Chapter 2: The Biological Perspective Flashcards
Overview of Neuroscience and the Nervous System
Nervous System: An extensive, complex network of specialized cells that carries information to and from all parts of the human body.
Neuroscience: The branch of the life sciences that deals with the biological structure, function, development, genetics, and biochemistry of neurons, nerves, and nervous tissue forming the nervous system.
Behavioral Neuroscience (Biological Psychology): A specific subfield within psychology that focuses on the biological bases of psychological processes, overt behavior, thought, and learning.
Structure and Cellular Components of the Neuron
Neuron: The basic functional cell that makes up the nervous system; it is uniquely structured to receive, process, and send messages within that system.
Anatomical Parts of a Neuron:
Dendrites: Branch-like structures extending outward from the cell body that receive incoming chemical signals from other neurons.
Soma (Cell Body): The central portion of the neuron responsible for maintaining the life and metabolic health of the cell; contains the nucleus.
Axon: A long, single tube-like fiber extending from the soma that conducts the electrical neural impulse away from the cell body toward other cells.
Axon Terminals (Terminal Buttons/Knobs): Swollen, rounded areas located at the ends of the axon branches, responsible for communicating with adjacent nerve cells, muscle cells, or glands.
Glial Cells and Myelination:
Glial Cells (Glia): Non-neuronal brain cells that provide physical scaffolding for neurons to grow on and around, deliver nutrients to neurons, produce myelin insulation, and clean up cellular waste products and dead neurons.
Oligodendrocytes: A specialized type of glial cell that produces myelin sheaths for axons located in the Central Nervous System (CNS) (the brain and spinal cord).
Schwann Cells: A specialized type of glial cell that produces myelin sheaths for axons located in the Peripheral Nervous System (PNS) (the rest of the body).
Myelin Sheath: A fatty substance produced by oligodendrocytes and Schwann cells that coats and wraps around the axons of neurons to insulate, protect, and significantly speed up the transmission of the neural impulse.
Nodes of Ranvier: Unmyelinated gaps along the axon sheath where the electrical impulse regenerates.
Neural Impulse Generation and Electrical Conduction
Ions and Membrane Charge:
Ions: Electrically charged particles located inside and outside the cell fluid.
Interior Charge: Inside the neuron, the intracellular environment is negatively charged relative to the outside when at rest.
Exterior Charge: Outside the neuron, the extracellular fluid is positively charged.
Diffusion: The physical process driving ions to move from areas of high ion concentration to areas of low ion concentration.
Resting Potential:
The state of a neuron when it is not actively firing a neural impulse.
Maintains a stable negative electrical charge of approximately .
Action Potential Dynamics:
Triggering Action Potential: When a neuron receives sufficient stimulation reaching its threshold (approximately to ), voltage-gated sodium channels open.
Ion Influx: Positively charged sodium ions () rapidly enter the inside of the cell, causing a sudden reversal of the electrical charge within the axon (depolarization), reaching a peak of approximately .
Repolarization: Potassium ions () exit the cell, bringing the voltage back down toward resting conditions.
Hyperpolarization: A brief period where the membrane potential becomes slightly more negative than resting potential before stabilizing back to .
Time Course: An action potential event occurs rapidly over to (measured dynamically across to windows).
All-or-None Law:
A neuron either fires its action potential completely at full strength or does not fire at all, functioning analogously to a binary light switch (ON/OFF).
Stronger stimuli do not increase the voltage or strength of a single action potential; instead, they increase the overall frequency/rate of firing.
Chemical Communication Between Neurons
Synaptic Anatomy and Signal Release:
Synapse (Synaptic Gap / Synaptic Cleft): Microscopic fluid-filled space existing between the axon terminals of the presynaptic sending neuron and the dendrites or surface of the postsynaptic receiving cell.
Synaptic Vesicles: Tiny sac-like structures found inside the rounded axon terminal that store chemical signaling agents.
Neurotransmitter: A chemical substance stored inside synaptic vesicles that, upon release into the synapse, diffuses across the gap to bind to and affect the receiving cell.
Receptor Sites: Specific three-dimensional protein molecules embedded on the cell membrane surface of dendrites, muscle cells, or glands, shaped to selectively fit precise neurotransmitters (operating via a "lock and key" mechanism).
