Podcast
Questions and Answers
What mechanism does calcium play in smooth muscle contraction?
What mechanism does calcium play in smooth muscle contraction?
- Calcium ions are stored in the extracellular matrix before use.
- Calcium acts as a secondary messenger that inhibits contraction.
- Calcium released from the sarcoplasmic reticulum induces contraction. (correct)
- Calcium is entirely responsible for relaxing smooth muscle tissues.
Which of the following factors directly leads to vasodilatation of smooth muscle?
Which of the following factors directly leads to vasodilatation of smooth muscle?
- Excess hydrogen ion concentration. (correct)
- Increased blood pressure around the vessel.
- Increased levels of nitric oxide only.
- Accumulation of oxygen in local tissues.
Which substance is NOT mentioned as causing local vasodilatation?
Which substance is NOT mentioned as causing local vasodilatation?
- Lactic acid
- Increased potassium ions
- Carbon monoxide (correct)
- Adenosine
Which of the following correctly describes the role of cAMP and cGMP in smooth muscle function?
Which of the following correctly describes the role of cAMP and cGMP in smooth muscle function?
What role do hormones play in smooth muscle function according to the information presented?
What role do hormones play in smooth muscle function according to the information presented?
What distinguishes multi-unit smooth muscle fibers from unitary smooth muscle fibers?
What distinguishes multi-unit smooth muscle fibers from unitary smooth muscle fibers?
Which component is absent in smooth muscle that is present in skeletal muscle contributing to contraction regulation?
Which component is absent in smooth muscle that is present in skeletal muscle contributing to contraction regulation?
What is the primary method by which multi-unit smooth muscle fibers are controlled?
What is the primary method by which multi-unit smooth muscle fibers are controlled?
Which statement accurately describes the mechanism of contraction in smooth muscle?
Which statement accurately describes the mechanism of contraction in smooth muscle?
What role does ATP play during the contraction of smooth muscle?
What role does ATP play during the contraction of smooth muscle?
Which type of smooth muscle typically exhibits control largely from non-nervous stimuli?
Which type of smooth muscle typically exhibits control largely from non-nervous stimuli?
What is a unique structural feature of multi-unit smooth muscle fibers?
What is a unique structural feature of multi-unit smooth muscle fibers?
What is the approximate threshold for eliciting action potentials in most visceral smooth muscle?
What is the approximate threshold for eliciting action potentials in most visceral smooth muscle?
Which type of muscle has a prolonged period of contraction linked to specific action potentials?
Which type of muscle has a prolonged period of contraction linked to specific action potentials?
What role do calcium ions play in the action potential generation of smooth muscle?
What role do calcium ions play in the action potential generation of smooth muscle?
What initiates spontaneous action potentials in visceral smooth muscle?
What initiates spontaneous action potentials in visceral smooth muscle?
Which of the following statements regarding slow waves is correct?
Which of the following statements regarding slow waves is correct?
Why is there less participation of sodium in the action potential generation of smooth muscle?
Why is there less participation of sodium in the action potential generation of smooth muscle?
What distinguishes calcium channels from sodium channels in smooth muscle fibers?
What distinguishes calcium channels from sodium channels in smooth muscle fibers?
What effect does the plateau phase have on the muscle contraction of visceral smooth muscle?
What effect does the plateau phase have on the muscle contraction of visceral smooth muscle?
What is the consequence of a decrease in overall negativity of the membrane potential in smooth muscle?
What is the consequence of a decrease in overall negativity of the membrane potential in smooth muscle?
In smooth muscle, what is primarily responsible for initiating contractions in multi-unit smooth muscle?
In smooth muscle, what is primarily responsible for initiating contractions in multi-unit smooth muscle?
Which type of muscle is primarily influenced by the flow of calcium ions for action potential generation?
Which type of muscle is primarily influenced by the flow of calcium ions for action potential generation?
What is a defining characteristic of slow waves in visceral smooth muscle?
What is a defining characteristic of slow waves in visceral smooth muscle?
Which component is NOT involved in the contraction of multi-unit smooth muscle?
Which component is NOT involved in the contraction of multi-unit smooth muscle?
How long can the delay in repolarization of a muscle fiber membrane last?
