8-14 Properties Of Cardiac Muscle

Question 1

Extrasystole and Compensatory
Pause

When a sufficiently stronger stimulus is applied in the relative refractory period, an extra contractile response occurs called
___________.

The next impulse from the SA node
will fall in the refractory period of the extrasystole and will not evoke a response (contraction is missed).

Answer 1

extrasystole

Question 2

This is why a long pause is seen
following the extrasystole, which is
called a ________ pause.

Extrasystole is not uncommon in
real life, and it may not be always
pathological, usually, arises from an
ectopic focus in the ventricle.

The magnitude of contraction
following the compensatory pause
is usually a higher one as the
ventricle gets more time for filling
during the pause.

Answer 2

compensatory

Question 3

The _______ law states that the magnitude of response of a tissue to stimuli remains same irrespective of the strength of stimuli.

2. The response may change if the condition is changed. For example, if heart is stimulated following the
   sympathetic activation, the magnitude of contraction increases.

In this case, the excitability and contractility of the heart are changed by ______ stimulation and therefore the change in magnitude of
contraction.

Answer 3

1. All-or-None Law
2. sympathetic

Question 4

Allso called the treppe
phenomenon or _________

If the cardiac muscle is stimulated
by successive maximal stimuli,
the 1st few contractions show a
gradual increase in magnitude
which is represented graphically
as a staircase.

After that, the strength of
contraction becomes stable at its
normal level.

Answer 4

1. Staircase Phenomenon, Bowditch
   effect.

Question 5

Length-Tension Relationship

The force of contraction is directly proportional to the initial length (the length of the muscle fiber prior to the contraction) of the muscle fiber, within the physiological limit, which is known as the ____________ of the
heart.

Note that as the ⬆️ ventricular filling increases (the increase in end-diastolic volume), the stroke volume ⬆️ increases. This is called _____________ of the heart.

Answer 5

Frank-Starlings Law
heterometric autoregulation

Question 6

⬆️ Increase in force of contraction due to ⬆️ increase in heart rate (frequency) is known as __________.

However, ⬆️ increase in myocardial performance is restricted to a limited
⬆️ increase in ________

Answer 6

Frequency-Force Relationship
frequency