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AP Psychology39Updated Sep 18, 20264 pages

AP Psychology Unit 2: Biological Bases of Behavior

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Leticia Siburian@leticiasbrn29
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The nervous system is your body's command center, coordinating everything from your heartbeat to your thoughts. This guide breaks down how genes, hormones, neurons, and brain structures work together to control your behavior, emotions, and bodily functions—essential knowledge that helps explain why you think and act the way you do.
AP Psych unit 2 – page 1

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Genetics and the Nervous System

Ever wonder why you might act like your parents? Behavioral geneticists study how genes and environment shape who we are. Twin and adoption studies are particularly revealing—identical twins share the same genes but not identical copies, making them perfect for studying nature versus nurture influences.

Your body's communication networks are fascinating! The endocrine system works through glands that release hormones into your bloodstream. Unlike the lightning-fast nervous system, hormones work more slowly but have longer-lasting effects. Key players include the pituitary gland (releasing growth hormone and oxytocin for bonding), adrenal glands (triggering fight-or-flight responses), and the pancreas (regulating blood sugar).

The nervous system is your body's electrochemical messaging network. It divides into the Central Nervous System (brain and spinal cord) and Peripheral Nervous System (everything else). When you touch something hot, a reflex kicks in—your spinal cord processes this information and sends a response before your brain even registers what happened!

Did you know? The autonomic nervous system has two opposing branches: the sympathetic system gets you pumped up for action, while the parasympathetic system calms you back down—like having both an accelerator and brakes for your body!

AP Psych unit 2 – page 2

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Neurons and Neurotransmitters

Neurons are the superheroes of your nervous system! These specialized cells relay messages throughout your body. Each neuron has dendrites that receive information, a cell body that processes it, and an axon that sends the message onward. The axon is often covered with a myelin sheath that speeds up transmission—like adding a turbo boost to your neural messages.

For a message to travel, the neuron must reach its threshold to trigger an action potential. This works on an all-or-none principle—either the message fires completely or not at all. Think of it as flipping a light switch—there's no halfway on!

Your brain uses chemical messengers called neurotransmitters to communicate between neurons. Some are excitatory (like pushing an accelerator), while others are inhibitory (like hitting the brakes). Each neurotransmitter has specific functions: acetylcholine enables muscle action and memory, dopamine influences movement and emotion, and serotonin affects mood and sleep.

Brain Chemistry Alert: Many drugs affect your neurotransmitters—depressants like alcohol slow neural activity, stimulants like caffeine speed things up, and hallucinogens like LSD distort perceptions. Understanding these effects helps explain why substances alter your thoughts and behaviors so dramatically!

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Brain Structure and Function

Your brain is like the world's most complex command center! The brainstem handles basic survival functions—the medulla controls heart rate and breathing, while the cerebellum coordinates movement and balance. These structures evolved first and are found in many animals.

Moving inward, the limbic system is your emotional headquarters. The amygdala processes emotions (especially fear), the hypothalamus maintains your body's balance, and the hippocampus forms explicit memories. When you remember your first day of school or feel nervous before a test, you're experiencing your limbic system at work!

The outer layer—your cerebral cortex—is where higher thinking happens. Different lobes handle specific functions: frontal lobes for decision-making, parietal lobes for touch sensations, occipital lobes for vision, and temporal lobes for hearing. The corpus callosum connects your brain's left hemisphere (analytical) with your right hemisphere (creative).

Mind Blown: Scientists can now see your brain in action! EEG and PET scans show activity patterns, while CT scans and MRIs reveal physical structures. These technologies help us understand how thinking happens and what goes wrong in brain disorders.

AP Psych unit 2 – page 4

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Brain Plasticity and Sleep

Your brain is incredibly adaptable! Neuroplasticity is your brain's remarkable ability to reorganize itself—creating new connections and even growing new neurons (neurogenesis). This is how you learn new skills and recover from brain injuries. Your brain is constantly reshaping itself based on your experiences.

Ever feel sleepy around the same time each night? That's your circadian rhythm—your body's internal clock. The pineal gland produces melatonin when it gets dark, signaling that it's time to sleep. This rhythm helps coordinate your body's functions with the 24-hour day.

Sleep isn't just rest—it's critical for your brain! As you cycle through sleep stages, different brain waves dominate. Light sleep NREM−1NREM-1 features theta waves and possible hallucinations. NREM-2 includes sleep spindles that help with memory. Deep sleep NREM−3NREM-3 shows delta waves and releases growth hormones. Finally, REM sleep brings vivid dreams while your body is paralyzed—protecting you from acting out those dreams!

Sleep Science: Dreams aren't just random stories! Some psychologists distinguish between the manifest content (the actual dream story) and latent content (hidden meanings). Whether dreams help process emotions or are just neural noise, they're a fascinating window into your sleeping mind.

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