How long can the delay in repolarization of a muscle fiber membrane last?
How many smooth muscle fibers must depolarize to generate a self-propagating action potential in visceral unitary smooth muscle?
How many smooth muscle fibers must depolarize to generate a self-propagating action potential in visceral unitary smooth muscle?
What role do calcium ions play during the action potential of smooth muscle fibers?
What role do calcium ions play during the action potential of smooth muscle fibers?
What is the main reason why action potentials do not typically develop in multi-unit smooth muscles?
What is the main reason why action potentials do not typically develop in multi-unit smooth muscles?
Which statement about smooth muscle contractions is correct?
Which statement about smooth muscle contractions is correct?
What triggers the rhythmic contractions in the gut's smooth muscle fibers?
What triggers the rhythmic contractions in the gut's smooth muscle fibers?
What determines the static force of contraction in smooth muscle cells?
What determines the static force of contraction in smooth muscle cells?
Which process directly leads to relaxation of smooth muscle?
Which process directly leads to relaxation of smooth muscle?
Which statement correctly describes the role of calmodulin in smooth muscle contraction?
Which statement correctly describes the role of calmodulin in smooth muscle contraction?
Why does smooth muscle use little energy during contraction?
Why does smooth muscle use little energy during contraction?
What primarily differentiates the types of signals that stimulate smooth muscle contraction from those of skeletal muscle?
What primarily differentiates the types of signals that stimulate smooth muscle contraction from those of skeletal muscle?
What is an effect of decreased intracellular Ca++ concentration in smooth muscle?
What is an effect of decreased intracellular Ca++ concentration in smooth muscle?
Which element of smooth muscle contraction involves the transformation of ATP during the contraction process?
Which element of smooth muscle contraction involves the transformation of ATP during the contraction process?
How do different receptor proteins affect smooth muscle contraction?
How do different receptor proteins affect smooth muscle contraction?
What mechanism maintains tension in smooth muscle while minimizing energy usage?
What mechanism maintains tension in smooth muscle while minimizing energy usage?
Which hormone is known to inhibit contraction in the smooth muscle of the intestine?
Which hormone is known to inhibit contraction in the smooth muscle of the intestine?
What primarily triggers the entry of calcium ions into smooth muscle cells during contraction?
What primarily triggers the entry of calcium ions into smooth muscle cells during contraction?
What is the main difference in the source of calcium ions between smooth muscle and skeletal muscle?
What is the main difference in the source of calcium ions between smooth muscle and skeletal muscle?
What type of muscle contraction occurs when the membrane of smooth muscle cells depolarizes without generating action potentials?
What type of muscle contraction occurs when the membrane of smooth muscle cells depolarizes without generating action potentials?
Which of the following hormones is least likely to be involved in the contraction of smooth muscle?
Which of the following hormones is least likely to be involved in the contraction of smooth muscle?
What is the primary physiological benefit of smooth muscle's low energy requirement for sustained contraction?
What is the primary physiological benefit of smooth muscle's low energy requirement for sustained contraction?
In what manner does smooth muscle react to a sudden decrease in fluid volume?
In what manner does smooth muscle react to a sudden decrease in fluid volume?
How does the contraction time of smooth muscle compare to that of skeletal muscle?
How does the contraction time of smooth muscle compare to that of skeletal muscle?
What phenomenon allows smooth muscle to maintain similar pressure despite varying changes in volume?
What phenomenon allows smooth muscle to maintain similar pressure despite varying changes in volume?
Which aspect of calcium's role is crucial in initiating smooth muscle contraction?
Which aspect of calcium's role is crucial in initiating smooth muscle contraction?
What is the role of ATP in the contraction process of smooth muscle?
What is the role of ATP in the contraction process of smooth muscle?
What is the total contraction time of smooth muscle when excited?
What is the total contraction time of smooth muscle when excited?
What is the primary ionic mechanism responsible for generating action potentials in most smooth muscle fibers?
What is the primary ionic mechanism responsible for generating action potentials in most smooth muscle fibers?
What is the role of the plateau phase in the action potential of smooth muscle?
What is the role of the plateau phase in the action potential of smooth muscle?
