5.1 - Control of heart rate

Question 1

What does autonomic mean?

Hence, what does the autonomic nervous system do?

Answer 1

self-governing.

It controls the involuntary activities of internal muscles and glands.

Question 2

How can the autonomic nervous system be divided?

Answer 2

The sympathetic nervous system.

The parasympathetic nervous system.

Question 3

What is the sympathetic nervous system?

Answer 3

It stimulates effectors and speeds up activity.

Helps us cope with stressful situations by heightening our awareness and preparing us for activity.

Question 4

What is the parasympathetic nervous system?

Answer 4

It inhibits effectors, slowing down activity.
Controls activities under normal resting conditions.
Concerned with conserving energy and replenishing the body’s resources.

Question 5

Why is it essential heart rate can be altered?

Answer 5

To meet the varying demands for oxygen.

Question 6

What is the controller for heart rate?

Answer 6

Medulla oblongata - a section of the brain.

Question 7

What word best describes the balance of the sympathetic and parasympathetic nervous systems?

Answer 7

Antagonistic - the activities of internal glands and muscles are regulated by a balance of these.

Question 8

What two centres does the medulla oblongata have? What are they linked to?

Answer 8

• A centre increasing heart rate, linked to the SAN by the sympathetic nervous system.
• A centre decreasing heart rate, linked to the SAN by the parasympathetic nervous system.

Question 9

What two changes result in one of the centres in the medulla oblongata ring stimulated?

Answer 9

Chemical and pressure changes in the blood.

Question 10

Where are chemoreceptors found?

Answer 10

The wall of the carotid arteries (serving the brain).

Question 11

What do chemoreceptors detect?

Answer 11

Changes in pH resulting from changing levels of CO2 in the blood.

Question 12

What is the first stage in control by chemoreceptors?

Answer 12

When the blood has a higher than normal concentration of CO2, pH is lowered.

Question 13

What is the second stage in control by chemoreceptors?

Answer 13

The chemoreceptors in the wall of carotid arteries and aorta detect this. They increase the frequency of nervous impulses to the medulla oblongata’s centre to increase heart rate.

Question 14

What is the third stage in control by chemoreceptors?

Answer 14

This centre increases the frequency of impulses via the sympathetic nervous system to the SAN, increasing the heart rate.

Question 15

What is the fourth stage in control by chemoreceptors?

Answer 15

The increased blood flow leads to more CO2 being removed by the lungs, so the CO2 level of the blood returns to normal.

Question 16

What is the fifth stage in control by chemoreceptors?

Answer 16

The pH of the blood rises to normal, so the chemoreceptors in the carotid arteries and aorta reduce the impulse frequency to normal.

Question 17

What is the last stage in control by chemoreceptors?

Answer 17

The medulla oblongata reduces the frequency of impulses to the SAN, decreasing the heart rate to normal.

Question 18

Where are pressure receptors?

Answer 18

Walls of the carotid arteries and aorta.

Question 19

When blood pressure is higher than normal, what do pressure receptors cause?

Answer 19

Transmit a nervous impulse to the centre in the medulla oblongata that decreases heart rate. This sends impulses via Parasympathetic Nervous System to the SAN, decreasing heart rate.

Question 20

When blood pressure is lower than normal, what do pressure receptors cause?

Answer 20

Transmit a nervous impulse to the centre in the medulla oblongata that increases heart rate. This sends impulses via Sympathetic Nervous System to the SAN, increasing heart rate.