Lecture 11- Physiology Of The Heart

Question 1

Structural and functional properties of cardiac muscle

Answer 1

Striated
Cells are short, fat and branched
One or two large centrally located nuclei
Cells connected by intercalated discs
Have many large mitochondria

Question 2

Intrinsic conduction system

Answer 2

sets the basic rhythm of the heart.

Question 3

Extrinsic innervation of the heart

Answer 3

modifies the basic rhythm.

Question 4

Why is the heart refractory period longer?

Answer 4

To prevent tetanus contractions

Question 5

Pacemaker cells

Answer 5

Approx. 1% of cardiac muscle cells

self-excitable and initiate own depolarization, as well as set the rhythm for depolarizing the rest of the cardiac muscle.

Question 6

Does heart depend on nervous system?

Answer 6

No

It relies on gap junctions to conduct impulses throughout the heart and the intrinsic conduction system.

Question 7

Sinoatrial nose (SA)

Answer 7

Located in the right atrium and is the primary pacemaker for the heart.

Question 8

Atrioventricular (AV) node

Answer 8

in the interatrial septum, delays firing slightly, in order to allow the atria to finish contracting before the ventricles contract.

Question 9

Atrioventricular (AV) bundle (bundle of His)

Answer 9

only electrical connection between the atria and the ventricles and conducts impulses into the ventricles from the AV node.

Question 10

Right and left bundle branches

Answer 10

conduct impulses down the interventricular septum.

Question 11

Subendocardial conducting network (purkinje fibres)

Answer 11

penetrates throughout the ventricular walls, distributing impulses through
the ventricles.

Question 12

Order impulses pass through cardiac pacemaker cells

Answer 12

Sinoatrial (SA) node

Atrioventricular (AV) node

Atrioventricular (AV) bundle (bundle of His)

Right and left bundle branches

Subendocardial conducting network (purkinje fibres)

Question 13

Arrhythmias

Answer 13

Irregular heart rhythms

Question 14

Fibrillation

Answer 14

rapid, irregular, ineffective contractions.

During ventricular fibrillation, even though the heart is still moving, it becomes useless for pumping blood, causing circulation to cease.

Treatment = defibrillation; disrupting the chaotic twitching and resetting the heart to regular, normal depolarizations.

Question 15

Cardioaccelatory centre

Answer 15

In medulla oblongata

projects to sympathetic neurons throughout the heart, increasing both heart rate and contractile force.

Question 16

Cardioinhibitory centre

Answer 16

In medulla oblongata

sends impulses to the parasympathetic dorsal vagus nucleus in the medulla oblongata, which stimulates the vagus nerve to the heart, decreasing the heart rate.

Question 17

When cardiac muscle cells are stimulated…

Answer 17

Fast voltage-gated Na+ channels allow Na+ to enter cell, resulting in rapid depolarization.

Depolarization opens slow Ca2+ channels, allowing Ca2+ to enter cell, even as K+ exits, producing a phase of the action potential that delays repolarization.

After 0.2 seconds, Ca2+ channels inactivated, additional K+ channels open, and cell repolarizes back to resting membrane potential.

Question 18

Why is slow contraction of heart sustained?

Answer 18

to ensure all of the blood is squeezed out of heart.

The heart then has a long refractory period so it can be refilled with blood before beating again.

Question 19

Electrocardiograph

Answer 19

Monitors and amplifies the electrical signals of heart and records it as an electrocardiogram (ECG)

Question 20

ECG three deflections

Answer 20

1. P wave, indicating depolarization of the atria.
2. QRS complex, resulting from ventricular depolarization
3. T wave, caused by ventricular repolarization

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