Psych Unit 3 Notes
Nervous System Foundations and Neuronal Communication
Neurodiversity represents the biological concept that human brains process information, function, and exhibit behavior through a wide spectrum of variations. Neurodivergence refers to having a brain that operates differently from an established societal average or neurotypical norm. Common manifestations include autism, attention-deficit/hyperactivity disorder (ADHD), and dyslexia, which represent innate pathways of brain development and environmental perception.
Behavioral and sensory accommodations for neurodivergent individuals directly align with distinct nervous system processing styles:
Sensory sensitivities to sound may prevent attendance at loud environments like rap concerts.
Tactile requirements may necessitate specific fabric choices or the complete removal of clothing tags to prevent continuous cutaneous irritation.
Movement requirements in academic or professional settings can involve flexible seating (such as yoga balls instead of standard chairs), movement breaks, and fidget tools.
Neurons are specialized messenger cells that receive, integrate, and transmit information throughout the organism using a combination of electrical impulses and chemical signals. The human nervous system comprises billions of neurons forming an estimated ( or ) connections.
Anatomical Division of the Nervous System:
Central Nervous System (CNS): Includes the brain and spinal cord, housing more than of all nerve cells in the human body.
Brain: Serves as the central processing organ that interprets sensory inputs, formulates cognitive decisions, and issues motor commands.
Spinal Cord: A pencil-thick bundle of nerve fibers traversing the length of the spine. Acts as the primary communication highway and directly mediates reflex arcs.
Peripheral Nervous System (PNS): Encompasses all neural structures situated outside the central nervous system, connecting the CNS to limbs, organs, and peripheral tissues.
Peripheral System Subdivisions and Reflex Mechanisms
Somatic Nervous System: A major division of the peripheral nervous system controlling voluntary muscle structures and conveying conscious sensory information via dedicated pathways.
Sensory Pathway (Afferent): Transmits sensory signals from external receptors toward the central nervous system.
Motor Pathway (Efferent): Transmits motor commands from the central nervous system outward to skeletal muscle groups.
Pathology: Damage to somatic nerve fibers causes peripheral neuropathy, characterized by severe pain and loss of sensation in the feet, legs, and hands. High blood glucose levels in diabetes represent one of the primary causes of peripheral neuropathy, alongside autoimmune diseases, trauma, and infectious conditions.
Autonomic Nervous System: Regulates involuntary visceral functions including respiratory rate, cardiac cycle, glandular secretions, and digestive motility through neural centers situated on or near the spinal cord.
Sympathetic Division: Operates as the emergency and stress response pathway, orchestrating the fight, flight, or freeze state. Physiological alterations include pupillary dilation, inhibition of salivation, acceleration of heart rate, suppression of gastrointestinal motility, and secretion of adrenaline.
Parasympathetic Division: Mediates the calm and vegetative state, restoring physiological stability and supporting homeostasis. Actions include pupillary constriction, stimulation of salivation, deceleration of heart rate, and activation of digestive processes.
Reflex Arcs: Neural circuits in the spinal cord that execute automatic, involuntary motor responses without requiring immediate cerebral intervention.
Pain or heat receptors (sensory neurons) detect a harmful stimulus (such as contact with a hot stove or metal comb) and send rapid impulses to interneurons (relay neurons) in the spinal cord.
Interneurons instantly trigger motor neurons in nearby muscles to contract and pull the limb away prior to conscious pain perception in the cerebral cortex.
Structural and Functional Classification of Neurons
Primary Functional Types of Neurons:
Sensory Neurons (Afferent Neurons): Detect physical or chemical environmental stimuli and transmit corresponding signals into the spinal cord and brain.
Motor Neurons (Efferent Neurons): Carry processed motor commands from the brain or spinal cord out to muscles and target glands.
Interneurons (Relay Neurons): Located within the CNS between sensory and motor pathways, integrating local signaling and executing complex processing networks.
Mirror Neurons: Specialized neurons observed initially in macaque monkey motor cortex studies when primates either executed an action (such as picking up a peanut) or observed another individual performing that same action. These neurons facilitate observational learning, behavioral imitation, and emotional empathy.
Neuronal Architecture:
Dendrites: Branching, treelike cellular extensions that serve as reception sites for incoming chemical signals from adjacent neurons.
