Human Physiology: Endocrine and Nervous System Fundamentals

Comprehensive vocabulary flashcards covering neural signaling, action potentials, synaptic transmission, CNS neuroanatomy, motor and sensory control, and endocrine energy and growth metabolism.

Broca's Area

A functional region located in the left hemisphere of the frontal cortex responsible for speech formation and language expression in spoken or written word.

Wernicke's Area

A cerebral cortical area located in the left hemisphere responsible for language comprehension across spoken word, written word, and hand signals.

Non-REM Sleep

Slow-wave sleep phase induced by the neurotransmitter adenosine and modulated by melatonin, characterized by reflexive bursts of involuntary activity, parasympathetic dominance, increased brainstem activity, and logical dreams.

REM Sleep

Paradoxical sleep phase induced by acetylcholine and the pons, characterized by postural muscle paralysis, heightened brain and sympathetic nervous system activity, and increased creativity in dreams.

Ascending Reticular Activating System (ARAS)

A network in the brainstem that relays signals through the thalamus to excite and wake up the cerebral cortex, utilizing neurotransmitters including acetylcholine, histamine, serotonin, norepinephrine, dopamine, and glutamate.

Long-Term Potentiation (LTP)

The persistent strengthening of synapses through repetition, resulting in increased sensitivity to neurotransmitters or greater neurotransmitter release, larger EPSP size, and increased likelihood of generating an action potential.

Associative Learning

A learning process that links two or more stimuli together, such as using mnemonics or word associations.

Habituation

A form of non-associative learning involving repetitive exposure to a single stimulus, resulting in acclimatization and reduced responsiveness because the stimulus is deemed unimportant.

Sensitization

A form of non-associative learning involving repetition of an important stimulus, resulting in heightened awareness and increased responsiveness.

Procedural Memory

Implicit memory for learned motor skills and behaviors that requires no conscious effort, mediated primarily by the cerebellum, basal nuclei, and pons.

Declarative Memory

Explicit memory for learned facts and events that requires conscious effort to recall, consolidated and stored primarily via the hippocampus and temporal lobe.

Reflex Arc

The functional pathway mediating an involuntary reflex, consisting of a sensory receptor, an afferent neuron, a central nervous system integration center, an efferent neuron, and an effector organ.

Stretch Reflex

A spinal, somatic, innate, monosynaptic reflex triggered by muscle spindle stretch that directly activates motor neurons to contract the stretched muscle and prevent rapid-activation injury.

Withdrawal Reflex

A spinal, somatic, innate, polysynaptic reflex elicited by painful or noxious stimuli that activates ipsilateral flexor muscles to retract a limb.

Crossed-Extensor Reflex

A spinal, somatic, innate, polysynaptic reflex that pairs with the withdrawal reflex to contract contralateral extensor muscles, maintaining body balance.

Reciprocal Inhibition

A neural reflex mechanism in which collateral interneurons simultaneously inhibit the motor neurons of an antagonistic muscle during agonist contraction.

Pupillary Light Reflex

A cranial, autonomic, innate, polysynaptic reflex in which photoreceptor stimulation signals the midbrain to constrict the smooth muscle of both pupils, limiting light entry.

Lower (Alpha) Motor Neurons

Efferent neurons originating in the ventral horn of the spinal cord that directly innervate skeletal muscle fibers via an always excitatory signal.

Choroid Plexus

Vascular tissue lined by ependymal cells located within the brain ventricles that produces approximately $400\text{ to }500\,\text{mL}$ of cerebrospinal fluid per day.

Arachnoid Villi

Projections of the arachnoid mater that extend into dural venous sinuses to reabsorb cerebrospinal fluid from the subarachnoid space back into the venous bloodstream.

Blood-Brain Barrier (BBB)

A protective barrier formed by brain capillary endothelial cells joined by tight junctions, surrounded by astrocyte foot processes that restrict hydrophilic solute diffusion while allowing hydrophobic solutes to cross.

Basal Nuclei

Subcortical gray matter structures including the caudate nucleus, putamen, and globus pallidus that modify voluntary movement, facilitate habit and procedural learning, and contain dopamine-rich pleasure reward centers.

Diencephalon

A core forebrain division comprising the thalamus, hypothalamus, epithalamus (pineal gland), and subthalamus, arranged around the third ventricle.

Limbic System

A ring of interconnected forebrain structures including the amygdala, hippocampus, cingulate gyrus, and fornix that governs emotions, learning, memory, and autonomic drives.

Electrical Synapse

A direct junction between two excitable cells linked by gap junctions, allowing rapid, bidirectional movement of ions and second messengers with capability for both excitation and inhibition.

Chemical Synapse

A unidirectional junction where the arrival of an action potential at a presynaptic terminal triggers calcium influx, causing neurotransmitter exocytosis across the synaptic cleft to bind postsynaptic receptors.

Synaptic Delay

The interval of $0.5\text{ to }5\,\text{msec}$ between action potential arrival at the presynaptic terminal and the electrical response in the postsynaptic cell, caused by calcium entry, vesicle docking, and neurotransmitter exocytosis.

