Phys: Cardiac Muscle Flashcards
Atrioventricular valves:
-mitral valve
-tricuspid valves
Semilunar valves:
-pulmonic valves
-aortic valve
Major vessels of the heart:
-aorta
-pulmonary artery
Abnormal atrioventricular valves :
-mitral stenosis
-mitral regurgitation
-tricuspid stenosis
-tricuspid regurgitation
Abnormal semilunar valves:
-pulmonic stenosis
-pulmonic regurgitation
-aortic stenosis
-aortic regurgitation
The right side of the heart pumps the blood to…
The lungs
The left side of the heart pumps the blood to the….
Peripheral organs
What exists between atrium and ventricle?
Fibrous insulator
3 layers of pericardium:
-Fibrous pericardium
-parietal pericardium
-epicardium (visceral pericardium)
What lies between the parietal pericardium and epicardium?
Pericardial space
Pericardium is innervated by:
Phrenic nerve
Pericarditis can cause:
Referred pain to the neck, arms, or one or both shoulders
**more often the left
Cardiac muscle is ____________,_____________muscle
Involuntary, striated
Cardiac muscle cells are connected by __________________ and contain electrical connections called _____________
Intercalated disks, gap junctions
Cardiac muscle cells have ___________ resting membrane potential
Unstable
Cardiac muscle action potentials:
-very long
-200x longer than neurons
-long refractory period
Cardiac muscle contraction is similar to skeletal muscle contraction, except cardiac is ______________
Longer
SA node:
-cardiac pacemaker
-(60-100bpm)
AV node:
-impulse is delayed to allow atria to contract before ventricles
-(40-60bpm)
Bundle of His:
-left and right bundle branches
-(20-40 bpm)
Purkinje fibers:
-takes impulses to all parts of ventricles
-(<20 bpm)
Resting membrane potential of cardiac muscle:
-85 to -95 mV
mV of cardiac muscle action potential:
105 mV
Cardiac muscle plateau lasts ___-____ seconds in ventricular muscle
0.2-0.3 seconds
Phase 0 in cardiac muscle AP:
-rapid depolarization
-opening of activation gates on Na channels
-inward Na current
Phase 1 of cardiac muscle AP:
-initial/early repolarization
-inactivation of the voltage-gated Na+ channels
-outward K+ current
Phase 2 of cardiac muscle AP:
-plateau
-stable, depolarized membrane potential
-inward Ca2+ current (L-type channels)
-outward K+ current
Calcium channel blocking drugs:
-nitrendipine
-nimodipine
-nifedipine
Ca2+ induced Ca2+ release is when…
Ca2+ entry during the plateau initiates the release of more Ca2+ from intracellular stores
Phase 3 of cardiac muscle AP:
-rapid repolarization
-decrease inward Ca2+ current
-increase in outward K+ current
Phase 4 of cardiac muscle AP:
-resting membrane potential
-fully repolarized and returned to resting level
-inward and outward currents are equal
What does it mean when we say electrical events precede mechanical events?
The contraction FOLLOWS an action potential (AP always first)
Excitation-contraction coupling (ECC) is a process where an action potential triggers…
A myocyte to contract, followed by a relaxation
Course of the action potential when depolarization occurs in cardiac ECC
AP courses along the sarcolemma into T tubules which depolarize the cell membrane
DHP receptors open for calcium entry in to the cell during which phase of the AP?
Phase 2
Calcium influx into the cardiac muscle triggers __________ _________ to releases Ca2+ and increase the Ca2+ concentration
Sarcoplasmic reticulum
Free calcium binds to ____________ that induces a conformational change
Troponin C
The conformational change after Ca2+ binds to troponin C allows for:
-actin to bind to myosin ATPase
-ATP is hydrolyzed, and actin and myosin slide past each other
Calcium entry into the cells slows when it is sequestered by __________ back into the sarcoplasmic reticulum
SERCA
Role of T-tubules in cardiac muscle contraction:
They provide the amount of Ca2+ to provide a strong enough muscle contraction
T tubules in cardiac muscle have a much __________diameter compared to those of skeletal muscle
LARGER
What binds to the store of Ca2+ ions to keep them available for diffusion into T tubules?
Large amounts of mucopolysaccharides
Strength of cardiac muscle contraction depends on the…
Concentration of calcium ions in the extracellular fluids
Where are T tubules located in cardiac muscle?
At the Z-lines
Why does cardiac muscle have more mitochondria?
-There is high metabolic demand and oxygen consumption
-heart is very sensitive to ischemia and hypoxia
Cardiac muscle gets 30% of its calcium from…
ECF through L-type Ca2+ channel (DHPR)
Cardiac muscle gets 70% of its calcium from…
SR through RyR
ECC in cardiac muscle is termed _____________coupling
Electrochemical coupling
In skeletal muscle Ca2+ release from the SR does not involve entry across sarcolemma but results from an…
Induced conformational change in the DHPR
Calcium entry is controlled by____/______activity
SNS/PNS
Sympathetic stimulation increases the cytosolic concentration of..