How does the intrinsic stretch of visceral smooth muscle contribute to action potential generation?
How does the intrinsic stretch of visceral smooth muscle contribute to action potential generation?
Why does visceral smooth muscle generate action potentials differently than skeletal muscle?
Why does visceral smooth muscle generate action potentials differently than skeletal muscle?
What characterizes the 'slow waves' in visceral smooth muscle?
What characterizes the 'slow waves' in visceral smooth muscle?
What does the phosphorylation of the regulatory chain in myosin heads influence during muscle contraction?
What does the phosphorylation of the regulatory chain in myosin heads influence during muscle contraction?
What is the approximate threshold value that must be reached for action potentials to be elicited in smooth muscle?
What is the approximate threshold value that must be reached for action potentials to be elicited in smooth muscle?
What effect does stretching of visceral smooth muscle have on the overall membrane potential?
What effect does stretching of visceral smooth muscle have on the overall membrane potential?
What characterizes the latch mechanism in muscle contraction?
What characterizes the latch mechanism in muscle contraction?
Which type of muscle displays prolonged periods of contraction due to specific action potentials?
Which type of muscle displays prolonged periods of contraction due to specific action potentials?
How does the activation of myosin phosphatase affect muscle contraction?
How does the activation of myosin phosphatase affect muscle contraction?
Which of the following best describes the role of calcium channels in smooth muscle fiber membranes?
Which of the following best describes the role of calcium channels in smooth muscle fiber membranes?
What is the result of a decrease in the activity of myosin kinase and myosin phosphatase enzymes?
What is the result of a decrease in the activity of myosin kinase and myosin phosphatase enzymes?
What is the potential action resulting from the opening of potassium channels in smooth muscle cells?
What is the potential action resulting from the opening of potassium channels in smooth muscle cells?
Which statement best describes the energy consumption during sustained smooth muscle contraction?
Which statement best describes the energy consumption during sustained smooth muscle contraction?
What is the consequence of the action potentials that occur at each peak of the slow wave in smooth muscle?
What is the consequence of the action potentials that occur at each peak of the slow wave in smooth muscle?
What occurs as myosin kinase activity declines in muscle contraction?
What occurs as myosin kinase activity declines in muscle contraction?
What is a possible cause for the slow wave rhythm observed in smooth muscle contraction?
What is a possible cause for the slow wave rhythm observed in smooth muscle contraction?
Which factor primarily characterizes the response of smooth muscle to calcium levels during contraction?
Which factor primarily characterizes the response of smooth muscle to calcium levels during contraction?
What effect do local tissue chemical factors have on smooth muscle contraction?
What effect do local tissue chemical factors have on smooth muscle contraction?
How do certain hormones affect smooth muscle contraction in the absence of altered membrane potential?
How do certain hormones affect smooth muscle contraction in the absence of altered membrane potential?
During the latch mechanism, how does muscle maintain contraction despite reduced excitation?
During the latch mechanism, how does muscle maintain contraction despite reduced excitation?
What condition occurs within smooth muscle cells when there is an increase in negativity inside the cell?
What condition occurs within smooth muscle cells when there is an increase in negativity inside the cell?
What happens to muscle contraction when high levels of calmodulin-calcium complex are present?
What happens to muscle contraction when high levels of calmodulin-calcium complex are present?
What is implied about half of all smooth muscle contractions based on the content?
What is implied about half of all smooth muscle contractions based on the content?
What process occurs if inhibitory factors influence smooth muscle by closing ion channels?
What process occurs if inhibitory factors influence smooth muscle by closing ion channels?
In a situation where there is no nervous supply, how can smooth muscle still function effectively?
In a situation where there is no nervous supply, how can smooth muscle still function effectively?
Which mechanism is primarily responsible for muscle contraction in smooth muscle without nerve stimulation?
Which mechanism is primarily responsible for muscle contraction in smooth muscle without nerve stimulation?
What distinguishes smooth muscle from other muscle types in terms of contraction triggers?
What distinguishes smooth muscle from other muscle types in terms of contraction triggers?
What distinguishes unitary smooth muscle from skeletal muscle in terms of its structural arrangement?
What distinguishes unitary smooth muscle from skeletal muscle in terms of its structural arrangement?
