CONTROL OF HEART RATE IN MAMMALS Flashcards
(19 cards)
What is the heart rate controlled by? (1)
Controlled by the automatic nervous system
What is the heart rate known as? (1)
The heart rate is myogenic in origin.
What is meant by myogenic? (1)
Activity that originates within muscles rather than through the nervous system
Where does the heart beat originate? (1)
In a structure in the muscle of the wall of the ight atrium called the sine-atrial node, also known as the natural pacemaker.
What triggers contraction? (1)
Muscle radiating out from the SAN conduct impulses to the muscles of both atria, triggering atrial systole (contraction)
What triggers ventricular systole? (1)
The atrio-ventricular node situated at the base of the right atrium picks up the excitation and passes it to the ventricles through modified muscles fibres called the Purkyne fibres.
What is the refractory period? (1)
After every contraction, cardiac muscle has a period of insensitivity to stimulation (in effect, a period of enforced non-contraction, which we may call a rest) when the heart refills with blood
How is the activity of the pacemaker regulated? (1)
Forebrain may send sensory impulses
What is the main centre of the heart rate? (1)
Is situated in the cardiovascular centre in the medulla of the hindbrain. This has both a cardiac inhibitory region and a cardiac accelerator region.
What nerves does the heart receive impulses from? (2)
-a sympathetic nerve, part of the sympathetic nervous system, from the accelerator centre
-a branch of the vagus nerve, part of the parasympathetic nervous system, from the inhibitory centre
What are the sympathetic and vagus nerve? (1)
They have opposite effects in this matter of regulation of heart beat, we say they are antagonistic.
What does the cardiovascular centre need in order to work effectively? (1)
In order to respond correctly it needs information from sense organs, e.g it receives impulses from stretch receptors located in the walls of the aorta, in the carotid arteries and in the wall of the right atrium, when changes in the blood pressure occur at these positions.
What happens when changes occur to the blood pressure? (2)
When blood pressure is high in the arteries, the rate of heart beat is lowered by impulses from the cardiovascular centre, via the vagus nerve.
When blood pressure is low, the rate of the heart beat is increased.
Explain how the oxygenation of blood affects the control of the heart beat. (1)
Chemoreceptors in the main arteries also provide information to the cardiac centre through sensory nerves, they are sensitive to pH levels. Rising carbon dioxide levels in the blood lower the pH during exercise and trigger impulses, which stimulate the cardiac accelerator centre and increase impulses in the sympathetic nerve.
What are chemoreceptors? (1)
Sensory receptors that initiate action potentials in response to changes in their chemical environment
How does adrenaline and noadrenaline affect the heart rate? (1)
They have a powerful effect on raising heart rate
How does the parasympathetic vagus nerve affect the heart beat?
The parasympathetic vagus nerve releases the neurotransmitter acetylcholine in bringing about its inhibitory effect.
