Module 3 Section 2 : Heart Activity Flashcards
What type of muscle controls regular beating of the heart
Cardiac muscle
Cardiac muscle is…..
Myogenic
Why is the heart said to be myogenic
It can contract and relax without receiving signals from nerves. This patterns of contractions controls the regular heartbeat
Where does the process of producing a heartbeat start
At the sino-atrial node (SAN)
Where is the SAN located
In the wall of the right atrium
What is the SAN also known as
The pacemaker
How does the SAN set the rhythm of the heartbeat
It sets the rhythm of the heartbeat by sending out regular waves of electrical excitation to the atrial walls
The wave of electrical excitation causes what
It causes the right and left atria to contract at the same time
What prevents the wave of electrical excitation from being passed directly from the atria to the ventricles
A band of non conducting collagen tissue prevents the wave of electrical excitation from being passed directly from the atria to the ventricles
Because of the non conducting layer how does the wave of electrical excitation start its journey towards the walls of the ventricles
The wave of electrical excitation travels from the SAN across the atria to the AVN
What does the AVN stand for
Atrioventricular Node
What is the AVN responsible for
Passing the waves of electrical excitation on to the bundle of his. But there is a slight delay
Why is there a slight delay before the AVN reacts
It delays to make sure the ventricles contract after the atria have emptied
What is the bundle of his
The bundle of his is a group of muscle fibres responsible for conducting the waves of electrical excitation to finer muscle fibres in the right and left ventricles walls
What are purkinje fibres
Finer muscle groups in the right and left ventricle walls
The purkinje fibres carries the….
Wave of electrical excitation into the muscular walls of the right and left ventricles causing them to contract simultaneously, from the bottom up
Describe the pathway of the wave of electrical excitation
- SAN emits wave of electrical excitation
- Wave of electrical excitation spread across atria
- Non conducting layer stops wave from passing from atria to ventricles
- Delay before AVN reacts so ventricles contract after atria empties
- Wave is picked up by the AVN
- The Wave travels down the bundle of his
- the wave branches out into purkinje fibres
- purkinje fibres carries the wave to the left and right ventricle walls causing them to contract simultaneously
How does a doctor check someone’s heart function
By using an electrocardiograph
What is an electrocardiograph
A machine that records electrical activity of the heart
What does an electrocardiograph record
It records when the heart muscle depolarises when it contracts and repolarises when it relaxes. It does this by placing electrodes placed on the patients chest
What is the P wave
- The P wave is the contraction (depolarisation) of the atria. AKA - Atrial systole.
- Identifiable by the first bump of the full heartbeat trace
What is the QRS complex
- The main peak of the heartbeat, together with dips at either side
- First dip = Q
- The peak = R
- Second dip = S
- Caused by contraction (depolarisation) of the ventricles. AKA - ventricular systole
What is the T wave
The T wave is due to relaxation (repolarisation) of the ventricles (Diastole)
What does the height of the wave indicate
How much electrical charge is passing through the heart. A bigger wave means more electrical charge so for the P and R waves a bigger wave means a stronger contraction
How do doctors use ECG’s to diagnose heart problems
Doctors compare their patients ECG’s with a normal trace. This helps them to diagnose any heart problems
What is tachycardia
- A heartbeat that is too fast. Around 120bpm.
- may be ok during exercise but at rest it shows the heart isn’t pumping blood efficiently
What is Bradycarida
- A heartbeat that is too slow - below 60bpm
- people may have because they are fit - training makes the heart beat slower and efficient
- severe bradycardia can be severe and may require an artificial pakemaker
What is an ectopic heartbeat
- An extra heartbeat
- Caused by an earlier contraction of the atria than in the previous heartbeats.
- signalled by the P wave looking different and that it comes earlier than it should)
- it can be caused by early contraction of the ventricles too
- Occasional ectopic heartbeats in a healthy person don’t cause a problem
What is fibrillation
- A really irregular heartbeat
- The atria or ventricles completely lose their rhythm and stop contracting properly
- Can result in anything from chest pains and fainting to lack of pulse and death
