Electrcal Control

Question 1

Heart muscle is…

Answer 1

Myogenic

• can generate its own impulse/ contraction
• does not need to be stimulated by a nerve to make it contract

Question 2

ECG stands for…

Answer 2

ElectroCardioGram

Question 3

Sino-Atrial node

Answer 3

• Stimulus to contract originates in it
• Acts as pacemaker and in wall of right atrium
• Generates electrical impulse/ wave of excitation
• Transmitted across atria
• Causes depolarisation of atria and atrial systole
• May be stimulated by hormones, exercise, temp…

Question 4

Connective tissue

Answer 4

Prevents impulse/ stimulus form passing to ventricles and causing them to contract downwards

Question 5

AtrioVentricular Node

Answer 5

• At the bottom of the wall separating the atria
• Receives wave of excitation/ impulse from SAN
• Allows 0.1 second delay before wave passed to ventricles
  - Prevents aria and ventricles contracting at the same time
  - Allows ventricles to fill with blood before contraction
  - Complete atrial systole
• Passes impulse onto the Bundle of His in the septum

Question 6

Bundle of His and Purkyne/ Purkinje fibres

Answer 6

• Carries impulse from AVN to the apex of the heart
• Purkinje fibres spread cardiac impulse through walls of ventricles (conveyed upwards) to the top
• Causes ventricular systole
• They contract from bottom/ apex upwards
• No more conductive tissue and impulse terminates
• Heart goes into diastole

Question 7

Septum role

Answer 7

• Prevents direct transfer of wave of excitation to ventricles
• Atria and ventricles don’t contract at the same time
• Allows time for ventricles to fill

Question 8

P Wave

Answer 8

• SAN generates electrical impulse
• Depolarisation of atria
• Atrial systole

Question 9

PR Interval

Answer 9

Time taken for excitation to spread form atria to ventricles through AVN

Question 10

QRS Complex

Answer 10

• AVN passes on electrical impulse
• Through Bundle of His in the septum
• Depolarisation of ventricles
• Ventricular systole

Question 11

T Wave

Answer 11

• Repolarisation of ventricles

- Ventricular diastole/ relaxation of ventricles

Question 12

Exercise effect (2)

Answer 12

• Shorter distance between consecutive P waves

- Shorter PR interval/ segment