Lecture 11- Physiology Of The Heart Flashcards
Structural and functional properties of cardiac muscle
Striated
Cells are short, fat and branched
One or two large centrally located nuclei
Cells connected by intercalated discs
Have many large mitochondria
Intrinsic conduction system
sets the basic rhythm of the heart.
Extrinsic innervation of the heart
modifies the basic rhythm.
Why is the heart refractory period longer?
To prevent tetanus contractions
Pacemaker cells
Approx. 1% of cardiac muscle cells
self-excitable and initiate own depolarization, as well as set the rhythm for depolarizing the rest of the cardiac muscle.
Does heart depend on nervous system?
No
It relies on gap junctions to conduct impulses throughout the heart and the intrinsic conduction system.
Sinoatrial nose (SA)
Located in the right atrium and is the primary pacemaker for the heart.
Atrioventricular (AV) node
in the interatrial septum, delays firing slightly, in order to allow the atria to finish contracting before the ventricles contract.
Atrioventricular (AV) bundle (bundle of His)
only electrical connection between the atria and the ventricles and conducts impulses into the ventricles from the AV node.
Right and left bundle branches
conduct impulses down the interventricular septum.
Subendocardial conducting network (purkinje fibres)
penetrates throughout the ventricular walls, distributing impulses through
the ventricles.
Order impulses pass through cardiac pacemaker cells
Sinoatrial (SA) node
Atrioventricular (AV) node
Atrioventricular (AV) bundle (bundle of His)
Right and left bundle branches
Subendocardial conducting network (purkinje fibres)
Arrhythmias
Irregular heart rhythms
Fibrillation
rapid, irregular, ineffective contractions.
During ventricular fibrillation, even though the heart is still moving, it becomes useless for pumping blood, causing circulation to cease.
Treatment = defibrillation; disrupting the chaotic twitching and resetting the heart to regular, normal depolarizations.
Cardioaccelatory centre
In medulla oblongata
projects to sympathetic neurons throughout the heart, increasing both heart rate and contractile force.
Cardioinhibitory centre
In medulla oblongata
sends impulses to the parasympathetic dorsal vagus nucleus in the medulla oblongata, which stimulates the vagus nerve to the heart, decreasing the heart rate.
When cardiac muscle cells are stimulated…
Fast voltage-gated Na+ channels allow Na+ to enter cell, resulting in rapid depolarization.
Depolarization opens slow Ca2+ channels, allowing Ca2+ to enter cell, even as K+ exits, producing a phase of the action potential that delays repolarization.
After 0.2 seconds, Ca2+ channels inactivated, additional K+ channels open, and cell repolarizes back to resting membrane potential.
Why is slow contraction of heart sustained?
to ensure all of the blood is squeezed out of heart.
The heart then has a long refractory period so it can be refilled with blood before beating again.
Electrocardiograph
Monitors and amplifies the electrical signals of heart and records it as an electrocardiogram (ECG)
ECG three deflections
- P wave, indicating depolarization of the atria.
- QRS complex, resulting from ventricular depolarization
- T wave, caused by ventricular repolarization
SEE DIAGRAM FOR VISUAL