How does the diameter of smooth muscle fibers generally compare to that of skeletal muscle fibers?
How does the diameter of smooth muscle fibers generally compare to that of skeletal muscle fibers?
What is the primary advantage of smooth muscle contracting as a single mass?
What is the primary advantage of smooth muscle contracting as a single mass?
What mechanism primarily governs the contraction of smooth muscle fibers despite their smaller size?
What mechanism primarily governs the contraction of smooth muscle fibers despite their smaller size?
What is the significance of multi-point adhesion in cell membranes of smooth muscle fibers?
What is the significance of multi-point adhesion in cell membranes of smooth muscle fibers?
What structural feature defines the fibers of unitary smooth muscle?
What structural feature defines the fibers of unitary smooth muscle?
In what way does the size of smooth muscle fibers impact their physiological function?
In what way does the size of smooth muscle fibers impact their physiological function?
What specific type of muscle exhibits a plateau phase during its action potential leading to prolonged contraction?
What specific type of muscle exhibits a plateau phase during its action potential leading to prolonged contraction?
Which of the following correctly describes the effect of stretching on visceral smooth muscle contraction?
Which of the following correctly describes the effect of stretching on visceral smooth muscle contraction?
Which ion is primarily responsible for generating action potentials in most types of smooth muscle?
Which ion is primarily responsible for generating action potentials in most types of smooth muscle?
What characteristic distinguishes pacemaker waves in smooth muscle from typical action potentials?
What characteristic distinguishes pacemaker waves in smooth muscle from typical action potentials?
What primarily limits the contribution of sodium channels in generating action potentials in smooth muscle?
What primarily limits the contribution of sodium channels in generating action potentials in smooth muscle?
What primarily contributes to the slow cycling of myosin cross-bridges in smooth muscle compared to skeletal muscle?
What primarily contributes to the slow cycling of myosin cross-bridges in smooth muscle compared to skeletal muscle?
How does the latch mechanism benefit smooth muscle contraction?
How does the latch mechanism benefit smooth muscle contraction?
In smooth muscle, what is typically observed regarding the attachment time of cross-bridges compared to skeletal muscle?
In smooth muscle, what is typically observed regarding the attachment time of cross-bridges compared to skeletal muscle?
What is a significant characteristic of stress-relaxation in smooth muscle?
What is a significant characteristic of stress-relaxation in smooth muscle?
What is the relationship between energy use and force maintenance in smooth muscle?
What is the relationship between energy use and force maintenance in smooth muscle?
How does the structure of myosin in smooth muscle differ from that in skeletal muscle?
How does the structure of myosin in smooth muscle differ from that in skeletal muscle?
What factor primarily influences the rate of cross-bridge cycling in smooth muscle?
What factor primarily influences the rate of cross-bridge cycling in smooth muscle?
What is a consequence of the reduced ATPase activity in smooth muscle's myosin cross-bridges?
What is a consequence of the reduced ATPase activity in smooth muscle's myosin cross-bridges?
Which of the following statements accurately describes the contractions of smooth muscle?
Which of the following statements accurately describes the contractions of smooth muscle?
How does the force of contraction in smooth muscle change following elongation or shortening?
How does the force of contraction in smooth muscle change following elongation or shortening?
Which of the following accurately describes the structural arrangement of unitary smooth muscle fibers?
Which of the following accurately describes the structural arrangement of unitary smooth muscle fibers?
What characteristic differentiates multi-unit smooth muscle from unitary smooth muscle?
What characteristic differentiates multi-unit smooth muscle from unitary smooth muscle?
Which of the following locations is NOT typically associated with visceral smooth muscle?
Which of the following locations is NOT typically associated with visceral smooth muscle?
How does the response of smooth muscle fibers to stimuli compare to other muscle types?
How does the response of smooth muscle fibers to stimuli compare to other muscle types?
In terms of contraction mechanisms, which statement about smooth muscle is incorrect?
In terms of contraction mechanisms, which statement about smooth muscle is incorrect?
What is a unique feature of the smooth muscle found in the walls of most visceral organs?
What is a unique feature of the smooth muscle found in the walls of most visceral organs?
Which statement best describes the role of gap junctions in smooth muscle contractions?
