14.5 Control of heart rate Flashcards
What is the autonomic nervous system
It controls subconscious activities of internal muscles and glands
What are the two divisions of autonomic nervous system
Sympathetic nervous system and parasympathetic nervous system
What does the sympathetic nervous system do
It stimulates effectors so speeds up any activity
It controls effectors when we exercise strenuously or experience powerful emotions
It can help us prepare for dangerous situations by heightening our awareness and preparing us for activity
(fight or flight response)
What does the parasympathetic nervous system do
It inhibits effectors and slows down any activity.
It controls activities under normal resting conditions
It is concerned with conserving energy and replenishing our bodys reserves
How are the sympathetic and parasympathetic nervous systems antagonistic
The actions oppose one another
If one system contracts a muscle the other relaxes it
So internal glands are regulated by the balance of two systems
The heart is myogenic, what does this mean
Contraction is initiated from within the muscle itself rather than by nervous impulses outside (neurogenic)
The SAN (sinoatrial node) is found in the wall of the right atrium of the heart
What are these, and what are they also known as
A group of cells that make the initial stimulus for muscle contraction
It has a basic rhythm of stimulation that determines the beat of the heart
Often referred to as pacemakes
Describe the sequence of events that control the basic heart rate
- Sinoatrial node releases wave of electrical excitation that spreads out across both atria and makes them
contract - A layer of non conductive tissue (atrioventricular septum) prevents the wave spreading to ventricles
- The wave of excitation enters the second group of cells called atrioventricular node which lies between the atria
- After a short delay this node releases a wave of electrical excitation between the ventricles along a series of specialised muscle fibres called Purkyne tissue which collectively make up a structure called Bundle Of His
- The bundle of His conducts the wave through the atrioventricular septum to the base of ventricles. The bundle branches into smaller fibres of Purkyne tissue
- The wave of excitation is released from Purkyne tissue causing ventricles to contract quickly at the same time, from the bottom of the heart upwards.
When doing exercise, heart rate has to be modified eg increase to pump enough oxygen to respiring cells around the body
What region of the brain controls this
Medulla oblongata
The medulla oblongata has two centres concerned with heart rate
- A centre that increases heart rate which is linked to sinoatrial node by the sympathetic nervous system
- A centre that decreases heart rate which is linked to sinoatrial node via parasympathetic nervous system
What are chemoreceptors
. Found in the walls of carotid arteries (the arteries that serve the brain)
. They are sensitive to changes in PH of the blood that result to changes in CO2 concentration
Describe process of chemoreceptors
- When exercising, cells aerobically respire to release CO2 which lowers PH of blood
- Chemoreceptors in the walls of carotid and aorta arteries detect this and produce more nervous impulses to the medulla oblongata, which increases heart rate
- This centre increases frequency of impulses via sympathetic nervous system to sinoatrial node. So more electrical waves are produced by it and heart rate increases
- This increase in heart rate means more CO2 is carried away from the blood to the lungs, so the concentration returns to normal
- As a consequence, PH of the blood rises and returns to normal and the chemoreceptors in the walls of carotid arteries and aorta reduce the frequency of nervous impulses to medulla oblongata
- So medulla oblongata reduces frequency of nervous impulses to the sinoatrial node, so reduction in heart rate
How do pressure receptors work when blood pressure is too high
Where are they found
Found in carotid arteries and aorta
- Pressure receptors detect that blood pressure is too high so increase frequency of nerve impulses to the centre in medulla oblongata that decreases heart rate.
- This centre sends impulses via parasympathetic nervous system to the sinoatrial node of the heart
- So decreases heart beat
What do pressure receptors do when blood pressure is too low
- Pressure receptors detect that blood pressure is too low so increase frequency of nerve impulses going to section of medulla oblongata involved in increasing heart rate
- This centre sends impulses via sympathetic nervous system to sinoatrial node of the heart
- So increases heart rate
