AP Psychology Unit 1 (Biological Bases of Behavior): Biological Bases Study Notes

The Nervous System

When psychologists talk about “biological bases of behavior,” they’re often pointing to the nervous system—your body’s fast-acting communication network. It matters because nearly every psychological process you study (sensation, emotion, learning, memory, motivation, sleep) depends on patterns of neural communication. If you understand the organization of the nervous system, you can explain why different kinds of injuries, drugs, or diseases create specific behavioral changes.

Big picture: two major divisions

A useful starting map is to split the nervous system into:

• Central nervous system (CNS): the brain and spinal cord. This is the main control center—where information is integrated and decisions are made.
• Peripheral nervous system (PNS): all the nerves that carry information to the CNS (sensory input) and from the CNS (motor output). The PNS connects the CNS to the rest of the body.

A common misconception is that the brain “does everything” and the rest is just wiring. In reality, the PNS and spinal cord do significant processing—especially for reflexes and basic movement patterns.

The spinal cord and reflexes

The spinal cord is not just a cable; it’s a two-way highway and a rapid-response center. A reflex is an automatic response to a stimulus that occurs without needing the brain’s full involvement.

How a reflex works (reflex arc)

1. A sensory receptor detects something (like pain from touching a hot surface).
2. A sensory neuron carries the signal into the spinal cord.
3. Interneurons in the spinal cord quickly route the signal.
4. A motor neuron sends a command to muscles, pulling your hand away.
5. The brain is informed a moment later—so you become consciously aware of pain after the withdrawal begins.

This matters psychologically because it shows that not all behavior is conscious or deliberate, and that “reaction time” can differ depending on whether the brain must interpret the situation.

The peripheral nervous system: somatic vs autonomic

The PNS is often divided into:

• Somatic nervous system: controls voluntary skeletal muscle movements (like writing, walking) and carries sensory information to the CNS.
• Autonomic nervous system (ANS): controls involuntary bodily functions (heart rate, digestion, pupil dilation). The ANS is central to stress and emotion.

Sympathetic vs parasympathetic

The ANS has two main branches that usually work in opposition—like a gas pedal and a brake.

• Sympathetic nervous system: arouses the body for action (fight-or-flight).
• Parasympathetic nervous system: calms the body and conserves energy (rest-and-digest).

A key idea: the sympathetic system doesn’t just mean “fear,” and parasympathetic doesn’t just mean “relaxed.” Both are active, adaptive systems used in many contexts (exercise, digestion, recovery, focusing attention).

Example in action: If you’re about to give a speech, sympathetic activation may increase heart rate and sweating. Afterward, parasympathetic processes help return your body to baseline.

Nerves, neurons, and direction of information

A nerve is a bundle of axons (many neuron “wires”) in the PNS. Information flow is often described as:

• Afferent (sensory): toward the CNS.
• Efferent (motor): away from the CNS.

Students often mix these up; a memory trick is: Afferent Arrives at the CNS; Efferent Exits the CNS.

Exam Focus

• Typical question patterns:
  • Identify whether a scenario involves CNS vs PNS, or somatic vs autonomic control.
  • Predict which ANS branch is active given bodily symptoms (pupil changes, heart rate, digestion).
  • Explain reflexes and why they can occur before conscious awareness.
• Common mistakes:
  • Treating “autonomic” as meaning “unimportant” or “only emotions”—it controls crucial homeostatic functions.
  • Saying the parasympathetic system “turns off” the sympathetic system; they often operate simultaneously in balance.
  • Confusing afferent/efferent; use the Arrives/Exits cue.

The Brain and Its Functions

The brain is the CNS command center that integrates information, coordinates movement, and enables cognition and emotion. In AP Psychology, you’re expected to know major structures, what they do, and how scientists study them. This is less about memorizing isolated “parts” and more about understanding systems: networks of regions working together.

How psychologists study the brain (methods you should recognize)

Because you can’t always experimentally manipulate the human brain, psychologists use converging methods:

• Lesion studies: examining behavior after brain tissue damage (from injury, surgery, or disease). This supports function-location links, but damage can affect multiple areas and connections.
• Electroencephalogram (EEG): records electrical activity through electrodes on the scalp. Great for timing (like sleep stages), limited for pinpointing deep sources.
• CT (computed tomography) scan: X-ray “slices” of brain structure. Useful for detecting structural damage.
• PET (positron emission tomography) scan: shows brain activity by tracking glucose/metabolic processes (often via a tracer). Useful for comparing activity patterns across tasks.
• MRI (magnetic resonance imaging): detailed structural images of soft tissue.
• fMRI (functional MRI): shows changes associated with blood flow/oxygenation as a proxy for activity, combining decent spatial detail with functional information.

