Electrical Activity And Muscle Contraction

Question 1

What are heart cells called and the 2 types

Answer 1

Myocytes

1- conducting cells : fast spread of AP

2- work cells : cells which generate contraction force

Question 2

Where are work cells found

Answer 2

In both Atria and ventricles

Question 3

What are the 2 ways ap can spread in heart

Answer 3

Through conducting fibres

Cell to cell via gap junctions

Question 4

Which cells have spontaneous depolarisation which causes contraction

Answer 4

SAN

Question 5

When is the SAN

Answer 5

Right atrium

Question 6

Where does AP spread from the san

Answer 6

To internodal pathways and then spread across both atria

Question 7

How is ap spread to both atria before going to the AVN

Answer 7

Through gap junctions

Question 8

Why is there a delay in ap spread down AVN

Answer 8

To allow all the blood to leave the atria after contraction

Question 9

How does ap spread to the apex of heart

Answer 9

Down bundle of his , purkinje fibres

Question 10

What do purkinje fibres on both sides of heart all

Answer 10

Ventricle contraction upwards of the heart

Question 11

What is the spontaneous depolarisation of the SAN called

Answer 11

Pacemaker potential

Question 12

What channel opens in the initial depolarisation in the SAN (pacemaker potential)

Answer 12

Non specific cation channels open and cations + flood into cell

Question 13

Which channels open at the SAN to cause rapid depolarisation once reached threshold

Answer 13

Ca2+ channels

Question 14

Which channels cause repolarisation at the SAN

Answer 14

Voltage gated K+ channels

Question 15

Ap in the ventricle cells is different. What causes depolarisation

Answer 15

Voltage gated NA channels

Question 16

Which channels initially cause repolarisation in ventricle cells

Answer 16

Fast opening K+ channels

Question 17

Why is there a plateau phase in repolarisation at ventricle cells

Answer 17

Voltage gated ca channels open and counteract the K+ channels leaving the cells

Question 18

What are the ca2+ called in ventricle AP

Answer 18

Trigger calcium

Question 19

What happens after plateau phase

Answer 19

Ca channels shut

Slow opening K channels open and cause repolarisation again

Goes to resting potential

Question 20

How is contraction triggered in ventricle cells

Answer 20

By the trigger ca flooding which bind at the SR to release Ca2+

Question 21

what are the channels which ca flood out of and later bind to troponin to cause contraction

Answer 21

Ryanodine receptor channels

Question 22

What are the 2 ways relaxation occurs

Answer 22

Removal of ca back to the sr via ca2ATPase channels

Or

Removal out of the cell via NA/ ca anti Porter

Question 23

Why can na/ca anti Porter work to remove ca out of cell

Answer 23

Gradient produced by the na/k pump

Question 24

What factor affects force/ contraction

Answer 24

Number of myosin actin cross bridges which is dependant on number of ca bound to troponin via trigger ca release out of SR

Question 25

When does muscle contraction first occur in response to an AP

Answer 25

At the plateau phase when trigger calcium enters cell

Question 26

How does the heart avoid tetanus

Answer 26

It has a long refractory period which allows muscle to relax first via removal of ca

Question 27

What machine records depolarisation and repolarisation of working cells(contracting)

Answer 27

Electrocardiogram ECG

Question 28

Why is ecg different to ap

Answer 28

Because it records sum of of electrical activity of all working cells

Question 29

What is the point in the ecg which is where heart is relaxed

Answer 29

Isoelectric point

Question 30

Which wave is first in an ecg and what does it represent

Answer 30

P wave Represents atrial depolarisation

Question 31

What happens after P wave

Answer 31

QRS complex

Question 32

What is the dip at Q representing

Answer 32

Initial ventricular depolarisation

Question 33

What does R represent

Answer 33

Ventricular depolarisation

Question 34

What does S represent (downward curve at QRS)

Answer 34

Depolarisation upwards by purkinje fibres up the heart muscle

Question 35

What wave comes after the QRS complex and what does it show

Answer 35

T wave It shows ventricular repolarisation

Question 36

What is the interval called between P and the R wave and what does it show

Answer 36

Pr interval It shows the conduction down the AVN and bundle of His

Question 37

What is the interval called between S/Q and T

Answer 37

ST interval Start of repolarisation of the ventricle

Question 38

What is an irregular rhythm called

Answer 38

Arrhythmias

Question 39

What are the 2 types of arrhythmia

Answer 39

1- impulse propagation : random AP occurrence and slow firing 2- impulse initiation : uncontrollable AP firing in atria or ventricle = atrial fibrillation/ ventricular fibrillation