Which statement best describes the role of gap junctions in smooth muscle contractions?
What is a defining characteristic of visceral smooth muscle when compared to skeletal muscle?
What is a defining characteristic of visceral smooth muscle when compared to skeletal muscle?
Which factor influences the physical dimensions of smooth muscle tissue?
Which factor influences the physical dimensions of smooth muscle tissue?
How long does it typically take for a smooth muscle tissue to reach full contraction after stimulation?
How long does it typically take for a smooth muscle tissue to reach full contraction after stimulation?
What is the energy efficiency comparison between smooth muscle and skeletal muscle during sustained contraction?
What is the energy efficiency comparison between smooth muscle and skeletal muscle during sustained contraction?
What occurs during reverse stress-relaxation in smooth muscle?
What occurs during reverse stress-relaxation in smooth muscle?
What is the typical contraction time for an average skeletal muscle fiber compared to smooth muscle?
What is the typical contraction time for an average skeletal muscle fiber compared to smooth muscle?
What is the primary regulatory factor for smooth muscle contraction?
What is the primary regulatory factor for smooth muscle contraction?
What happens to pressure in the urinary bladder when fluid volume increases suddenly?
What happens to pressure in the urinary bladder when fluid volume increases suddenly?
Which of the following best describes the energy requirement for sustained contraction in smooth muscle?
Which of the following best describes the energy requirement for sustained contraction in smooth muscle?
What effect does continued stretching of the bladder wall have on pressure over time?
What effect does continued stretching of the bladder wall have on pressure over time?
What is the significance of the slow cycling of cross-bridges in smooth muscle contraction?
What is the significance of the slow cycling of cross-bridges in smooth muscle contraction?
Flashcards
Smooth Muscle Fibers
Smooth Muscle Fibers
Muscle cells that lack the organized striations of skeletal muscle, contracting in a different way.
Multi-unit Smooth Muscle
Multi-unit Smooth Muscle
Smooth muscle fibers that contract independently of each other, primarily controlled by nerve signals.
Unitary Smooth Muscle
Unitary Smooth Muscle
Smooth muscle fibers that contract as a coordinated unit, influenced by non-nervous stimuli.
Actin and Myosin Filaments
Actin and Myosin Filaments
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Troponin Complex
Troponin Complex
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Calcium Ions
Calcium Ions
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ATP (Adenosine Triphosphate)
ATP (Adenosine Triphosphate)
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Smooth Muscle Contraction
Smooth Muscle Contraction
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Smooth Muscle Relaxation
Smooth Muscle Relaxation
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Myosin Light Chain Kinase (MLCK)
Myosin Light Chain Kinase (MLCK)
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Myosin Light Chain (MLC)
Myosin Light Chain (MLC)
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Calcium Ions (Ca++)
Calcium Ions (Ca++)
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Calmodulin
Calmodulin
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Phosphorylation
Phosphorylation
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Myosin Phosphatase
Myosin Phosphatase
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Nervous and Hormonal Control of Smooth Muscle
Nervous and Hormonal Control of Smooth Muscle
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Smooth Muscle Action Potential
Smooth Muscle Action Potential
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Slow Wave Potential
Slow Wave Potential
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Plateau Phase of Smooth Muscle
Plateau Phase of Smooth Muscle
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Calcium Channels in Smooth Muscle
Calcium Channels in Smooth Muscle
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Sodium Channels in Smooth Muscle
Sodium Channels in Smooth Muscle
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Action Potential Threshold in Smooth Muscle
Action Potential Threshold in Smooth Muscle
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Visceral Smooth Muscle
Visceral Smooth Muscle
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Stretch-induced Action Potential
Stretch-induced Action Potential
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Pacemaker Waves
Pacemaker Waves
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Prolonged Contraction
Prolonged Contraction
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Calcium Channels
Calcium Channels
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Plateau Action Potentials
Plateau Action Potentials
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Action Potential
Action Potential
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Depolarization
Depolarization
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Peristaltic Waves
Peristaltic Waves
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Local Feedback Control
Local Feedback Control
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Vasodilation
Vasodilation
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Second Messengers
Second Messengers
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How Does Calcium Affect Smooth Muscle?
