Cardiac muscle characteristics Flashcards
What are three causes of parasympathetics innervation on the heart?
- Slows HR (prolongs depolarization time)
- neg chronotropic effect - Slows rate of spontaneous depolarization of membrane
- Initial hyper-polarization of resting membrane potential is decreased
What is released from the sympathetics onto the heart?
Norepinephrine
- increases diastolic inward currents I(f) through HCN channels
What is the net effect of sympathetics innervation on the heart?
Speeds HR by shortens time to depolarize
- also increases rate of spontaneous depolarization of membrane
What is preload?
Passive resting tension placed on cardiac muscle cells before contraction
- a function of volume and pressure at the end of diastole
What causes increased preload?
Hypervolemia
Regurgitation
Heart Failure
What is afterload?
Active tension placed on cardiac muscle cells during contraction
- a function of resistance the left ventricle must over come to circulate blood
What causes increased afterload?
HTN
Vasoconstriction
What are the 3 differences between striated and cardiac muscle action potentials?
- Self- generating
- conducted directly from cell to cell
- Long duration (long refractory period)
Which ions are higher outside the cell and inside the cell?
Sodium and calcium
Potassium
What form of ion passage is most used?
Ion channels
- membranes permeability is the net status of the ion channels (high perm to Na means many ion channels open)
What are the 3 states of both the inactivation gates and activation gates? Which are open and closed when?
- Closed- Activation gate in the close; Inactive gate is not
- Active- Both gates are open and out of the way
- Inactive- Activation gate is open; Inactivation gate is closed
Do activation gates response quickly or slowly to depolarization?
quickly
Do inactivation gates respond quickly or slowly to depolarization?
Slowly
- Limits time channel can remain open
What are the 2 types of cardiac muscle cells?
- Myocardial contractile cells (similar AP’s to other cells)
- Myocardial autorhhythmic or pacemaker cells
- generate APs spontaneously cause of Unstable membrane
Which reponse slow or fast is pacemaker and contractile cells respectively?
Slow and fast
- think Pace yourself for slow
What does rectifier mean?
Allows for flow of ions in only one direction
- ex. inward rectifier only lets K+ into the cell during repolarization
How many phases does the myocardial pacemaker cells have and what are they?
Three
- Ca(l)- long lasting Ca channels; causes depolarization after Ca(t)’s have opened
- Ca(t)- causes slow upward swing that leads into Ca(l)’s depolarization
- I(f)
Which phases are missing in pacemaker cells?
1 and 2
Which period are cells fast response AP’s found in most of the time?
Absolute refractory period
- thus cannot be stimulated to contract again and this fights against tetanic contractions
what is a intercalated disk?
Specialized adheren juction structions that connects ends of two adjacent cells
What makes up an intercalated disk?
- Gap junctions - connexin is protein that forms these channels that permit passage of ions between cells= (Increased efficiency of spread of AP’s)
- Fasica adherens - anchors actin
- Macula adherens (desmosomes) - joins intermediate filaments
What is the purpose of the desmosomes and fascia adherens?
Ensure the transmission of force from one muscle cell to the next
What is the purpose of gap juctions?
Facilitate the transmission of electrical impulse from cell to cell
- the more GP’s means faster AP transmitted to the next cell
- this idea is how the AV nodes slows the 100BPM coming from the SA node
What is an electrocardiogram?
Record of how the voltage between 2 points on the body surface changes with time as a result of the electrical events of the cardiac cycle.
What is needed to increase/decrease the automaticity of the intrincic rate and where do they synapse?
Sympathetic and para NS
- on the SA node
How doe parasympathetic fibers interact with the SA node and what is its cause?
Via vagus and Acetylcholine
- Increases perm of resting membrane K+
- Leads to more negative resting membrane and thus increases threshold potential
- Decreases diastolic I(f) current thru HCN channels
