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

involuntary (subconscious) activities of internal muscles + glands

Question 3

What are the two divisions of the autonomic nervous system?

Answer 3

sympathetic nervous system

parasympathetic nervous system

Question 4

What does the sympathetic nervous system in general stimulate?

Answer 4

effectors and so speed up any activity

Question 5

What does the sympathetic nervous system act like?

Answer 5

emergency controller

Question 6

What does the sympathetic nervous system control?

Answer 6

when we exercise strenuously or experience powerful emotions

Question 7

What does the sympathetic nervous system help us cope with?

Answer 7

help us cope with stressful situations by heightening our awareness + preparing us for activity (fight or flight response)

Question 8

What does the parasympathetic nervous system in general do?

Answer 8

in general inhibits effectors + so slows down any activity

Question 9

What does the parasympathetic nervous system control?

Answer 9

controls activities under normal resting conditions

Question 10

What is the parasympathetic nervous system concerned with?

Answer 10

conserving energy + replenishing body’s reserves

Question 11

What are the actions of the sympathetic and parasympathetic nervous system like?

Answer 11

normally oppose one another

Question 12

As the actions of the sympathetic and parasympathetic nervous system normally oppose one another, what are they called?

Answer 12

antagonistic

Question 13

What is the muscles of the heart known as?

Answer 13

cardiac muscle

Question 14

Why are the cardiac muscle myogenic?

Answer 14

its contraction initiated from within muscle itself, rather than by nervous impulses from outside (neurogenic)

Question 15

Where is the sinoatrial node (SAN) located?

Answer 15

within wall of right atrium of heart

Question 16

What originates at the SAN?

Answer 16

initial stimulus for contraction originates

Question 17

What does the SAN have that determines the beat of the heart?

Answer 17

has a basic rhythm of stimulation

Question 18

As the SAN has a basic rhythm of stimulation that determines the beat of the heart, what is it called?

Answer 18

pacemaker

Question 19

Sequence of events that control basic heart rate: what spreads out from the SAN? #1

Answer 19

wave of electrical excitation spreads out from sinoatrial node across both atria, causing them to contract

Question 20

Sequence of events that control basic heart rate: what does a layer of non-conductive tissue (atrioventricular septum) do? #2

Answer 20

prevents wave crossing to ventricles

Question 21

Sequence of events that control basic heart rate: where does the wave of excitation enter after causing the atria to contract? #3

Answer 21

enters second group of cells called atrioventricular node (AVN), which lies between atria

Question 22

Sequence of events that control basic heart rate: what does the AVN do after a short delay? #4

Answer 22

conveys wave of electrical excitation between ventricles along series of specialised muscle fibres called Purkyne tissue which collectively make up structure called bundle of His

Question 23

Sequence of events that control basic heart rate: what does the bundle of His do the wave? #5

Answer 23

conducts wave through AV septum to base of ventricles, where bundle branches into smaller fibres of Purkyne tissue

Question 24

Sequence of events that control basic heart rate: where is the wave of excitation released from? #6

Answer 24

from Purkyne tissue, causing ventricles to contract quickly at same time, from bottom of heart upwards

Question 25

What is the resting heart rate of a typical adult human around?

Answer 25

70 beats per minute

Question 26

What region of the brain controls the changes to the heart rate?

Answer 26

medulla oblongata

Question 27

What two centres does the medulla oblongata have that's concerned with heart rate and how are they linked to the SAN?

Answer 27

centre that increases heart rate, which is linked to SAN by sympathetic nervous system centre that decreases heart rate, which is linked to SAN by parasympathetic nervous system

Question 28

Where are chemoreceptors found?

Answer 28

in wall of carotid arteries (arteries that serve brain)

Question 29

What are chemoreceptors sensitive to?

Answer 29

sensitive to changes in pH of blood that results from changes in CO2 conc.

Question 30

In solution what does CO2 form, and so what does this do?

Answer 30

CO2 forms acid and so lowers pH

Question 31

When the blood has a higher than normal conc. of CO2, how is this detected?

Answer 31

chemoreceptors in wall of carotid arteries + aorta detect this + increase frequency of nervous impulses to centre in medulla oblongata that increase heart rate

Question 32

What does the centre in the medulla oblongata do? (when blood acidic from higher than normal CO2 conc.)

Answer 32

centre increases frequency of impulses via sympathetic nervous system to SAN in turn increases rate of production of electrical waves by SAN + so increases heart rate

Question 33

What does an increased blood flow lead to? (when blood acidic from higher than normal CO2 conc.)

Answer 33

leads to more CO2 being removed by lungs and so CO2 conc. of blood returns to normal

Question 34

When the pH of the blood rises to normal, what happens? (when blood acidic from higher )

Answer 34

chemoreceptors in wall of carotid arteries + aorta reduce frequency of nerve impulses to medulla oblongata

Question 35

What does the medulla oblongata do when the blood pH has risen to normal? (when blood acidic from higher than normal CO2 conc.)

Answer 35

reduces frequency of impulses to SAN, which leads to reduction in heart rate

Question 36

Where do pressure receptors occur?

Answer 36

within walls of carotid arteries and aorta

Question 37

How do pressure receptors operate when blood pressure higher than normal?

Answer 37

pressure receptors transmit more nervous impulses to centre in medulla oblongata that decreases heart rate centre sens impulses via parasympathetic nervous system to SAN of heart which leads to decrease in rate at which heart beats

Question 38

How do pressure receptors operate when blood pressure lower than normal?

Answer 38

pressure receptors transmit more nervous impulses to centre in medulla oblongata that increase heart rate centre sends impulses via sympathetic nervous system to SAN, which increases rate at which heart beats