Human Physiology: Principles of Homeostasis, Cellular Function, and Neural Systems

Comprehensive vocabulary flashcards covering the introductory principles of Human Physiology (PHAR272), including homeostasis, cell physiology, membrane potentials, neural communication, central nervous system functional anatomy, afferent sensory receptors, and efferent nervous system divisions.

Homeostasis

The self-regulating process by which biological systems maintain internal stability while adjusting to changing external conditions.

Physiology

The study of the functions of living things, focusing on the underlying physical and chemical mechanisms of body processes.

Intracellular Fluid (ICF)

The fluid collective contained within all body cells.

Extracellular Fluid (ECF)

The fluid outside the cells that constitutes the body's internal environment; comprises interstitial fluid and plasma.

Interstitial Fluid

The portion of the extracellular fluid that directly surrounds, bathes, and nourishes the tissue cells.

Negative Feedback

A homeostatic regulatory mechanism in which a change in a monitored variable triggers a response that opposes the initial change, driving the variable in the opposite direction toward the set point.

Positive Feedback

A control mechanism where an output enhances or amplifies an initial deviation so that the controlled variable continues to move in the direction of the initial change.

Feedforward Mechanism

A physiological response initiated in anticipation of a change before the variable actually deviates from normal (e.g., digestive secretions preparing for ingested food).

Ubiquitin-Proteasome Pathway

A cellular degradation system wherein flawed, damaged, or unneeded proteins are tagged with ubiquitin and selectively destroyed by proteasomes.

Lysosomes

Small, membrane-enclosed organelles containing hydrolytic enzymes that degrade extracellular debris brought in by endocytosis as well as worn-out intracellular organelles.

Peroxisomes

Membranous organelles housing oxidative enzymes that detoxify harmful wastes and produce $H_2O_2$, which is then degraded into $H_2O$ and $O_2$ by catalase.

Tight Junction

An impermeable cell-to-cell junction that seals adjacent epithelial cells together, preventing the unregulated passage of materials between compartments of different composition.

Desmosome

An anchoring cell junction that adheres adjacent cells together under mechanical stress and stretching, while remaining permeable to water and ions.

Gap Junction

A communicating junction composed of small connecting tunnels that permit direct passage of ions and small molecules between adjacent cells for electrical signaling.

Tonicity

A measure of the effective osmotic pressure gradient that determines whether a cell maintains its volume, swells, or shrinks when immersed in a solution.

Transport Maximum ($T_m$)

The upper limit of the rate of carrier-mediated transport across a membrane, reached when all available carrier binding sites are fully saturated.

Primary Active Transport

A carrier-mediated transport mechanism that directly hydrolyzes $\text{ATP}$ to transport a substance against its concentration gradient (e.g., $\text{Na}^+\text{-}\text{K}^+$ ATPase).

Secondary Active Transport

A carrier-mediated transport process driven by an electrochemical gradient established by primary active transport, moving a second solute against its concentration gradient via symporters or antiporters.

Equilibrium Potential ($E_{\text{ion}}$)

The membrane potential at which the chemical concentration gradient and electrical gradient for a specific permeant ion are equal in magnitude and opposite in direction, resulting in no net diffusion.

Resting Membrane Potential (RMP)

The stable electrical potential difference across the plasma membrane of an excitable cell at rest (approximately $-70\,\text{mV}$ in neurons), primarily established by passive outward diffusion of $K^+$ through leak channels.

Depolarization

A decrease in potential wherein the membrane becomes less polarized and less negative inside relative to resting membrane potential.

Hyperpolarization

An increase in potential wherein the membrane becomes more polarized and more negative inside than resting membrane potential.

Graded Potential

A local change in membrane potential whose magnitude and duration vary with the strength and duration of the triggering event, spreading decrementally by passive current flow over short distances.

Action Potential

A rapid, transient, large ($100\,\text{mV}$) reversal in membrane potential characterized by an all-or-none propagation over long distances without decrement.

Absolute Refractory Period

The timeframe following an action potential during which voltage-gated $Na^+$ channels are either open or inactivated, completely preventing the initiation of a subsequent action potential.

Relative Refractory Period

The interval during which a second action potential can be triggered only by a stronger-than-normal stimulus, occurring when $Na^+$ channels have reset but lingering open $K^+$ channels produce hyperpolarization.

Saltatory Conduction

The rapid jumping mode of action potential propagation along a myelinated axon from one unmyelinated node of Ranvier to the next.

Excitatory Postsynaptic Potential (EPSP)

A small local depolarization of the postsynaptic membrane produced when neurotransmitter binding opens nonspecific cation channels, moving the membrane potential closer to threshold.

Inhibitory Postsynaptic Potential (IPSP)

A small local hyperpolarization of the postsynaptic membrane produced when neurotransmitter binding increases permeability to $K^+$ or $Cl^-$, moving the potential farther from threshold.

Temporal Summation

The algebraic addition of postsynaptic potentials occurring in response to rapid, repetitive firing from a single presynaptic axon terminal before preceding potentials subside.

Spatial Summation

The summing of simultaneous postsynaptic potentials generated from multiple distinct presynaptic inputs at different locations on the postsynaptic neuron.

Presynaptic Facilitation

An enhancement of synaptic transmission caused by a third neuron prolonging the presynaptic action potential and increasing calcium influx, thereby increasing neurotransmitter release.

Paracrine

A local chemical messenger released into the extracellular fluid that diffuses across short distances to act on neighboring non-neuronal cells.

