14.5 Control of Heart Rate Flashcards
What does autonomic mean
Self-governing
What does the Autonomic nervous system control
The subconcious activities of the internal muscles and glands
What are the two divisions of the autonomic nervous system
- The sympathetic nervous system
2. The parasympathetic nervous system
What does the sympathetic nervous system do
Stimulates effectors and so SPEEDS UP activity
What does the parasympathetic nervous system do
Inhibits effectors and so SLOWS DOWN activity
What do the actions of the SNS and PNS usually do
Oppose eachother, they are antagonistic pairs.
If one system contracts a muscle, the other relaxes it
What is the muscle of the heart
Cardiac muscle
What is cardiac muscle
Myogenic
What does myogenic mean
That contraction is initiated from inside the muscle itself, rather than by nervous impulses outside (neurogenic)
What is within the right atrium
A group of cells called the sinoatrial node (SAN)
What originates from the SAN
It is where the initial stimulus for contraction originates
What does the basic rhythm of the SAN determine
The beat of the heart
Describe the sequence of events that control the beating of the heart
- 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 electrical excitation enters a second group of cells called the atrio-ventricular node, which lies between the atria
- After a delay, the AVN conveys a wave of electrical excitation between the ventricles along a series of collective specialised muscle fibres called purkyne tissue which collectively make up the bundle of His
- The bundle of His conducts this wave through the atrioventricular septum to the base of the ventricles, where the bundle branches into smaller fibres of purkyne tissue
- The wave of electrical excitation is released from the purkyne tissue, causing the ventricles to contract quickly from the bottom up.
What is the resting heart rate
70 BPM
Why is it essential that heart rate can be modified
To meet the demands for oxygen that occur during exercise
What region of the brain controls heart rate
The Medulla Oblongata
What are the two centres of the Medulla Oblongata
- Centre that increases heart rate and is linked to the SAN by the SNS
- Centre that decreases heart rate and is linked to the SAN by the PNS
Describe control of heart rate by chemoreceptors
- When blood has a higher than normal CO2 concentration, its pH is lowered
- Chemoreceptors in the carotid arteries and aorta detect this increase and increase the frequency of nervous impulses to the region of the MO that increases heart rate
- This centre increases the frequency of impulses via the SNS to the SAN. This, in turn, increases the rate of production of electrical waves and therefore increase heart rate
- Increased blood flow that this causes results in more CO2 being removed and the chemoreceptors detect this return to normal and reduce the frequency of nerve impulses sent by the medulla oblongata
- The medulla oblongata reduces the frequency at which impulses are sent to the SAN, leading to a reduction in heart rate.
What happens to CO2 in the blood
It dissolves and forms carboxylic acid, lowering blood pH
Where are pressure and chemoreceptors found
In the carotid arteries (in the brain) and the aorta
What happens when blood pressure is higher than normal
Pressure receptors transmit more nervous impulses to the centre of the medulla oblongata that decreases heart rate. This centre sends impulses to the SAN via the PNS, causing a reduction in heart rate
What happens when blood pressure is lower than normal
Pressure receptors transmit more impulses to the centre of the medulla oblongata that increases heart rate. This centre sends impulses to the SAN via the SNS, causing an increase in heart rate
