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55 Cards in this Set
- Front
- Back
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Smooth Muscle are what length? what diameter?
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Diameter: 1 to 5 microns
Length: 20 to 500 microns |
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What are the two principle types of smooth muscle?
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1. Multiunit
2. Visceral (unitary) |
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Control of contraction of Multiunit smooth muscle is by what input?
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Autonomic nervous system.
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What is the definition of multiunit smooth muscle?
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they are discrete muscle fibers, insulated from one another and can contract independently of others.
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what are examples of multiunit smooth muscle?
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ciliary muscle, iris of the eye, piloerector muscle.
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what principle smooth muscle does not exhibit spontaneous contraction?
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multiunit smooth muscle
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what is the definition of Visceral muscle fibers?
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they are arranged in sheets or bundles that depolarize and contract as a single unit.
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what is a Functional Syncytium?
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when cell membrane of individual fibers come into contact with GAP JUNCTIONS, which exist between individual fibers forming a muscle unit that depolarizes and contracts together..
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What exists between individual fibers in the Visceral Smooth muscle?
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Gap Junctions or Nexi.
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In what principle smooth muscle does spontaneous contraction frequently occur?
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Visceral smooth muscle.
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Where is Visceral Smooth muscle often found? 4 places.
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1. Walls of the gastrointestinal system
2. The ureters 3. The uterus 4. Blood vessels. |
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What does Actin not contain in smooth muscle?
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troponin
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what ion activates the contraction process in smooth muscle?
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Ca++
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What provides the energy for contraction in smooth muscle?
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ATP
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Actin filaments are attached to what in smooth muscle? what is this analogous to in skeletal muscle?
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They are attached to DENSE BODIES. In skeletal muscle this would be Z DISCS
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Actin filaments that are attached to dense bodies are located when in the cell? 2 possible places
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1. Bound to the cell membrane
2. Dispersed in the sarcoplasm. |
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Actin filaments overlap myosin filaments located between what?
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DENSE BODIES
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What happens during contraction of smooth muscle? (with regards to actin and myosin?
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myosin heads interact with the actin filaments, causing muscle shortening by the SLIDING FILAMENT MODEL.
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What is the onset (msec) and duration (sec) of smooth muscle contraction?
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onset: 50-100 msec
duration: 1-3 seconds. |
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What is the resting membrane potential of smooth muscle?
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-50 to -60 mV
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What are the two types of action potentials in visceral smooth muscle?
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1. Spike potentials
2. Plateau action potentials. |
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What is the duration of spike potentials? How is it elicited?
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1. Duration: 10- to 50 msec
2. Elicited by neurotransmitters, hormones, stretch, spontaneous depolarization (waves) |
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What is the duration of plateau action potentials? Where does it produce prolonged contraction?
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1. it has a prolonged duration. several hundred milliseconds or more
2. produces prolonged contraction in smooth muscle of the ureters, uterus and blood vessel walls. |
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Action potentials in smooth muscle are due to what?
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Due to the opening of the voltage-gated Ca++ channels or SLOW CHANNELS. in the muscle cell membrane.
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where does the action potential start in smooth muscle?
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Ca++ channels in the MUSCLE CELL MEMBRANE.
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What does the influence of stretch do to visceral smooth muscle?
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Stretch of the visceral smooth muscle can decrease the membrane potential and can cause action potentials to generate spontaneously.
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What is the definition of SLOW WAVES?
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They are rhythmic changes in cell membrane potential.
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Another name for slow waves?
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Pacemaker Waves
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Are slow waves action potentials?
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They are not action potentials, but they can give rise to action potentials.
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Where are slow waves important in the body?
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Important in generative rhythmic contractions of visceral smooth muscle in the gut. (peristalsis)
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How are multiunit smooth muscle depolarized?
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The decrease in a membrane potential in response to a neurotransmitter (acetylcholine, norepinephrine) action on the muscle cell membrane, then the neurotransmitter is released from a nerve ending.
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what is sufficient enough to elicit a contraction in multiunit smooth muscle?
