Chapter 19 Part 2 Terms

Conduction system

The system of structures in the heart that initiates and conducts electrical events to ensure proper timing of contractions

Conduction System

Specialized conducting cardiac muscle cells that have action potentials but do not
contract
o Its activity is influenced by autonomic nervous system

Sinoatrial Node

The structure that initiates heartbeat (pacemaker)
o Located high in posterior wall of right atrium

Atrioventricular Node

The structure that receives and delays the action potential that passes through the atria. Located in floor of right atrium (near right AV valve)

Atrioventricular Bundle

The bundle of conductive cells that Extends from AV node though interventricular septum

Bundle Branches

The atrioventricular bundle divides into the left and right __________

Subendocardial Branches (Purkinje fibers)

The fibers with a large diameter that extend from left and right bundles at heart’s apex. They course through walls of ventricles and bring the AP to the myocardium of the ventricles.

Cardiac Center

The reflex center that influences the heart rate and contraction through autonomic innervation. Located in the medulla oblongata.

Baroreceptors and Chemoreceptors

What receptors send signals to the cardiac center?

Baroreceptors

These receptors detect blood pressure and send signals to the cardiac center in the medulla oblongata.

Chemoreceptors

These receptors detect changes in oxygen and carbon dioxide concentration and send signals to the cardiac center in the medulla oblongata.

Autonomic

The _________ nervous system innervates the heart

Modifies

Autonomic innervation of the heart ___________ heart rate and force of contraction.

Parasympathetic

____________neurons extend from cardioinhibitory center of cardiac center
and are relayed via vagus nerves (CN X) right to SA node; left to AV node

Decreases

Parasympathetic innervation __________________ heart rate

Sympathetic

____________________ motor neurons extend from cardioacceleratory center of cardiac center and are relayed via neurons from T1–T5 segments of spinal cord to the cardiac nerve then extend to SA node, AV node, myocardium, and coronary arteries
▪ Increases coronary vessel dilation

Increases

Sympathetic stimulation __________________ heart rate and force of contraction

Conduction System

The ___________ initiates and propagates an action potential

Cardiac Muscle

__________ cells initiate action potentials and contract
▪ This process happens first in the atria and then the ventricles

Na+ and Ca2+

What ions are found in higher concentrations outside of cells?

Anion proteins and K+

What ions are found in higher concentration inside of cells?

Negative

The cytosol is more __________ than the ECF in a resting state.

Depolarization and Repolarization

As in nerve and other muscle tissue, opening of membrane channels will cause
______________________ and _____________________

Spontaneously

Sinoatrial Nodal cells initiate heartbeat as the _______________ depolarize and generate action potential

-60mV

What is the resting membrane potential of a SA nodal cell?

No, they have a funny current

Do SA nodal cells have a stable RMP?

Pacemaker potential

Ability to reach threshold without stimulation

Resting Membrane Potential

Na+/K+ pumps, Ca2+ pumps, leak channels are used to maintain ____________________________.

B: Slow voltage-gated Na+ channels, fast voltage-gated Ca2+ channels,
voltage-gated K+ channels

SA nodal cells have

a) Fast voltage-gated Na+ channels, slow voltage-gated Ca2+ channels,
voltage-gated K+ channels

or

b) Slow voltage-gated Na+ channels, fast voltage-gated Ca2+ channels,
voltage-gated K+ channels

Autorhythmicity

SA node cells exhibit _______________________________ (spontaneous firing) —> they are capable of depolarizing and initiating an action potential spontaneously without external influence.

Slow voltage-gated Sodium Channels

The SA nodes achieve pacemaker potential by the opening of __________________________ which allow the inflow of Na+

-40 mV

What is the threshold value in SA nodal cells

Depolarization

The reversal of the SA nodal cell charge from + to - due to the inflow of Calcium.

Fast voltage-gated calcium channels

Depolarization occurs when ________________ open and Ca2+ flows in
▪ Membrane potential changes from −40 mV to just above 0 mV

Just above 0 mV

What is the value reached at the peak of depolarization in SA nodal cells?

Repolarization

When the SA nodal cell returns to resting membrane potential as K+ channels open and K+ leaves the cell.

voltage-gated potassium channels

During repolarization, Calcium channels close, ________________open, K+ flows out and the membrane potential goes back to rest value (RMP = −60 mV

Slow voltage-gated sodium channels

When the SA nodal cells are repolarized what channels reopen?

0.8

The SA node action potential starts about _________ seconds after the last

75 bpm

What is the average resting heart rate maintained by the SA node with vagal tone?

100

Inherently the SA node would fire faster than avg resting heart rate at about __________ bpm.

Vagal

In the body, _________________ tone (parasympathetic activity relayed by the
vagus nerve) keeps resting heart rate slower than that of SA node firing alone.

SA

Conduction system of the heart: After starting at _______ node the action potential (AP) spreads through the atria.

Gap Junctions

The excitation travels rapidly through the atria due to _________ ____________ which allows for the chambers to acts as a functional syncytium.