Signal Modulation (Excitatory vs. Inhibitory):
Excitatory Neurotransmitters: Cause the receiving cell to depolarize and increase the likelihood of firing an action potential.
Inhibitory Neurotransmitters: Cause the receiving cell to hyperpolarize and decrease the likelihood of firing an action potential.
Exogenous Chemical Interactions:
Agonists: Chemical substances that mimic or enhance the effects of a specific neurotransmitter on receptor sites, increasing or altering cell activity.
Antagonists: Chemical substances that block or inhibit a cell's normal response to natural neurotransmitters or other chemicals.
Synaptic Inactivation Mechanisms:
Reuptake: The enzymatic/cellular mechanism by which released neurotransmitter molecules are actively pumped back into the presynaptic vesicles for recycling.
Enzymatic Degradation: Breakdown of neurotransmitter molecules in the synaptic gap by specialized enzymes (e.g., acetylcholinesterase rapidly clearing acetylcholine, necessary because muscle contractions require immediate turn-off where reuptake would be too slow).
Cocaine Mechanism Example: Cocaine blocks dopamine reuptake transporters, trapping excess dopamine in the synaptic cleft, continuously stimulating dopamine receptors, and intensifying feelings of pleasure.
Major Neurotransmitters and Their Psychological Functions
Acetylcholine (ACh): Excitatory or inhibitory; directly involved in physiological arousal, focused attention, memory formation, and controlling skeletal muscle contractions.
Norepinephrine (NE): Primarily excitatory; plays key roles in autonomic arousal, alertness, vigilance, and mood regulation.
Dopamine (DA): Excitatory or inhibitory; essential for motor movement control, executive coordination, and experiencing sensations of pleasure and reinforcement.
Serotonin (5-HT): Excitatory or inhibitory; critically involved in regulating sleep architecture, mood, anxiety states, and appetite.
GABA (Gamma-Aminobutyric Acid): The primary major inhibitory neurotransmitter in the central nervous system; regulates sleep cycles and inhibits involuntary motor movement.
Glutamate: The primary major excitatory neurotransmitter in the brain; crucial for learning processes, long-term memory formation, nervous system development, and synaptic plasticity.
Endorphins: Inhibitory neuropeptides acting as natural neural regulators; involved in endogenous pain suppression, relief, and feeling pleasure.
Structural and Functional Organization of the Nervous System
The entire human nervous system is hierarchically categorized into two main structural networks: the Central Nervous System (CNS) and the Peripheral Nervous System (PNS).
The Central Nervous System: Brain and Spinal Cord Dynamics
Brain: The command core of the nervous system; interprets and stores incoming sensory information, makes decisions, and sends precise outgoing commands to muscles, glands, and organs.
Spinal Cord: A long bundle of neural fibers and pathways connecting the brain to the peripheral nervous system; carries information to and from the body and manages rapid protective reflexes.
The Reflex Arc (Three Fundamental Neuron Types):
Sensory (Afferent) Neurons: Neurons carrying sensory information from external or internal receptors toward the central nervous system.
Motor (Efferent) Neurons: Neurons transmitting motor commands from the central nervous system out to body muscles and glands.
Interneurons: Centralized processing neurons located within the spinal cord and brain that receive sensory inputs from afferent neurons and send direct commands to efferent neurons; enable fast, automated, life-saving spinal reflexes without waiting for conscious thought processing from the brain.
CNS Recovery and Structural Change:
Neuroplasticity: The extraordinary capability of the brain and individual neural cells to constantly alter both structure and function in direct response to environmental experience or physical trauma.
Neurogenesis: The biological process involving the formation and integration of brand-new functional neurons in specific brain regions.
The Peripheral Nervous System: Somatic and Autonomic Divisions
Peripheral Nervous System (PNS): Comprises all nerves and neurons not enclosed within the brain and spinal cord; branches throughout the body to connect the CNS to sensory organs, muscles, and internal organs.
Somatic Nervous System:
Controls the voluntary skeletal muscles of the body and processes conscious sensory input.
Sensory Pathway (Afferent): Nerves carrying incoming sensory messages from sense organs up to the CNS.
