Physiological Properties Of The Heart & Nerve Supply

Question 1

What are the physiological properties of the heart muscle?

Answer 1

• Rhythmicity
• Excitability
• Conductivity
• Contractility

Question 2

Rhythmicity means…

Answer 2

…the ability of the heart to beat regularly without external stimulation

Question 3

The rhythmicity of the heart - neurogenic or myogenic?

Answer 3

Myogenic

Question 4

There are nerves that increase or reduce contraction of the heart. True or false?

Are they needed for the heart to beat?

Answer 4

True. No.

Question 5

What is the the primary pacemaker of the heart?

Answer 5

The cells of SAN in the posterior wall of right atrium

Question 6

Where are the cells of the SAN?

Answer 6

Posterior wall of the RA

Question 7

The SAN beats at…

Answer 7

110 beats/min

Question 8

The highest rate of beat is produced by…

Answer 8

The SAN

Question 9

The AVN beats at…

Answer 9

90 beats/min

Question 10

Who does the work of heartbeat when there is a problem with the SAN?

Answer 10

The AVN

Question 11

What is the conductivity of the heart?

Answer 11

The ability to conduct impulses from one cell to another.

Question 12

The ease of impulse transfer from one part of the cardiac muscle to another is facilitated by…

Answer 12

…the presence of intercalated discs between these cells, which contain gap junctions that transmit electrical currents

Question 13

The contractility of the heart is controlled by…

Answer 13

The All or None Law

Question 14

State The All or None Law

Answer 14

The cardiac muscle contracts either maximally or not at all (under constant conditions)

Question 15

The atria and ventricles contract as one unit. True or false?

Answer 15

True

Question 16

The cardiac muscle can be stimulated through which means?

Answer 16

Physical
Electrical
Chemical

Question 17

What is the refractory period of the heart?

Answer 17

The period in which a new impulse, irrespective of the magnitude cannot bring about stimulation.

Question 18

Types of refractory period

Answer 18

Absolute

Relative

Question 19

Difference between both types of refractory period

Answer 19

A measure of stimulation can be achieved during the relative refractory period but none can be achieved during the absolute refractory period

Question 20

Relationship between refractory period of heart muscle and skeletal muscle

Answer 20

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.

Question 21

What is the Staircase or Treppe Phenomenon?

Answer 21

It states that rapidly repeated stimulation of the cardiac muscle will produce gradual increase in the strength of contraction

Question 22

What is responsible for the Staircase or Treppe phenomenon?

Answer 22

Earlier contractions produce better conditions for subsequent ones so the strength of contraction increases

Question 23

States the starling law

Answer 23

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

Question 24

The heart muscle is under autonomic control. True or false?

Answer 24

True

Question 25

Effects of the SNS on the heart

Answer 25

Increased ionotropy (contractility), leading to increased

• heart rate
• blood pressure
• cardiac rate
• coronary blood flow

Question 26

Effects of the PNS on the heart

Answer 26

Decreased ionotropy (contractility)