14.5: Control of Heart rate

Question 1

Where does the sensory information that reaches out central nervous system originate from

Answer 1

From receptors within our bodies responding to internal stimuli

Question 2

Importance of our internal systems needing to work efficiently

Answer 2

Our internal systems need to work efficiently so they are ready to adapt to the changing demand made upon them at different points.

This requires the coordination of a vast amount of information

Question 3

What is the Autonomic nervous system

Answer 3

The self-governing system which controls the involuntary activities of internal muscles and glands

Question 4

What are the two types of the autonomic nervous system

Answer 4

1. The sympathetic nervous system

2. The parasympathetic nervous system

Question 5

What is the role of the Sympathetic nervous system

Answer 5

Stimulates effectors and speeds up any activity

• Acts like an emergency controller
• Controls effectors when we exercise strenuously or experience powerful emotion

Heightens our awareness

Question 6

What is the role of the Parasympathetic nervous system

Answer 6

Inhibits effectors and slows down any activity

• Controls activities under normal resting conditions
• It is concerned with conserving energy and replenishing the bodies reserves

Question 7

How are the sympathetic and parasympathetic nervous systems linked

Answer 7

They oppose eachother - they are known as antagonistic pairs

If one contracts a muscle, the other relaxes it

Question 8

What is the name of the muscle that the heart is made of

Answer 8

Cardiac muscles

Question 9

What is the heart known as

Answer 9

Myogenic

Question 10

What does myogenic mean

Answer 10

That contraction is initiated from within the muscle itself

Question 11

What is the opposite of myogenic

Answer 11

Neurogenic, this is where nervous impulses from outside the muscle initiate contraction

Question 12

Where is the Sinoatrial Node (SAN)

Answer 12

The SAN is present in the wall of the right atrium

Question 13

What is the Sinoatrial Node (SAN)

Answer 13

A bundle of cells, it is the initial stimulus for contraction

Question 14

What is the significance of the SAN’s basic rhythm

Answer 14

The basic rhythm is the basic rhythm of stimulation that determines the beating of the heart

Question 15

What is the SAN referred to

Answer 15

The pacemaker

Question 16

What are the sequences of events regarding the control of heart rate (5)

Answer 16

1. A wave of electrical excitiation spreads out from the SAN across both atria, causing them to contract
2. The wave of excitation enters a second group of cells called the Atrioventricular Node (AVN), which lies between the atria
3. After a delay, the AVN conveys a wave of electrical excitation between the ventricles, along a series of Purkinje fibres, collectively making up the Bundle of His
4. The Bundle of His conducts the wave through the Atrioventricular septum to the base of the ventricles, where the bundle branches off into smaller Purkinje fibres
5. The wave of excitation is released from the Purkinje fibres, causing the ventricles to contract quickly at the same time, from the bottom of the heart upwards.

Question 17

What is the resting heart rate of an adult

Answer 17

70 BPM

Question 18

Why is it essential heart rate can be altered

Answer 18

So it can meet the demand for oxygen

Question 19

How are changes to heart rate controled

Answer 19

By a region of the brain known as the Medulla Oblongata.

Question 20

What are the two centres of the Medulla Oblongata

Answer 20

1. A centre that increases heart rate, which is linked to the SAN by the sympathetic nervous system
2. A centre that decreases heart rate, which is linked to the SAN by the parasympathetic nervous system

Question 21

Which two centres will be stimulated

Answer 21

The two centres that will be stimulated depends upon the nerve impulses they receive from chemo or pressure receptors

Question 22

Where are chemoreceptors found

Answer 22

In the walls of Carotid Arteries (connecting to the brain) and aorta

Question 23

What are chemoreceptors sensitive to

Answer 23

pH changes in the blood, these changes occur as a result of Carbon Dioxide concentration in the blood

Question 24

Why does Carbon Dioxide concentration change the pH of blood

Answer 24

In solution, it dissolves into acid - lowering the pH

Question 25

Process of Chemreceptor sensitivity

Answer 25

1. When the blood has a higher than normal Co2 concentration, its pH lowers
2. Chemoreceptors in the carotid arteries and the aorta detect this, and increase the frequency of nervous impulses to the centre in the Medulla Oblongata that increases heart rate
3. This centre increases the frequency of impulses via the sympathetic nervous system to the Sinoatrial Node. In turn, this increases the rate of electrical wave production by the SAN - increasing heart rate.
4. The increased blood flow lowers the Co2 in the blood, normalising the pH of the blood.
5. As a consequence, the pH heightens and chemo-receptors recognise this - reducing the frequency of nerve impulses to the medulla oblongata
6. The medulla oblongata reduces the frequency of impulses to the SAN, in turn reducing heart rate

Question 26

Where are pressure receptors found

Answer 26

In the carotid arteries (connected to the brain) and to the aorta

Question 27

What are pressure receptors sensitive to

Answer 27

Blood pressure

Question 28

What occurs when blood pressure is higher than normal

Answer 28

1. Pressure receptors detect the increase in blood pressure, transmitting more nervous impusles to the centre in the Medulla Oblongata that decreases heart rate
2. This centre sends impulses via the parasympathetic nervous system to the sinoatrial node of the heart, leading to a decrease in heart beat

Question 29

What occurs when blood pressure is lower than normal

Answer 29

1. Pressure-receptors in the Carotid arties and aorta detect the decreased blood pressure
2. The pressure receptors transmit more nervous impulses to the centre in the medulla that increases heart rate
3. This centre sends impulses via the sympathetic nervous system to the Sinoatrial Node, increasing heart rate and the rate at which it beats