Soma (Cell Body): Main metabolic core of the neuron housing the nucleus, responsible for cellular growth, protein synthesis, and basic cellular maintenance.
Axon: A single long, trunk-like fiber extending from the soma that propagates electrical action potentials along its length. Axons can measure thinner than a human hair while stretching lengths exceeding .
Axon Terminals (Terminal Buttons): Specialized bulbous swellings at the terminus of an axon containing synaptic vesicles loaded with chemical neurotransmitters.
Glial Cells and Myelination:
Glial Cells: Non-neuronal support cells that physically anchor neurons into cohesive nerve bundles, maintain local biochemical homeostasis, provide nutritional support, and remove cellular debris.
Schwann Cells: Specialized glial cells in the peripheral nervous system that synthesize the myelin sheath—a protective, insulating layer composed of fat and protein wrapped around the axon.
Nodes of Ranvier: Unmyelinated gaps occurring at regular intervals along a myelinated axon. Action potentials jump directly from node to node (saltatory conduction), significantly accelerating neural transmission speeds from up to .
Neurophysiology: Action Potentials and Synaptic Transmission
Resting Potential Mechanics:
Neural cell membranes are semipermeable and polarized when at rest.
Positively charged sodium ions () are maintained in high concentrations outside the cell membrane, while negatively charged proteins and potassium ions () remain primarily inside.
This unequal ion distribution maintains a stable resting electrical charge of approximately .
Action Potential Generation:
Stimulation of dendrites increases local membrane permeability, causing an influx of positively charged sodium ions into the soma.
When influx pushes the internal charge past a minimum depolarization voltage (the threshold), the cell depolarizes completely, reversing polarity from to approximately .
All-or-Nothing Principle: A neuron either fires a complete action potential at maximum intensity or does not fire at all; increasing stimulus intensity above the threshold does not alter the amplitude or velocity of the resulting impulse.
Propagation occurs along the axon in a unidirectional wave of sodium channel openings lasting approximately ().
Refractory Period:
Immediately following an action potential, sodium channels close for approximately ().
Potassium ions exit the cell and active membrane pumps transport sodium ions back to the extracellular space to restore resting potential at .
During this brief refractory period, the hyperpolarized cell membrane cannot initiate another action potential regardless of stimulus strength.
Chemical Messengers and Synaptic Dynamics
The Synaptic Gap (Synapse): A minute physical space separating the presynaptic axon terminal from the postsynaptic dendrite receptor site.
Neurotransmitter Dynamics:
Action potentials arriving at the axon terminal cause synaptic vesicles to merge with the presynaptic membrane and dump chemical neurotransmitters into the synaptic cleft.
Neurotransmitters cross the gap and bind to specific dendritic receptors in a precise structural lock-and-key mechanism.
Excitatory Postsynaptic Potential: Binding increases the probability that the postsynaptic neuron will reach threshold and fire an action potential.
Inhibitory Postsynaptic Potential: Binding decreases the probability that the postsynaptic neuron will reach threshold, hyperpolarizing the cell.
Reuptake: The metabolic recycling process wherein released neurotransmitters are transported back into the presynaptic cell terminal for repackaging, terminating signal transmission.
Key Neurotransmitters and Physiological Roles
Acetylcholine (ACh): Found across the CNS and PNS. Controls muscle contraction, arousal, attention, and memory encoding. Black widow spider venom forces massive ACh release into neuromuscular junctions, inducing lethal muscular spasms. Severe deficiencies in ACh are linked to Alzheimer's disease.
Norepinephrine: Excitatory neurotransmitter and hormone modulating alertness, vigilance, and stress responses. Directly accelerates heart rate and blood pressure during perceived threats.
Dopamine: Regulates voluntary motor control, cognitive pleasure, and reinforcement pathways. Hyperactivity of dopamine in specific cerebral circuits is linked to schizophrenia; loss of dopamine-producing neurons leads to Parkinson's disease, manifesting as muscular rigidity, resting tremors, and postural instability.
Serotonin: Regulates affective mood states, sleep cycles, hunger, and pain sensitivity. Deficiencies are strongly linked to clinical depression and anxiety disorders. Selective Serotonin Reuptake Inhibitors (SSRIs) block reuptake channels, increasing synaptic serotonin concentration.
