heart rate Flashcards
The heart muscle is myogenic. What is meant by myogenic?
It can generate an electrical impulse to initiate contraction and then responds by contracting. Thus, the electrical impulse that causes contraction originates in the heart muscle itself rather than in neurones.
. Describe the role of receptors in the control of heart rate.
- Pressure receptors called baroreceptors in the aorta and carotid artery monitor blood pressure.
- chemical receptors called chemoreceptors in the aorta and the carotid artery detect changes in pH due to changes in dissolved carbon dioxide.
Electrical impulses from these receptors are sent along sensory neurones to the medulla oblongata in the brain, the medulla oblongata sends impulses along autonomic motor neurones to the SAN to alter heart rate.
Describe the role of the chemoreceptors in increasing the heart rate in response to exercise.
Chemoreceptors in the aorta and carotid artery detect the increase in CO2 levels (or decrease in pH); Impulses are sent to the medulla oblongata in the brain; the medulla oblongata sends more impulses to the SAN; through the sympathetic nervous system;
Explain how a rise in blood pressure results in a decrease in the rate of heartbeat.
pressure receptors in aorta and carotid arteries;
send impulses to medulla oblongata; increased impulses via parasympathetic nerves; to SAN; decreases impulses from SAN; decreases impulses to AVN .
How can damage to the nervous system change the hearts response to high or low blood pressure?
Damage to autonomic nervous system would mean heart rate cannot be controlled; pressure receptors in aorta or carotid arteries don’t work as well; or there could be damage to medulla oblongata in the brain; if damage occurs to the sympathetic system, heart rate will not increase enough, if damage to parasympathetic system, heart rate doesn’t slow down enough.
Why can the pulse felt be used to measure heart rate?
Caused by pressure and surge of blood; From one contraction of the left ventricle.
When a wave of electrical activity reaches the AVN, there is a short delay before a new wave leaves the AVN. Explain the importance of this short delay
Allow atria to empty and the ventricles to fill;
Before ventricles contract;
The sinoatrial node (SAN) is in the right atrium of the heart. Describe the role of the sinoatrial node.
Sends out electrical activity impulses;
Initiates the heartbeat and acts as a pacemaker to stimulate contraction of atria;
What is the relationship between heart rate (R), stroke volume (V) and cardiac output (CO)?
What is the relationship between heart rate (R), stroke volume (V) and cardiac output (CO)?
How do the parasympathetic and sympathetic nervous systems affect the heart rate?
Parasympathetic slows down the heart rate and sympathetic increases the heart rate
What neurotransmitters are used to alter heart rate?
Parasympathetic motor neurones release acetylcholine onto the cells of the SAN which decreases heart rate.
Sympathetic motor neurones release noradrenaline onto the cells of the SAN which increases heart rate.
Describe how a heartbeat is initiated and coordinated.
- SAN generates and releases a wave of electrical activity which spreads across the atria causing both atria to contract at the same time.
- Non-conductive tissue separating the atria and ventricles prevents transmission of signal to ventricles.
- Short delay allows the ventricles to fill.
- AVN relays electrical activity after this short delay.
- Impulse travels down the bundle of His in the septum.
- Spreads along the Purkyne fibres.
- Contraction of the ventricles from the bottom up at the same time.
When the heart beats both ventricles contract at the same time. Explain how this is coordinated in the heart after initiation of the heart by the SAN.
The AV node generates an electrical impulse which is conducted down the Bundle of His only to the base of the ventricles. It spreads along the Purkinje fibres up and then across each ventricle resulting in contraction from the base up.
