Quiz 2 - Cardiovascular System Flashcards
What is a heart contraction?
the electrical impulse that triggers contraction of cardiac muscle (contractile) cells is (arises in the heart itself) → intrinsic (stimulation from nervous system not required)
What makes up the intrinsic conduction system?
Conducting cells - special cardio cures that initiate and distribute action potentials in heart
Nodes = clusters of authorhythmic cells that generate spontaneous action potentials in heart.
autorhythmic cells in nodes have an unstable resting potential (Na+ leaks in)
Gradual depolarization occurs -> “prepotential” develops
at threshold → opening of voltage gated Ca++ channels (Ca++ rushes in from ECF) -> spontaneous action potential
What are the 6 steps of a autorhythmic cell in node with unstable resting potential?
- Na+ enters through Na+ leak channels
2.cell develops pre-potential - at threshold voltage gated Ca++ channels open
- Ca++ influx causes depolarization (API)
- Ca++ channels close; K+ channels open
- K+ efflux causes repolarization
Where are a.p. Initiated by a pace maker?
And how is it transmitted and to where?
S.A. Node
Conducting cells to heart muscle
How many times does the SA node depolarize?
100times/min
What are the steps involved with having a pacemaker?
- Sinoatrial node (S.A.) “pacemaker” (in posterior wall of r.atrium)
- internodal pathway - Atrioventricular node (a.V.) (in floor of r. atrium) a.p. delayed here to allow time for the atria to contract
- A.V. Bundle (in interatrial septum)
- Right + left bundle branches (in interventricular septum)
- Purkinje fibers (in walls of ventricles)
If the intrinsic contraction rate established by the pacemaker (sa node) is 100 bpm, then why is the resting heart rate slower than this?
Parasympathetic nervous system innervates nodes acetylcholine SLOWS heart down
How does heart rate increase?
Sympathetic nervous system innervates nodes, norepinephrine SPEEDS heart up.
Why does the pacemaker firing triggers all-or-none contraction of whole heart?
All cells are connected by gap junctions at intercalated discs
What is the function of gap junctions at intercalated discs?
Allows ions to move from cell to cell
What is the function of desmosomes?
anchoring proteins prevent separation of contracting cells
What is the function of having many michrochondria?
cardiac muscle very fatigue resistant
t-tubules trigger release of what?
Calcium from sarcoplasmic reticulum
Action potential spreads form what to what within heart?
Nodal conducting cells to contractile cells
What are the steps of AP in cardiac muscle?
- Voltage gated Na+ channels open @ threshold causing depolarization
- Voltage gated Na+ channels close quickly and then voltage gated K+ channels open BUT… change in membrane potential also opens voltage gated Ca++ Chanel’s in cell membrane causes influx of Ca++ from ECF
- Causing a plateau in membrane potential as Ca++ moves in while K+ moves out (repolarization is delayed)
- a.p. about 30x slower in cardiac muscle cells than in skeletal muscle cells
