BIOL 252 Module 2

Myocardium

cardiac muscle tissue

Autorhythmicity

ability to initiate own electrical potential at a fixed rate that spreads rapidly from cell to cell to trigger contractile mechanism

Myocardial contracting cells

99% of cells in heart, responsible for contractions that pump blood through the body

Myocardial conducting cells

1% of cells in heart, responsible for conduction system of the heart

Purkinje Cells

specialized myocardial conducting cells that carry electrical impulses to the ventricles

Cardiomyocytes

cardiac muscle cells

Myofibril

long, thin thread inside muscle cell

Sarcomere

arrangement of Z-line to Z-line, makes up myofibrils

Z-line

contractile unit of cardiomyocyte

T-tubules

extensions of sarcolemma that penetrate into cell, rapidly transmit action potentials from surface to interior of muscle cell, found at Z-lines

Sarcolemma

cell membrane

Sarcoplasmic Reticulum

stores calcium ions

Desmosomes

specialized linking proteoglycans

Actin

thin filament

Myosin

thick filament

Excitation-Contraction Coupling

action potential triggers flow of calcium ions into cardiomyocyte

Troponin-Tropomyosin Complex

when calcium ions bond to troponin, shifting the complex to expose active sites where myosin heads bind and undergo power stroke to contract and relax

Active Site

where myosin binds on actin filament

M-line

center of sarcomere

H-band

band of thick filament around the M-line, gets narrower when muscle contracts

Sinoatrial (SA) Node

specialized cluster of cardiac conducting cells, pacemaker of the heart, establishes normal sinus rhythm

Sinus Rhythm

normal electrical pattern followed by contraction of the heart

Atrioventricular (AV) Node

specialized myocardial conducting cells, located within atrioventricular septum of right atrium, delays impulse to allow atria time to fully contract and fill ventricles

Bundle of His

branches through interventricular septum, splits into two atrioventricular bundle branches - left and right bundle branches

Myoglobin

oxygen-binding protein found in muscle cells

Depolarization

shift from a negative to a positive charge

Repolarization

return of cell’s membrane potential from positive charge back to negative charge after action potential

Plateau Phase

sustained depolarization

Refractory Period

when cell is unable to undergo action potentials

Absolute Refractory Period

cell cannot respond to any stimulus at all, 200 milliseconds

Relative Refractory Period

cell is in process of repolarization and has partially regained its ability to respond to strong stimuli only, 50 milliseconds

Bradycardia

heart rate lower than 50 bpm

Electrocardiogram (EKG/ECG)

created by surface electrodes, measures heart’s electrical activity

Holter Monitor

portable device which tracks heart’s electrical activity for 24 - 48 hours

P Wave

represents atrial depolarization, small rounded wave

PR Interval

from beginning of P wave to beginning of QRS complex, represents electrical signal traveling from SA node to AV node

QRS Complex

comprised of Q, R, and S waves, represents depolarization of ventricles and repolarization of atria

R wave

represents ventricular depolarization, large, pointed wave

ST Segment

from end of QRS complex to beginning of T wave, time between ventricular depolarization and repolarization

T Wave

represents repolarization and relaxation of ventricles, smaller, rounded wave

QT Interval

starts at Q wave and ends after T wave, represents time between atrial depolarization and ventricular repolarization

Cardiac Cycle

series of pressure changes that occur within the heart from beginning of heartbeat to beginning of the next

Systole

period of contraction heart undergoes while it pumps blood into circulation

Diastole

period of relaxation

End Systolic Volume (ESV)

blood remaining in ventricle following contraction

Stroke Volume

amount of blood that is pumped from the ventricles

Vascular Ejection Phase

contraction of ventricular muscle raises ventricular pressure higher than pulmonary trunk and aorta

End Diastolic Volume (EDV)

blood remaining in ventricles following atrial contraction prior to ventricular contraction

Auscultation

listening to heart sounds with stethoscope

Cardiac Output (CO)

measurement of amount of blood pumped by each ventricle in one minute, multiplying stroke volume by heart rate

Ejection Fraction

measurement of blood that is pumped or ejected from the heart with each contraction

Cardiac Reserve

difference between resting and maximum cardiac output

Cardioaccelerator Centers

stimulate activity via stimulation of cardioaccelerator nerves and increase heart activity

Cardioinhibitory Centers

decrease heart activity via parasympathetic stimulation of cranial nerve X

Sympathetic Ganglia

cervical ganglia plus superior thoracic ganglia T1 - T4

Norepinephrine (NE)

binds to beta-1 receptor, shortens repolarization period, increases heart rate

Beta Blockers

block beta-1 receptors, slow heart rate

Cardiac Reflexes

group of impulses that allow cardiovascular centers to regulate heart function properly

Proprioreceptors

fire with increased physical activity, detect position and movement, located in muscles, joint capsules, and tendons

Baroreceptors

stretch receptors located in aortic sinus, carotid bodies, and venae cavae

Atrial Reflex/Bainbridge Reflex

detects blood volume changes in vena cavae and atria

Chemoreceptors

detect chemical stimulation

Limbic System

emotional brain, controls emotions, memories, and basic physiological functions

Cortisol

stress hormone

Preload

stretch on ventricles prior to contraction

Filling Time (FT)

duration of ventricular diastole during which filling occurs

Venous Return (VR)

process of blood flowing back into the ventricles

Frank-Starling Mechanism

force of contraction is directly proportional to the initial length of muscle fiber

Positive Inotropic Factors

factors that increase contractility, sympathetic stimulation, thyroid hormones, glucagon

Negative Inotropic Factors

factors that decrease contractility, parasympathetic stimulation, hyperkalemia, beta blockers, calcium channel blockers

Hyperkalemia

excessive potassium

Afterload

tension ventricles must develop to pump blood effectively against resistance of vascular system

Vasoconstriction

narrowing of blood vessels

Vasodilation

widening of blood vessels

Atherosclerosis

chronic condition characterized by accumulation of fatty deposits, cholesterol, and other substances in arterial walls, can impair blood flow

Cholesterol

type of fat in the blood

Ischemia

occurs when there is insufficient blood supply to organs or body part due to blockage in artery

Myocardial Infarction

portion of heart muscle dies due to lack of oxygen caused by blockage in coronary vessel, heart attack

Heart Failure

heart is unable to pump blood effectively, causes fluid buildup, fatigue, and shortness of breath

Arrhythmia

irregular heartbeat

Palpitations

sensation of skipped or added heartbeat

Tachycardia

abnormally fast heart rate above 100 bpm

Aspirin

reduces coagulation

Propranolol

blocks sympathetic stimulation to slow heart rate

Nitroglycerin

vasodilator, reduces afterload

Calcium Ion Channel Blockers

reduce contractility

Balloon Angioplasty

plastic tube is threaded into artery of arm or leg then guided toward heart, then inflated at blockage to force vessel open

Coronary Artery Bypass Graft (CABG)

segment of another blood vessel is stitched to end of aorta and coronary artery past point of obstruction