14.5- Control of heart rate

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  • Created by: Megan2413
  • Created on: 12-11-17 12:11
What is the autonomic nervous system?
It controls the involuntary (subconscious) activities of internal muscles and glands
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What are the two divisions of the autonomic nervous system called?
Parasympathetic and sympathetic nervous systems
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What does the sympathetic nervous system control?
It stimulates effectors and so speeds up any activity. It controls effectors when we exercise strenuously or experience powerful emotions
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What does the parasympathetic nervous system control?
It inhibits effectors and so slows down any activity. It controls normal resting conditions and is concerned with conserving energy and replenishing the body's reserves
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The actions of the sympathetic and parasympathetic nervous system are antagonistic- what does this mean?
They oppose each other
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The cardiac (heart) muscle is myogenic- what does this mean?
Its contraction is initiated from within the muscle itselfrather than by nervous impulses from outside (neurogenic)
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Where is the sinoatrial node (SAN) found?
In the wall of the right atrium of the heart
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Why is the SAN normally referred to as the pacemaker?
It controls the heart rate hence the rhythm of the heart contractions
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Where is the atrioventricular node located?
Between the atria
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What is the bundle of His?
It is made up of Purkyne tissue and is a series of specialised muscle fibres
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Where is the bundle of His loacted?
Throughout the atrioventricular septum
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What is the sequence of events that controls the basic heart rate?
- A wave of electrical excitation spreads out from the SAN across both atria causing them to contract- A layer of non-conductive tissue (atrioventricular septum) prevents the wave crossing to the ventricles - The wave of excitation enters the AVN -->
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which lies between the atria - The AVN after a short delay convey a wave of electrical excitation between the ventricles along the bundle of His - The bundle of His conducts the wave through the atrioventricular septum to the base of the -->
ventricles where the bundle branches into smaller fibres of Purkyne tissue - The wave of excitation is released from the Purkyne tissue, causing the ventricles to contract quickly at the same time from the bottom of the heart upwards
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When a wave of excitation reaches the AVN, there is a short delay before a new wave leaves the AVN- why?
The short delay allows all the blood from the atria to be forced into the ventricles as the atria contract before the ventricles will contract and push blood out again
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What is the formula for stroke volume?
Stroke volume = Cardiac output/resting heart rate
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Changes to the heart rate are controlled by a region of the brain called?
The medulla oblongata
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What are the two centres found within the medulla oblongata?
- A centre that increases heart rate - A centre that decreases heart rate
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What are these two centres each connected to?
The centre that increases heart rate is connected to the SAN by the sympathetic nervous system and the centre that decreases heart rate is connected to the SAN by the parasympathetic nervous system
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What does the stimulation of either centre depend on?
The nerve impulses they receive from two types of receptor, which respond to stimuli of either chemical or pressure changes in the blood
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Where are chemoreceptors found?
In the wall of the carotid arteries (the arteries that serve the brain) and aorta
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What are chemoreceptors sensitive to?
Changes in pH of the blood that result from changes in the carbon dioxide concentration as in solution it is acidic hence lowers the pH
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How do chemoreceptors work when doing strenuous exercise?
- Increased muscular activity, higher CO2 concentration in the blood, lowering the pH - Chemoreceptors in the wall of the carotid arteries and aorta detect this change and increase the frequency of nervous impulses to the centre in the medulla -->
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oblongata that increases heart rate - This centre increases the frequency of impulses via the sympathetic nervous system to the SAN hence increasing heart rate - the increasesd blood flow causes more CO2 to be removed by the lungs hence a decrease ->
in concentration - This increases the pH of the blood which causes the chemoreceptors to decrease the frequency of nervous impulses to the medulla oblongata which will reduce the frequency of impulses to the SAN leading to a reduction in heart rate
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How do pressure receptors respond to pressure changes?
When the pressure increases the chemoreceptors transmit more nervous impulses to the centre that decreases heart rate in the medulla oblongata. When the blood pressure is lower than usual the chemoreceptors will transmit more nervous impulses to -->
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the centre that increases heart rate in the medulla oblongata
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Card 2

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What are the two divisions of the autonomic nervous system called?

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Parasympathetic and sympathetic nervous systems

Card 3

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What does the sympathetic nervous system control?

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Card 4

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What does the parasympathetic nervous system control?

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Card 5

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The actions of the sympathetic and parasympathetic nervous system are antagonistic- what does this mean?

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