Motor Pathway (Efferent): Nerves carrying outgoing motor instructions from the CNS out to voluntary skeletal muscles.
Autonomic Nervous System (ANS):
Automatically regulates smooth involuntary muscles, internal organs, cardiac tissue, blood vessels, pupil dilation, digestion, and systemic gland secretion.
Sympathetic Division ("Fight-or-Flight"): Reacts to stressful stimuli, threats, and heightened bodily arousal; mobilizes energy resources. Functionally dilates pupils, inhibits tear production, decreases salivation, accelerates heart rate, dilates bronchial passages, suppresses stomach and intestinal digestion, suppresses pancreatic activity, and inhibits bladder contraction.
Parasympathetic Division ("Eat-Drink-and-Rest"): Restores the body to baseline normal functioning after stressful arousal; conserves energy and controls routine day-to-day internal functions. Functionally constricts pupils, stimulates tear glands, increases salivation, slows heart rate, constricts bronchial passages, stimulates stomach and intestinal digestion, activates pancreatic activity, and allows bladder contraction.
The Endocrine Gland System
Endocrine Glands: Specialized ductless glands that secrete chemical messengers called hormones directly into the circulatory bloodstream.
Hormones: Blood-borne chemicals that travel to distant target tissues, organs, and glands, modulating slow-acting bodily functions, metabolic states, emotional regulation, and sexual behavior.
Major Endocrine Structures and Functions:
Pituitary Gland: Located in the brain beneath the hypothalamus; referred to as the "master gland" because its chemical signals control all other endocrine glands; secretes human growth hormone (HGH).
Pineal Gland: Positioned near the base of the cerebrum; secretes the hormone melatonin to track daily light/dark cycles and govern sleep-wake rhythms.
Thyroid Gland: Found in the neck; secretes hormones regulating body metabolic rate.
Parathyroid Glands: Embedded inside or near the thyroid; secretes hormones maintaining precise systemic calcium levels.
Pancreas: Controls blood sugar levels through the secretion of insulin and glucagon.
Gonads: Sex glands (Ovaries in females, Testes in males) that secrete hormones regulating sexual maturation, secondary sex characteristics, reproductive cycles, and sexual behavior.
Adrenal Glands: Positioned atop each kidney; produce over distinct steroid hormones (e.g., cortisol, epinephrine, norepinephrine) to manage physiological stress, regulate salt/water balance, and supply a secondary source of sex hormones during puberty.
Brain Research Methods and Neuroimaging Techniques
Lesioning and Surgical Techniques:
Lesioning Studies: A technique where an insulated wire electrode is inserted into a specific brain structure and an electrical current is passed through to deliberately destroy target cells, allowing researchers to observe behavioral deficits.
Electrical Stimulation of the Brain (ESB): Passing a mild electrical current through implanted electrodes to safely cause target neurons to fire as if naturally activated.
Noninvasive and Invasive Brain Stimulation:
Deep Brain Stimulation (DBS): An invasive procedure where electrodes are surgically placed in deep brain regions and connected to an implanted pulse generator under the chest skin to treat movement or psychiatric disorders.
Transcranial Magnetic Stimulation (TMS / rTMS): A noninvasive procedure applying rapid electromagnetic pulses to the cortex using handheld copper coils positioned over the scalp to stimulate or disrupt localized cortical activity.
Transcranial Direct Current Stimulation (tDCS): Passing weak direct electrical currents across scalp electrodes to alter underlying cortical excitability.
Structural Neuroimaging Methods:
Computed Tomography (CT) Scan (Introduced 1971): A computerized X-ray imaging technique producing cross-sectional structural slices of the brain; useful for identifying bone fractures, stroke damage, and tissue swelling (especially safe when metal is present in the patient's body).
Magnetic Resonance Imaging (MRI) (Introduced 1980s): Uses powerful magnetic fields and radio waves to align hydrogen atoms in body tissue, creating high-resolution structural images; superior spatial resolution for visualizing cell atrophy, tissue degeneration, widening of sulci, and ventricular enlargement.
Functional Neuroimaging Methods:
Electroencephalogram (EEG): Scalp electrodes record the temporal summed electrical activity of cortical surface neurons; measures spontaneous brain waves (classified into delta, theta, alpha, and beta frequency bands) and Event-Related Potentials (ERP).
