Week 6: Muscles, Movement, and Cardiovascular Physiology

Vocabulary flashcards covering major terms and concepts from lecture notes on muscles, neural reflexes, and cardiovascular physiology.

Skeletal Muscle

Striated, multinucleate muscle attached to bones for voluntary movement.

Cardiac Muscle

Striated muscle with intercalated disks; forms the heart and contracts involuntarily.

Smooth Muscle

Non-striated muscle in organs and vessels; contracts slowly and can maintain force long-term.

Muscle Fiber

Single muscle cell containing myofibrils, sarcoplasmic reticulum, and T-tubules.

Sarcomere

Contractile unit of striated muscle between two Z disks.

A Band

Dark band of a sarcomere containing thick filaments; length remains constant during contraction.

I Band

Light region with only thin filaments; shortens during contraction.

H Zone

Central region of A band with only thick filaments; shortens in contraction.

Z Disk

Protein boundary of sarcomere where thin filaments anchor.

M Line

Sarcomere center where thick filaments attach.

Titin

Elastic protein that stabilizes myosin and returns sarcomere to resting length.

Nebulin

Giant protein that helps align actin filaments in sarcomere.

T-Tubule

Invagination of sarcolemma that conducts action potentials into muscle fiber.

Sarcoplasmic Reticulum (SR)

Intracellular organelle storing Ca²⁺ for muscle contraction.

Troponin

Ca²⁺-binding regulatory protein on actin that moves tropomyosin.

Tropomyosin

Regulatory protein blocking myosin-binding sites on actin when muscle is relaxed.

Crossbridge

Connection formed between myosin head and actin during contraction.

Power Stroke

Pivoting action of myosin head that pulls actin filament, using ADP + Pi energy.

Phosphocreatine

High-energy compound that rapidly regenerates ATP at onset of exercise.

Muscle Tension

Force created by contracting muscle fibers.

Isotonic Contraction

Muscle generates force and changes length, moving a load.

Concentric Action

Isotonic contraction in which muscle shortens.

Eccentric Action

Isotonic contraction in which muscle lengthens while generating force.

Isometric Contraction

Muscle develops tension without changing length or moving load.

Motor Unit

One somatic motor neuron and all muscle fibers it innervates.

Motor Unit Recruitment

Process of increasing the number of active motor units to boost force.

Length-Tension Relationship

Optimal sarcomere length maximizes force output.

Summation

Increase in muscle tension from rapid, repeated action potentials.

Tetanus (Complete)

Maximum sustained contraction when stimuli are so frequent no relaxation occurs.

Central Fatigue

Reduced CNS drive causing perceived inability to continue exercise.

Peripheral Fatigue

Failure within muscle fiber due to factors like Pi, H⁺, or Ca²⁺ handling problems.

Excitation-Contraction Coupling

Sequence linking muscle action potential to Ca²⁺ release and contraction.

DHP Receptor

Voltage-gated L-type Ca²⁺ channel in T-tubule sensing depolarization.

Ryanodine Receptor (RyR)

Ca²⁺ release channel in SR opened by DHP receptor in skeletal muscle.

Myogenic Contraction

Contraction initiated by stretch-activated Ca²⁺ channels in smooth muscle.

Calmodulin (CaM)

Ca²⁺-binding protein activating MLCK in smooth muscle.

Myosin Light Chain Kinase (MLCK)

Enzyme phosphorylating smooth muscle myosin, increasing ATPase activity.

Single-Unit Smooth Muscle

Cells connected by gap junctions that contract as a unit (e.g., intestine).

Multiunit Smooth Muscle

Cells act independently; finer control (e.g., iris, piloerector).

Monosynaptic Reflex

Reflex with one afferent and one efferent neuron (e.g., knee jerk).

Polysynaptic Reflex

Reflex involving interneurons and multiple synapses.

Muscle Spindle

Stretch receptor in skeletal muscle monitoring length and preventing overstretch.

Golgi Tendon Organ

Proprioceptor in tendon sensing tension, triggering relaxation reflex.

Flexion-Crossed Extensor Reflex

Withdrawal of limb from pain with contralateral limb extension for support.

Parkinson’s Disease

Degeneration of dopamine neurons in basal ganglia causing motor deficits.

Pressure Gradient (ΔP)

Driving force for blood flow; flows from high to low pressure.

Resistance (R)

Opposition to blood flow; inversely proportional to radius⁴.

Mean Arterial Pressure (MAP)

Average arterial pressure driving blood into tissues; MAP ≈ CO × R.

Stroke Volume (SV)

Blood volume ejected per ventricle per beat (EDV – ESV).

Cardiac Output (CO)

Blood volume pumped per ventricle per minute (HR × SV).

Frank-Starling Law

SV increases as EDV (stretch) increases, within physiological limits.

Inotropic Effect

Change in contractility; positive agents (e.g., NE) increase force.

Pacemaker Potential

Unstable membrane potential of SA node drifting to threshold.

SA Node

Primary cardiac pacemaker; ~70 beats/min in normal adults.

AV Node Delay

Slow conduction through AV node allowing atrial contraction before ventricles.

ECG P Wave

Electrical representation of atrial depolarization.

ECG QRS Complex

Ventricular depolarization (and atrial repolarization hidden).

ECG T Wave

Ventricular repolarization.

Systole

Phase of cardiac contraction and blood ejection.

Diastole

Phase of cardiac relaxation and filling.

Intercalated Disk

Specialized junction linking cardiac cells; contains desmosomes and gap junctions.

Gap Junction

Protein channel allowing electrical coupling between adjacent cells.

Angiogenesis

Formation of new blood vessels from existing vasculature.

Elastic Recoil

Arterial property maintaining pressure during ventricular diastole.

Myogenic Autoregulation

Vascular smooth muscle constricts when stretched to keep flow constant.

Baroreceptor Reflex

Negative feedback adjusting HR, SV, and vessel diameter to stabilize BP.

Atherosclerosis

Arterial plaque buildup narrowing lumen and reducing elasticity.

Hypertension

Chronic high arterial pressure; risk factor for CVD.

High-Density Lipoprotein (HDL-C)

‘Good’ cholesterol associated with lower cardiovascular risk.

Low-Density Lipoprotein (LDL-C)

‘Bad’ cholesterol linked to coronary artery disease.

Edema

Swelling from excess interstitial fluid due to filtration-absorption imbalance or lymph blockage.

Lymphatic System

Network returning interstitial fluid, fats, and proteins to circulation and filtering pathogens.

Capillary Filtration

Bulk flow of fluid out of capillaries driven by hydrostatic pressure.

Capillary Absorption

Fluid movement into capillaries driven by colloid osmotic pressure.

Sympathetic Vasoconstriction

Norepinephrine acting on α-receptors to decrease vessel radius and raise resistance.

Skeletal Muscle Pump

Venous return aid from muscle contraction compressing veins.

Respiratory Pump

Thoracic pressure changes during breathing that enhance venous return.

Essential Hypertension

High BP with no identifiable cause; largely genetic.