AP Psych Zero: How Does a Signal Get From One Neuron to the Next?
You're sitting on the edge of an exam table, and the doctor taps the tendon just below your knee with a little rubber hammer. Your lower leg swings out on its own.
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AP Psych Zero: How Does a Signal Get From One Neuron to the Next?
This episode continues Unit 1, Biological Bases of Behavior, with its third topic: the neuron, the cell that carries a message. It is the lesson on what the message travels in, how one cell fires it down its length, and how that cell hands it to the next one.
What you will learn
- The two common types of neural cells, and which one actually carries the message.
- The three neurons of a reflex arc, and why the arc can answer a stimulus before the brain registers it.
- The six-step life of a signal inside a cell, from resting potential to reuptake.
- The eight neurotransmitters and the five hormones the exam is limited to.
- What the framework leaves out of this topic, and the study time that saves you.
Learning map
| Term | What happens | Why it matters |
|---|---|---|
| Resting potential | A neuron at rest holds a charge, with its inside negative relative to its outside | It is the cell's readiness, the state that makes firing possible |
| Threshold | Enough arriving signals tip the charge at the start of the cell | It is where everything landing on the cell gets added up into a yes |
| Depolarization | The charge flips, and the change runs down the length of the cell | It is the impulse itself, travelling from one end to the other |
| All-or-none principle | The cell fires at the same size every time | A stronger stimulus shows up as more frequent firing, not a larger impulse |
| Refractory period | A brief moment after firing when the cell cannot fire again | It caps how fast signals travel and keeps them moving one direction |
| Reuptake | The sending cell takes its neurotransmitter back up | It clears the gap so the message can repeat cleanly, and it is the step many drugs act on |
Those six terms are the framework's own list for the transmission process. 1
The arc that moves your leg runs in one direction: a sensory neuron carries the message inward from the body, an interneuron connects inside the spinal cord, and a motor neuron carries the command out to the muscle. Because the turn happens in the spinal cord, the command can be on its way back down before the brain has registered the tap.
The eight neurotransmitters the exam covers, with the job each is usually attached to:
- Dopamine — movement and reward.
- Serotonin — mood and sleep.
- Norepinephrine — alertness and arousal.
- Glutamate — the main excitatory transmitter, making firing more likely.
- GABA — the main inhibitory transmitter, making firing less likely.
- Endorphins — the body's own pain relief.
- Substance P — carries pain signals.
- Acetylcholine — carries commands to muscles and is involved in memory.
The five hormones, which act outside the nervous system and travel in the bloodstream:
- Adrenaline — raises the heart rate and readies the body for action.
- Leptin — signals that you are full.
- Ghrelin — signals hunger.
- Melatonin — sets the timing of sleep.
- Oxytocin — tied to bonding and to childbirth.
Study check
Answer these without replaying the final minutes:
- What are the two common types of neural cells, and which one transmits information?
- Name the three types of neurons in a reflex arc and the direction each carries a message.
- A neuron fires at the same size whether the stimulus was mild or intense. What is that rule called, and how does the nervous system signal a stronger stimulus?
- Which two of the eight neurotransmitters are the main excitatory and the main inhibitory ones?
- Which chemical system uses the bloodstream rather than the gap between two cells, and name two of its five hormones.
The four questions to carry out of this episode: what kind of cell is this, where does the message enter and leave, did the cell fire all at once or not at all, and how did the message cross the gap?
Scope and sources
The College Board's Course and Exam Description names two common types of neural cells in the brain: neurons, which transmit information, and glial cells, which provide structure, insulation, communication, and waste transport. It calls these the building blocks of all behavior and mental processes. It places the reflex arc in the spinal cord, where sensory neurons, motor neurons, and interneurons work together, and it lists the transmission process as the all-or-none principle, depolarization, refractory period, resting potential, reuptake, and threshold, with multiple sclerosis and myasthenia gravis as examples of what disruption can cause. 1
Three exclusion statements in the framework change what you need to study here. The sodium-potassium pump is outside exam scope, so the resting charge matters but the machinery that maintains it does not. The exam will only address the eight neurotransmitters listed above, and only the five hormones. Specific information about the glands of the endocrine system is outside scope as well, with one exception, the pituitary gland, which is referenced in the brain topic. The AP Psychology course page is the course's public entry point. 2
The third objective of this topic, how psychoactive drugs act on neural transmission through agonists, antagonists, and reuptake inhibitors, is the next lesson.
This episode is a study aid. Use your teacher's current materials and the current College Board framework for course-specific assignments and exam details.
References
- 1AP Psychology Course and Exam Description — College Board
apcentral.collegeboard.org
- 2AP Psychology Course — AP Central, College Board
apcentral.collegeboard.org
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