heart activity

Question 1

Explain how the hearts cardiac muscle having cross bridges between fibres, and intercalated discs help to ensure efficient transmission of the contraction throughout the heart.

Answer 1

-they help to conduct the wave of excitation all over the muscle, helping to create a squeezing action, rather then a contraction in one direction

Question 2

Give 2 reasons why cardiac muscle is special.

Answer 2

• it never tires= will continuously contract and relax without ever becoming exhausted
• It is myogenic (originates from muscle) so doesn’t require any stimulation from a nerve to make it contract

Question 3

Explain the process of cardiac muscle contractions which make the regular heartbeat.

Answer 3

1. Starts in the sino-atrial node (SAN), found in the wall of the right atrium. These cells generate electrical impulses that pass rapidly across the walls of the atria, making the right and left atria contract at the same time (atrial systole)
2. A band of non-conducting collagen tissue prevents the waves of electrical activity from being passed directly from the atria to the ventricles
3. Instead, these waves of electrical activity are transferred from the SAN to the atrioventricular node AVN. This acts as a relay point, so electrical activity can be passed to the bundle of His. There is a delay here, to make sure the ventricles contract after the atria has emptied.
4. The bundle of His is a group of muscle fibres, that spread down the septum between the 2 ventricles. It’s responsible for conducting the electrical impulses to the finer muscle fibres in the right and left ventricle walls, called the Purkyne tissue.
5. The impulse causes the muscular ventricle walls to contract from the apex upwards, (ventricular systole)

Question 4

What does an ECG stand for?

Answer 4

electrocardiogram

Question 5

What do ECGs measure and why is this good?

Answer 5

• Electrical activity going on in the heart as it beats.
• It is a quick and very important way of collecting information to diagnose problems affecting the heart

Question 6

How is an ECG recorded?

Answer 6

• person lies on a bed and relaxes
• electrodes are attached to the chest, wrists and ankles using sticky pads
• a special gel is used with the pads which is a good electrical contact to pick up the electrical activity
• when heart muscle contracts, area outside cells becomes negatively charged, and it regains charge when it relaxes-this changes in electrical activity is detected on the surface of the body through the electrodes.

Question 7

What does the P wave in an ECG represent. Explain why

Answer 7

• What does the P wave in an ECG represent. Explain why
• as the muscle in the SAN contracts, it produces an electrical impulse which sweeps through all of the muscle in the atria of the heart, making the atria muscle contract

Question 8

What does the delay in between the P wave and point Q on a ECG represent? Explain why

Answer 8

• the impulse reaching the atrioventricular node (AVN)
• the AVN is the only way that the electrical impulse can get from the atria to the ventricles, but there is a short delay of the impulse before it travels down into the ventricles

Question 9

What does the Q, R, and S part of an ECG represent. Explain why.

Answer 9

• Q to R- shows the electrical impulse moving down to the septum of the heart through the bundle of His
• R to S- shows the electrical impulse sweeping upwards from the apex of the heart through the Purkyne tissue, through the ventricle walls.

Question 10

What does the T wave on an ECG represent. Explain why

Answer 10

• the ventricles relaxing
• the muscle in the SAN then contracts again and the whole sequence repeats

Question 11

Describe what a ventricular fibrillation ECG trace is. Refer to appearance of trace, cause, effect, and treatment.

Answer 11

-where the ECG shows no pattern

Cause: muscle in ventricle wall just flutters. This could be because of a heart attack or electric shock

Effect: victim has no blood circulation, and is usually unconscious. Without immediate treatment they will die

Treatment: use of a defibrillator. If they survive, surgery may be required to address root cause

Question 12

What is an atrial fibrillation ECG trace?

Answer 12

-very small and unclear P wave on ECG

Question 13

Describe what a bradychardia ECG trace is. Refer to appearance of trace, cause, effect, and treatment.

Answer 13

-heart rate is slower then normal (usually with a heart rate of less than 60 bpm). ECG appears normal but with intervals of more then 1 second between waves

Cause: can be a sign of a healthy heart in a fit person. Can also suggest SAN is not functioning properly

Effect: Only if it’s severe, person may feel tired as insufficient blood is reaching the organs

Treatment: If there is a problem with the SAN, an artificial pacemaker may be fitted

Question 14

Describe what a tachycardia ECG trace is.

Answer 14

-heart rate is faster then normal. (Around 120 bpm). ECG appears normal but the intervals between the waves are much shorter then normal, showing the heart isn’t pumping blood efficiently.

Question 15

Describe what a heart block ECG trace is. Refer to appearance of trace, cause, effect, and treatment.

Answer 15

• complete heart block is when atria contracts at a faster rhythm to the ventricles, reducing blood flow around the body
  Cause: electrical impulses are not passing normally through the heart. If taking too long could be as a result of damaged Purkyne fibres

Effects: No symptoms if not serious heart block

Treatment: If not serious, no treatment is needed, but other types of heart block may require an artificial pacemaker

Question 16

What is meant by an ectopic heartbeat?

Answer 16

• An extra heartbeat
• can be from an earlier contraction of the atria, or ventricles, then in previous heartbeats

Question 17

why would blood not be pumped efficiently without the purkyne tissue? (2 marks)

Answer 17

• they pass electrical signals up sides of ventricle, causing them to contract upwards
• wave of excitation