AP Psychology – Neuron and Neural Firing (Action Potential, Neurotransmitters)

AP Psychology – Neuron and Neural Firing (Action Potential, Neurotransmitters)

AP Psychology: Neuron and Neural Firing (Action Potential, Neurotransmitters) – Exam-Ready Study Guide

What This Is

This topic covers how neurons (nerve cells) communicate through electrical and chemical signals. It’s foundational for understanding biological bases of behavior, a major unit on the AP exam. Think of neurons like text messages: an electrical impulse (action potential) travels down the neuron, then chemicals (neurotransmitters) jump to the next neuron to pass the message. Real-world example: When you touch a hot stove, sensory neurons fire an action potential to your spinal cord, which triggers a reflex to pull your hand away—all in milliseconds!

Key Terms & Concepts

• Neuron: A nerve cell; the basic building block of the nervous system. Three types:
• Sensory neurons (afferent): Carry messages to the brain (e.g., pain from a stubbed toe).
• Motor neurons (efferent): Carry messages from the brain to muscles/glands (e.g., "move your hand!").

• Interneurons: Connect sensory and motor neurons (e.g., in reflexes).

• Dendrites: Branch-like extensions that receive messages from other neurons (like antennae).

• Soma (Cell Body): Contains the nucleus; keeps the neuron alive.
• Axon: Long fiber that transmits the electrical impulse (action potential) away from the soma.
• Myelin Sheath: Fatty layer covering the axon; speeds up neural impulses (like insulation on a wire). Deterioration-multiple sclerosis (MS).
• Action Potential: A brief electrical charge that travels down the axon. All-or-none principle: It either fires (at full strength) or doesn’t—like a gun trigger.
• Resting Potential: The neuron’s stable, negative charge (-70 mV) when inactive. Polarized = inside is negative, outside is positive.
• Threshold: The minimum stimulation needed to trigger an action potential (~ -55 mV). Example: Like a toilet flushing—you need enough pressure to pull the handle.
• Depolarization: Sodium (Na?) ions rush into the neuron, making it positive (+30 mV). This triggers the action potential.
• Repolarization: Potassium (K?) ions rush out, restoring the negative charge.
• Refractory Period: Brief time after firing when the neuron can’t fire again (like a toilet refilling).
• Synapse: The gap between neurons where neurotransmitters are released.
• Neurotransmitters: Chemical messengers that cross the synapse. Key examples:
• Dopamine: Reward/motivation (too much-schizophrenia; too little-Parkinson’s).
• Serotonin: Mood/sleep (low levels-depression).
• Acetylcholine (ACh): Muscle action/memory (Alzheimer’s = low ACh).
• GABA: Inhibitory (calms neural activity; low GABA-anxiety).
• Glutamate: Excitatory (too much-migraines/seizures).
• Reuptake: Neurotransmitters are reabsorbed by the sending neuron (like recycling). SSRIs (e.g., Prozac) block serotonin reuptake to treat depression.

Step-by-Step: How an Action Potential Works

1. Resting State: Neuron is polarized (-70 mV). Sodium (Na?) is outside; potassium (K?) is inside.
2. Stimulation: Dendrites receive a signal (e.g., heat, neurotransmitter). If the signal reaches threshold (-55 mV), the action potential starts.
3. Depolarization: Na? channels open-Na? rushes in-neuron becomes positive (+30 mV).
4. Repolarization: Na? channels close; K? channels open-K? rushes out-neuron returns to negative.
5. Hyperpolarization: K? overshoots-neuron becomes too negative (below -70 mV).
6. Refractory Period: Na?/K? pumps restore resting potential. Neuron can’t fire again yet.
7. Synaptic Transmission: Action potential reaches axon terminals-neurotransmitters are released into the synapse-bind to receptors on the next neuron’s dendrites.

AP Exam Tip: Draw this process as a graph (voltage vs. time) to visualize depolarization/repolarization!

Common Mistakes

• Mistake: Confusing action potential with neurotransmission. Correction: Action potential = electrical impulse within a neuron. Neurotransmission = chemical communication between neurons.

• Mistake: Thinking neurons fire at different strengths (e.g., "a strong stimulus = stronger action potential"). Correction: All-or-none principle—neurons fire at full strength or not at all. A strong stimulus = more neurons firing or firing more frequently.

• Mistake: Forgetting the role of the myelin sheath. Correction: Myelin speeds up action potentials (saltatory conduction). Without it, signals slow down (e.g., MS).

• Mistake: Mixing up excitatory and inhibitory neurotransmitters. Correction:

• Excitatory (e.g., glutamate) = increases likelihood of action potential.

• Inhibitory (e.g., GABA) = decreases likelihood.

• Mistake: Ignoring the refractory period. Correction: Neurons can’t fire during this time (like a toilet refilling). This limits how fast neurons can fire.

AP Exam Insights

1. Multiple-Choice Traps:
2. Tricky distinction: "Which part of the neuron receives messages?" (Answer: dendrites, not axons).
3. Neurotransmitter functions: Know the specific roles (e.g., dopamine = reward, ACh = muscle action).

4. Agonists vs. Antagonists:

   • Agonist = mimics a neurotransmitter (e.g., morphine mimics endorphins).
   • Antagonist = blocks a neurotransmitter (e.g., Botox blocks ACh).

5. FRQ Likelihood:

6. 2019 FRQ: "Explain how neurotransmitters affect behavior" (e.g., serotonin and depression).
7. 2017 FRQ: "Describe the process of neural transmission" (action potential + synapse).

8. Common prompt: "Explain how a drug (e.g., cocaine) affects neurotransmission."

9. Key Theorists/Experiments:

10. Santiago Ramón y Cajal: Discovered neurons are separate cells (not one big network).
11. Otto Loewi: Proved neurotransmission is chemical (frog heart experiment).

Quick Check Questions

1. Multiple Choice: Which of the following is the correct sequence of an action potential? a) Resting potential-depolarization-repolarization-hyperpolarization b) Depolarization-resting potential-repolarization-hyperpolarization c) Hyperpolarization-repolarization-depolarization-resting potential Answer: a. The neuron starts at rest, depolarizes (Na? in), repolarizes (K? out), then hyperpolarizes.

2. Short FRQ: Explain how an SSRI (e.g., Prozac) affects neurotransmission and mood. Answer: SSRIs block serotonin reuptake, increasing serotonin in the synapse-improves mood by enhancing serotonin’s effects.

3. Multiple Choice: A neuron’s refractory period is most similar to: a) A gun reloading after firing b) A light switch turning on c) A car accelerating Answer: a. The refractory period is a brief "reloading" time when the neuron can’t fire again.

Last-Minute Cram Sheet

1. Neuron parts: Dendrites (receive)-soma-axon (transmit)-terminals (release neurotransmitters).
2. Action potential: All-or-none; -70 mV (resting)--55 mV (threshold)-+30 mV (depolarization).
3. Myelin sheath: Speeds up impulses; damage = MS.
4. Neurotransmitters:
5. Dopamine = reward; ACh = muscle action; serotonin = mood.
6. Agonist vs. Antagonist: Agonist mimics; antagonist blocks.
7. Refractory period: Neuron can’t fire again (like a toilet refilling).
8. Reuptake: Neurotransmitters are recycled (SSRIs block this).
9. Excitatory vs. Inhibitory: Glutamate (excite) vs. GABA (inhibit).
10. All-or-none: Neurons fire at full strength or not at all.
11. Synapse: Gap between neurons (chemical transmission).