Control of Heart Rate

Question 1

What does autonomic mean?

Answer 1

Self-governing

Question 2

What does the autonominc nervous system controls?

Answer 2

The involutonaty (subscious) activities of internal muscles and glands

Question 3

What are the two divisions of autonomic nervous system?

Answer 3

1. Sympathetic nervous sytem
2. Parasympathetic nervous sytem

Question 4

What is the sympathetic nervous system?

Answer 4

• Stimulates effectors and speeds up anxiety
• It acts rather like an emergency controller
• It controlls effectors when we execise stimultaneous or experience powerful emotion
• In other words, it helps us to cope with stressful situations by heightening our awareness and preparing us for activity (fight or flight response)

Question 5

What is the parasympathetic nervous sytem?

Answer 5

• In general it inhibts effectors and slow down any activity
• It controls activities under normal resting conditions
• It is concerned with conversing energy and replenishing body’s reserves

Question 6

How is sympathetic and parasympathetic nervous systems antagonistic?

Answer 6

They oppose each other

one system contracts a muscle and other releaxes

The activities of internal glands and muscles therefore regulated by a balance of two systems

e.g control of heart rate

Question 7

What is caradiac muscle?

Answer 7

Muscle of heart

Question 8

Why is the caradiac muscleis myogenic?

Answer 8

The contraction is initiated from the muscle itself rather than by nervous impulses from outside (neurogenic) as it with case with other muscles

Question 9

Where is the SAN?

Answer 9

In the right atrium

Question 10

What is SAN 9sinoartial node)

Answer 10

It is from here that inital stimulus for contraction originates

It has a basic rhythm of stimulation that determine the beat of heart

This is why it is referred to a pace maker

Question 11

Sequence of events that control heart rate

Answer 11

1. A wave of electrical excitation spreads from sinortial node across both atria causing them to contract
2. A layer of non-conductive tissue (atrioventricular septum) prevents the wave crossing to ventricles
3. Wave of excitation leads to a second group of cells AVn
4. AVN conveys a wave of electrical excitiation between ventricles along purkyne tissue
5. Bundle of His conducts a wave through AV septum to base of ventricles where bundle branches into smaller fibres of purkyne tissue
6. A wave of excitation released from purkyne tissue causing the ventricles to contract quickly from bottom of heart and upwards

Question 12

What does AVN stand for?

Answer 12

Atrioventricular node lies between atria

Question 13

What is purkyne tissue?

Answer 13

Collectively makes up structure of bundle of His

Question 14

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

Answer 14

70 beats per minute

however essential this rate altered to meet varying demands of oxygen e.g exercise the resting heart rate more than double

Question 15

What is medulla oblongata?

Answer 15

Changes to hert rate is controleld by this part of region in the brain

Question 16

What are the two centres in the medulla oblongata that concerned with heart rate?

Answer 16

1. A centre that icnreases heart rate linked with sinoartial node by sympathetic nervous sytem
2. A centre that decreases heart rate linked with sinoartial node linked with parasympathetic system

Question 17

How do these centres in the medulla oblongata depend upon?

Answer 17

Nerve impulses which recieve two types of receptor which respond to stimuli or either chemical or pressure changes in the blood

Question 18

Where are chemoreceptors found?

Answer 18

In the wall of carotid arteries (arteries serve the brain)

Question 19

Whar are chemoreceptors sensitive to?

Answer 19

Changes to the blood as a result of changes in carbon dioxide concenrration insolution

carbon dioxide forms an acid therefore lowers pH levels

Question 20

Control by chemoreceptors:

Answer 20

1. Increased msucular/metabolic acitivtiy
2. More carbon dioxide produced in tissue from icnreased respiration
3. Blood pH is lowered
4. Chemical receptors in carotid artieres increase frequency of impulses to medulla oblongata
5. Centrein medulla oblongata speeds heart rate and increases frequency of impulses to SA node via sympathetic nervous system
6. SA node increases heart rate
7. Increased blood flowremovescarbon dioxide faster
8. Carbon dioxide concentration returns to normal

Question 21

What happens when blood pressure is higher than normal?

Answer 21

1. Pressure receptors transmit more nervous impulses to centre of medulla oblongata to decrease heart rate
2. This centre sends impulses via parasympathetic nervous sytem to sinoartial node of heart
3. Leads to decrease rate of heart beats

Question 22

What happens when blood pressure is lower than normal

Answer 22

• Pressure receptors transmit more nervous impulses to the centre of medulla oblongata that increase heart rate
• This centre sneds impulses via sympathetic nervous system to sinoartial node which increases heart beat