Lab 9 Flashcards
? are striated and joined to adjacent cells by ? that appear as dark staining lines (?) when viewed with a light microscope.
- Myocardial cells
- gap junctions
- intercalated discs
Since the myocardial cells are electrically coupled, the mass of myocardial cells joined together by the intercalated discs acts as one unit, a ? known as a ?.
- functional syncytium
- myocardium
In a normal heart, (1) cells in the (2) initiate action potentials that allow the heart to beat. This (3) or (4) rhythm is brought about without nervous system input, but can be modified by the ANS or by increased venous return to the heart chambers.
- autorhythmic
- sinoatrial (SA) node
- automatic
- intrinsic
The autorhythmic cells initiate (1) that allow the myocardium to function as a unit. The cells have an (2), causing them to (3) to threshold.
- action potentials
- unstable resting membrane potential
- spontaneously depolarize (pacemaker potential)
The spontaneous depolarization to threshold is caused by channels (?) that open in response to a hyperpolarization or an increase in cyclic nucleotide second messengers.
HCN, hyperpolarization cyclic nucleotide channels
The ? involve a slow influx of Ca2+ which will trigger the excitation contraction coupling events for cardiac muscle to contract.
myocardial action potentials
The ? of the heart consists of ? that distribute impulses in a coordinated fashion so that the atrial and ventricular contractions are controlled.
- intrinsic conduction system
- nodal tissues
nodal tissues include
the SA node, three internodal tracts, the atrioventricular (AV) node, the atrioventricular
bundle (AV bundle or bundle of His), right and left bundle branches, and Purkinje fibers.
The SA node is the ? of the heart, discharging at about 70-80 times per minute; the characteristic rhythm of the heart is thus called ?.
- primary pacemaker
- sinus rhythm
The AV node (?, 40-60 beats per minute) will become the primary pacemaker should something happen to the SA node.
secondary pacemaker
The junction between the atria and the ventricles is associated with an interval between atrial and ventricular activity (?).
A-V delay
junctional fibers propagate excitation at velocities as low as 5 cm/sec. This slow propagation accounts for the interval of “A-V delay”, but is important in allowing the atria to contract fully (?) before the ventricles contract.
atrial systole
The Purkinje fibers are also capable of their own intrinsic pacemaker rhythms
(?, 30-40 discharges per minute).
tertiary pacemakers
Ventricular contraction (?) immediately follows the depolarization of the ventricles.
ventricular systole
? of the myocardium signifies the relaxation of the heart muscle and is termed ?.
- Repolarization
- diastole
continual cycling of the electrical conduction (and thus systolic contractions followed by diastolic relaxation) is termed the ?.
cardiac cycle
A ventricular rate that is slower than 60 beats per minute is referred to as ?.
bradycardia
A ventricular rate that is faster than 100 beats per minute is termed ?.
tachycardia
a graphic recording of the electrical currents generated by the cardiac cycle.
electrocardiogram (ECG or EKG)
During a cardiac cycle, three distinct waves can be seen on the ECG:
the P wave, the QRS complex, and the T
wave.
represents the depolarization of the atria.
The P wave
represents depolarization of the ventricles.
The QRS complex (0.08 sec)
represents repolarization of the ventricles.
The T wave
Critical measurements in an electrocardiogram are
- the P-R interval
- the S-T segment
- the Q-T interval
