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60 Cards in this Set
- Front
- Back
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where is the nucleus in smooth muscle?
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centrally placed
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how are thin filaments arranged in smooth muscle?
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bundles attached to dense bodies (alpha-actin) on either side of sarcolemma or cytoskeleton
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what is the shape of a smooth muscle?
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spindle shaped
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how does the endoplasmic reticulum of smooth muscle differ from that of skeletal muscle?
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the ER of smooth muscle is poorly developed and sparse, no t-tubule or terminal cistenae so contraction requires extracellular calcium
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what regulates the ER of smooth muscle?
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ANS and hormones
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T/F
the cycling of myosin cross-bridges in smooth muscle are slower than skeletal muscle |
true
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why is there less energy required for smooth muscle?
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because there are fewer cycles and therefore less ATP to split
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how long does it take for smooth muscle to reach full contraction?
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.5 seconds
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how long does it take the smooth muscle to relax?
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1-3 or up to 30 seconds
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T/F
skeletal muscle has a higher force of contraction than smooth |
false
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what is the force of contraction for smooth muscle (numerically)?
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4-6 kg/cm2
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what is required for the initiation of contraction?
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calcium
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smooth muscle contains _____ which activates the ______ cross-bridges
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calmodulin; myosin
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how many calcium ions bind to calmodulin?
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four
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what enzyme does the calmodulin calcium complex activate?
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Myosin light chain kinase (MLCK)
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as long as _____ is phosphorylated, the cross-bridge cycling can continue
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MLC
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instead of troponin, what serves as the intermediary in smooth muscle?
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Caldesmon
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what happens in smooth muscle when calcium ions are in short supply?
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caldesmon forms a complex with TM and actin restricting the ability of myosin to bind to actin and preventing contraction
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what does epinephrine bind to in order to raise cAMP?
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B-adrenergic receptors
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what activates PKA in the regulation of Calcium handling?
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elevated cAMP
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PKA reduceds the affinity of _____ for CaCM and _______ the strength of contractions generated by elevated cytosolic calcium
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MLCK and modulates
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where is the additional ATP necessary in the cross-bridge cycle of smooth muscle?
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phosphorylation at a specific site on a MLC
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what is a phasic contraction?
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a brief period of stimulation is associated with calcium mobilization followed by cross-bridge phosphorylation and cycling and cycling to produce a brief phasic, twitch like contraction
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what produces a tonic contraction?
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prolonged stimulation
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why is tonic contraction held at a reduced calcium concentration?
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to lower ATP consumption and lower shortening velocities
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how many cross-bridge states does covalent regulation allow in smooth muscle?
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8
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what dephosphorylates MLC in smooth muscle?
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Myosin light chain phosphatase
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what is the purpose of the latch mechanism?
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to maintain tonic contraction with reduced cross bridge cycling and has extrenely low energy expenditure
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where is most of the calcium derived from in smooth muscle?
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extracellular fluid
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what is a multi-unit smooth muscle?
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each fiber can contract independently and is usually innervated by a single nerve ending
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why is neural integration important in multi-unit smooth muscles?
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the smooth muscle has no electrical coupling
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how are the fibers of a multi-unit smooth muscle insulated from each other?
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by a covering of collagen and flycoprotein fibrillae
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what are some examples of multi-unit smooth muscles?
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ciliary muscles of eye, iris, piloerector muscles
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what is a unitary smooth muscle?
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aggregates of hundreds or thousands of fibers that act as a single unit
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why are membranes adherent to one another in unitary smooth muscle?
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in order to transmit generated force
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how are the fibers of unitary smooth muscle connected?
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gap junctions
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because unitary smooth muscles are connected via gap junctions, _______ and ________ are simultaneous.
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action potential and contractions
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what are examples of unitary smooth muscle?
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walls of viscera, gut, bile ducts, ureters, uterus and many blood vessels
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what is the most common smooth muscle arrangement?
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single unit fashion
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what three things can initiate contraction of smooth muscles?
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1) intrinsic activity of pacemaker cells, 2) neurally released transmitter and 3) circulating or locally generated hormones or signaling molecules.
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in a somatic neuron, what is the pathway between the CNS and effector cell?
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monosynaptic
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what is released from the preganglionic neurons of the ANS?
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ach
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what is the postsynaptic receptor of parasympathetic ANS neurons?
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muscarinic
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is muscarinic ionotrophic or metabotrophic?
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metabotrophic
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what is the neurotransmitter for sympathetic postganglionic neurons?
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norepinephrine
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what is the receptor for the sympathetic postganglionic neuron?
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metabotropic, adrenergic receptor of 2 major subtypes alpha and beta
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what is the typical resting membrane potential of smooth muscle?
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-50 to -60mV
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what type of voltage gated Calcium channels does smooth muscle have?
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L-type
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T/F
calcium channels open slower and stay open longer allowing some cells to have plateaus in skeletal muscle |
false : in smooth
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what does SAC stand for?
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stretch-activated cation-permeable channels
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what does stretching of the visceral muscle muscle generate?
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spontaneous action potential
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what inhibits smooth muscle contractions in the guy, but stimulates contraction in vascular smooth muscle?
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norepi
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what does alpha 1 couple with in smooth muscle? what does their coupling result in?
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G2; increased cellular calcium which results in smooth muscle contraction
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what does alpha 2 couple with in smooth muscle? what does their coupling result in?
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Gi; decreased cAMP activity which results in smooth muscle relaxation
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what does beta 2 couple with in smooth muscle? what does their coupling result in?
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Gs; increased cAMP which results in smooth muscle relaxation
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what is the agonist potency order for alpha 1 receptor and what is the mechanism?
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norepi>epi>>isoprenaline; phospholipase C activated, IP3, and calcium up
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what is the agonist potency order for alpha 2 receptor and what is the mechanism?
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epi>norepi>>isoprenaline; adenylate cyclase inactivated, cAMP down
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what is the agonist potency order for beta 2 receptor and what is the mechanism?
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isoprenaline>epi>>norepi; adenylate cyclase activated, cAMP up
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what are maximal shortening velocities with no load directly dependent on>
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cross-bridge phosphorylation by MLCK
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near maximal stress can be generated with only _____ to _____ of cross-bridges in the phosphorylated state
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20-30%
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