-cAMP (cyclic adenosine monophosphate to Dr. Younger)
The increase in cAMP with sympathetic stimulation leads to
Phosphorylation of several proteins by protein kinase A(PKA)- Phospholamban (PLN) and troponin 1
Phospholamban increases activity of
SERCA
Increased SERCA activity leads to an increase in
Calcium stores
In sympathetic stimulation, An A kinase anchor protein (AKAP) adjacent to the L-type calcium channel facilitates
Phosphorylation of the channel and possible nearby SR calcium channels
Parasympathetic stimulation decreases the cytosolic concentration of _____.
-cAMP
In parasympathetic stimulation muscarinic agonist like Ach inhibit
The sympathetic cascade by inhibiting the production of cAMP by adenylate cyclase
How do potassium channel blockers affect Phase 3?
Prolongs phase 3
-allows less potassium to leave
How does hyperkalemia effect phase 3?
-raises resting potential
-shortens phases 2 and 3 by promoting potassium effluent
-can also reduce conduction velocity
How does hypokalemia affect phase 3?
-lowers resting potential
-lengthens phases 2 and 3 by reducing potassium efflux
Absolute refractory period (ARP) is when..
Absolutely no stimulus is large enough to generate another action potential
During ARP, sodium activation gates are
Closed
ARP affects which phases of contraction
1, 2, and early 3
Effective refractory period (ERP) is when
A conducted action potential cannot be generated
ERP includes ARP but is slightly
Longer
At the end of the ERP, the sodium channels
Start to recover and become available to carry inward current
Relative refractory period (RRP) is when
A smaller AP can be induced with a greater than normal stimulus
The RRP begins at the end of the
ARP and continues until the cell membrane has almost fully repolarized
If a second action potential is generated during the RRP, it will
Have an abnormal configuration and a shortened plateau phase
Supranormal period (SNP) follows the
RRP
During the supranormal period, the cell is more ___________
Excitable than normal
During the SNP, action potential fire more or less easily?
More easily
Alpha 1 receptors increase
Pupillary dilator muscle contraction(mydriasis)
Alpha 2 receptors decrease
Aqueous humor production
beta 1 receptors are in the
Heart
Beta 2 receptors are in the
Lungs
Beta 2 receptors increases
Aqueous humor production
M3 receptors increase
Pupillary sphincter muscle contraction (miosis), and ciliary muscle contraction (accommodation)
M1 and M3 receptors used G
Gq
M1 and M3 increase ___ concentration from smooth muscle contraction
Ca2+
M2 and alpha 2 uses G__ to inhibit _______
use Gi, to inhibit myosin light-chain kinase(smooth muscle)
The sinus node is a
Specialized cardiac muscle connected to atrial muscle
Thr membrane potential for the pacemaker cardiac muscle is
-55 to -60mV
The cardiac muscle has a higher resting membrane potential than skeletal muscle due to
The constant leak of Na+
When pacemaker cardiac muscle resting membrane potential reaches -40mV, what happens?
Slow Na+Ca++ channels (funny channel) open causing action potential
For pacemaker cardiac muscle, after 100-150msec, Ca++ channels…
Close and K+ channels open more thus returning membrane potential to -55mV
The phases for pacemaker APs are
4,0, and 3
SLow action potentials are
-Sinoartial node
-atrioventricular node
Fast action potentials
- atrial myocytes
-ventricular myocytes
-conducting cells (purkinje fibers and bundle branches)
Pacemaker action potential phase 0 is
The upstroke
Phase 0 is the opening of
Voltage-gated Ca2++ channels
During phase 0, fast voltage gated Na+ channels are
Permanently inactivated because of the less negative resting potential of these cells
Phase 0 results in:
-slow conduction velocity that the AV node uses to prolong transmission from atria to ventricles
pacemaker action potential phase 3 is the
Repolarization phase
During phase 3:
-inactivation of Ca++ channels and increase activation of K+ channels
The result of phase 3 is
Increase K+ efflux
Phase 4 in sinus node fibers is the…
Slow spontaneous diastolic depolarization
Phase 4 involves what type of channels?
Funny current channels
Funny current channels are responsible for
For a slow, mixed Na+/K+ inward current
Phase 4 accounts for the
-the automaticacity of SA and AV node
The slope of phase 4 in the SA node determines
Heart rate
Sympathetic(norepinephrine)- positive chronotrophy increases:
-rate of conduction
-force of contraction
-SA node discharge
Parasympathetic (Ach)- negative chronotrophy decreases what via M2 receptors:
-slows heart rate
-reduces funny channel
Parasympathetic Ach decreases SN ______ and ________ of AV fibers
SN discharge and excitability of AV fibers
Once an action potential is initiated, the cardiomyocyte becomes
Inexcitable
The refractory period acts as a
Protective mechanism by preventing multiple compounded action potentials
Refractories is a determinant of susceptibility to
Arrhythmias
order of fastest conduction velocity to slowest
Purkinje fibers, atria, ventricles, and AV node
Why are purkinje fibers the fastest conductors?
They have lots of gap junctions
-are the slowest generators tho
The effects of the autonomic nervous system on conduction velocity are called
Dromotropic effects
Positive dromtropic leads to
Increase in conduction velocity
Negative dromotropic leads to
Decrease in conduction velocity
if the SA node fails, what takes over?
The AV node
