initiating heart contraction

Question 1

what is fibrillation

Answer 1

uncoordinated contraction of the atria and ventricles

Question 2

what is myogenic muscle

Answer 2

muscle that can initiate its own contraction

Question 3

what is Purkyne tissue

Answer 3

consists of specially adapted muscle fibres that conduct the wave of excitation from the AVN down the septum to the ventricles

Question 4

what is the sinoatrial node

Answer 4

the hearts pacemaker. it is a small patch of tissue that sends out waves of electrical excitation at regular intervals in order to initiate contractions

Question 5

what can cardiac muscle do

Answer 5

initiate muscle contraction

Question 6

why can heart muscle initiate its own muscle contractions

Answer 6

it is myogenic and has its own intrinsic rhythm at around 60 beats per minute

Question 7

can heart muscle still relax and contract even its not connected to the body

Answer 7

yes

Question 8

which muscle contracts at a higher frequency

Answer 8

the atrial muscle

Question 9

what is the benefit of myogenic contraction

Answer 9

it prevents the body wating resources maintaining the basic heart rate

Question 10

what is the average resting heart rate of an adult

Answer 10

70bpm

Question 11

which factors can affect heart rate

Answer 11

exercise, excitement, stress

Question 12

what can cause inefficient pumping

Answer 12

if the contractions of the chambers aren’t synchronised

Question 13

what is the term for unsynchronised contractions

Answer 13

fibrillation

Question 14

what are myocytes

Answer 14

muscle cells

Question 15

what do myocytes have

Answer 15

a slight electrical charge across their membrane - they are polarised

Question 16

what happens when the electrical charge across the membrane is reversed

Answer 16

they are depolarised and this causes them to contract

Question 17

where is depolarisation initiated

Answer 17

in the sinoatrial node

Question 18

what is another term for the sinoatrial node

Answer 18

the pacemaker

Question 19

where is the SAN located

Answer 19

near the point where the vena cava empties blood into the right atrium

Question 20

what does the SAN do

Answer 20

initiate a wave of excitation at regular intervals (55-80x a minute in humans)

Question 21

what is the SAN a patch of

Answer 21

cardiac muscle that controls the cardiac cycle

Question 22

what are the names of the two nodes

Answer 22

the sinoatrial node and the atrioventricular node

Question 23

how are heart muscle contractions coordinated

Answer 23

electrical impulses are sent from the SAN to the AVN

Question 24

what do the cell membranes of the two nodes allow

Answer 24

a charge to be maintained across the membrane.

Question 25

what happens at rest

Answer 25

the nodes in the heart become polarised

Question 26

what happens at polarisation

Answer 26

a positive charge builds up on the inside of the node and a negative on the outside. this is caused by ions building up

Question 27

when do the nodes become depolarised

Answer 27

when a contraction occurs

Question 28

what happens at depolarisation

Answer 28

positively charged ions move out of the nodes stimulating a move in the electrical activity of the heart

Question 29

what happens at atrial systole

Answer 29

- the sinoatrial node sends a wave of depolarisation throughout the atria - this causes the walls of the atria to contract almost simultaneously - blood is forced through the bicuspid and tricuspid valves into the ventricles

Question 30

what happens at ventricular systole

Answer 30

- the AVN picks up the wave from the SAN and initiates its own wave of depolarisation down the Bundle of His then into the Purkyne tissues - this causes the ventricular walls to contract - this forces blood out of the semilunar valves through the aorta and the pulmonary artery

Question 31

describe the electrical coordination of the heartbeat

Answer 31

- the sinoatrial node initiates the electrical impulses that set the heartbeat. a wave of depolarisation spreads from the SAN over the atria. the atria depolarise causing them to contract and push blood into the ventricles. an electrical signal reaches the AVN which waits for the atria to fully contract and for the ventricles to fill with blood. the electrical impulses travel down the Bundle of His and along the Purkyne fibres into the ventricles. the Purkyne fibres cause the ventricles to depolarise and contract therefore pumping blood through the arteries to the lungs and the rest of the body. the ventricles repolarise and the heart muscle cells return to their resting state waiting for the next cycle. the heart undergoes diastole and the atria fills with blood from the vena cava and pulmonary waiting for the next systole

Question 32

why is there a brief delay when the impulse reaches the AVN

Answer 32

to ensure the atria have emptied completely and stopped contracting

Question 33

what is the bundle of his

Answer 33

bundle of conducting tissue made up of Purkyne fibres