Gamma-Aminobutyric Acid (GABA): Principal inhibitory neurotransmitter in the brain that acts as an enzymatic brake system on neural excitation. Low levels of GABA correlate with chronic anxiety and seizure disorders; pharmacological agents like Valium enhance GABAergic inhibition.
Glutamate: Principal excitatory neurotransmitter critical for synaptic plasticity, long-term potentiation, learning, and memory. Excessive glutamate accumulation causes toxic excitotoxicity, triggering severe migraines and epileptic seizures.
Endorphins: Inhibitory neuropeptides that suppress nociceptive pain signals and heighten positive subjective states. Responsible for mediating systemic analgesic effects observed during placebos.
Oxytocin: Neuropeptide and hormone controlling social bonding, interpersonal trust, maternal empathy, labor contractions, lactation, and sexual orgasm.
Summary Mnemonic System ("Eggos and Pies, Ma'am"):
E = Endorphins -> P = Pain reduction
G = GABA -> I = Inhibitory
G = Glutamate -> E = Excitatory
O = Oxytocin -> S = Social
S = Serotonin -> M = Mood
A = Acetylcholine -> A = Arouse
N = Norepinephrine -> A = Activate
D = Dopamine -> M = Movement
Pharmacology, Drug Action, and Neuroglial Diseases
Agonists and Antagonists:
Agonists: Exogenous chemicals or drugs that increase neurotransmitter activity, either by direct receptor activation or by inhibiting reuptake mechanisms.
Antagonists: Drugs or chemicals that bind to neuroreceptors and block endogenous neurotransmitters from binding, suppressing normal downstream signal transduction.
Psychoactive Substance Mechanisms:
Cocaine: Blocks the reuptake transporter proteins for dopamine, causing accumulation of dopamine in the synaptic gap, producing heightened alertness and euphoria.
Ecstasy (MDMA): Direct agonist that causes massive synaptic release of serotonin, yielding transient feelings of euphoria and social connectedness; subsequent serotonin depletion frequently causes acute post-use depression.
Hallucinogens (Psilocybin, LSD): Bind directly to serotonergic receptor networks, distorting sensory processing and generating vivid visual and auditory hallucinations.
Alcohol: Powerful CNS depressant that acts as a GABA agonist. High blood alcohol concentrations inhibit motor coordination in the cerebellum and suppress brainstem activity, risking blackout, respiratory arrest, and death.
Nicotine: Activates nicotinic acetylcholine and glutamate pathways, stimulating central cognitive alertness.
Cannabis (Marijuana): Tetrahydrocannabinol (THC) impacts both GABAergic (inhibitory) and glutamatergic (excitatory) pathways simultaneously. Decreases short-term memory encoding via cannabinoid receptors in the hippocampus. Absence of cannabinoid receptors in the brainstem prevents fatal respiratory depression during acute overdose.
Glial Pathology and Synaptic Pruning:
Microglia and Astrocytes execute essential synaptic pruning—removing structural connections during developmental windows. Aberrant pruning pathways are implicated in schizophrenia, autism, and epilepsy.
Multiple Sclerosis (MS): An autoimmune neurodegenerative disorder wherein the body's immune system attacks and destroys the fatty myelin sheath surrounding CNS axons, exposing bare nerve fibers and impairing motor control, balance, and vision.
Research Findings on Anandamide:
Historical assumptions attributed the euphoria of exercise ("runner's high") entirely to endorphins. Controlled rodent studies demonstrated that blocking endorphins left stress reduction and pain tolerance intact following prolonged treadmill exercise. Blocking the endocannabinoid anandamide eliminated exercise-induced pain relief and anxiety reduction, indicating that endocannabinoids drive runner's high responses.
Macrostructural Organization of the Brain
The Hindbrain (Evolutionationally Oldest Region):
Medulla Oblongata: Situated directly above the spinal cord entrance into the skull. Controls autonomic survival functions including respiration, arterial blood pressure, and cardiac rate.
Pons: Neural bridge connecting lower hindbrain areas to higher cortical centers; coordinates bilateral motor output and regulates REM sleep muscle inhibition.
Cerebellum: Houses roughly of all central neurons. Coordinates fine motor dynamics, posture, equilibrium, and procedural learning; impaired rapidly by ethanol consumption.