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depolarization is alone sufficient enough to mobilize Ca++ and elicit and contraction. ACTION POTENTIALS ARE TYPICALLY NOT GENERATED.
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What ion is required for Excitation-contration coupling?
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Ca++
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Where does Ca++ enter the muscle cell for contraction of smooth muscle?
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Ca++ enters the cell from the extracellular fluid.
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What is poorly developed in smooth muscle compared to skeletal muscle?
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the sarcoplasmic reticulum.
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Depolarization of smooth muscle does what?
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Opens voltage-gated Ca++ channels in the cell membrane. Calcium diffuses into the cell in response to a change in Concentration and A Voltage change.
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Calcium diffuses into a smooth muscle cell in response to what?
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1. Voltage change
2. change in concentration. |
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Ca++ binds to what protein in the sarcoplasm of the smooth muscle? (what is it analogous to in skeletal muscle)
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Ca++ binds to the protein: CALMODULIN in the sarcoplasm.
Smooth muscle does not contain troponin, which is in skeletal muscle. |
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What does the Calcium-Calmodulin complex do?
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it activates myosin head groups, allowing interaction between myosin and actin fibrils.
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How is Ca++ removed from the sarcoplasm in smooth muscle?
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It is removed from the sarcoplasm during relaxation by Ca++-ATPase on the cell membrane and SR.
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When is Ca++ removed from the sarcoplasm in smooth muscle?
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During relaxation, by Ca++ ATPase pumps on the cell membrane and SR.
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How fast do Ca++-ATPase pumps act on the sarcoplasm in smooth muscle?
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They act slowly compared to those in smooth muscle. Thus contributing to the prolonged contractions typically seen in smooth muscle.
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What is the version of skeletal muscular junctions in smooth muscle?
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Autonomic nerve endings (axon varicosities) lie close to smooth muscle fibers and contain secretory vesicles.
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What are the 2 things that secretory vesicles can contain in smooth muscle? (as the neurotransmitter)
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acetylcholine, or norepinephrine
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What are the 3 unique characteristics that the neurotransmitter in the smooth muscle contain?
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can be:
excitatory inhibitory 2 neurotransmitters can act antagonistically in a particular tissue. |
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Where do receptors lie? regarding the smooth muscle.
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On the smooth muscle cell membrane.
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Neurotransmitter binding to the muscle cell receptors causes what? what is it analogous to in the skeletal muscle cell?
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Neurotransmitter binding to the muscle cell receptor cause a Junctional Potential.
It is analogous to the end plate potential in skeletal muscle. |
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How does depolarization occur in smooth muscle?
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It occurs in response to an inhibitory neurotransmitter.
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Where do local chemical factors affect smooth muscle tone?
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It acts directly on the smooth muscle cells. It affects local interstitial concentrations
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What are the 5 chemical factors that affect smooth muscle tone?(affected by
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1. oxygen
2. carbon dioxide 3. hydrogen ions 4. electrolytes (K+ Ca++) 5. Metabolic end products (lactic acid, adenosine) |
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Control of smooth muscle tone by local factors is particularly important in what 3 things?
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1. Blood vessels
2. metarterioles 3. precapillary sphincters |
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Certain hormones can cause what two things?
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1. smooth muscle contraction
2. smooth muscle relaxation |
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What is the direct action of hormones in smooth muscle tone?
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Hormones bind to a specific ligand-gated receptor on the muscle cell membrane. Ca++ channels open, Ca++ diffuses into the cell (down a change in C) and the muscle cell is depolarized. An action potential does not necessarily occur, the influx of Ca++ triggers contraction.
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What is the indirect action of hormones in smooth muscle tone?
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Indirect action is done via an INTRACELLULAR SECOND MESSENGER.
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What does a second messenger do regarding indirect action of hormone in smooth muscle tone?
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The second messenger hormone binds to a specific receptor on the muscle cell membrane and stimulates the production/release of an intracellular substance (second messenger) that, in turn, causes contraction or relaxation.
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