Transport in Animals - Control of the Cardiac Cycle

Question 1

describe cardiac muscle

Answer 1

• cardiac muscle is myogenic, therefore cells grown in culture will contract and relax rhythmically
• cardiac cells joined together contract in unison

Question 2

why do contractions of the cardiac muscle need to be coordinated

Answer 2

to prevent fibrillation and ensure the efficient pumping of blood

Question 3

what is the sino-atrial node

Answer 3

a small patch of tissue in the wall of the right atrium that initiates an electrical wave of excitation

Question 4

what does the initial wave of excitation do

Answer 4

passes over the walls of both atria, causing them to contract

Question 5

what prevents the electrical wave passing to the ventricles

Answer 5

a band of non-conducting collagen fibres between the atria and the ventricles

Question 6

what is the atrio-ventricular node

Answer 6

a small gap in the non-conductive collagen fibres at the top of the septum which allows the wave of depolarisation through with a small delay

Question 7

after passing the atrio-ventricular node, what does the electrical wave then do

Answer 7

travels down conductive Purkyne tissue which runs down the septum

Question 8

what is the function of Purkyne tissue

Answer 8

• transmits the excitation very rapidly to the apex of the ventricles
• it then conducts the wave upwards and outwards through the ventricle walls
• this causes muscles to contract from bottom up

Question 9

why should the ventricles contract from bottom up

Answer 9

to ensure all the blood is pumped out of the ventricles