Lesson 10.3 - Action of the heart Flashcards
Heart beat is initiated from within the heart itself.
Heart does not need an external signal to beat. Myogenic.
Where is the sino-atrial node?
In the wall of the right atrium
Other name for sino-atrial node?
Pacemaker
What happens to cells in the sino-atrial node?
They depolarise and become electrically excited.
What happens when the cells in the sino-atrial node depolarise?
They trigger a wave of electrical excitation to spread across the atria. This causes the atria to contract.
Why can’t the electrical excitement in the atria pass directly into the ventricles?
Ventricles are separated from the atria by a layer of non-conducting tissue.
- This layer of tissue will not pass the electrical excitement through it.
Where is the atrio-ventricular node?
Between the atria
What is the AVN connected to?
Conducting fibres called Purkyne fibres.
What is the structure where lots of Purkyne fibres are bonded together?
Bundle of His
Structure of the AVN?
Bundle of His.
Branches with Purkyne fibres running down to the apex / base of the heart and then up the walls of the ventricles.
How does the atrio-ventricular node work?
Detects electrical excitement passing over the atria. After a short delay, the AVN transmits the electrical excitation down the Purkyne fibres.
This causes the ventricles to contract.
How do ventricles contract?
Contract from the apex upwards. This ensures that the maximum volume of blood is pumped out of the ventricles.
Why is there a slight delay before AVN triggers electrical excitement down the Purkyne fibres?
Ensure that ventricles contract after the ventricles have contracted.
Myogenic
Has its own intrinsic rhythm at about 60 bpm.
Average resting heart rate of an adult?
70 bpm
