GACE Behavioral Science (6–12) (736)

The nervous system serves as the body's primary communication network, divided into two main components: the central nervous system (CNS) and the peripheral nervous system (PNS).

The central nervous system consists of the brain and spinal cord. The brain functions as the command center for all bodily processes, cognition, emotion, and behavior. The spinal cord serves as a conduit for information traveling between the brain and the rest of the body while also controlling certain reflexive actions independently.

The peripheral nervous system includes all neural tissue outside the CNS. It divides into the somatic nervous system and the autonomic nervous system. The somatic nervous system controls voluntary movements and transmits sensory information to the CNS. The autonomic nervous system regulates involuntary functions such as heart rate, digestion, and respiration.

The autonomic nervous system further subdivides into the sympathetic and parasympathetic divisions. The sympathetic nervous system activates the fight-or-flight response, preparing the body for action by increasing heart rate, dilating pupils, and redirecting blood flow to muscles. The parasympathetic nervous system promotes rest-and-digest functions, slowing heart rate, stimulating digestion, and conserving energy.

Neurons are the fundamental units of the nervous system. A typical neuron consists of three main parts: the cell body (soma), dendrites, and axon. The cell body contains the nucleus and maintains cellular functions. Dendrites receive incoming signals from other neurons. The axon transmits signals away from the cell body toward other neurons, muscles, or glands.

Neural communication occurs through electrochemical processes. When a neuron is at rest, it maintains a resting potential of approximately -70 millivolts due to the distribution of ions inside and outside the cell membrane. When stimulation reaches threshold, an action potential occurs—a rapid depolarization that travels down the axon.

Action potentials follow the all-or-none principle: they either fire completely or not at all. The intensity of a stimulus is coded by the frequency of action potentials rather than their magnitude.

At the axon terminal, the action potential triggers the release of neurotransmitters into the synaptic cleft. These chemical messengers bind to receptors on the postsynaptic neuron, potentially generating excitatory or inhibitory effects.

Key neurotransmitters include:

Acetylcholine (ACh) plays essential roles in muscle contraction, attention, and memory. Deficits in ACh are associated with Alzheimer's disease.

Dopamine regulates movement, motivation, reward, and pleasure. Imbalances are linked to Parkinson's disease (deficit) and schizophrenia (excess in certain pathways).

Serotonin influences mood, sleep, appetite, and impulse control. Low serotonin levels are associated with depression and anxiety disorders.

Norepinephrine affects alertness, arousal, and the stress response. It plays a role in attention and mood regulation.

GABA (gamma-aminobutyric acid) is the primary inhibitory neurotransmitter in the brain. It reduces neural excitability and is implicated in anxiety disorders.

Glutamate is the primary excitatory neurotransmitter, involved in learning and memory. Excess glutamate can cause excitotoxicity and neural damage.

Endorphins are natural pain relievers that also produce feelings of pleasure and well-being.

The brain consists of three major divisions: the hindbrain, midbrain, and forebrain.

The hindbrain includes the medulla oblongata, pons, and cerebellum. The medulla controls vital autonomic functions including breathing, heart rate, and blood pressure. The pons assists in sleep regulation and relays information between the cerebellum and cortex. The cerebellum coordinates voluntary movement, balance, and motor learning.

The midbrain contains structures involved in vision, hearing, motor control, and arousal. The reticular formation, extending through the midbrain, regulates alertness and sleep-wake cycles.

The forebrain comprises the cerebral cortex, thalamus, hypothalamus, limbic system, and basal ganglia. The thalamus serves as a sensory relay station, directing incoming information to appropriate cortical areas (except olfaction, which bypasses the thalamus). The hypothalamus regulates homeostatic functions including hunger, thirst, body temperature, and circadian rhythms. It also controls the pituitary gland, linking the nervous and endocrine systems.

The limbic system includes structures critical for emotion and memory. The amygdala processes emotional responses, particularly fear. The hippocampus is essential for forming new declarative memories. The cingulate cortex contributes to emotional processing and attention.

The basal ganglia coordinate voluntary movement and are involved in procedural learning and habit formation. Degeneration of basal ganglia structures underlies Parkinson's disease symptoms.

