14.5 Control of Heart Rate

Question 1

What does autonomic mean

Answer 1

Self-governing

Question 2

What does the Autonomic nervous system control

Answer 2

The subconcious activities of the internal muscles and glands

Question 3

What are the two divisions of the autonomic nervous system

Answer 3

1. The sympathetic nervous system

2. The parasympathetic nervous system

Question 4

What does the sympathetic nervous system do

Answer 4

Stimulates effectors and so SPEEDS UP activity

Question 5

What does the parasympathetic nervous system do

Answer 5

Inhibits effectors and so SLOWS DOWN activity

Question 6

What do the actions of the SNS and PNS usually do

Answer 6

Oppose eachother, they are antagonistic pairs.

If one system contracts a muscle, the other relaxes it

Question 7

What is the muscle of the heart

Answer 7

Cardiac muscle

Question 8

What is cardiac muscle

Answer 8

Myogenic

Question 9

What does myogenic mean

Answer 9

That contraction is initiated from inside the muscle itself, rather than by nervous impulses outside (neurogenic)

Question 10

What is within the right atrium

Answer 10

A group of cells called the sinoatrial node (SAN)

Question 11

What originates from the SAN

Answer 11

It is where the initial stimulus for contraction originates

Question 12

What does the basic rhythm of the SAN determine

Answer 12

The beat of the heart

Question 13

Describe the sequence of events that control the beating of the heart

Answer 13

1. A wave of electrical excitation spreads out from the SAN across both atria, causing them to contract
2. A layer of non-conductive tissue (atrioventricular septum) prevents the wave crossing to the ventricles
3. The wave of electrical excitation enters a second group of cells called the atrio-ventricular node, which lies between the atria
4. After a delay, the AVN conveys a wave of electrical excitation between the ventricles along a series of collective specialised muscle fibres called purkyne tissue which collectively make up the bundle of His
5. The bundle of His conducts this wave through the atrioventricular septum to the base of the ventricles, where the bundle branches into smaller fibres of purkyne tissue
6. The wave of electrical excitation is released from the purkyne tissue, causing the ventricles to contract quickly from the bottom up.

Question 14

What is the resting heart rate

Answer 14

70 BPM

Question 15

Why is it essential that heart rate can be modified

Answer 15

To meet the demands for oxygen that occur during exercise

Question 16

What region of the brain controls heart rate

Answer 16

The Medulla Oblongata

Question 17

What are the two centres of the Medulla Oblongata

Answer 17

1. Centre that increases heart rate and is linked to the SAN by the SNS
2. Centre that decreases heart rate and is linked to the SAN by the PNS

Question 18

Describe control of heart rate by chemoreceptors

Answer 18

1. When blood has a higher than normal CO2 concentration, its pH is lowered
2. Chemoreceptors in the carotid arteries and aorta detect this increase and increase the frequency of nervous impulses to the region of the MO that increases heart rate
3. This centre increases the frequency of impulses via the SNS to the SAN. This, in turn, increases the rate of production of electrical waves and therefore increase heart rate
4. Increased blood flow that this causes results in more CO2 being removed and the chemoreceptors detect this return to normal and reduce the frequency of nerve impulses sent by the medulla oblongata
5. The medulla oblongata reduces the frequency at which impulses are sent to the SAN, leading to a reduction in heart rate.

Question 19

What happens to CO2 in the blood

Answer 19

It dissolves and forms carboxylic acid, lowering blood pH

Question 20

Where are pressure and chemoreceptors found

Answer 20

In the carotid arteries (in the brain) and the aorta

Question 21

What happens when blood pressure is higher than normal

Answer 21

Pressure receptors transmit more nervous impulses to the centre of the medulla oblongata that decreases heart rate. This centre sends impulses to the SAN via the PNS, causing a reduction in heart rate

Question 22

What happens when blood pressure is lower than normal

Answer 22

Pressure receptors transmit more impulses to the centre of the medulla oblongata that increases heart rate. This centre sends impulses to the SAN via the SNS, causing an increase in heart rate