Magnetoencephalography (MEG): Measures tiny magnetic fields naturally generated by active neuronal electrical signals.
Positron Emission Tomography (PET): Injects a radioactive glucose tracer into the bloodstream; a computer tracks regional cellular glucose consumption to create color-coded maps of functional activity.
Single Photon Emission Computed Tomography (SPECT): Functional brain imaging technique similar to PET that uses longer-lasting radioactive tracers.
Functional MRI (fMRI): Tracks localized changes in blood oxygen levels (the BOLD signal) over time, combining structural resolution with real-time functional activation tracking.
Functional Near-Infrared Spectroscopy (fNIRS): Utilizes near-infrared light spectrum absorption to noninvasively monitor cortical blood oxygenation changes.
Hindbrain and Brainstem Anatomy
Medulla (Medulla Oblongata): The lowest part of the brainstem, located directly superior to the spinal cord; controls vital life-sustaining autonomic functions such as heart rate, respiration, and swallowing.
Pons: The prominent swell located above the medulla that connects the upper brain to lower structures; plays a key role in sleep stages, dreaming, left-right body movement coordination, and general physiological arousal.
Reticular Formation (RF): An extended network of interneuronal fibers running through the center of the medulla and pons; responsible for maintaining conscious alertness, arousal, and selective attention filtering.
Cerebellum: Located at the base of the skull behind the pons; controls and coordinates rapid, fine, complex motor movements, posture, balance, and voluntary/involuntary motor skill execution (e.g., maintaining balance on a narrow beam).
Subcortical Structures: The Limbic System
Limbic System: A group of subcortical forebrain structures arranged beneath the cortex involved in emotional processing, memory formation, learning, and basic motivational drives.
Thalamus: The central sensory relay station of the brain; receives, processes, and directs incoming sensory information (from visual, auditory, tactile, and gustatory pathways—excluding smell) to corresponding target regions of the cerebral cortex.
Hypothalamus: A small structure positioned superior to the pituitary gland and directly beneath the thalamus; serves as the master regulator of homeostasis and basic motivated drives, including hunger, thirst, thermal regulation, sleep cycles, fear, aggression, and sexual behavior.
Hippocampus: A curved, sea-horse-shaped structure situated inside each temporal lobe; vital for converting short-term experiences into long-term declarative memories and encoding spatial location information ("A Place to Remember").
Amygdala: An almond-shaped neural nucleus located near the hippocampus; primary area responsible for processing fear responses, forming fear memories, regulating emotional motivation, and interpreting nonverbal emotional expressions in others.
Cingulate Cortex: The primary cortical component of the limbic fold involved in executive cognitive tasks, attention control, error monitoring, and emotional processing.
The Cerebral Cortex and the Four Lobes
Cortex Structure and Folding:
Cortex: The outermost covering of densely packed, unmyelinated neuronal cell bodies (gray matter) responsible for complex cognitive processes and sensory interpretation.
Corticalization: The evolutionary wrinkling and folding of the cortex (forming gyri and sulci) allowing a large surface area of tissue to fit inside the compact human skull.
Cerebral Hemispheres: The two distinct left and right symmetrical halves of the cerebrum.
Corpus Callosum: A dense, wide band of over myelinated axon fibers that directly connects the left and right cerebral hemispheres, facilitating interhemispheric communication.
The Four Cortical Lobes:
Occipital Lobe: Located at the rear and bottom of each cerebral hemisphere; houses the Primary Visual Cortex (processes direct raw visual input from the eyes) and the Visual Association Cortex (interprets, identifies, and gives meaning to visual scenes).
Parietal Lobe: Located at the top and back of each hemisphere; contains the Somatosensory Cortex (a strip running along the postcentral gyrus responsible for processing tactile skin senses, thermal receptors, body position/proprioception, and taste inputs).
Temporal Lobe: Located behind the temples on both sides; contains the Primary Auditory Cortex (processes raw pitch and auditory tone) and the Auditory Association Cortex (interprets complex auditory information and speech sounds).
