Hallucinogens are substances that profoundly alter sensory perception, and many users experience hallucinations—sensory experiences without external stimuli. This happens because many hallucinogens strongly affect the brain’s perceptual processing, often by acting on serotonin receptors in the cortex, which can distort how sights, sounds, and time are experienced. Classic examples include LSD, psilocybin, and mescaline, all of which are well known for inducing vivid perceptual changes and, at times, true hallucinations. In contrast, stimulants boost brain activity to increase alertness and energy (think stronger focus, faster speech, greater drive) and don’t inherently produce the hallmark perceptual distortions. Depressants slow down CNS activity, leading to sedation or impaired coordination rather than altered perception. Hypnosis isn’t a psychoactive substance class at all; it’s a psychological technique or state that can change attention and perception without introducing a drug into the body.

The scientific method is the process researchers use to study mind and behavior in a systematic, evidence-based way. It describes a repeatable sequence: observe phenomena, formulate hypotheses and predictions, test those predictions through empirical research, draw conclusions from the results, and evaluate those conclusions in light of limitations and possible alternative explanations. This approach keeps findings grounded in data and open to replication, which is essential in psychology. Understanding the other terms helps see why this fits best: a theory is a broad, testable framework that explains many findings and can generate specific hypotheses; a hypothesis is a specific, testable prediction; descriptive research focuses on describing behaviors or phenomena without necessarily testing cause-and-effect or following the full investigative cycle. The scientific method encompasses the entire cycle, making it the best fit for outlining how scientists study mind and behavior.

Action potential is the nerve impulse that travels as a brief wave of positive charge down the axon. When a neuron is at rest, it has a negative resting potential. Gradual, local changes in potential (graded potentials) occur on the dendrites and cell body and vary with stimulus; they’re not the fast, all-or-none spike that travels along the axon. The action potential starts when depolarization reaches threshold, Na+ channels rush the inside positive, and the membrane depolarizes quickly. Na+ channels then inactivate and K+ channels open to repolarize the membrane, with a brief moment of hyperpolarization before returning to resting potential. This spike propagates along the axon to trigger neurotransmitter release at the synapse.

The peripheral nervous system is the network of nerves outside the brain and spinal cord that connects the central nervous system to the rest of the body, carrying out its commands. It transmits motor signals from the brain and spinal cord to muscles and glands and brings sensory information from the body back to the CNS for processing. This distinguishes it from the central nervous system, which consists of the brain and spinal cord themselves, and from the autonomic and endocrine systems, which handle automatic body functions and SAMPLEhormonal signaling, respectively.