Cardiac and Smooth Muscle Flashcards
What is the mitochondria and vascularity content of cardiac muscle relative to skeletal muscle?
More mitochondria and vascularity in cardiac muscle
What structures allow for cell-to-cell propagation of the action potential in cardiac muscle?
Gap junctions
What is the length of cardiac muscle’s refractory period relative to skeletal muscle’s?
Cardiac muscle has a longer refractory period
What is the physiologic advantage a longer refractory period in cardiac muscle?
The cardiac muscle cannot be excited again, preventing it from contracting again, and giving the heart time to fill
What facilitates the re-uptake of Ca++ into the sarcoplasmic reticulum?
Phosphorylation of phospholamban
What is the normal action of phospholamban?
Inhibition of Ca uptake into the SR
True or false: cardiac muscle cannot be modulated by hormones
False
What physiologic event results in the plateau phase of the cardiac muscle action potential?
Slow opening of voltage-gated L-type Ca++ channels [DHP]
To what kind of receptor on cardiac tissue will norepinephrine released by the sympathetic nervous bind
Beta 1 adrenergic receptor
What serves as regulatory proteins in smooth muscle?
Myosin Light Chain Kinase and Myosin Light Chain Phosphatase
What molecules modulate the rate of ATPase activity in smooth muscle?
Calponin and Caldesmon
What is the pattern of smooth muscle filament arrangement?
Diagnonal orientation
What is the equivalent of Z lines in smooth muscle?
Dense bodies
True or false: smooth muscle cells contain T tubules?
False
What is the size of smooth muscle sarcoplasmic reticulum relative to skeletal muscle SR? What is the significance of this?
Smooth muscle cells have a smaller volume of SR, which means smaller calcium storage; Smooth muscle relies on extracellular calcium for contraction
Which types of muscle contain gap junctions?
Cardiac and smooth muscle
What are the two functional types of smooth muscle?
Single unit and multiunit
What is the main type of visceral muscle?
Single unit smooth muscle
What type of smooth muscle has rich ANS innervation?
Multiunit
What is the result of stretching single unit smooth muscle?
Stretch produces tension which leads to contraction
What is the relative level of gap junctions in multiunit smooth muscle compared to unitary smooth muscle?
Fewer or no gap junctions in multiunit smooth muscle
What type of smooth muscle has a more stable membrane potential?
Multiunit
What does the contractile response of multiunit smooth muscle depend on?
Number of muscle fibers activated and frequency of nerve stimulation
What mechanisms can stimulate smooth muscle contraction and relaxation?
Electrical depolarization, chemical stimuli, and mechanical stimuli (stretching)
True or false: An action potential is required for smooth muscle contraction?
False
What are the two types of smooth muscle action potentials?
Spikes and plateaus
True or false: an increase in cytosolic calcium is necessary for smooth muscle contraction?
True
What are store operated channels in smooth muscle cells?
Channels that sense when the SR stores of Ca++ are insufficient and can activate the influx of additional Ca++
What can activate RyR channels in smooth muscle?
Ca++ induced Ca++ release or IP3 activation
To what molecule will calcium bind in smooth muscle?
Calmodulin
What are the actions of the calcium-calmodulin complex in smooth muscle?
It activates Myosin Light Chain Kinase as well as CaCM-dependent kinase (CAMK)
What is the function of activated myosin light chain kinase?
It phosphorylates myosin light chain, activating it and increasing myosin ATPase activity
What phosphorylates calponin? What is the effect of this phosphorylation?
CaCM-dependent kinase; blocks inhibition of myosin ATPase
What is the activity of Myosin Light Chain Phosphatase?
Continuously decreases MLC phosphorylation
What are the two ways to cause smooth muscle relaxation?
Dephosphorylation of myosin light chain through myosin phosphatase or removal of cytosolic calcium
What molecule is responsible for the phosphorylation and inactivation of myosin phosphatase?
Rho-Kinase
During pregnancy, what is the effect of an increase in estrogen?
Smooth muscle hypertrophy and increase in gap junction expression
What is the effect of oxytocin on smooth muscle contraction
Potent stimulator of smooth muscle contraction
What is the effect of nitric oxide in smooth muscle? What is the pathway/mechanism of this action?
Nitric oxide activates guanylyl cylcase, increasing the amount of cGMP, and enhancing smooth muscle relaxation
What is the effect of Protein Kinase G activation?
Smooth muscle relaxation
What is the mechanism of viagra?
Inhibition of cGMP breakdown
What is the mechanism of amlodipine?
Calcium channel blocker that blocks calcium influx
What is Raynaud’s Syndrome?
When exposed to cold temperature, patients’ digits become pale and cold because of vasoconstriction of blood vessels