Excitatory Postsynaptic Potential (EPSP)

A graded depolarization of the postsynaptic membrane, most commonly mediated by glutamate opening channels permeable to both $\text{Na}^+$ and $\text{K}^+$.

Inhibitory Postsynaptic Potential (IPSP)

A graded hyperpolarization or membrane stabilization of the postsynaptic cell, most commonly mediated by GABA opening channels permeable to $\text{K}^+$ or $\text{Cl}^-$.

Temporal Summation

The integration of postsynaptic potentials generated by the repeated arrival of action potentials from the same presynaptic input close together in time.

Spatial Summation

The integration of postsynaptic potentials generated simultaneously from multiple different presynaptic terminals converging on the same postsynaptic cell.

Presynaptic Facilitation

An axoaxonic synaptic interaction that enhances calcium influx at the postsynaptic neuron's axon terminal, thereby increasing neurotransmitter release.

Presynaptic Inhibition

An axoaxonic synaptic interaction that reduces calcium influx at the postsynaptic neuron's axon terminal, thereby decreasing neurotransmitter release.

Choline Acetyltransferase (CAT)

The enzyme localized within the axon terminal of cholinergic neurons that synthesizes acetylcholine from choline and acetyl CoA.

Absorptive State

The fed metabolic state dominated by insulin, characterized by nutrient storage, glucose uptake into tissues, protein synthesis, glycogen synthesis, and lipogenesis.

Postabsorptive State

The fasting metabolic state dominated by glucagon, sympathetic activity, and epinephrine, characterized by nutrient mobilization via glycogenolysis, gluconeogenesis, lipolysis, and glucose sparing.

Insulin

An anabolic peptide hormone secreted by pancreatic beta cells in response to elevated blood glucose and amino acids, stimulating cellular nutrient uptake and storage.

Glucagon

A catabolic peptide hormone secreted by pancreatic alpha cells in response to decreased blood glucose, stimulating hepatic glycogenolysis, gluconeogenesis, and ketone synthesis.

Insulin-like Growth Factors (IGFs)

Peptides released by the liver and other tissues in response to growth hormone that act systemically as hormones and locally as paracrines to mediate cell division, protein synthesis, and tissue growth.

Calorigenic Effect

The elevation of basal metabolic rate and body temperature induced by thyroid hormones via increased $\text{Na}^+/\text{K}^+$ pump activity, mitochondrial enlargement, and enhanced oxidative phosphorylation enzymes.

General Adaptation Syndrome

Hans Selye's three-stage stress response model comprising the alarm stage (fight-or-flight mediated by SNS), the resistance stage (sustained hormonal mobilization), and the exhaustion stage (energy depletion).

Graded Potential

A localized, variable-magnitude change in membrane potential that decays over distance and time through electrotonic conduction.

Action Potential

A rapid, large, all-or-none depolarization of an excitable membrane originating at the axon hillock and traveling undiminished to axon terminals for long-distance communication.

Absolute Refractory Period

The period following an action potential during which voltage-gated $\text{Na}^+$ channel inactivation gates are closed, rendering the membrane completely incapable of generating another action potential.

Relative Refractory Period

The period following an action potential when some voltage-gated $\text{Na}^+$ channels have reset to resting configuration while $\text{K}^+$ channels remain open, requiring a suprathreshold stimulus to evoke a new action potential.

Saltatory Conduction

The rapid propagation of action potentials along myelinated axons whereby depolarization jumps from one node of Ranvier to the next.

Anterograde Transport

Fast axonal transport moving vesicles, neurotransmitter-synthesizing enzymes, and proteins forward from the soma toward the axon terminal using kinesin motor proteins along microtubules.

Retrograde Transport

Axonal transport carrying recycled vesicle membranes, chemical signals, and degraded materials backwards from the axon terminal to the soma along microtubules.

Oligodendrocyte

A glial cell of the central nervous system that produces multiple myelin sheaths, myelinating segments of several surrounding axons.

Schwann Cell

A glial cell of the peripheral nervous system that wraps around a single axon segment to form one myelin sheath.

Resting Membrane Potential

The stable electrical voltage difference across an unstimulated neuronal membrane (approximately $-70\,\text{mV}$), maintained primarily by high resting permeability to $\text{K}^+$ relative to $\text{Na}^+$ and active $\text{Na}^+/\text{K}^+$ pumping.

Tropic Hormone

A hormone whose primary physiological function is to stimulate or inhibit the secretion of another hormone from an endocrine target gland.

Hypothalamic-Pituitary Portal System

A specialized vascular arrangement of two capillary beds connected by a portal vein that carries hypothalamic releasing and inhibiting tropic hormones directly to the anterior pituitary.

Permissiveness

An endocrine interaction where the presence and action of one hormone is necessary for another hormone to exert its full physiological effect.

Synergism

An endocrine interaction where the combined effect of two or more hormones acting simultaneously exceeds the additive sum of their individual effects.