The cardiac cycle Flashcards
What is the pacemaker impulse in the lobster heart?
The pacemaker impulse in the lobster heart comes from the cardiac ganglion (neurogenic).
What is the pacemaker impulse in the human heart?
The pacemaker impulse in the human heart is built in (myogenic).
What did Stannius discover about pacemakers in the frog heart?
Stannius demonstrated that there is a hierarchy of pacemakers in the frog heart. The primary pacemaker is located in the sinus venosus, and there are secondary pacemakers in the atria and ventricles, which are slower.
What happened when Stannius tied a ligature between the sinus venosus and atria in the frog heart?
Tying a ligature between the sinus venosus and atria slowed the heart rate, showing that the sinus venosus is the primary pacemaker.
What was the result of Stannius tying a second ligature between the atria and ventricle in the frog heart?
The heart rate slowed further, indicating that the atria contain a secondary, slower pacemaker.
What is the hierarchy of pacemakers in the frog heart as demonstrated by Stannius’s experiment?
The hierarchy is:
Primary pacemaker: Sinus venosus
Secondary pacemaker: Atria
Tertiary pacemaker: Ventricles (driven by Purkinje fibers)
What is the primary pacemaker of the mammalian heart?
The primary pacemaker is the sinoatrial (SA) node, located at the top corner of the right atrium just below the superior vena cava.
What characteristic do the muscle cells in the sinoatrial (SA) node have?
The muscle cells in the SA node have an action potential with a sloping diastolic potential. This means the membrane potential is unstable and depolarizes up to a threshold before firing the next action potential.
How does the wave of excitation spread in the heart after the sinoatrial node?
The wave of excitation spreads from the SA node through the right atrium to the atrioventricular (AV) node, and then through the Bundle of His, the right and left bundle branches, and the Purkinje fibers in the ventricles.
Which structures in the mammalian heart have intrinsic pacemaker activity?
The sinoatrial node, atrioventricular node, Bundle of His, right and left bundle branches, and Purkinje fibers all have intrinsic pacemaker activity, meaning they beat regularly without external stimulus
How do the action potentials in the atrium and ventricles differ from the pacemaker structures?
The action potentials in the atrium and ventricles have a flat, stable resting membrane potential between beats, unlike the pacemaker structures that have a sloping resting membrane potential and can generate action potentials without external stimuli.
Which pacemaker structure in the mammalian heart has the fastest intrinsic rate?
The sinoatrial (SA) node has the fastest intrinsic rate and determines the rate of all the other structures in the heart.
How does the SA node control the heart rate in relation to other pacemaker structures?
The SA node sets the tempo, and the other pacemaker structures (AV node, Bundle of His, Purkinje fibers) follow the rhythm it generates, even though they each have their own intrinsic rates.
What is the hierarchy of pacemaker structures in terms of their intrinsic rate?
What happens if pacemaker structures in the heart start firing off at faster rates or abnormal intervals?
If pacemaker structures fire at abnormal rates or intervals, it can lead to cardiac arrhythmias.
Where is the sinoatrial (SA) node located in the heart?
The SA node is located at the top of the right atrium, at the junction of the superior and inferior vena cavae
what is the sinoatrial node bounded by
thick ridge of atrial muscle called the crista terminalis
What 3 types of cells are found in the SA node?
The SA node contains a mixture of specialized nodal cells, atrial cells, and connective tissue.
How much connective tissue is present in the SA node?
The SA node contains up to 50-90% connective tissue, depending on the species and age.
Why is the mixture of cell types in the SA node important?
The heterogeneous mixture of cell types in the SA node is essential for the normal functioning of the pacemaker.
What are the three types of cells found in the sinoatrial (SA) node?
The three types of cells in the SA node are:
- Spindle cells (from the center of the node)
- Elongated spindle cells (probably from the periphery)
- Spider cells
where are spindle cells located
Spindle cells – located in the center of the node.
where is an elongated spindle cell located
likely from the periphery.
what is the location of spider cells
location unclear.