Control of heart beatControl of heart beat

Please hand in your homework

What is wrong?

Starter question

1 square = 1mm

• Cardiac muscle is myogenic

• It does not need nerve impulses to contract

• These contractions must be controlled so that cells work in unison

SAN

• Sino atrial node

• Small patch of muscle in right atrium wall

• Pacemaker

• Their contractions spread a wave of electrical activity in the atrial walls

• Cardiac muscle responds, making the atria contract in time with the SAN

• Both atria contract together

• The excitation wave is briefly delayed by a bunch of fibres which do not conduct the electrical activity

• This delay is to ensure that the ventricles contract after the atria

AVN

• Atrio ventricular node

• Small patch of conducting fibres high up in septum

• Allows the electrical activity to spread slowly from the atria to the ventricles

• Passes on to the purkyne tissue

Purkyne tissue

• Fibres in septum

• Cause contractions in ventricle walls from bottom up

• Squeezing blood upwards

Diagram of heart showing SAN, AVN and purkyne tissue

Summary diagram

Blood vessels

• We will examine and draw some prepared slides

• Extension – if you would like to examine your own blood under the microscope you may do so, using a lancet

• HomeworkHomework to hand in next thurs– read about the 3 types of blood vessels – make a labelled diagram of each and describe the differences.