1-7 Properties Of Cardiac Muscle

Question 1

1. It is the ability to initiate its own beat and it is due to the presence of ________.
2. The cardiac muscle to continue to contract regularly even in the absence of its ________.
3. This is possible due to the spontaneous generation of impulses by the ________.

Answer 1

1. Automaticity, P cell
2. nerve supply
3. SA node

Question 2

Refers to the rhythmic excitation of the heart called _________.
This occurs due to regularity in rhythmic discharge of the SA node.

The rate of discharge of SA node is ________ per minute, the highest among all the pacemakers.

Answer 2

1. Rhythmicity, autorhythmicity
2. 60–100 / min

Question 3

Pacemaking Tissues in the Heart

1. _______________ include the SA node, AV node and His Purkinje fibers. However, when the intrinsic pacemakers fail to discharge, __________ generates the pacemaking activity.
2. Any of the pacemakers can initiate the heartbeat however, the
   pacemaker with highest frequency (__________) triggers the action potential that propagates throughout the heart.
3. Cardiac pacemakers have a hierarchy among themselves. Failure of SA nodal rhythm results in activation of ________, the next in the hierarchy to take over the pacemaker activity.

Answer 3

1. Intrinsic pacemaking tissues, ventricular muscle
2. the SA node
3. AV node

Question 4

PacemakingTissues in the Heart

4. Thus, AV node and other cardiac
   pacemakers are called secondary or _________ pacemakers .
5. In sudden A-V bundle block
   (interruption of impulse transmission
   from the atria to the ventricles), the
   _________ does not begin to emit its intrinsic rhythmical impulses until ______________ later, during this time the ________ fail to pump blood, and the person faints because of lack of blood flow to the brain (__________ syndrome)

Answer 4

4. ectopic
5. Purkinje system, 5 to 20 seconds, ventricles, Stokes-Adams syndrome

Question 5

Impulse produced in SA node is conducted by specialized conducting pathway to the ventricular muscle. The impulse then spreads rapidly in cardiac muscle to the different parts of the heart.

Answer 5

Conductivity

Question 6

1. ________ is the inherent strength and vigor of the heart’s contraction
   during systole. and also called _________.
2. Directly related to the concentration of ________ within the cardiomyocyte so any factors that ⬆️ increase intracellular calcium levels will ⬆️ increase _______ contractility.
3. Can be estimated by the ____________ (stroke volume/end-diastolic volume), which is normally 50-75%.

Answer 6

1. Contractility, inotropism
2. calcium, cardiac
3. ejection fraction

Question 7

1. _______ inotropic factors produce an increase in contractility.
2. Sympathetic stimulation (catecholamines) via β1 receptors.
   It ⬆️ increases the _______ during the plateau. It ⬆️ increases the activity of the ________ of the SR
3. __________ (digitalis) Inhibiting Na+, K+-ATPase in the myocardial cell, this will result to diminished ________ exchange and ⬆️ increased intracellular [Ca2+]

Answer 7

1. Positive
2. inward Ca2+ current, Ca2+ pump
3. Cardiac glycosides, Na+–Ca2+

Question 8

1. ________ inotropic factors produce a decrease in contractility
2. Parasympathetic stimulation (ACh) via _______ receptors decreases the _________ in the atria

Answer 8

1. Negative
2. muscarinic, force of contraction

Question 9

1. Excitability (_______) is the ability of the cardiac muscle to respond to different stimuli.

Answer 9

bathmotropism

Question 10

1. The ability to stretch due to compliance.
   This property helps in the filling of atrial and ventricular
   chambers.
2. ⬇️Decreased ________ distensibility, ⬇️ decreases end ________ volume.

Answer 10

1. Distensibility;
2. ventricular, diastolic

Question 11

Refractory Period

Unlike skeletal muscles, the heart cannot sustain a ________.
This is because the atria and ventricles behave as one muscle cell; as a single
unit and contracts as a unit.

2. The heart normally cannot be stimulated again until after it has relaxed from its previous contraction because ______ cells have long refractory periods.

Answer 11

1. contraction
2. myocardial

Question 12

1. Cardiac muscle does not show any response at all.
2. It extends from ________ to half of ________ of the action potential ie. until the membrane potential reaches approximately - 50 m V during repolarization.

Answer 12

1. Absolute Refractory Period (ARP)
2. phase 0, phase 3

Question 13

1. The muscle shows response if the strength of stimulus is increased to maximum.
2. It extends from second half of _______ to _______
   of the action potential.

The refractory period of atrial muscle is much _________ than that for the ventricles (about 0.15 second for the atria compared with 0.25 to 0.30 second for the ventricles).

Answer 13

1. Relative Refractory Period.
2. phase 3, phase 4
3. Shorter

Question 14

All muscle fibers contract almost simultaneously

Answer 14

Functional Syncytium