Podcast
Questions and Answers
Which structural feature is unique to smooth muscle cells, distinguishing them from skeletal and cardiac muscle cells?
Which structural feature is unique to smooth muscle cells, distinguishing them from skeletal and cardiac muscle cells?
- Abundance of actin and myosin
- Presence of gap junctions
- Interconnected network of intermediate filaments
- Absence of sarcomeres and striations (correct)
How is the 'single-unit' organization of smooth muscle cells characterized?
How is the 'single-unit' organization of smooth muscle cells characterized?
- Coordinated contraction achieved through gap junctions (correct)
- Independent contraction of individual cells due to lack of communication
- Reliance on multiple motor neurons for synchronous activation
- Contraction initiated by a single nerve impulse affecting all cells equally
Which mechanism primarily mediates the activation of smooth muscle contraction via metabotropic receptors?
Which mechanism primarily mediates the activation of smooth muscle contraction via metabotropic receptors?
- Direct influx of calcium ions through voltage-gated channels
- Activation of stretch-activated channels leading to membrane depolarization
- Release of intracellular calcium from the sarcoplasmic reticulum via IP3R activation (correct)
- Calcium-induced calcium release through ryanodine receptors
Why does smooth muscle exhibit a significantly longer twitch duration compared to skeletal muscle?
Why does smooth muscle exhibit a significantly longer twitch duration compared to skeletal muscle?
How does the role of calmodulin (CaM) in smooth muscle contraction differ from the role of troponin-C (TnC) in striated muscle contraction?
How does the role of calmodulin (CaM) in smooth muscle contraction differ from the role of troponin-C (TnC) in striated muscle contraction?
What is the functional consequence of myosin light chain (MLC) phosphorylation in smooth muscle contraction?
What is the functional consequence of myosin light chain (MLC) phosphorylation in smooth muscle contraction?
What is the role of dense bodies in smooth muscle cells?
What is the role of dense bodies in smooth muscle cells?
How do autonomic nerves influence smooth muscle contraction?
How do autonomic nerves influence smooth muscle contraction?
What is the primary mechanism for smooth muscle relaxation?
What is the primary mechanism for smooth muscle relaxation?
Which of the following is a common location for smooth muscle tissue?
Which of the following is a common location for smooth muscle tissue?
What is the role of myosin light chain phosphatase in smooth muscle relaxation?
What is the role of myosin light chain phosphatase in smooth muscle relaxation?
What is the role of intermediate filaments in smooth muscle cells?
What is the role of intermediate filaments in smooth muscle cells?
How does calcium influx in smooth muscle cells lead to contraction?
How does calcium influx in smooth muscle cells lead to contraction?
Which type of receptor is responsible for stretch-activated calcium influx in smooth muscle?
Which type of receptor is responsible for stretch-activated calcium influx in smooth muscle?
In the excitation-contraction coupling of smooth muscle cells, how does the role of inositol trisphosphate (IP3) contribute to the process?
In the excitation-contraction coupling of smooth muscle cells, how does the role of inositol trisphosphate (IP3) contribute to the process?
What is the mechanism by which store-operated calcium channels (SOCCs) contribute to sustained smooth muscle contraction?
What is the mechanism by which store-operated calcium channels (SOCCs) contribute to sustained smooth muscle contraction?
How does the arrangement of actin and myosin filaments in smooth muscle contribute to its unique contractile properties?
How does the arrangement of actin and myosin filaments in smooth muscle contribute to its unique contractile properties?
Which mechanism is responsible for desensitization of smooth muscle to calcium ions during prolonged contraction?
Which mechanism is responsible for desensitization of smooth muscle to calcium ions during prolonged contraction?
What structural protein connects dense bodies in smooth muscle cells, thereby coordinating their contractile activity?
What structural protein connects dense bodies in smooth muscle cells, thereby coordinating their contractile activity?
What is the function of caveolae in smooth muscle cells?
What is the function of caveolae in smooth muscle cells?
Which of the following patterns of action potentials is characteristic of smooth muscle?
Which of the following patterns of action potentials is characteristic of smooth muscle?
What is the role of the Na+/Ca2+ exchanger in smooth muscle relaxation?
What is the role of the Na+/Ca2+ exchanger in smooth muscle relaxation?
Following calcium influx, what is the first direct step in the process of smooth muscle contraction?
Following calcium influx, what is the first direct step in the process of smooth muscle contraction?
