I/E: Control of Heart Rate

Question 1

Cardia muscle is myogenic - what does this mean?

Answer 1

It can contract and relax without receiving signals from nerves.

Question 2

Sinoatrial nerve

• Where is it found?*
• What does it do?*

Answer 2

Found in the wall of the right atrium and sets the rhythm of the heartbeat.

Question 3

Describe the process which controls the regular beating of the heart:

Answer 3

1. SAN sends out regular waves of electrical activity to the atrial walls.
2. Causes the right and left atria to contract simultaneously.
3. Electrical activity is transferred from the SAN to the atrioventicular node.
4. AVN passes this wave to the bundle of His after a slight delay - this ensures atria is empty before ventricles contract.
5. Purkyne tissue carries electrical activity into the muscular walls of the right and left ventricles causing them to contract simultaneously, from the bottom up.

Question 4

What stops the wave of electrical activity in the heart from passing directly from the atria to the ventricles?

Answer 4

A band of non-conducting collagen tissue.

Question 5

Bundle of His

What does it split into?

Answer 5

A group of muscle fibres responsible for conducting the waves of electrical activity between the ventricles to the apex of the heart.

Splits into finer muscle fibres in the right and left ventricle walls- Purkyne tissues.

Question 6

Purkyne tissue

Answer 6

Finer muscle fibres branching off from the bundle of His, which carries the waves of electrical activity into the muscular walls of the right and left ventricles.

Question 7

What controls the rate at which the SAN fires?

Answer 7

Medulla oblongata (unconsciously)

Question 8

What part of the nervous system does control of heart rate involve?

Answer 8

The brain and the autonomic nervous system.

Question 9

What are internal stimuli detected by?

Answer 9

• Pressure receptors - baroreceptors
• Chemical receptors - chemoreceptors

Question 10

Where are baroreceptors found?

Answer 10

Aorta and carotid arteries (in the neck).

Question 11

What are baroreceptors stimulated by?

Answer 11

High and low blood pressure

Question 12

Where are chemoreceptors found?

Answer 12

Aorta, carotid arteries and medulla

Question 13

What do chemoreceptors monitor?

Answer 13

Oxygen, carbon dioxide and pH in the blood.

Question 14

What does the medulla do?

Answer 14

Processes the information.

Sends impulses to the SAN along sympathetic or parasympathetic neurones.

Question 15

How does the heart respond to high blood pressure?

Answer 15

• Baroreceptors detect high blood pressure.
• Impulses sent to medulla.
• Medulla sends impulses along parasympathetic neurones.
• Acetylcholine is secreted.
• Binds to receptors on the SAN.
• Cardiac muscles slow heart rate down to reduce blood pressure.

Question 16

How does the heart respond to low blood pressure?

Answer 16

• Baroreceptors detect low blood pressure.
• Impulses are sent to medulla.
• Impulses sent along sympathetic neurones.
• Noradrenaline is secreted.
• Binds to receptors on SAN.
• Cardiac muscles speed up heart rate to increase blood pressure.

Question 17

How does the heart respond to high blood O₂, low CO₂ or high pH levels?

Answer 17

• Chemoreceptors detect chemical changes.
• Impulses are sent to medulla.
• Sent along parasympathetic neurones.
• Acetylcholine is secreted.
• Binds to receptors on the SAN.
• Cardiac muscles decrease heart rate.

Question 18

How does the heart respond to low blood O2, high CO2 or low pH levels?

Answer 18

• Chemoreceptors detect chemical changes.
• Impulses are sent to the medulla.
• Impulses are sent along sympathetic neurones.
• Noradrenaline is secreted.
• Binds to receptors on SAN.
• Cardiac muscles increases heart rate.