Common misconception: Brain scans “read thoughts.” They don’t. They measure correlates of activity (electrical signals or blood flow), and interpretation is statistical and indirect.

The brainstem: survival functions

The brainstem is an older (evolutionarily) region important for automatic survival functions.

• Medulla: controls vital functions like heartbeat and breathing.
• Pons: involved in sleep/arousal and helps coordinate movement; also relays information.
• Reticular formation: a network involved in arousal, alertness, and filtering incoming stimuli.

Why it matters: If these systems are disrupted, basic life-sustaining processes and consciousness can be affected. Many drug effects (sedation, alertness) tie back to these systems.

Cerebellum: coordination and more

The cerebellum (at the back of the brain) is classically linked to balance, coordination, and fine motor control. In AP Psychology, it’s also often connected to procedural memory—learning skills and habits (like typing).

Example: A person with cerebellar damage might have trouble with smooth movements or balance even if they understand what they want to do.

Thalamus: sensory relay hub

The thalamus routes most sensory information (except smell) to appropriate cortical regions. You can think of it as a switching station that helps decide where sensory messages go.

Misconception to avoid: The thalamus doesn’t “process all perception” by itself; it relays and integrates, but the cortex does much of the detailed interpretation.

The limbic system: emotion, motivation, memory

The limbic system is a set of structures involved in emotion, motivation, and memory.

• Amygdala: processes emotional significance—especially threat-related cues; important for fear and aggression.
• Hippocampus: helps form and consolidate new explicit (declarative) memories.
• Hypothalamus: regulates hunger, thirst, body temperature, and drives; controls the pituitary gland and is central in linking the nervous system to the endocrine system.

Example: If the hippocampus is damaged, a person may struggle to form new long-term explicit memories while older memories and skills can remain.

The cerebral cortex: higher-level processing

The cerebral cortex is the wrinkled outer layer of the brain, associated with complex cognition, perception, and voluntary movement. It’s divided into lobes, each with characteristic functions.

The four lobes (and what questions tend to test)

• Frontal lobes: planning, decision-making, impulse control, and voluntary movement.
• Parietal lobes: processing touch/body sensations and spatial awareness.
• Occipital lobes: visual processing.
• Temporal lobes: auditory processing, language comprehension, and memory-related processing.

Motor and sensory cortex

Two strips of cortex are especially common on AP questions:

• Motor cortex (frontal lobe): controls voluntary movements. Different body areas map onto different regions (often shown as a “homunculus”).
• Somatosensory cortex (parietal lobe): registers touch, pressure, pain, and body position.

The mapping emphasizes that body parts needing fine control or high sensitivity take up more cortical space (hands, face).

Association areas

Association areas are cortical regions not devoted to basic sensory or motor functions; they integrate information for higher mental functions like learning, remembering, thinking, and language.

A frequent student error is to treat association areas as a single “place.” They’re distributed throughout the cortex.

Language: Broca’s and Wernicke’s areas

Language is often used to demonstrate localization of function.

• Broca’s area (typically in the left frontal lobe): involved in speech production. Damage can lead to slow, effortful speech (Broca’s aphasia) while comprehension may be relatively better.
• Wernicke’s area (typically in the left temporal lobe): involved in language comprehension. Damage can produce fluent but nonsensical speech with poor understanding (Wernicke’s aphasia).

Common misconception: People often think Broca’s equals “speaking” and Wernicke’s equals “hearing.” More accurately, Broca’s is about producing language, and Wernicke’s is about understanding meaningful language.

Hemispheric specialization and split brain

The brain has two hemispheres connected by the corpus callosum, a thick band of nerve fibers enabling communication.

• Hemispheric specialization (lateralization): some functions are more dominant in one hemisphere (language is often left-lateralized; certain spatial tasks often rely more on the right).
• Split-brain research: in rare cases, the corpus callosum is cut to reduce severe seizures. This can reveal how each hemisphere can process information somewhat independently.

Classic idea (how it shows up on exams): If an image is presented to the left visual field, it goes primarily to the right hemisphere. If language centers are primarily in the left hemisphere, the person may have difficulty verbalizing what was seen—yet may still be able to select or draw it.

Be careful: AP questions usually focus on the logic of information flow rather than expecting extreme claims like “the right brain is creative and the left brain is logical.” That popular myth oversimplifies how integrated the brain really is.

Brain plasticity

Plasticity is the brain’s ability to change by reorganizing after damage or through experience. This matters because it helps explain:

• recovery patterns after injury
• how learning changes neural connections
• why early experience can have long-term effects

Plasticity is not unlimited. For example, some functions are harder to regain after certain types of damage, and reorganization may be more effective at younger ages.