How does smooth muscle contraction affect the pupil?
How does smooth muscle contraction affect the pupil?
How does smooth muscle contraction affect the uterus?
How does smooth muscle contraction affect the uterus?
How effective is the bladder without smooth muscle?
How effective is the bladder without smooth muscle?
What is the function of the actin and myosin motor proteins?
What is the function of the actin and myosin motor proteins?
What happens when an individual multi-unit smooth muscle cell contracts?
What happens when an individual multi-unit smooth muscle cell contracts?
Flashcards
Smooth Muscle Appearance
Smooth Muscle Appearance
Smooth muscle lacks sarcomeres, resulting in a non-striated appearance under a microscope.
Single-Unit Smooth Muscle
Single-Unit Smooth Muscle
Groups of smooth muscle cells contract as one unit due to gap junctions, creating wave-like movements.
Multi-Unit Smooth Muscle
Multi-Unit Smooth Muscle
Individual smooth muscle cells contract independently.
Dense Bodies
Dense Bodies
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Common Activation Pathway
Common Activation Pathway
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Activation of Ionotropic Receptors
Activation of Ionotropic Receptors
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Stretch-Activated Ca2+ Channels
Stretch-Activated Ca2+ Channels
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Metabotropic Receptor Activation
Metabotropic Receptor Activation
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Calmodulin (CaM)
Calmodulin (CaM)
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MLCK Activation
MLCK Activation
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Myosin Light Chain Phosphorylation
Myosin Light Chain Phosphorylation
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Myosin Light Chain Dephosphorylation
Myosin Light Chain Dephosphorylation
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Smooth Muscle Twitch Duration
Smooth Muscle Twitch Duration
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Study Notes
Smooth Muscle Overview
- Smooth muscle cells are functionally diverse, found in organs like the gastrointestinal tract, lungs, urinary bladder, uterus, arterioles, and eyes.
- Their name reflects the lack of sarcomeres, resulting in a smooth appearance without microscopic striations.
Structure and Organization
- Smooth muscle lacks sarcomeres, hence no striation pattern.
- Motor proteins are actin and myosin II.
- Single-unit smooth muscle: Achieved by gap junctions to connect neighboring cells, and contractions spread through a network, creating wave-like contractions.
- Multi-unit smooth muscle: Individual cells contract independently.
- Synchronous contractions can occur via autonomic nerve coordination, which releases neurotransmitters like acetylcholine and noradrenaline.
Contraction
- Actin attaches to dense bodies, protein assemblies corresponding to the Z-disk, are connected via intermediate filaments (e.g., vimentin).
- Motor proteins contract towards the dense bodies, leading to a ball shape.
Excitation-Contraction Coupling
- A common pathway involves increasing cytosolic Ca2+ concentration through ionotropic receptors, stretch-activated channels, metabotropic receptors (e.g., muscarinic ACh receptors), and intracellular Ca2+ release from the sarcoplasmic reticulum via IP3R.
- Calcium-induced calcium release provides positive feedback on RyR Ca2+ channels.
Action Potentials
- Smooth muscle exhibits variety of AP patterns with contraction patterns dependent on the input.
Excitation Until Contraction
- Myosin light-chain kinase (MLCK) bound with Ca2+ allows CaM to becomes active.
- Active MLCK hydrolyzes ATP and activates smooth muscle myosin
- Calcium ions bind to calmodulin (CaM).
- CaM responds to a rising [Ca], similar to troponin-C (TnC) in striated muscle.
- The Ca2+-CaM complex activates myosin light chain kinase (MLCK).
- MLCK phosphorylates the myosin light chain through covalent modification.
- Unphosphorylated myosin light chain (MLC) has low ATPase activity, while phosphorylated MLC has high ATPase activity.
- Phosphorylated myosin hydrolyzes ATP for power strokes along actin filaments.
- As actin and myosin run along variable directions, the cell contracts concentrically.
Relaxation
- Ca ATPases pump Ca2+ back, either via the plasma membrane into ECF or via SERCA back into the SR.
- Na/Ca exchanger
- Myosin light chain phosphatase dephosphorylates and inactivates myosin.
- CaM-Ca dissociates
Twitch Duration
- Smooth muscles have the longest twitch duration.
- Myosin light chain (de-)phosphorylation is slower than non-covalent Pi binding.
- Skeletal: ~20 - 200 ms
- Cardiac: ~200 - 400 ms
- Smooth: < 1s - hours
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