The Midbrain:
Contains specialized nuclei processing auditory and visual reflexes; measures approximately in length.
Brainstem: Structural integration of the medulla oblongata, pons, and midbrain, connecting the cerebrum to the spinal cord.
Reticular Formation: Diffuse ascending and descending neural network extending through the midbrain and hindbrain that regulates sleep-wake arousal, conscious alertness, and basic drive states. Over-aroused reticular formations correlate with introverted behavioral traits, whereas under-aroused systems drive extraverted stimulus-seeking behaviors.
The Forebrain:
Limbic System: Subcortical structures regulating emotional processing, memory formation, and biological drives.
Hippocampus: Bilateral seahorse-shaped structure essential for consolidating short-term declarative information into permanent long-term memory storage.
Amygdala: Almond-shaped nuclear complex governing emotional learning, conditioned fear responses, and rapid threat evaluation.
Thalamus: Central sensory relay hub that processes incoming visual, auditory, gustatory, and somatosensory information before routing it to target cortical zones (olfaction bypasses the thalamus directly to olfactory bulbs).
Hypothalamus: Master autonomic controller positioned beneath the thalamus that maintains internal physiological homeostasis (thermoregulation, hunger, thirst, satiety, circadian rhythm, and biological drives) via direct control over the pituitary gland. 4 F: Fight, flight, feeding, forenicasion (sexual)
Functional Specialization of the Cerebral Cortex and Lobes
Cerebral Cortex Overview:
Gray matter outer layer of the cerebrum measuring approximately in thickness.
Corticalization: Extensive evolutionary wrinkling and folding (gyri and sulci) allowing an estimated to of flattened cortical tissue to fit inside the human cranium.
Hemispheric Lateralization:
Left Hemisphere: Mediates sequential, analytical processing, verbal speech output, and direct control over the right side of the physical body.
Right Hemisphere: Mediates holistic, spatial, non-verbal visual patterns, musical appreciation, emotional recognition, and direct control over the left side of the physical body.
Corpus Callosum: Dense tract of white matter axon fibers physically joining the two cerebral hemispheres, enabling rapid interhemispheric communication. Surgical transection of the corpus callosum to manage intractable epilepsy yields split-brain phenomena where visual information restricted to one hemisphere cannot be verbally named by the opposite hemisphere.
Functional Lobes of the Cerebrum:
Occipital Lobes: Positioned at the posterior cranium; contains the primary visual cortex and visual association areas responsible for color, shape, and motion perception. (Sight/visual information)
Temporal Lobes: Located bilaterally superior to the ears; houses the primary auditory cortex and auditory association zones for pitch, tone, and spoken language processing. (Auditory/hearing: Right = language centers, while the left hemisphere is more involved in music perception and emotional tone, illustrating the nuanced distribution of auditory processing across the temporal lobes.)
Parietal Lobes: Positioned at the upper-rear cortex; handles spatial awareness, proprioception (body movement and positioning awareness), and somatosensory processing. Coordinates with cerebellum for balance.
Somatosensory Cortex: Strip of parietal tissue processing physical touch, thermal sensations, and pain. Mapped by the sensory homunculus, where sensitive anatomical zones (fingertips, lips) occupy disproportionately large cortical areas.
Frontal Lobes: Anterior cortical regions managing higher-order executive functioning, emotional self-regulation, impulse inhibition, goal-directed planning, and working memory.
Neuroplasticity-brain can rewire itself in response to learning, experience, or injury, enabling functional compensation for lost abilities and the acquisition of new skills.
Prefrontal Cortex: Executive center mediating complex decision-making and abstract reasoning; does not achieve full structural myelination and synaptic maturation until approximately age 25.
Primary Motor Cortex: Posterior frontal strip initiating voluntary physical movement. Mapped by the motor homunculus, dedicating extensive tissue to high-dexterity structures like the hands and speech apparatus.
Psychological Neuro-Myths Disproven by Empirical Research:
Visual, Auditory, and Kinesthetic "learning styles" do not improve objective educational outcomes.
Structural binary wiring differences dividing male and female brains into rational versus emotional types are socially constructed myths unsupported by neuroscience.
Individual dominance as
Contralateral control refers to the neurological phenomenon where one hemisphere of the brain controls the opposite side of the body, highlighting the intricate relationship between brain structure and functional abilities in learning.