Exam Focus

• Typical question patterns:
  • Match a brain structure to a function (e.g., medulla with breathing, hippocampus with forming new memories).
  • Interpret a short vignette (patient symptoms) to infer which region may be affected (e.g., Broca’s vs Wernicke’s aphasia).
  • Compare brain-imaging methods (what each measures, strengths/limits).
• Common mistakes:
  • Saying “the thalamus controls all senses including smell” (smell is the key exception commonly tested).
  • Overstating left/right brain differences as absolute; AP tends to emphasize specialization with communication.
  • Confusing Broca’s and Wernicke’s; anchor them to production vs comprehension.

Neural Firing and Neurotransmitters

To connect biology to behavior, you need a clear model of neural communication. Neurons are the basic units that receive, process, and transmit information. What makes this psychological (not just biological) is that changes in neural communication help explain changes in mood, learning, attention, pain, and disorders.

Neurons: the building blocks

A neuron is a specialized cell that communicates via electrical and chemical signals.

Key parts (what they are and why they matter):

• Dendrites: branch-like structures that receive messages from other neurons.
• Cell body (soma): contains the nucleus; integrates incoming signals.
• Axon: a long fiber that carries signals away from the cell body.
• Myelin sheath: fatty insulation around axons (formed by glial cells) that speeds transmission.
• Axon terminals: endings that release chemical messengers.

Glial cells (glia) support neurons by feeding them, cleaning up waste, and helping form myelin. A common misconception is that glia are just “glue” and don’t matter; in reality, they’re essential for healthy signaling.

The action potential: how a neuron “fires”

Neurons communicate internally using an action potential, a brief electrical impulse that travels down the axon.

Core ideas to understand (how it works):

1. Resting potential: when not firing, a neuron has a stable negative charge inside relative to outside.
2. Threshold: if incoming signals push the neuron past a certain point, an action potential begins.
3. All-or-none response: once threshold is reached, the neuron fires completely; if threshold isn’t reached, it doesn’t fire. Stronger stimuli generally increase rate of firing, not size of the action potential.
4. Refractory period: a brief time after firing when the neuron can’t fire (or is less likely to), helping ensure signals move one direction and preventing burnout.
5. Myelination speeds transmission because the signal effectively “jumps” along the axon between gaps in myelin.

Example in action: If you touch something painfully hot, sensory neurons fire rapidly. The pain isn’t because each action potential is “bigger,” but because the neurons fire more often and more neurons are recruited.

Synapses: where chemical communication happens

Between neurons is a tiny gap called the synaptic cleft. The junction is the synapse.

How synaptic transmission works (step by step):

1. An action potential reaches the axon terminals.
2. Vesicles release neurotransmitters into the synaptic cleft.
3. Neurotransmitters bind to receptor sites on the receiving neuron.
4. This binding produces either:
   • an excitatory effect (more likely to trigger an action potential), or
   • an inhibitory effect (less likely to trigger an action potential).
5. Neurotransmitters are cleared by reuptake (taken back into the sending neuron), enzymatic breakdown, or diffusion.

A common student mistake is thinking “excitatory means good and inhibitory means bad.” Inhibitory signals are crucial (for coordinated movement, calm states, preventing seizures).

Neurotransmitters you’re expected to recognize

In AP Psychology, neurotransmitters are frequently tied to both everyday functioning and clinical conditions. You don’t need medical-level detail—focus on the broad psychological associations.

Two important cautions:

• Exams often reward directional thinking (too much/too little) more than perfect clinical nuance.
• Avoid assuming “one neurotransmitter causes one disorder.” Most disorders involve multiple systems and brain regions.

Agonists and antagonists: how drugs affect synapses

A lot of biological psychology questions describe a drug and ask you what it does at the synapse.

• Agonist: increases a neurotransmitter’s action (by mimicking it, releasing more, or blocking reuptake/breakdown).
• Antagonist: decreases a neurotransmitter’s action (by blocking receptors or reducing release).

Example: If a drug blocks dopamine receptors, it acts as a dopamine antagonist. If it prevents serotonin reuptake, it acts as a serotonin agonist in the sense that more serotonin remains available in the synapse.

Putting it together: from neurons to behavior

Neural firing is the “language” of the nervous system, and neurotransmitters are like the words that pass between cells. Changes in:

• firing rates,
• receptor sensitivity,
• reuptake efficiency,
• and neurotransmitter availability

can shift attention, mood, pain, movement, and learning. That’s why drugs (therapeutic or recreational) can change psychology so powerfully: they change synaptic communication.