How Does Calcium Affect Smooth Muscle?
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Hormones and Smooth Muscle
Hormones and Smooth Muscle
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Smooth Muscle Excitation
Smooth Muscle Excitation
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Smooth Muscle Inhibition
Smooth Muscle Inhibition
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Calcium Source for Smooth Muscle
Calcium Source for Smooth Muscle
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Hormone Receptors
Hormone Receptors
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Stress-Relaxation
Stress-Relaxation
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Reverse Stress-Relaxation
Reverse Stress-Relaxation
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Energy Usage
Energy Usage
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Slow Contraction?
Slow Contraction?
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Calcium's Role
Calcium's Role
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Smooth Muscle's Energy Saver
Smooth Muscle's Energy Saver
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Why is smooth muscle important?
Why is smooth muscle important?
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Plateau Phase
Plateau Phase
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Latch Mechanism
Latch Mechanism
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How does Calcium activate smooth muscle?
How does Calcium activate smooth muscle?
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What happens when Calcium levels decrease?
What happens when Calcium levels decrease?
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How does the 'Latch' Mechanism conserve energy?
How does the 'Latch' Mechanism conserve energy?
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How does the velocity of contraction change?
How does the velocity of contraction change?
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Why are smooth muscle cells important?
Why are smooth muscle cells important?
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Slow Wave Rhythm
Slow Wave Rhythm
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Junctional Potential
Junctional Potential
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Electrotonic Spread
Electrotonic Spread
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Smooth Muscle Contraction without Action Potentials
Smooth Muscle Contraction without Action Potentials
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Local Tissue Chemical Factors
Local Tissue Chemical Factors
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Hormonal Control of Smooth Muscle
Hormonal Control of Smooth Muscle
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Hyperpolarization
Hyperpolarization
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Sodium and Calcium Channels
Sodium and Calcium Channels
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Potassium Channels
Potassium Channels
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Membrane Potential
Membrane Potential
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What are the differences between unitary and multi-unit smooth muscle?
What are the differences between unitary and multi-unit smooth muscle?
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How does smooth muscle contraction occur?
How does smooth muscle contraction occur?
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How does smooth muscle relaxation occur?
How does smooth muscle relaxation occur?
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What is the significance of the 'latch' mechanism in smooth muscle?
What is the significance of the 'latch' mechanism in smooth muscle?
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Syncytial Smooth Muscle
Syncytial Smooth Muscle
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Gap Junctions
Gap Junctions
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Plateau Phase (Smooth Muscle)
Plateau Phase (Smooth Muscle)
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Calcium Channels (Smooth Muscle)
Calcium Channels (Smooth Muscle)
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Prolonged Contraction (Smooth Muscle)
Prolonged Contraction (Smooth Muscle)
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Sidepolar Cross-Bridges
Sidepolar Cross-Bridges
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Slow Cycling of Myosin Cross-Bridges
Slow Cycling of Myosin Cross-Bridges
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Stress-Relaxation of Smooth Muscle
Stress-Relaxation of Smooth Muscle
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Why is ATPase Activity Less in Smooth Muscle?
Why is ATPase Activity Less in Smooth Muscle?
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What is the Role of Calcium Ions in Smooth Muscle?
What is the Role of Calcium Ions in Smooth Muscle?
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How Does Smooth Muscle Relax?
How Does Smooth Muscle Relax?
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What is the Importance of the Latch Mechanism?
What is the Importance of the Latch Mechanism?
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How Does Smooth Muscle Contraction Differ from Skeletal Muscle Contraction?
How Does Smooth Muscle Contraction Differ from Skeletal Muscle Contraction?
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How Does the Force of Contraction Change in Smooth Muscle?
How Does the Force of Contraction Change in Smooth Muscle?
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Why is Slow Contraction Important?
Why is Slow Contraction Important?
