Physiology Week 1 Flashcards
NCX
Na/Ca exchanger in plasma membrane. Move Ca uphill by exploiting the Na gradient. Can work in reverse.
PMCA
plasma membrane Ca ATPase. Not v. important to cardiac myocytes, but it is present. Moves ca out of cell
What does SERCA do?
transports calcium back to the sarcoplasmic reticulum. SR and outside cell have similar Ca levels.
How are calcium gradients maintained?
By SERCA and NCX
How do large amounts of ions move?
Through channels - much faster/greater volume than through pumps and transporters. Ex: L-type Ca channel, Na channel
What are some differences between cardiac and skeletal muscle?
Cardiac muscle requires extracellular calcium influx to contract, skeletal muscle does not (vast majority from SR).
Skeletal muscle requires activation by neurons at neuromuscular junctions, cardiac muscle does not.
Skeletal muscle contractions can sum to a larger contraction, cardiac cannot.
Both cardiac and skeletal muscle contraction are fast (versus slow smooth m., smooth muscle also not arranged in sarcomeres)
What is the A band?
middle, thick filaments, dArk
what is the I band?
area that does not contain thick filaments, lIght.
What is the Z line?
scaffolding proteins (alpha actinin) that anchor thin filaments. In middle of I band.
What are thick filaments made of?
myosin heavy and light chains
What are thin filaments made of?
actin, tropomyosin, troponin
How do cross bridges form in cardiac and skeletal muscle?
Calcium binds to troponin-C, causing tropomyosin on thin filaments to change conformation
so binding site is exposed and myosin can bind to actin.
How does skeletal muscle excitation occur?
Motor neurons release Ach at neuromuscular jxn. Ach binds to nicotinic cholinergic receptors in motor endplate. Na flux through the Ach receptors initiates skeletal muscle action potential.
Tetanus?
Chronically contracted muscle
What’s different about smooth muscle?
No troponin/tropomyosin. Actin and myosin interaction occurs when myosin light chain is phosphorylated. MLCK is activated by calcium binding, regulated by calmodulin. Contraction can occur with or without APs. Uses many diff sources of calcium
What stimulates contraction in smooth muscle?
alpha adrenergic stimulation - produces IP3 and Ca is released from SR.
What stimulates relaxation in smooth muscle?
beta adrenergic stimulation and nitric oxide. BAS activates adenylyl cyclase and cAMP inhibits MLCK. NO similar in that it activates guanylyl cyclase.
What is the order of conduction through the heart?
sinoatrial node - atrium - atrioventricular node - bundle of His/bunde branches - Purkinje fibers - ventricles
What’s an SA nodal cell like?
SA nodal cell IS a muscle cell, doesn’t really contract much though. NOT neurons within myocardium - they fire spontaneously. SA cells don’t need to pump blood, don’t need to be as big.
Note that it never goes back down to -85 like a ventricular cell, more like -60.
What are the ion movements in a ventricular AP?
0) Na influx (upstroke)
1) Na in vs. K out (notch)
2) Ca in and K out (plateau)
3) K out (repolarization)
4) K out and NCX in (resting membrane)
What are the ion movements during an SA nodal AP?
0) Ca influx (upstroke)
1) not listed
2) Ca in vs. K out (plateau)
3) K out (repolarization)
4) NCX in AND funny current If in (resting)
What’s a negative current?
positive charge flowing into the cell. A positive current would be positive charge flowing out of the cell.
What’s the deal with L-type calcium currents?
channels open at more positive voltages, opens and closes more slowly than sodium. Otherwise looks like sodium.
supply a significant amount of Ca for AP plateau/SR Ca release in ventricular myocytes
Are the AP upstroke in SA and AV nodal myocytes
Reversal potentials?
K= positive above -90 Na= negative below +70 Ca= negative below +130