Exam Focus

• Typical question patterns:
  • A scenario describing synaptic events (release, reuptake, receptor blocking) and asking whether a drug is an agonist or antagonist.
  • Matching neurotransmitters to broad functions (ACh with muscle/memory, dopamine with movement/reward, GABA with inhibition).
  • Explaining all-or-none firing and how intensity is coded (rate of firing, number of neurons).
• Common mistakes:
  • Saying a stronger stimulus makes a “bigger” action potential; it usually increases firing frequency.
  • Treating inhibitory neurotransmitters as “bad” rather than necessary for control and stability.
  • Mixing up agonist vs antagonist; focus on whether the drug increases or decreases the neurotransmitter’s effect.

The Endocrine System

The endocrine system is the body’s slower, longer-lasting chemical communication system. Instead of using electrical impulses along neurons, endocrine glands release hormones into the bloodstream. This matters because many psychological states—stress, mood changes, sexual motivation, energy levels—are shaped by hormones interacting with the brain.

Nervous system vs endocrine system (why you need both)

A helpful way to compare them:

• The nervous system is like a text message: fast, targeted, and brief.
• The endocrine system is like a radio broadcast: slower to start, more widespread, and often longer lasting.

They are deeply connected, especially through the hypothalamus, which helps regulate hormone release and maintains homeostasis (internal stability).

Major glands and what they do

An endocrine gland secretes hormones directly into the bloodstream.

Hypothalamus and pituitary: the control link

• Hypothalamus: in the brain; influences the endocrine system and drives (hunger, thirst, temperature). It helps control the pituitary.
• Pituitary gland: often called the “master gland” because it influences other endocrine glands. It releases hormones that regulate growth and other gland activity.

Be careful with the phrase “master gland”: it’s a useful simplification for AP Psych, but the hypothalamus is a major controller of the pituitary—so “master” doesn’t mean “independent.”

Adrenal glands and the stress response

The adrenal glands sit on top of the kidneys and are central to stress.

• They release epinephrine (adrenaline) and norepinephrine, which support sympathetic nervous system arousal (increasing alertness, heart rate, energy availability).
• They also release other stress-related hormones (commonly discussed in relation to longer-term stress regulation).

Example in action: Before an exam, stress can trigger adrenal activity, making you feel alert and keyed up. A little arousal can help performance, but too much can impair concentration.

Thyroid and metabolism

The thyroid gland influences metabolic rate—how quickly your body uses energy. Thyroid imbalances can affect energy, mood, and weight changes, which is why endocrine issues can sometimes resemble psychological disorders.

Pancreas and blood sugar

The pancreas regulates blood glucose by releasing hormones like insulin. Although AP Psychology doesn’t focus heavily on diabetes biology, the key psychological link is that blood sugar regulation can influence energy and mood.

Gonads: sex hormones

The gonads (ovaries and testes) secrete sex hormones (commonly emphasized are estrogen and testosterone). These hormones influence sexual development and aspects of behavior.

A common misconception is that sex hormones determine behavior in a simple, one-way manner. In reality, hormones interact with environment, learning, culture, and cognition.

Pineal gland and sleep

The pineal gland is associated with secretion of melatonin, which helps regulate sleep-wake cycles. This connection often appears when discussing circadian rhythms.

Feedback loops and homeostasis

Endocrine regulation often uses negative feedback: when hormone levels rise to an appropriate range, signals reduce further release, keeping the system stable.

Even without memorizing specific pathways, you should understand the logic: endocrine systems are often self-correcting to maintain balance.

Interaction with the nervous system: stress as a combined response

Stress is a good example of how these systems cooperate.

• The nervous system (especially sympathetic activation) creates rapid bodily arousal.
• The endocrine system releases hormones that sustain energy and alertness over a longer period.

This combined response can be adaptive in emergencies, but chronic activation can contribute to health and mood problems—one reason psychology pays close attention to stress physiology.

Exam Focus

• Typical question patterns:
  • Distinguish nervous vs endocrine communication based on speed and method (electrical impulses vs hormones in blood).
  • Identify which gland is involved in a described function (thyroid with metabolism, adrenals with arousal/stress, pituitary with regulating other glands).
  • Explain how the hypothalamus links the brain to the endocrine system.
• Common mistakes:
  • Saying the pituitary acts alone as the “master” without hypothalamic control; remember the hypothalamus-pituitary connection.
  • Confusing epinephrine (a hormone in the endocrine context) with neurotransmitters; the same chemical can function differently depending on how it’s released.
  • Assuming hormones always act instantly; endocrine effects are typically slower and longer lasting than neural signals.