Control of Heart rate Flashcards
the heart muscle is myogenic. What does this mean?
The heart can contract and relax without recieving signals from the nerves.
Describe how the cardiac muscle controls the regular beating of the heart (i.e. regular contractions)
- The process starts in the sinotrial node (SAN) in the wall of the right atrium.
- The SAN is like a pacemaker and send out regular waves of electrical activity to the atrial walls (it sets the rythm).
- This causes the right and left atria to contract at the same time.
- A band of non-onducting collagen tissue prevents the waves of electrical activity from being passed directly from the atra o the ventricles.
- Instead, they travel fom the SAN to the atrioventricular node (AVN).
- the AVN passes the waves of electrical activity to the bundle of His, but, there’s a delay before the AVN reacts to make sure the atria hav emptied before the ventricles contract.
- the bundle of His splits into finer muscle fibres called purkyne tissues.
the purkyne tissue carries waves of electriacl activity to the walls of the ventricles,causing them to contract simultaneously, from the bottom up.
What are the two things involved in controlling the rate of the heart beat?
The brain and the autonomic nervous system.
Outline how the heart rate is controlled.
The sinoatrial node (SAN) generates electrical impulses that cause th cardiac muscle to contact.
The rate the SAN fires (i.e. heart rate) is unconciously controlled by the medulla oblongata.
electrical impulses from receptors are sent to the medulla along sensory neurones. The medulla processes the information and sends impulses to the SAN along the sympathetic or parasympathetic neurones (which are part of the autonomic nervous system).
Why might animals need to alter their heart rate.
to respond to internal stimuli.
e.g. to prevent fainting duue to low blood pressure
OR
to make sure the eart rate is high enough to supply the body with enough oxygen.
How are internal stimuli detected?
by pressure and chemical receptors
- pressure (baroreceptors)
- in aorta + carotid arteries
- stimultaed by high and low blood pressure
- chemical receptors (chemoreceptors)
- in aorta, carotid arteries and medulla
- stimulated by the levels of oxygen
OR
by CO2 and pH levels (which are indicators of O2 level)
How does the heart respond respond to the stimulus:
High blood pressure
Stimulus: high blood pressure
Receptor: Baroreceptors detect high blood pressure
Neurone and neurotransmitter:
impulses are sent to the medulla, which sends impulses along the parasympathetic neurones. These secrete acetylchloline (a neurotransmitter), which binds to receptors on the SAN.
Effector: cardiac muscles
Response: HR slows doen to reduce the blood pressre back to normal.
What are the neurone, neurotransmitter and effector involved in increasing the heart rate (in response to low blood pressure)
Neurone and neurotransmitter:
Impulses are sent to the medulla, which sendsimpulses along sympathetic neurones.
These secrete noradrenaline, which binds to receptors in the SAN.
Effector: cardiac muscles
What neurone, neurotransmitter and effector are involved in responding to high blood O2 (or low blood CO2/pH).
What is the response?
Neurone and neurotransmitter:
Impulses are sent to the medulla, which sends impulses long the parasympathetic neurones.
These secrete acetylcholine, which binds to receptors on the SAN.
Effectors: cardiac muscles
Response: HR dec. to return O2, CO2 and pH levels back to normal.
Q2 Exercise causes an increase in the levels of carbon dioxide in the blood.
a) Explain how increased blood CO, leads to an increased heart rate.
b) State two other chemical stimuli that cause the heart rate to increase during exercise.a)
a) E.g. chemoreceptors in the aorta/carotid artery/medulla detect the high CO2 concentration.
Impulses are sent from the receptors to the medulla, which sends impulses along sympathetic neurones to the sinoatrial node (SAN).
These neurones secrete noradrenaline, which binds to receptors on the SAN.
This increases the SAN activity, which increases heart rate.
b) Low blood O2, low blood pH level. The low blood pH level is caused by the increased CO2 level.
Q3 Atrial fibrillation (AF) is a condition that can result in a fast and irregular heartbeat because an abnormally high number of impulses are passed from the atria to the ventricles. Surgical treatment of AF can involve AVN ablation, which involves injuring the AVN so it no longer functions.
a) Suggest how this treatment helps to manage the condition.
b) After undergoing AVN ablation, patients also need to have a pacemaker implanted (an electronic device that sends out electrical impulses to control heart rate). Suggest why this is necessary.
3 a) The AVN passes waves of electrical activity on to the bundle of His and the Purkyne tissue to make the ventricles contract.
By stopping the AVN from functioning, the rapid irregular impulses from the atria aren’t transmitted via the bundle of His and the Purkyne tissue to the ventricles, so they can’t affect the heart rate (i.e. make it high and/or irregular)
b) Without a functioning AVN the ventricles can’t contract normally.
A pacemaker is needed to generate electrical impulses that cause the ventricles to contract normally.
Diagram of the heart with nodes.
