D4 The heart Flashcards
What is cardiac muscle unique to?
The heart
What are the similarities between cardiac muscle and skeletal muscle?
- striated in appearance
- the arrangement of the contractile proteins actin and myosin is similar
What are the similarities between cardiac muscle and skeletal muscle?
- striated in appearance
- the arrangement of the contractile proteins actin and myosin is similar
What are the differences between cardiac and skeletal muscle? (4)
Cardiac muscles are
* shorter and wider
* most commonly have just one nucleus per cell
* Not under voluntary control
* Can contract even in the absence of sitmulation by nerves for the entire life of the organism
What shape are cardiac muscles cells?
Y-shaped
How are cardiac muscles cells joined?
are joined end to end in a complex network of interconnected cells
What is an intercalarted disc?
A specialized junction where the end of one cell contacts the end of another cell
What structure only appears in cardiac muscles?
Intercalated discs
What does the intercalated disc consist of?
double membrane containing gap junctions
What does the gap junctions in the double membrane of intercalated disc provide?
A connected cytoplasm between the cells
What does a connected cytoplasm between cells in an intercalated disc allow for?
- rapid movement of ions
- low electrical resistance
What allows for the synchronization of cardiac muscle contraction?
- Being connected because of their Y shapes and being electrically connected due to gap junctions
- Allows a wave of depolarization to pass easily from one cell to a network of other cells
- Leading to the synchronization of muscle contraction
What does the network of cardiac muscle cells contract like?
As if it was one large cell
What does the orange and blue represent?
Cardiac muscle fibrils
What does the red represent? What does it do?
Mitochondria
* supply the muscle cells with energy
What are the narrow dark blue lines representing? What do they mark?
Transverse tubules
* they mark the division of the myofibrils into contractile units (sarcomeres)
What are the narrow dark blue lines representing? What do they mark?
Transverse tubules
* they mark the division of the myofibrils into contractile units (sarcomeres)
What is the wavy dark blue line representing?
In the centre is the intercalated disc
What is the wavy dark blue line representing?
In the centre is the intercalated disc
What is the cardiac cycle?
- A repearting sequence of actions in the heart which result in the pumping of blood to the lungs and all other parts of the body
- Represents all of the events from the beginning of one heartbeat to the beginning of the next
What do cardiologists refer to contraction and relaxation of the heart’s chamber as?
Contraction: systole
Relaxation: Diastole
What happens in atrial systole?
- When ventricles are ~70% full,
- atria will contract (atrial systole),
- increasing pressure in the atria
- forcing blood into ventricles
What happens in ventricular systole?
- ventricles contract
- ventricular pressure exceeds atrial pressure and AV valves close to prevent back flow
- With both sets of heart valves closed, pressure rapidly builds in the contracting ventricles (isovolumetric contraction)
- When ventricular pressure exceeds blood pressure in the aorta, the aortic valve opens and blood is released into the aorta
What happens during diastole?
- ventricular pressure falls as blood exits the ventricle and travels down the aorta
- When ventricular pressure drops below aortic pressure, the aortic valve closes to prevent back flow (second heart sound)
- When the ventricular pressure drops below the atrial pressure, the AV valve opens and blood can flow from atria to ventricle
What is the SA node?
- a collection of uniquely structured cardiac cells that spontaneously initiate action potentials without stimulation by other nerves
Where is the SA node?
In the wall of the right atrium
What is the SA node sometimes referred to as?
The pacemaker of the heart
What allows the contraction which originated in the SA node to spread rapidly across the entire atrium?
Gap junctions allow electric charges to flow freely between cells, the contraction which originated in the SA node spreads very rapidly
What does the SA node cause?
causes the atria to undergo systole and contract as if it were one cell
What can the signals from the SA node not travel to?
Signal from the SA node that cause the atria to contract cannot pass directly from the atria to ventricles
Where does the signal from the SA node reach after causing the atria to contract?
the signal from the SA node reaches the atrioventricular (AV) node
How does the electrical signal form the SA node spread throughout the heart?
- it reaches the AV node
- via specialized Purkinje fibres spread through the heart
What are purkinje fibres?
specialized heart muscle tissue that spreads the signal from the SA node and AV node throughout the heart
What does signal from the prukinje fibres cause?
- causes the ventricle to undergo systole
- snaps the AV valves shut
- after the ventricles are emptied, the semilunar valves close