The cerebral cortex is the outer layer of the cerebrum, responsible for higher cognitive functions. It divides into four lobes:

The frontal lobe controls executive functions, planning, decision-making, voluntary movement, and speech production. The prefrontal cortex handles complex cognitive processes including working memory and impulse control. The motor cortex, located in the precentral gyrus, controls voluntary movements. Broca's area, typically in the left frontal lobe, is essential for speech production.

The parietal lobe processes somatosensory information including touch, temperature, pain, and proprioception. The somatosensory cortex lies in the postcentral gyrus. This lobe also contributes to spatial awareness and attention.

The temporal lobe processes auditory information and is involved in language comprehension, memory, and object recognition. Wernicke's area, typically in the left temporal lobe, is critical for language comprehension. The temporal lobe also houses portions of the hippocampus and amygdala.

The occipital lobe is primarily dedicated to visual processing. The primary visual cortex receives input from the eyes via the thalamus.

The cerebral hemispheres demonstrate functional asymmetry. In most individuals, the left hemisphere specializes in language, logic, analytical thinking, and sequential processing. The right hemisphere excels at spatial processing, facial recognition, emotional expression, and holistic processing.

The corpus callosum connects the two hemispheres, allowing communication between them. Split-brain studies, conducted on patients with severed corpus callosum, revealed the extent of hemispheric specialization.

The endocrine system communicates through hormones secreted into the bloodstream. The hypothalamus links the nervous and endocrine systems by controlling the pituitary gland.

The pituitary gland, often called the master gland, releases hormones that regulate other endocrine glands. The anterior pituitary secretes growth hormone, thyroid-stimulating hormone, adrenocorticotropic hormone (ACTH), and gonadotropins. The posterior pituitary releases oxytocin and antidiuretic hormone.

The adrenal glands sit atop the kidneys. The adrenal medulla secretes epinephrine and norepinephrine during stress. The adrenal cortex produces cortisol, which mobilizes energy and suppresses immune function during prolonged stress.

The thyroid gland regulates metabolism through thyroid hormones. The gonads (ovaries and testes) produce sex hormones including estrogen, progesterone, and testosterone.

Behavioral genetics examines how genetic and environmental factors influence behavior. Genes are segments of DNA that provide instructions for protein synthesis. Humans have approximately 20,000-25,000 genes organized on 23 pairs of chromosomes.

Genotype refers to an organism's genetic makeup. Phenotype refers to observable characteristics resulting from gene-environment interactions.

Heritability estimates indicate the proportion of variance in a trait attributable to genetic differences within a population. High heritability does not mean a trait is unaffected by environment.

Twin studies compare concordance rates between monozygotic (identical) and dizygotic (fraternal) twins. Higher concordance in identical twins suggests genetic influence. Adoption studies examine whether adopted children resemble biological or adoptive parents more closely for particular traits.

Epigenetics studies how environmental factors can modify gene expression without altering DNA sequences. These modifications can sometimes be transmitted across generations.

Sensation refers to the detection of physical energy by sensory receptors. Perception involves the interpretation and organization of sensory information.

Transduction is the process by which sensory receptors convert physical energy into neural signals. Different receptors respond to different forms of energy: photoreceptors respond to light, mechanoreceptors to pressure, chemoreceptors to chemical substances, and thermoreceptors to temperature.

The absolute threshold is the minimum stimulus intensity detectable 50% of the time. The difference threshold (just noticeable difference or JND) is the smallest difference between two stimuli that can be detected 50% of the time.

Weber's Law states that the JND is proportional to the original stimulus intensity. Larger stimuli require larger differences to be detected.

Signal detection theory proposes that detection depends not only on stimulus strength but also on psychological factors including motivation, expectation, and attention. It distinguishes between sensitivity (ability to detect signals) and response bias (tendency to report detection).

Sensory adaptation occurs when sensitivity to a constant stimulus decreases over time. This allows the sensory system to remain responsive to changes rather than unchanging conditions.

Light enters the eye through the cornea, which begins focusing. It passes through the pupil, the opening controlled by the iris. The lens further focuses light onto the retina, the light-sensitive tissue at the back of the eye.

The retina contains two types of photoreceptors. Rods, concentrated in the periphery, detect low levels of light and enable peripheral and night vision but do not detect color. Cones, concentrated in the fovea (center of the retina), require more light but detect color and enable detailed vision.

