Cardiac Muscle Flashcards
What are some similarities between skeletal and cardiac muscle?
Both have striations, Cross bridge cycling and the need for an action potential to contract.
What are some differences between skeletal and cardiac muscle?
- Excitation-contraction coupling,
- Mechanisms to adjust the force of contraction,
- Number and placement of nuclei
- Intercalated disks
- Cytoplasmic size
Whats the main feature of the purkinje fibers?
They’re ventricular cells specialized for rapid conduction of APs.
Whats the main feature of the Nodal cells?
Found in SA and AV nodes; They are the pace making cells.
How are the T-tubules in cardiac muscle different than the skeletal muscle counterparts?
The invaginations of the cell membrane are at the Z-disks instead of the M-lines.
What are the key features of the intercalated disks?
- Fascia adherens: Actin filaments attach to the CM at the junctional site.
- Maculae adherens: Span the junction between the two cells. Act as desmosomes.
- Gap Junctions: Ions pass through propagating APs.
What is the key feature of the Atria?
The cells have secretory granules that act as hormones; Atriopeptinogen
Describe Excitation-Contraction coupling in cardiac muscle.
- Once T-tubule depolarizes, it activates Calcium channels on T-tubule membrane
- Small amounts of extracellular calcium enter cytosol; Activates RyR receptors on SR.
- Calcium released into cell from SR.
How is calcium removed in cardiac muscle?
Removed by a calcium pump AND sodium/calcium exchanger.
Discuss the mechanisms of force of contraction in skeletal and cardiac muscle
- Only skeletal muscle can do Spatial or Temporal summation.
- Both can have a length-tension relationship
- Only cardiac muscle can increase its contractile force.
What is a functional syncytium?
All cardiac muscles contract with every beat of the heart; Acts as one big cell.
Why can’t spatial or temporal summation occur in cardiac muscle?
Spatial summation can not happen because all heart cells are electrically connected so they beat at once. Temporal summation can not occur because cardiac APs are long to allow refilling of blood.
What is Starling’s Law of the Heart?
Filling the heart with blood during its period of relaxation results in a more forceful contraction during the next contraction; More filling, More blood ejected.
How is heart contractility increased?
Increasing cytosolic calcium during an AP or increasing troponin’s affinity for calcium.
- B1 adrenergic receptor activation
- Cardiac glycosides impair calcium removal from cytosol (digitalis)
- Increased heart rate
How is heart contractility decreased?
Decrease cytosolic calcium during an AP, decreasing troponin’s affinity for calcium or insufficient ATP.
- Block B1 adrenergic receptors.
- Decreased sympathetic activity
- Block T-tubule calcium channels.
