1.3 The Neuron and Neural Firing

TLDR

Neurons are cells that send signals through your nervous system using a mix of electrical impulses (the action potential) and chemical messengers (neurotransmitters), with glial cells providing support. In AP Psychology, you connect this process to behavior and mental processes: how neurotransmitters shape mood, learning, and movement, how disrupted transmission causes disorders like multiple sclerosis or myasthenia gravis, and how psychoactive drugs change neural firing.

AP Psych 1.3 Neurons and Neural Firing

AP Psych 1.3 is about how neurons communicate and how that communication affects behavior and mental processes. A neuron receives input, reaches threshold, fires an all-or-none action potential, releases neurotransmitters into the synapse, and then resets during the refractory period.

The exam focus is function, not labeling a neuron diagram. You should be able to explain what neurons and glial cells do, how excitatory and inhibitory messages affect firing, how neurotransmitters and hormones relate to behavior, and how psychoactive drugs act as agonists, antagonists, or reuptake inhibitors.

Why This Matters for the AP Psychology Exam

This topic shows up on the exam as questions about function, not labeling parts. You will not be asked to point out a dendrite or axon on a diagram. Instead, expect to explain how neural communication works, match neurotransmitters to their effects on behavior and mental processes, and predict what happens when transmission is disrupted.

On multiple-choice questions, you will apply concepts like the all-or-none principle, excitatory versus inhibitory signals, and how agonists or antagonists change firing. On the free-response questions, you may need to use neuron and neurotransmitter concepts as evidence when you explain a behavior or evaluate a scenario. Getting comfortable with this process now also pays off later, since memory (Unit 2) and psychological disorders (Unit 5) build on these biological foundations.

Key Takeaways

• Neurons transmit information; glial cells provide structure, insulation, communication, and waste cleanup.
• Neural firing follows a set order: resting potential, threshold, the all-or-none action potential with depolarization, neurotransmitter release, reuptake, and a refractory period.
• Each neurotransmitter has specific functions, and messages are either excitatory (firing more likely) or inhibitory (firing less likely).
• Hormones act like neurotransmitters but travel through the bloodstream and work more slowly.
• Psychoactive drugs work as agonists, antagonists, or reuptake inhibitors, and the main classes are stimulants, depressants, hallucinogens, and opioids.
• Drug use can lead to tolerance, addiction, and withdrawal.

Neural Cells in Behavior

Two types of cells drive everything the nervous system does.

• Neurons carry messages throughout the nervous system.
• Glial cells support neurons by providing structure, insulation (including forming myelin), communication between cells, and waste cleanup.

Together, these cells are the building blocks of all behavior and mental processes. Without glial support, neurons could not function well.

Spinal Reflex Arc

A reflex arc is a fast, automatic response that happens in the spinal cord, so you react before your brain fully processes the pain. Touching a hot stove and yanking your hand away is the classic example.

This shows how neurons in the central and peripheral nervous systems work together to respond to a stimulus, often faster than conscious thought.

The Neural Transmission Process

Neural firing follows a specific, orderly pattern:

1. Resting potential - The neuron is polarized, with a negative charge inside relative to outside, ready to fire.

2. Threshold - Incoming excitatory signals must reach a minimum level to trigger firing.

3. All-or-none principle - Once threshold is reached, the neuron fires completely. If threshold is not reached, it does not fire. There is no partial firing.

4. Action potential and depolarization - An electrical impulse travels down the axon as the neuron's charge briefly flips to more positive.

5. Neurotransmitter release - At the axon terminal, neurotransmitters are released into the synapse, the gap between neurons.

6. Receptor binding - Neurotransmitters bind to receptors on the next neuron and have excitatory or inhibitory effects.

7. Reuptake - Some neurotransmitters are reabsorbed by the sending neuron, ending the signal.

8. Refractory period - The neuron resets and cannot fire again right away.

Note: The sodium-potassium pump is not tested on the AP Psychology Exam.

Disruptions to this process can cause specific conditions:

• Multiple sclerosis - damage to the myelin disrupts neural signals.
• Myasthenia gravis - the immune system interferes with acetylcholine, weakening muscle control.

