20.5-20.8 anatomy

atrioventricular bundle

a bundle of modified heart muscle that transmits the cardiac impulse from the atrioventricular node to the ventricles through the bundle branches and purkinje fibers, causing the ventricles to contract

autorhythmicity

a feature of cardiac muscle tissue that allows the generation of action potentials without an external stimulus

absolute refractory period

a period immediately following stimulation during which a nerve or muscle is unresponsive to further stimulation. in cardiac muscle the plateau phase makes this period really long and is the time during which the cardiac muscle contracts and relaxes completely. it is important because it prevents tetanic contractions.

first heart sound

closing of AV valves and vibration of surrounding fluid which occurs during the period of isovolumetric contraction which is part of ventricular systole (lub)

second heart sound

closing of semilunar valves which occurs during the period of isovolumetric relaxation which is part of ventricular diastole (dupp)

cardiac muscle cells

elongated, branching cells that have one or two centrally located nuclei. they contain actin and myosin myofilaments that make up sarcomeres and theses are joined end to end forming myofibrils. this is what gives them a striated appearance.

depolarization phase (pacemaker potential)

depolarization of the SA node caused by voltage gated Ca channels being open and voltage gated K channels being all the way closed.

diastole

dilation or relaxation of a chamber

heart rate

number of heart beats per minute

ventricular diastole (isovolumetric relaxation)

occurs after the T wave appears in ECG Ventricles repolarize and relax (begin to expand) Semilunar valves close (second hear sound occurs - dub) as pressure in the ventricles drops below the pressure in the outflow arteries AV valves remain closed Ventricles expand but do not fill (no change in volume)

desmosomes

one of two structures located at the intercalated disks. these are anchoring junctions that prevents cells subjected to mechanical stress from being pulled apart. do not provide passageways between cells like gap junctions

gap junctions

one of two structures located at the intercalated disks. these provide cytoplasmic channels between adjacent cells, allowing ions and thus action potentials to easily pass between cells.

heart skeleton

plate of fibrous connective tissue between atria and ventricles. Fibrous rings around av and semilunar valves provides support, serves as electrical insulation between atria and ventricles, and provides attachment site for cardiac muscles.

atrioventricular node (AV)

receives electrical impulse very rapidly from SA node and slows down the impulse so the atria have time to contract and eject their blood into the ventricles

QRS complex

three waves that result from ventricular depolarization that also signal the onset of ventricular contraction

end diastolic volume

during ventricle diastole, the atria are both passively and actively filling the ventricles. since the ventricles are filled during their diastolic phase, this volume of blood is called (blank) and is usually 120-130mL

Repolarization phase (pacemaker potential)

repolarization of the SA node caused by voltage gated Ca channels closing and K channels being open.

ventricular systole (period of ejection)

second phase of ventricular systole. in this phase, the pressure from ventricular contraction increases until it is greater than the pressure in the great vessels, causing the opening of the semilunar valves

mean arterial pressure (MAP)

slightly less than the average blood pressure in the aorta. MAP = CO x PR

third heart sound

sound cause by blood flowing in a turbulent fashion into the ventricles. it is usually hard to hear but can be heard in people that are young and thin

stroke volume

the amount of blood pumped out by a ventricle with each beat (EDV - ESV). e.g. 120mL - 50mL = 70mL per beat

cardiac reserve

the difference between resting and maximal CO you just calculate your CO while at maximum exercise output and subtract your resting cardiac output from it.

QT interval

the interval from the beginning of the QRS complex to the END of the T wave. it is the time frame during which the ventricles contract and begin to relax

PQ interval (aka PR interval)

the interval from the beginning of the p wave and the beginning of the QRS complex. it is the time frame during which the atria contract and begin to relax. There is no wave for relaxation of the atria because it is masked by the QRS complex

pacemaker

the name given to the SA node because of its ability to generate action potentials at a greater frequency than other cardiac muscle cells.

calcium-induced calcium release (CICR)

the process where calcium that crossed the membrane from an action potential travels down the t tubules and binds to receptors on the sarcoplasmic reticulum, resulting in the opening of Ca channels which causes Ca ions to move out of the SR and activate the interaction between actin and myosin

P wave

the result of action potentials that cause depolarization of the atrial myocardium which signals the onset of atrial contraction

depolarization phase

the result of changes in the membrane permeability to Na, K and Ca, but this phase is predominantly the result of Na channels opening and letting Na+ in even though some slow Ca+ channels are open.

early repolarization and plateau

the result of the voltage gated Na channels closing, some Ca channels closing, and SOME voltage gated K+ channels opening which creates the plateau

peripheral resistance (PR)

the total resistance against which blood must be pumped

end systolic volume

the volume of blood left in the ventricle after the period of ejection (usually 50-60mL)

sarcoplasmic reticulum

this structure is also seen in skeletal muscle but in cardiac muscle it is irregularly arranged, and not as closely associated with t tubules as in skeletal m.

pacemaker potential

A spontaneous action potential that occurs in the SA node. it is triggered by a small number of Na channels opening, K+ channels from previous repolarization BEGINNING to close, and and Ca+ channels beginning to open

intercalated disks

These structures branch and connect cardiac cells. They contain specialized gap junctions and coordinate muscle contractions.

Ventricular diastole (passive ventricular filling)

Ventricular relaxation continues AV valves open semilunar valves still close Blood flows from atria into the relaxing ventricles and fills them (~70%)

electrocardiogram (ECG)

a recording of the summation of all action potentials transmitted by the cardiac muscle cells through the heart at a given time. important note: it records electrical activity NOT mechanical events. the ECG record shows electrical events that are followed by chemical events

cardiac cycle

a term that refers to the repetitive pumping process that begins with cardiac muscle contraction and ends with the beginning of the next contraction.

T wave

a wave that represents repolarization of the ventricles and precedes ventricular relaxation

cardiac output (CO)

amount of blood pumped by each ventricle in one minute. it is the product of heart rate and stroke volume e.g. if HR is 75bpm and SV comes out to 70 then CO = 75x70 = 5250ml or 5.25L

bundle branches

branches of the AV bundle that divide to the right and left sides of the interventricular septum

systole

contraction of a chamber

atrial systole (active ventricular filling)

contraction of the atria that occurs as a result of the SA node becoming depolarized. in terms of electrical events, this occurs right after the P wave (atrial depolarization).

ventricular systole (isovolumetric contraction)

first phase of ventricular systole. ventricular contraction pushes the AV valves closed and increases pressure inside the ventricle

ectopic focus

im not sure if we went over this in lecture but it is a word used to describe a situation in which another area of the heart other than the SA node generates an heartbeat. usually this area is the AV node which can generate beats just not as fast. it can be caused by blockage of conducting pathways or other parts of the heart

resting membrane potential

membrane potential when the cell is relaxed. this potential is dependent upon the low permeability of the resting membrane to Na and Ca and its high permeability to K which results in an inner negative/outer positive setup

sinoatrial node (SA)

modified cardiac cells that spontaneously generate AP's without neural stimulation. this structure is aka the pacemaker of the heart. it has fibers that extend to the atria, causing contraction.

final repolarization phase

voltage gated Ca2+ channels close and MANY voltage gated K+ channels open

dicrotic notch

when the aortic semilunar valve closes, pressure within the aorta increases slightly. this causes an incision in the pressure curve