Mechanisms Controlling The Heartbeat Flashcards
What important property does the heart have?
Automatism
What does the automatism of the heart mean?
It can contract and relax without any external stimuli
Where do the contractions of the heart begin?
In the muscle cells of the heart
What is a heartbeat?
The sound that results from each cardiac cycle
What instrument allows the heartbeat to be heard?
Stethoscope
What sound does the heart make?
Lub-dub
Which heartbeat sound is louder?
Lub
What causes the heart to beat?
An electrical impulse
What initiates the electrical impulse of the heart?
The SA node
What does the SA node stand for?
sino-atrial node
What is the SA node?
A group of specialised muscle cells
Where does the SA node occur?
In the wall of the right atrium
What is the SA node known as?
The pacemaker of the heart
What is the AV node?
Another group of specialised conducting cells
What does the AV node stand for?
Atrio-ventricular node
Where does the AV node occur?
Occurs at the lower end of the septum between the right atrium and left atrium
What conducts impulses from the atria to the ventricles?
Bundles of His
What is His?
Special muscle tissue
Where does His occur?
Throughout the septum between the two ventricles
What does the His do at the apex of the heart?
Branches Purkinje fibres
What are Purkinje fibres?
The network of fibres which is the extension of the bundles of His
Where do the Purkinje fibres occur?
Throughout the walls of the ventricles
What do the Purkinje fibres do?
Conduct impulses faster and more effectively
What is the route of the impulse and its effect during a cardiac cycle?
The contraction begins at the SA node and spreads across the two atria to the AV node
The two atria contract simultaneously
The impulse travels along the bundles of His between the two ventricles to the Purkinje fibres
This causes the ventricles to contract simultaneously from their lower ends
What controls the heartbeat?
The nervous system
Hormones
Which part of the nervous system controls the heartbeat?
The autonomic nervous system
How does the autonomic nervous system control the heartbeat?
By conducting impulses via two types of nerve fibres
What do types of nerve fibres conduct impulses to the heart?
Sympathetic
Parasympathetic
Where do the impulses conducted by the autonomic nervous system come from?
From the brain
To the SA node
What is the autonomic nervous system?
The part of the nervous system in vertebrates that controls the involuntary actions of smooth muscles, cardiac muscles and glands
What kind of nerve impulses do the sympathetic nerve fibres conduct?
Impulses that accelerate the heartbeat
What kind of nerve impulses do the parasympathetic fibres conduct?
Impulses that slow the heartbeat down to normal
Which two hormones affect the heartbeat?
Adrenaline
Thyroxine
What do adrenaline and thyroxine do?
Accelerate the heartbeat
When is adrenaline released?
During times of stress
Why does the heartbeat speed up in times of stress?
More oxygen is pumped to the brain and muscles, which improves the reactions of a person during stressful situations
How does exercise affect the heartbeat?
It accelerates the heartbeat
How many beats per minute can strenuous exercise increase the heartbeat to?
200 beats per minute
Why does exercise increase the heartbeat?
Cells need more energy They perform more cellular respiration More CO2 is released More oxygen is needed Heart pumps faster to supply it
How does the body know to increase the heartbeat during exercise?
Receptors in the carotid arteries detect the increase in CO2
It sends a message to the brain
Sympathetic fibres conduct impulses to increase the heartbeat
What is a pulse?
The regular contraction and relaxation of an artery, caused by blood pumped through the body
Where can ones pulse be felt?
Where an artery lies close to the surface
What is a pulse rate?
The number of heartbeats per minute
Which fingers are used to take ones pulse?
Index and middle finger
When a person exercises regularly, what happen to their pulse rate?
It decreases
Why does a fitter person have a lower pulse rate?
The heart muscle is strengthened
It doesn’t need to pump as many times to pump the same volume of blood