Neurotransmitters: Chemical Messengers

Neurotransmitters carry signals across the synapse. Their effect depends on where they act in the nervous system. Excitatory messages make an action potential in the next neuron more likely; inhibitory messages make it less likely.

Reminder: Only these neurotransmitters (dopamine, serotonin, norepinephrine, glutamate, GABA, endorphins, substance P, and acetylcholine) are tested on the AP Psychology Exam.

Hormones and Behavior

Hormones are chemical messengers like neurotransmitters, but they travel through the bloodstream and act more slowly.

You do not need to memorize the glands of the endocrine system for the exam (the pituitary gland is the exception, covered with brain structures).

Psychoactive Drugs and Behavior

How Drugs Affect the Brain

Psychoactive drugs change neurotransmitter function in three main ways:

The heroin, Prozac, and similar drug names here are examples that illustrate the mechanisms, not required AP content. The required idea is the agonist, antagonist, and reuptake inhibitor categories themselves.

Drug Class Effects

Psychoactive drugs have both psychological effects (mood, perception, thinking, consciousness) and physiological effects (heart rate, breathing, coordination, and other body functions).

• Stimulants, such as caffeine and cocaine, typically increase neural activity. They can raise alertness and energy as well as heart rate.
• Depressants, such as alcohol, typically decrease neural activity. They can reduce inhibitions and slow reaction time.
• Hallucinogens, such as marijuana, typically distort perception and cognition.
• Opioids, such as heroin, typically act as pain relievers and can slow body functions like breathing.

The required examples are caffeine and cocaine (stimulants), alcohol (depressant), marijuana (hallucinogen), and heroin (opioid). Other drug names like nicotine, LSD, or morphine are useful illustrations but are not required AP content.

Tolerance and Addiction

Repeated psychoactive drug use can lead to tolerance and addiction.

As the brain adapts to a drug, it can develop tolerance, meaning more of the drug is needed for the same effect.

Addiction involves:

• Compulsive drug-seeking despite harm
• Disruption to natural reward systems
• Risk of withdrawal when use stops

Withdrawal symptoms can be physical (shaking, sweating, nausea) or psychological (anxiety, cravings, low mood).

How to Use This on the AP Psychology Exam

MCQ

• Focus on function, not parts. Questions ask what a neurotransmitter does or what happens during transmission, not where a structure is.
• Connect each neurotransmitter to its role (for example, GABA calms activity, glutamate supports learning and memory, dopamine relates to reward and movement).
• Watch for excitatory versus inhibitory wording, since it determines whether firing becomes more or less likely.
• Know that disrupted transmission can produce disorders like multiple sclerosis (myelin damage) or myasthenia gravis (acetylcholine problems).

Free Response

• Use neuron and neurotransmitter concepts as precise evidence when you explain a behavior or analyze a scenario.
• Apply terms accurately. If a question describes a calm, less anxious state, an inhibitory neurotransmitter like GABA fits.
• When a scenario involves a drug, identify whether it acts as an agonist, antagonist, or reuptake inhibitor and connect that to the behavior described.

Common Trap

• Do not say a neuron fires "harder" with a stronger stimulus. The all-or-none principle means it either fires fully or not at all; a stronger stimulus changes how often it fires, not how strongly.

Common Misconceptions

• Neurons do not physically touch when they communicate. Neurotransmitters cross a tiny gap called the synapse.
• The all-or-none principle does not mean every neuron in the brain fires together. It means a single neuron either fires completely or does not fire.
• Excitatory does not mean "good" and inhibitory does not mean "bad." Both are normal and necessary; inhibitory signals keep activity in balance.
• A neurotransmitter does not have one fixed effect everywhere. Its function can change based on its location and the receptors it binds to.
• Hormones and neurotransmitters are not the same. Hormones travel through the bloodstream and act more slowly than neurotransmitters.
• Agonists and antagonists both bind to receptors. The difference is that agonists encourage firing while antagonists block or reduce it.

Related AP Psychology Guides

• 1.2 Overview of the Nervous System
• 1.4 The Brain
• 1.5 Sleep
• 1.6 Sensation
• 1.1 Interaction of Heredity and Environment