Three types of cones respond maximally to short (blue), medium (green), or long (red) wavelengths. Color perception results from the combined activity of these cone types, consistent with trichromatic theory.

Opponent-process theory explains color afterimages and certain aspects of color perception. It proposes that color is processed in opposing pairs: red-green, blue-yellow, and black-white.

Information travels from the retina via the optic nerve to the thalamus (lateral geniculate nucleus) and then to the primary visual cortex in the occipital lobe. Feature detectors in the visual cortex respond to specific stimulus features such as edges, angles, and movement.

Sound waves are collected by the outer ear and channeled through the ear canal to the tympanic membrane (eardrum), which vibrates. These vibrations pass through the ossicles (hammer, anvil, stirrup) in the middle ear to the oval window.

The cochlea in the inner ear contains fluid and the basilar membrane. Sound vibrations cause waves in the cochlear fluid, displacing the basilar membrane. Hair cells on the basilar membrane transduce mechanical energy into neural signals.

Place theory proposes that different frequencies activate different locations along the basilar membrane. High frequencies activate the base; low frequencies activate the apex. Frequency theory suggests that the rate of neural firing matches the frequency of the sound wave. Volley principle explains how groups of neurons can fire in alternating volleys to represent frequencies higher than a single neuron could encode.

Sound localization depends on interaural time differences (sound arriving at one ear before the other) and interaural intensity differences (sound being louder in one ear).

Taste (gustation) involves receptors in taste buds that detect five basic qualities: sweet, sour, salty, bitter, and umami. Taste perception interacts with smell to create flavor.

Smell (olfaction) involves receptors in the olfactory epithelium that respond to airborne molecules. Olfactory information travels directly to the olfactory cortex and limbic system without first passing through the thalamus, explaining the strong connection between smell and emotion/memory.

Touch involves multiple receptor types detecting pressure, temperature, and pain. The somatosensory cortex maps touch sensations, with more sensitive body areas receiving greater cortical representation (somatosensory homunculus).

Pain involves nociceptors that detect potentially damaging stimuli. Gate control theory proposes that spinal cord mechanisms can block or allow pain signals to reach the brain. Psychological factors significantly influence pain perception.

The vestibular sense detects head position and movement, contributing to balance. Receptors in the semicircular canals and otolith organs in the inner ear respond to rotation and linear acceleration.

Proprioception (kinesthesis) provides information about body position and movement through receptors in muscles, tendons, and joints.

Gestalt principles describe how we organize visual elements into coherent patterns. Key principles include:

Binocular cues require both eyes. Retinal disparity involves the slightly different images each eye receives; the brain uses this difference to compute depth. Convergence refers to the degree to which eyes turn inward for nearby objects.

Monocular cues can be detected with one eye. These include relative size (smaller objects appear farther), interposition (objects blocking others appear closer), linear perspective (parallel lines converging in the distance), texture gradient (finer texture indicates greater distance), and motion parallax (nearby objects appear to move faster when the observer moves).

Size constancy allows us to perceive objects as maintaining constant size despite changes in retinal image size with distance.

Shape constancy allows us to recognize objects as maintaining constant shape despite changes in the angle of view.

Color constancy allows us to perceive consistent color despite changes in lighting conditions.

Selective attention enables focus on particular stimuli while filtering out others. The cocktail party effect demonstrates our ability to attend to one conversation amid many while still noticing personally relevant information (like our name) in unattended channels.

Inattentional blindness occurs when we fail to perceive visible objects because attention is directed elsewhere. Change blindness refers to difficulty detecting changes in visual scenes.

Consciousness refers to awareness of internal and external stimuli. It exists on a continuum from full alertness to deep unconsciousness. States of consciousness vary in levels of awareness, attention, and responsiveness.

Circadian rhythms are biological cycles lasting approximately 24 hours. The suprachiasmatic nucleus (SCN) in the hypothalamus serves as the master biological clock, regulating sleep-wake cycles. Light exposure influences the SCN, which controls melatonin release from the pineal gland. Melatonin promotes sleepiness as darkness increases.

Sleep progresses through distinct stages, measured by electroencephalogram (EEG), electromyogram (EMG), and electrooculogram (EOG).

Stage 1 (N1) is light sleep, characterized by theta waves. Hypnagogic hallucinations and myoclonic jerks may occur.

Stage 2 (N2) features sleep spindles and K-complexes. Body temperature drops and heart rate slows.

