BIO 288 Exam 2 Review: Muscle Physiology and Cardiovascular System

Comprehensive vocabulary flashcards reviewing skeletal, smooth, and cardiac muscle physiology, excitation-contraction coupling, the cardiac cycle, hemodynamics, and vascular regulation.

Sarcomere

The basic repeating contractile unit of a muscle fiber, delimited by Z discs and containing actin thin filaments, myosin thick filaments, and elastic titin filaments.

F-actin (Filamentous actin)

A polymer consisting of two twisted rows of globular G-actin subunits whose active binding sites interact with myosin heads during crossbridge cycling.

Tropomyosin

A double-stranded regulatory protein that lies along the groove of actin filaments and physically blocks the myosin-binding sites on F-actin when skeletal muscle is at rest.

Troponin

A globular regulatory protein complex bound to tropomyosin and F-actin that binds $\text{Ca}^{2+}$, undergoing a conformational shift that pulls tropomyosin off the active sites of actin.

Titin

A large elastic filament protein within thick filaments that anchors myosin to the Z disc and recoils after stretching to maintain structural stability and restore resting muscle length.

Motor End Plate

The specialized, invaginated region of the skeletal muscle sarcolemma that contains nicotinic acetylcholine receptors aligned across the synaptic cleft from axon terminals.

End-Plate Potential (EPP)

A graded depolarization produced at the motor end plate when acetylcholine opens cation channels for $\text{Na}^+$ and $\text{K}^+$, generating net inward positive current that always triggers an action potential in normal muscle fibers.

Dihydropyridine (DHP) Receptor

A voltage-sensing protein located in the transverse (T) tubule membrane that detects action potentials and mechanically interacts with ryanodine receptors to trigger calcium release from the sarcoplasmic reticulum.

Crossbridge Cycle

The multi-step cyclical interaction between actin and myosin heads involving ATP binding, hydrolysis, power stroke, and detachment that produces muscle tension and contraction.

Power Stroke

The hinging movement of the bound myosin crossbridge head toward the M line that pulls the thin actin filament, occurring after inorganic phosphate ($\text{P}_i$) is released.

Rigor State

A transient low-energy phase of the crossbridge cycle wherein myosin remains attached to actin in the absence of ATP binding.

SERCA (Sarcoplasmic/Endoplasmic Reticulum Calcium ATPase)

A primary active transport pump embedded in the sarcoplasmic reticulum membrane that continuously pumps $\text{Ca}^{2+}$ back into the SR lumen to terminate muscle contraction.

Creatine Kinase

An enzyme that catalyzes the rapid and reversible transfer of a high-energy phosphate group between creatine phosphate and ADP to provide immediate ATP during active muscle contraction.

Length-Tension Curve

A physiological relationship illustrating that maximal isometric tension develops at an optimal resting muscle length ($100\%\text{--}120\%$), declining when overstretched or excessively shortened due to suboptimal filament overlap.

Dense Bodies

Protein structures scattered throughout the cytoplasm and plasma membrane of smooth muscle cells that anchor thin filaments and intermediate filaments, serving an anchoring function analogous to Z discs.

Calmodulin

A cytosolic calcium-binding protein in smooth muscle that, upon binding $\text{Ca}^{2+}$, undergoes a conformational change enabling it to bind and activate myosin light chain kinase (MLCK).

Myosin Light Chain Kinase (MLCK)

An enzyme activated by the $\text{Ca}^{2+}$-calmodulin complex that phosphorylates the regulatory light chain of myosin, enabling crossbridge cycling and contraction in smooth muscle.

Varicosities

Periodic neuroeffector swellings along autonomic postganglionic axons containing neurotransmitter vesicles that permit diffuse release over smooth muscle tissues.

Intercalated Discs

Specialized junctional complexes between adjacent cardiac myocytes containing desmosomes for mechanical linkage and gap junctions for low-resistance electrical current propagation.

Automaticity

The intrinsic capacity of specialized cardiac pacemaker cells in the sinoatrial (SA) node to generate spontaneous action potentials without external neural stimulation.

Pacemaker Potential

The slow spontaneous membrane depolarization occurring in SA node autorhythmic cells toward threshold, mediated primarily by sodium influx through funny channels.

Funny Channels ($\text{I}_f$)

Specialized voltage-gated channels in cardiac autorhythmic cells that open at negative hyperpolarized potentials, allowing an inward $\text{Na}^+$ leak that initiates pacemaker prepotentials.

Cardiac Action Potential Plateau (Phase 2)

A prolonged period of sustained depolarization in ventricular contractile myocytes produced by an influx of $\text{Ca}^{2+}$ through opened L-type voltage-gated calcium channels while potassium channels remain closed.

Calcium-Induced Calcium Release (CICR)

The process in cardiac myocytes whereby a small trigger influx of extracellular $\text{Ca}^{2+}$ through L-type sarcolemmal channels stimulates large-scale calcium release from the sarcoplasmic reticulum through ryanodine channels.

Isovolumetric Ventricular Contraction

The initial subphase of ventricular systole occurring when ventricular pressure rises above atrial pressure to close the AV valves while remaining below arterial pressure, resulting in no change in ventricular volume.

First Heart Sound (S1)

The acoustic 'lubb' sound produced during early ventricular systole by blood turbulence and vibrations associated with the closure of the atrioventricular (AV) valves.

Second Heart Sound (S2)

The acoustic 'dubb' sound produced at the start of ventricular diastole caused by blood vibrations accompanying the closure of the aortic and pulmonary semilunar valves.

Cardiac Output (CO)

The total volume of blood pumped by a ventricle per minute, calculated as the product of heart rate and stroke volume ($\text{Cardiac Output} = \text{Heart Rate} \times \text{Stroke Volume}$).

Stroke Volume (SV)

The volume of blood ejected by a ventricle during a single contraction, typically ranging from $70\text{--}100\,\text{mL}$ under resting conditions.

Mean Arterial Pressure (MAP)

The average pressure driving blood into the tissues across the cardiac cycle, determined by the formula: $\text{MAP} = \text{Heart Rate} \times \text{Stroke Volume} \times \text{Total Peripheral Resistance}$.

Poiseuille's Law

A hemodynamic equation demonstrating that volumetric blood flow ($F$) is directly proportional to pressure gradient ($\Delta P$) and vessel radius to the fourth power ($r^4$), and inversely proportional to fluid viscosity ($\eta$) and vessel length ($L$): $F \propto \frac{\pi \cdot r^4 \cdot \Delta P}{8 \cdot \eta \cdot L}$.

Arterioles

Small resistance blood vessels with abundant circular smooth muscle that regulate systemic vascular resistance and distribution of cardiac output via vasoconstriction and vasodilation.

Capillaries

Microscopic blood vessels composed only of a single endothelial cell layer with high resistance and large collective surface area, optimized for exchange of nutrients, fluids, and gases via diffusion.

Veins

Thin-walled, highly compliant blood vessels possessing one-way valves that operate under low pressure and function as volume reservoirs containing approximately $60\%$ of total blood volume.

Arterial Baroreceptor Reflex

A negative feedback neuroendocrine mechanism whereby reductions in arterial pressure lower baroreceptor firing, triggering the cardiovascular control center to reduce parasympathetic and elevate sympathetic activity to restore MAP.

Vasopressin (Antidiuretic Hormone / ADH)

A peptide hormone secreted by the posterior pituitary that promotes renal water reabsorption and induces systemic vasoconstriction, thereby increasing total peripheral resistance and blood pressure.