate reflex activity.
Which step did you miss? Retry without help, then explain why the method works.
The trap to avoid
Neurotransmitter crosses a synaptic gap; it does not carry the electrical message along the entire axon.
Without notes, can you…
- Explain the principle in your own words?
- Rebuild the diagram and its connections?
- Solve the exercise and justify the method?
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