Stage 3 (N3), also called slow-wave sleep or deep sleep, is dominated by delta waves. This stage is important for physical restoration and growth hormone release. It is most difficult to awaken from this stage.

REM (Rapid Eye Movement) sleep features brain activity similar to waking, rapid eye movements, and muscle atonia (paralysis). Most vivid dreaming occurs during REM. REM sleep is important for memory consolidation and emotional processing.

Sleep cycles through these stages approximately every 90 minutes, with REM periods increasing in duration toward morning while deep sleep decreases.

Sleep deprivation impairs attention, memory, decision-making, immune function, and emotional regulation. Chronic sleep debt increases risk for obesity, diabetes, cardiovascular disease, and mental health disorders. Microsleeps (brief involuntary sleep episodes) can occur during severe sleep deprivation, posing safety risks.

Insomnia involves difficulty falling asleep, staying asleep, or obtaining restorative sleep. It may be acute or chronic and has multiple causes including stress, medical conditions, and poor sleep hygiene.

Sleep apnea involves repeated breathing interruptions during sleep, causing fragmented sleep and daytime fatigue. Obstructive sleep apnea results from airway collapse; central sleep apnea involves failure of brain signals controlling breathing.

Narcolepsy causes excessive daytime sleepiness and sudden sleep attacks. It may include cataplexy (sudden muscle weakness triggered by emotion), sleep paralysis, and hypnagogic hallucinations.

Parasomnias include sleepwalking (somnambulism), sleep terrors (intense fear during sleep, usually in children), and REM sleep behavior disorder (acting out dreams due to failure of muscle atonia).

Dreams occur primarily during REM sleep, though some dreaming occurs in other stages. Dream content often incorporates recent experiences (day residue).

Freud's psychoanalytic theory proposed that dreams represent wish fulfillment, with manifest content (surface story) masking latent content (unconscious desires).

Activation-synthesis theory suggests dreams result from the brain's attempt to make sense of random neural activity during REM sleep.

Information-processing theory proposes that dreams help consolidate memories and process information from waking hours.

Threat simulation theory suggests dreams evolved to simulate threatening events, allowing rehearsal of threat responses.

Hypnosis is a state of heightened suggestibility and focused attention. Under hypnosis, individuals may experience altered perceptions, increased responsiveness to suggestions, and posthypnotic amnesia.

Social-cognitive theory explains hypnosis as a product of social expectations and role-playing rather than a distinct altered state.

Dissociation theory proposes that hypnosis involves a split in consciousness, with a hidden observer maintaining awareness.

Hypnosis has clinical applications including pain management, habit change, and anxiety reduction, though effectiveness varies across individuals.

Psychoactive drugs alter consciousness by affecting neurotransmitter activity. They are classified by their primary effects.

Depressants slow nervous system activity. Alcohol enhances GABA and inhibits glutamate, causing relaxation, impaired judgment, and motor coordination deficits. Barbiturates and benzodiazepines also enhance GABA activity.

Stimulants increase nervous system activity. Caffeine blocks adenosine receptors, promoting alertness. Nicotine activates acetylcholine receptors and triggers dopamine release. Amphetamines and cocaine increase dopamine, norepinephrine, and serotonin activity, producing euphoria and increased energy.

Opioids include morphine, heroin, and prescription painkillers. They bind to endorphin receptors, reducing pain and producing euphoria. They carry high addiction potential and overdose risk.

Hallucinogens distort perception and cognition. LSD and psilocybin primarily affect serotonin receptors. Cannabis (marijuana) contains THC, which binds to cannabinoid receptors, producing relaxation, altered perception, and impaired memory.

Tolerance occurs when repeated use requires increasing doses to achieve the same effect.

Physical dependence involves physiological adaptation such that discontinuation produces withdrawal symptoms.

Psychological dependence involves craving and compulsive drug-seeking behavior.

Addiction is characterized by compulsive use despite negative consequences, loss of control, and preoccupation with obtaining and using the substance.

Meditation practices involve focused attention or open monitoring to achieve relaxed awareness. Concentrative meditation focuses on a single object, sound, or sensation. Mindfulness meditation involves non-judgmental awareness of present-moment experiences.

Regular meditation practice is associated with reduced stress, improved attention, and alterations in brain structure and function.