14.5: Control of Heart rate Flashcards
Where does the sensory information that reaches out central nervous system originate from
From receptors within our bodies responding to internal stimuli
Importance of our internal systems needing to work efficiently
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
What is the Autonomic nervous system
The self-governing system which controls the involuntary activities of internal muscles and glands
What are the two types of the autonomic nervous system
- The sympathetic nervous system
2. The parasympathetic nervous system
What is the role of the Sympathetic nervous system
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
What is the role of the Parasympathetic nervous system
Inhibits effectors and slows down any activity
- Controls activities under normal resting conditions
- It is concerned with conserving energy and replenishing the bodies reserves
How are the sympathetic and parasympathetic nervous systems linked
They oppose eachother - they are known as antagonistic pairs
If one contracts a muscle, the other relaxes it
What is the name of the muscle that the heart is made of
Cardiac muscles
What is the heart known as
Myogenic
What does myogenic mean
That contraction is initiated from within the muscle itself
What is the opposite of myogenic
Neurogenic, this is where nervous impulses from outside the muscle initiate contraction
Where is the Sinoatrial Node (SAN)
The SAN is present in the wall of the right atrium
What is the Sinoatrial Node (SAN)
A bundle of cells, it is the initial stimulus for contraction
What is the significance of the SAN’s basic rhythm
The basic rhythm is the basic rhythm of stimulation that determines the beating of the heart
What is the SAN referred to
The pacemaker
What are the sequences of events regarding the control of heart rate (5)
- A wave of electrical excitiation spreads out from the SAN across both atria, causing them to contract
- The wave of excitation enters a second group of cells called the Atrioventricular Node (AVN), which lies between the atria
- 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
- 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
- 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.
What is the resting heart rate of an adult
70 BPM
Why is it essential heart rate can be altered
So it can meet the demand for oxygen
How are changes to heart rate controled
By a region of the brain known as the Medulla Oblongata.
What are the two centres of the Medulla Oblongata
- A centre that increases heart rate, which is linked to the SAN by the sympathetic nervous system
- A centre that decreases heart rate, which is linked to the SAN by the parasympathetic nervous system
Which two centres will be stimulated
The two centres that will be stimulated depends upon the nerve impulses they receive from chemo or pressure receptors
Where are chemoreceptors found
In the walls of Carotid Arteries (connecting to the brain) and aorta
What are chemoreceptors sensitive to
pH changes in the blood, these changes occur as a result of Carbon Dioxide concentration in the blood
Why does Carbon Dioxide concentration change the pH of blood
In solution, it dissolves into acid - lowering the pH
Process of Chemreceptor sensitivity
- When the blood has a higher than normal Co2 concentration, its pH lowers
- 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
- 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.
- The increased blood flow lowers the Co2 in the blood, normalising the pH of the blood.
- As a consequence, the pH heightens and chemo-receptors recognise this - reducing the frequency of nerve impulses to the medulla oblongata
- The medulla oblongata reduces the frequency of impulses to the SAN, in turn reducing heart rate
Where are pressure receptors found
In the carotid arteries (connected to the brain) and to the aorta
What are pressure receptors sensitive to
Blood pressure
What occurs when blood pressure is higher than normal
- Pressure receptors detect the increase in blood pressure, transmitting more nervous impusles to the centre in the Medulla Oblongata that decreases heart rate
- This centre sends impulses via the parasympathetic nervous system to the sinoatrial node of the heart, leading to a decrease in heart beat
What occurs when blood pressure is lower than normal
- Pressure-receptors in the Carotid arties and aorta detect the decreased blood pressure
- The pressure receptors transmit more nervous impulses to the centre in the medulla that increases heart rate
- This centre sends impulses via the sympathetic nervous system to the Sinoatrial Node, increasing heart rate and the rate at which it beats