Atrioventricular

The action potential reaches the _________________ and is delayed

Delayed

The action potential is ______________ at the AV node
due to small diameter and few gap junctions and Insulation of fibrous skeleton

Bottleneck

Insulation of fibrous skeleton means AV node is a ___________
▪ Delay allows ventricles to fill before they contract

Purkinje

AP passes through AV bundle to subendocardial branches (_________________ Fibers)

Ventricles

From the purkinje fibers, the AP spreads through the myocardium of the __________
▪ Gap junctions allow impulse to spread through cardiac muscle fibers
▪ Cells of the two ventricles contract nearly simultaneously

Large

Subendocardial branches (Purkinje fibers) relatively ______ in diameter
• Action potential extremely rapid
• Ensures ventricles contract at same time

Papillary Muscles

_____________ stimulated to contract immediately by the conduction system
• Muscles anchor chordae tendineae of AV cusps
• Start to pull on cusps just prior to increase in pressure in ventricles

Apex

Stimulation begins at heart ______ and moves superiorly
• Ensures blood efficiently ejected toward arterial trunks

Ectopic Pacemaker

pacemaker cells other than SA node. (Conduction system cells other than the SA node ex: AV node)

Slower

Ectopic pacemakers like the AV node also have ability to spontaneously depolarize but depolarize at _____________ rates than SA node

40-50

AV node the default pacemaker if SA node impaired with inherent rhythm of ___________ beats/min, fast enough to sustain life
• Cardiac muscle with rate of 20 to 40 beats/min, usually too slow to sustain life

Mechanical

A ___________ pacemaker can be implanted to send electrical impulses to sustain a sufficient heart rate

Na+/K+ pumps, Ca2+ pumps, leakage channels for Na+ and K+

What are the membrane proteins that cardiac muscle cells possess to maintain resting membrane potential?

-90 mV

Cardiac muscle cells have a resting membrane potential of ______________

Fast

Cardiac muscle cells have

_________voltage-gated Na+ channels
▪ Slow voltage-gated Ca2+ channels
▪ Voltage-gated K+ channels

Slow

Cardiac muscle cells have:

Fast voltage-gated Na+ channels

_________ voltage-gated Ca2+ channels
▪ Voltage-gated K+ channels

Closed

Unlike SA nodal cells all the voltage channels are __________ when the cell is at rest.

Sarcolemma

Propagation of the action potential within cardiac muscle cells occurs along the ______________.

Sarcomere

The functional unit that causes contraction of the muscle cells when stimulated is the ____________.

Depolarization

When fast-gated sodium channels open in cardiac muscle cells and the potential rapidly changes from -90 mV to +30 mV

Inactivate

When the cardiac muscle cells potential reached +30 mV voltage gated Na+ channels start to _____________.

Plateau

The phase in cardiac muscle cells where both the K+ voltage gated channels and the Ca2+ slow voltage-gated channels are open and the membrane remains depolarized. Ca2+ released from sarcoplasmic reticulum at this time.

Repolarization

The phase where voltage-gated Ca2+ channels close while K+ channels remain open and the membrane potential goes back to −90 mV

0.1 seconds

How long is the delay at the atrioventricular node?

No

Can fast voltage-gated sodium channels be restimulated during the plateau phase?

Calcium

Cross bridge cycling is initiated with the entry of __________ into the cytosol from both the interstitial fluid and the Sarcoplasmic Reticulum

Cardiac Muscle Contractions

Ca2+ enters cytosol from interstitial fluid and SR leading to ________________________

Troponin

Calcium binds to __________ which causes a shift in tropomyosin exposing myosin binding sites and allowing for cross-bridge formation.

Cross-bridge cycling

Cross-bridge formation (myosin head binds thin filament), power stroke,
release of myosin head, reset of myosin head

Sarcomere

Cross-bridge cycling results in shortening of the ____________ as the thick and thin filaments slide past each other.

Relaxation

Ca2+ levels decrease leading to cardiac muscle _______________________
▪ Channels close and pumps move it into SR and out of cell

Tetany

Cardiac muscle cannot exhibit ______________

Refractory

Unlike skeletal muscle, cardiac cells have a long ______________________
period (250 ms)
• Cell cannot fire a new impulse
• Occurs due to cardiac muscle cell’s plateau phase

Relax

The long refractory phase of cardiac muscle cells allows for the cell to contract and ________ before it can be stimulated again
• Makes sustained contraction (tetany) impossible

Electrocardiogram

A record of the electrical signals of the heart, detected by electrodes on the skin, used as a common diagnostic tool. Provides a composite tracing of all cardiac action potentials generated by myocardial cells

P wave

The ECG wave that reflect electrical changes of atrial depolarization.

0.08 to 0.1 seconds

How long does the P wave last?

QRS complex

The wave that represents the electrical changes associated with ventricular depolarization.

0.06 to 0.1 seconds

How long does the QRS complex last?

T wave

the electrical change associated with ventricular repolarization

Segments

the electrical events between waves that correspond with a plateau where there is no electrical change

P-Q segment

the segment associated with the atrial plateau

S-T segment

the segment associated with the ventricular plateau

P-R interval

The portion of the ECG representing the period of time from the beginning of the atrial depolarization to ventricular depolarization

P-R interval

The portion of the ECG that represents the time for the propagation of an action potential through the entire conduction system

P-R interval

The time from the beginning of the P wave to the beginning of the QRS complex

0.12-0.20 seconds

The time of the P-R interval

Heart Block

A P-R interval longer than 0.12 to 0.20 seconds may indicate this disorder

Q-T interval

The portion of the ECG that corresponds with the time from ventricular depolarization to ventricular repolarization. Time for the action potential to occur within the ventricle

Q-T interval

Time from beginning of QRS complex to end of t-wave. TIme depends on heart rate

0.2-0.4 seconds

How long does the Q-T interval last?

Long QT syndrome

Chronically long Q-T interval due to genetic disorder, medications, or metabolic disorder. May lead to tachyarrhythmia

Tachyarrhythmia

rapid, irregular heart rate.

Depolarization

Atrial ___________________________ is recorded as the P wave, and muscle cells of atria stimulated to contract

Plateau

Atrial ________ recorded as PQ segment, muscle cells of atria contract and relax

Repolarization

Atrial ____________________________