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Smooth Muscle, Slow and Steady
Smooth Muscle, Slow and Steady
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Smooth Muscle, Calcium's Role
Smooth Muscle, Calcium's Role
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Smooth Muscle, Latch Mechanism
Smooth Muscle, Latch Mechanism
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Smooth Muscle, Calcium Activation
Smooth Muscle, Calcium Activation
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Smooth Muscle, Calcium Decrease and Relaxation
Smooth Muscle, Calcium Decrease and Relaxation
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Smooth Muscle, Energy Conservation
Smooth Muscle, Energy Conservation
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Study Notes
Smooth Muscle Contraction
- Smooth muscle fibers are smaller (1-5 micrometers in diameter, 20-500 micrometers in length) than skeletal muscle fibers
- Contraction mechanisms are similar to skeletal muscle, involving myosin and actin filaments
- Smooth muscle lacks the troponin complex, differing in contraction control mechanisms
- Smooth muscle has various types: multi-unit and unitary (single-unit or syncytial)
Types of Smooth Muscle
- Multi-unit: Discrete, independent fibers, innervated by a single nerve ending, controlled mainly by nerve signals, found in the ciliary muscle of the eye, iris, and piloerector muscles
- Unitary (single-unit or syncytial): Hundreds to thousands of fibers contracting as a unit, fibers arranged in sheets/bundles, connected by gap junctions, regulated by non-nervous stimuli, located in the walls of internal organs (GI tract, ureters, uterus, etc.)
Multi-Unit Smooth Muscle
- Fibers operate independently
- Outer surfaces are covered by a basement membrane-like substance
- Contraction controlled mainly by nerve signals
Unitary Smooth Muscle
- Fibers contract together as a single unit
- Connected by gap junctions for ion flow and coordinated contraction
- Contraction often controlled by non-nervous stimuli (e.g., stretch, hormones)
Physical Basis of Smooth Muscle Contraction
- Actin and myosin filaments arranged differently than in skeletal muscle
- Actin filaments attached to dense bodies which are connected by intercellular bridges
- More actin filaments than myosin filaments (5-10x) in smooth muscle
- Cross-bridges in myosin filaments allow for pulling in opposite directions on actin filaments, allowing smooth muscle to contract more than 80% of its length compared to 30% for skeletal muscle
Comparison of Smooth Muscle and Skeletal Muscle Contraction
- Smooth muscle contraction is prolonged and tonic (hours/days), while skeletal muscle is rapid
- Smooth muscle has slower cycling of myosin cross-bridges
- Lower energy requirement for maintaining similar tension in smooth muscle compared to skeletal muscle (1/10-1/300)
- Slower onset and prolonged contraction in smooth muscle (50-100 ms onset, 1-3 s total) compared to skeletal muscle (fast)
- Maximum force of contraction is often greater in smooth muscle than in skeletal muscle (4-6 kg/cm² vs 3-4 kg/cm²)
- Latch mechanism in smooth muscle allows prolonged contraction with reduced energy expenditure
Slow Cycling of Myosin Cross-Bridges
- Myosin cross-bridges in smooth muscle have lower ATPase activity, leading to slower cycles of attachment and detachment
- Extended attachment leads to higher force of contraction
Regulation of Contraction by Calcium Ions
- Initiated by increased intracellular calcium ions
- Calcium binds to calmodulin, activates myosin kinase, which phosphorylates the myosin head, triggering contraction
- Myosin phosphatase dephosphorylates myosin head, leading to muscle relaxation when calcium levels decrease
Calcium Ions Combine with Calmodulin
- Calcium ions combine with calmodulin
- Calmodulin activates myosin light chain kinase (MLCK)
- MLCK phosphorylates myosin light chains
- Phosphorylated myosin heads interact with actin, causing contraction
Slow Waves in Unitary Smooth Muscle
- Slow waves (rhythmical electrical waves) can spontaneously generate action potentials in some smooth muscle
- Slow wave rhythm is a local property, doesn't spread like action potentials
- Slow waves cause depolarization to threshold, triggering action potentials, which lead to contraction
Nervous and Hormonal Control of Smooth Muscle
- Multiple signals can cause smooth muscle contraction (nervous signals, hormones, stretch, chemical changes)
- Smooth muscle cells have receptor proteins responding to various signals
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Description
Explore the fascinating world of smooth muscle contraction through this quiz. Learn about the differences between multi-unit and unitary smooth muscle, their structures, functions, and mechanisms of contraction. Test your understanding of how these muscle types contribute to bodily functions and their unique characteristics.
