LEC 2

Question 1

The heart is composed of three types of fibers

Answer 1

1. Atrial Muscle Fibers
2. Ventricular muscle Fibers
3. Conductive fibers:

Question 2

the only difference between Atrial and. Ventricular muscle Fibers

Answer 2

the ventricular muscle fibers are thicker than the atrial fibers producing stronger contraction

Question 3

Conductive fibers

Answer 3

Specialized fibers because they are neither nerves nor muscles

Question 4

Conductive fibers اهم ميزه

Answer 4

Self-excitable

Question 5

Conductive fibers Not nerves because

Answer 5

they don’t conduct the action potential as fast as the nerves.

Question 6

Conductive fibers Not muscles because

Answer 6

they are non-contractile fibers

Question 7

Self-excitable means

Answer 7

They are able to generate the impulse by their own and transmit it.

Question 8

SA Node (Sinoatrial node) near

Answer 8

the Superior vena cava.

Question 9

AV Node

Answer 9

Internodal (sub nodal) fibers – between the SA node and the AV node.

Question 10

AV Bundle (Bundle of His) divided into

Answer 10

A. Right Branch B. left Branch

Question 11

a fibrous tissue is considered

Answer 11

the point of origin and insertion for the cardiac muscle.

Question 12

the highest rate of excitation

Answer 12

SA node

Question 13

SA node has the highest rate of

excitation for a couple of reasons

Answer 13

1. The Resting membrane potential is around ( -60 mv ) which is higher than
   the other fibers and nearer to the threshold
   While in other tissue it is -70 mv so needs more time to reach the threshold
2. the SA node cells membrane is leaky to ( Na+ )

Question 14

الوقت اللازم لحتى ال atruim يتحفز

Answer 14

30 milliseconds

Question 15

duration of action potential to reach the AV node,

Answer 15

90 milliseconds

Question 16

duration of action potential in AVbundle

Answer 16

40 milliseconds

Question 17

emptying process of the atrium takes

Answer 17

130 milliseconds.

Question 18

in Purkinje fibers stimulate the ventricles

Answer 18

60 milliseconds

Question 19

The whole process from stimulating the SA node until ventricular contraction
needs about

Answer 19

220 milliseconds )

Question 20

The Highest rate of Excitation

Answer 20

SA Node

Question 21

The Highest velocity rate

Answer 21

Purkinje fibers

Question 22

plateau

Answer 22

after slow Ca2+ channels open allowing
Ca2+ ions to leak to the inside of the cell
( leak slowly ). This leakage takes a long
period of time (about200 ms

Question 23

Refractory period divided into two periods

Answer 23

1. Absolute refractory period

2. Relative refractory period

Question 24

When we can’t re‐stimulate the heart

Answer 24

Absolute refractory period

Question 25

Absolute refractory period represent

Answer 25

about 95% of refractory period

Question 26

Relative refractory period represent

Answer 26

the last 5% of refractory period.

Question 27

When we can re‐stimulate the heart

Answer 27

Relative refractory period

but we need a stronger stimulus

Question 28

Refractory period in the ventricles

Answer 28

0.25-0.3 seconds

Question 29

Refractory period in the atria.

Answer 29

0.15 s

Question 30

Refractory period includes

Answer 30

time periods during which the depolarization & the plateau

Question 31

premature contraction

Answer 31

Extra systolic beat
systole occurs (stimulation) during the
relative refractory period

Question 32

Frank-starling law

Answer 32

The greater the heart muscle is stretched
during filling, the greater is the force of
contraction and the greater the quantity
of blood pumped into the aorta