Frontal Lobe: Located at the front and top of the brain; responsible for high-level mental processes, executive function, reasoning, planning, decision-making, emotional restraint, and fluent speech production. Contains the Motor Cortex (a strip running along the precentral gyrus that sends voluntary motor command signals down to the somatic motor system).
Cortical Association Areas and Language Processing
Association Cortices: Areas embedded throughout all four lobes of the cortex that coordinate and integrate sensory inputs with stored memories to enable high-level mental tasks.
Broca's Area and Expressive Language:
Located specifically in the left frontal lobe.
Broca's Aphasia: An expressive language deficit resulting from damage to Broca's area; characterized by halting, non-fluent, labored speech, frequent mispronunciations, and struggle to articulate words, while comprehension of language remains largely unimpaired.
Wernicke's Area and Receptive Language:
Located specifically in the left temporal lobe.
Wernicke's Aphasia: A receptive language deficit resulting from damage to Wernicke's area; characterized by fluent, effortless articulation of speech that lacks meaningful semantic content ("word salad") and a severe breakdown in understanding spoken or written language.
Hemispheric Specialization and Prefrontal Functions
Functional Hemispheric Asymmetry:
Left Hemisphere Functions: Controls motor/sensory functions of the right hand and right side of the body; manages spoken language, written language, mathematical computations, logical/analytical thought processes, step-by-step sequential analysis, reading, and detail processing.
Right Hemisphere Functions: Controls motor/sensory functions of the left hand and left side of the body; manages nonverbal communication, visual-spatial processing, musical/artistic processing, emotional perception, holistic global processing ("processes the whole"), pattern recognition, and facial recognition.
Prefrontal Cortex Executive Functions:
Empathy: Understanding and sharing feelings of others.
Insight: Self-awareness and understanding inner mental states.
Response Flexibility: Pausing before reacting to choose adaptive actions.
Emotion Regulation: Balancing emotional responses.
Body Regulation: Regulating autonomic bodily states.
Morality: Ethical decision-making and social fairness.
Intuition: Nonconscious processing and gut-level awareness.
Attuned Communication: Interpersonal connection and resonance.
Fear Modulation: Overriding and controlling limbic fear activation.
Limbic Brain vs. Prefrontal Axis:
Limbic Brain: Mediates automatic fight, flight, or freeze stress responses; constantly evaluates basic safety ("Am I safe? Do people want me?"); serves as the biological seat of raw emotions.
Prefrontal Cortex: Executes top-down cognitive modulation, higher-order executive reasoning, and emotional regulation over limbic reactivity.
Biological Foundations and DSM-5 Criteria for Adult ADHD
Etiology: Attention-Deficit/Hyperactivity Disorder (ADHD) is a biological neurodevelopmental disorder linked to genetics, environmental factors (such as low-level environmental lead exposure), familial/hereditary traits, and altered structural/functional pathways connecting prefrontal and limbic networks.
DSM-5 Adult Diagnostic Criteria:
Requires the persistent presence of symptoms per category in adults, lasting at least .
Symptoms must have been present prior to age .
Symptoms must be present across distinct life settings (e.g., home, work, academic).
Symptoms must cause clear interference with or reduce the overall quality of social, academic, or occupational functioning.
Inattention Category Symptoms: a. Lacks attention to details or makes careless mistakes in tasks. b. Has difficulty sustaining attention during tasks or leisure activities. c. Does not seem to listen when spoken to directly. d. Does not follow through on instructions or complete duties. e. Has difficulty organizing tasks and complex activities. f. Avoids, dislikes, or hesitates to engage in tasks requiring sustained mental effort. g. Frequently loses or misplaces objects necessary for tasks. h. Is easily distracted by extraneous stimuli. i. Is forgetful in routine daily activities.
Hyperactivity and Impulsivity Category Symptoms: a. Fidgets with hands or feet, or squirms in seat. b. Leaves seat frequently in situations where remaining seated is expected. c. Experiences persistent feelings of restlessness. d. Is unable to engage quietly in leisure activities. e. Is always "on the go" or acts as if "driven by a motor." f. Talks excessively. g. Blurts out answers before questions are completely asked. h. Has difficulty awaiting his or her turn. i. Interrupts or intrudes on others during conversations or activities.
