Physiological Properties Of The Heart & Nerve Supply Flashcards
What are the physiological properties of the heart muscle?
- Rhythmicity
- Excitability
- Conductivity
- Contractility
Rhythmicity means…
…the ability of the heart to beat regularly without external stimulation
The rhythmicity of the heart - neurogenic or myogenic?
Myogenic
There are nerves that increase or reduce contraction of the heart. True or false?
Are they needed for the heart to beat?
True. No.
What is the the primary pacemaker of the heart?
The cells of SAN in the posterior wall of right atrium
Where are the cells of the SAN?
Posterior wall of the RA
The SAN beats at…
110 beats/min
The highest rate of beat is produced by…
The SAN
The AVN beats at…
90 beats/min
Who does the work of heartbeat when there is a problem with the SAN?
The AVN
What is the conductivity of the heart?
The ability to conduct impulses from one cell to another.
The ease of impulse transfer from one part of the cardiac muscle to another is facilitated by…
…the presence of intercalated discs between these cells, which contain gap junctions that transmit electrical currents
The contractility of the heart is controlled by…
The All or None Law
State The All or None Law
The cardiac muscle contracts either maximally or not at all (under constant conditions)
The atria and ventricles contract as one unit. True or false?
True
The cardiac muscle can be stimulated through which means?
Physical
Electrical
Chemical
What is the refractory period of the heart?
The period in which a new impulse, irrespective of the magnitude cannot bring about stimulation.
Types of refractory period
Absolute
Relative
Difference between both types of refractory period
A measure of stimulation can be achieved during the relative refractory period but none can be achieved during the absolute refractory period
Relationship between refractory period of heart muscle and skeletal muscle
The refractory period of the myocardial fibers is longer than that of skeletal muscle fibers and lasts approximately as long as the cardiac contraction so no continous contraction without relaxation (tetanus) can occur in heart.
What is the Staircase or Treppe Phenomenon?
It states that rapidly repeated stimulation of the cardiac muscle will produce gradual increase in the strength of contraction
What is responsible for the Staircase or Treppe phenomenon?
Earlier contractions produce better conditions for subsequent ones so the strength of contraction increases
States the starling law
Within limits, the greater the initial length of cardiac muscle fiber, the greater the force of contraction. That is the more the muscle is stretched, the greater the force of contraction
The heart muscle is under autonomic control. True or false?
True