Neurohormone

A hormone synthesized and released directly into the bloodstream by neurosecretory neurons to regulate distant target organs.

Astrocytes

The most abundant glial cells in the CNS that offer structural support, induce blood-brain barrier formation, buffer extracellular $K^+$, and clear released neurotransmitters.

Oligodendrocytes

Glial cells in the central nervous system that wrap their cytoplasmic projections around multiple axons to form myelin sheaths.

Microglia

Resident macrophage-like immune cells of the CNS that release nerve growth factor, eliminate redundant synapses, and phagocytose cell debris and pathogens upon activation.

Ependymal Cells

Ciliated glial cells lining the ventricles of the brain and central canal of the spinal cord that produce, circulate, and facilitate exchange of cerebrospinal fluid (CSF).

Blood-Brain Barrier (BBB)

A tightly regulated physiological barrier formed by brain capillary endothelial cells with tight junctions and astrocyte end-feet that restricts the exchange of solutes between blood and the CNS interstitial fluid.

Somatosensory Cortex

An area situated in the parietal lobes (postcentral gyrus) of the cerebral cortex that receives and localizes somesthetic and proprioceptive inputs from the opposite side of the body.

Primary Motor Cortex

A region located on the precentral gyrus of the frontal lobe that initiates voluntary motor commands to trigger skeletal muscle contractions on the contralateral side of the body.

Broca's Area

A cortical language region located in the left frontal lobe that programs and coordinates the muscular contractions required for speaking words.

Wernicke's Area

A language comprehension region located in the left cortex at the intersection of the parietal, temporal, and occipital lobes responsible for understanding spoken and written messages.

Basal Nuclei

Masses of cerebral gray matter located deep within white matter that inhibit muscle tone, suppress unnecessary motor activity, and coordinate slow, sustained postural contractions.

Thalamus

A sensory relay station within the diencephalon that filters, preliminarily processes, and routes incoming sensory inputs (excluding smell) to appropriate regions of the cerebral cortex.

Hypothalamus

A major diencephalic integrating center regulating homeostatic functions, including autonomic control, body temperature, thirst, urine volume, food intake, and endocrine secretions.

Limbic System

A functional loop of interconnected forebrain structures surrounding the brain stem that governs emotions, survival instincts, motivation, and learning.

Long-Term Potentiation (LTP)

A persistent strengthening of synaptic efficacy following repetitive use, initiated in the hippocampus by glutamate binding to postsynaptic AMPA and NMDA receptors.

Vestibulocerebellum

The functional cerebellar division responsible for maintaining body equilibrium and controlling reflex eye movements.

Spinocerebellum

The cerebellar subdivision that enhances muscle tone and coordinates skilled, voluntary skeletal muscle movements.

Cerebrocerebellum

The cerebellar subdivision involved in planning and initiating voluntary motor activities and storing procedural memories.

Reticular Formation

A widespread network of interconnected neurons running through the brain stem that maintains cortical alertness, consciousness, and sleep-wake cycles.

Dermatome

A distinct geographic zone of skin that receives its sensory innervation from afferent fibers belonging to a single spinal nerve root.

Receptor Potential

A local, graded potential generated at a sensory receptor ending by an adequate stimulus, which can initiate action potentials in the afferent nerve fiber.

Tonic Receptors

Slowly adapting or nonadapting sensory receptors that continuously generate action potentials to provide uninterrupted data on sustained conditions (e.g., muscle stretch and proprioception).

Phasic Receptors

Rapidly adapting sensory receptors that cease responding to a continuous stimulus, specialized for signaling sudden changes in stimulus intensity or duration.

Nociceptors

Sensory receptors with nonadapting properties that respond exclusively to tissue-damaging or potentially destructive stimuli, triggering pain perception.

Accommodation

The active adjustment of lens curvature and refractive power by ciliary muscle contraction to bring near objects into sharp visual focus on the retina.

Phototransduction

The process by which photoreceptor cells convert light energy into neural signals, involving light-induced retinal isomerization, cyclic GMP breakdown, $Na^+$ channel closure, and photoreceptor hyperpolarization.

Organ of Corti

The auditory receptor organ located within the cochlea of the inner ear, equipped with hair cells that transduce fluid oscillations into electrical impulses.

Semicircular Canals

Three fluid-filled loops in the inner ear oriented at right angles to one another that detect rotational head acceleration.

Otolith Organs

Inner ear structures comprising the utricle and saccule that utilize calcium carbonate crystals (otoliths) to sense linear acceleration and gravitational head tilt.

Autonomic Nervous System (ANS)

The involuntary efferent branch of the peripheral nervous system consisting of a two-neuron chain that innervates cardiac muscle, smooth muscle, and glands.

Somatic Nervous System (SNS)

The voluntary efferent motor division of the peripheral nervous system consisting of single motor neurons terminating exclusively on skeletal muscle fibers.

Dual Innervation

The simultaneous nerve supply of a visceral effector organ by both sympathetic and parasympathetic divisions, providing reciprocal, opposing physiological regulation.

Neuromuscular Junction (NMJ)

The chemical synapse formed between an efferent motor neuron terminal button and the motor end plate of a skeletal muscle fiber.

End-Plate Potential (EPP)

A graded depolarization produced at the motor end plate when acetylcholine binds to nicotinic receptor-channels, inducing a large influx of $Na^+$ that triggers an action potential in the adjacent sarcolemma.

Acetylcholinesterase

An enzyme localized on the motor end-plate membrane that rapidly hydrolyzes acetylcholine into acetate and choline, terminating the electrical excitation of the muscle fiber.