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What is one of the functions of smooth muscle related to the urinary system?
Which property differentiates smooth muscle from skeletal muscle regarding energy consumption?
What is the structural characteristic of the nucleus in smooth muscle cells?
Which of the following is NOT a property of smooth muscle?
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Which function relates to the smooth muscle's role in the respiratory system?
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What anatomical feature of smooth muscle allows for precise control of small structures like blood vessels?
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What is the simplest arrangement of smooth muscle found in the body?
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What is a common misconception about the neuromuscular junction in smooth muscle?
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What triggers contraction in muscle fibers?
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Which type of muscle is more energy-efficient during contraction?
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How do smooth muscle contractions typically compare to skeletal muscle contractions in terms of fatigue resistance?
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What regulates the contraction of smooth muscle?
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What type of contraction is characterized by maintaining tension over time?
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What is the resting membrane potential in smooth muscle capable of?
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Which statement about fatigue resistance is true for smooth muscle?
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How do cells communicate in single-unit smooth muscle?
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What determines whether smooth muscle is inhibited or excited?
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Which other stimuli apart from nerve stimulation can cause contraction in smooth muscle?
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What additional factor supports the storage function of calcium in smooth muscle aside from sarcoplasmic reticulum?
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What occurs when gated Ca2+ channels in caveolae open?
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What is a significant difference between smooth muscle and skeletal muscle in terms of control?
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What is the main effect of the neurotransmitters acetylcholine and norepinephrine on smooth muscle?
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How do chemical factors typically influence the function of smooth muscle cells?
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What characterizes the innervation of most smooth muscles?
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What is the typical resting membrane potential of most smooth muscles?
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Which type of action potential occurs in unitary smooth muscle?
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What largely determines the membrane potential in smooth muscle?
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Which of the following can elicit typical spike action potentials in smooth muscle?
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How long does a typical spike action potential last in smooth muscle?
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What characterizes the action potentials with plateau in smooth muscle?
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What is the primary reason for the less negative resting potential in smooth muscle compared to other muscle types?
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What effect does a lack of oxygen in local tissues have on smooth muscle?
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In which type of smooth muscle is the action potential with plateau particularly significant?
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Which of the following is a characteristic of smooth muscle contraction compared to skeletal muscle contraction?
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Which of the following local tissue factors can cause vasodilatation?
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Which hormone is NOT associated with smooth muscle contraction?
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What is the primary source of calcium for skeletal muscle contractions?
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What binds calcium to initiate contraction in smooth muscle?
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Which statement best describes the contraction speed of smooth muscle?
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Which factor does NOT contribute to smooth muscle contraction?
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Study Notes
Smooth Muscle Physiology
- Smooth muscle is a major component of hollow organs, including the gastrointestinal canal, respiratory airways, urogenital tract, and vasculature.
- Its functions include peristalsis, vasoconstriction, and controlling the activity of various organs and systems.
Smooth Muscle Properties
- Smooth muscle has a high metabolic economy, allowing it to sustain contractions for extended periods with minimal energy expenditure.
- Its small cell size enables precise control of tiny structures, like blood vessels.
- Smooth muscle is arranged circularly in structures like blood vessels, airways, and sphincters, allowing constriction through fiber shortening.
- It lacks a developed sarcoplasmic reticulum (SR), instead relying on a primitive SR and caveolae for calcium storage.
- It contains thin and thick filaments, but lacks a specific sarcomere structure.
- Smooth muscle cells possess a centrally located nucleus.
- It lacks T-tubules (transverse tubules).
- It does not contain the troponin complex.
- It lacks a defined neuromuscular junction.
- Smooth muscle cells typically measure 1 to 5 micrometers (µm) in diameter and 20 to 500 micrometers in length.
Smooth Muscle Contraction
- Many of the contraction principles of skeletal muscle apply to smooth muscle.
- The type of receptor dictates whether smooth muscle is inhibited or excited, determining the effectiveness of neurotransmitters like acetylcholine and norepinephrine.
Smooth Muscle Regulation
- Smooth muscle is subject to more complex controls than skeletal muscle, responding to nerve stimulation, hormonal and pharmacological stimuli, metabolites, cold, pressure, stretch, touch, and spontaneous activity.
- Most smooth muscle receives innervation from both divisions of the autonomic nervous system.
- Autonomic nerve axons traverse the tissue, containing swellings or varicosities that release transmitter substances in response to nerve impulses.
- Released excitatory or inhibitory transmitter molecules diffuse from the nerve to surrounding smooth muscle cells, triggering their effects.
Calcium Ion Sources in Smooth Muscle
- Smooth muscle has a limited sarcoplasmic reticulum (SR), relying on caveolae for calcium storage.
- Caveolae membranes contain gated Ca2+ channels that open in response to changes in membrane potential or ligand binding.
- When the channels open, Ca2+ concentrated inside the caveolae enters the cell.
- In smooth muscle, Ca2+ enters from the extracellular fluid in addition to being released from the SR.
Activation of Smooth Muscle Contraction
- Chemical factors regulate smooth muscle cell function
- Some factors act by opening or closing cell membrane ion channels, while others trigger the production of second messengers that diffuse to the cell's interior, causing further changes.
- Both mechanisms usually result in a change in intracellular Ca concentration, ultimately controlling the contractile process.
Membrane Potentials and Action Potentials in Smooth Muscle
- The membrane potential of smooth muscle varies depending on the muscle's momentary condition.
- In a resting state, the intracellular potential is typically -50 to -60 millivolts, less negative than skeletal muscle.
Action Potentials in Unitary Smooth Muscle
- Unitary smooth muscle (visceral muscle) generates action potentials in the same way as skeletal muscle.
- Action potentials in smooth muscle occur in two forms: spike potentials or action potentials with plateaus.
Typical Spike Action Potentials
- Similar to those seen in skeletal muscle, these action potentials last 10 to 50 milliseconds.
- They can be elicited by electrical stimulation, hormones, neurotransmitters, stretch, or spontaneous generation within the muscle fiber.
Action Potentials with Plateaus
- The onset of this action potential resembles that of the typical spike potential.
- However, repolarization is delayed for hundreds or thousands of milliseconds.
- The plateau prolongs contraction in smooth muscle types like the ureter, uterus, and certain vascular smooth muscles.
Calcium Dynamics in Smooth Muscle
- Calcium concentration is crucial for smooth muscle contraction, but it enters from both the extracellular fluid and the sarcoplasmic reticulum.
Relaxation of Smooth Muscle
- Smooth muscle relaxation occurs when the intracellular calcium concentration decreases.
- This can be achieved through calcium reuptake into the SR and the extracellular space.
- Additionally, the activity of enzymes like myosin light chain phosphatase (MLCP) reduces the phosphorylation of myosin, leading to muscle relaxation.
Smooth Muscle Contraction Without Action Potentials
- Local tissue factors and hormones often induce smooth muscle contraction without action potentials.
- Lack of oxygen, excess carbon dioxide, increased hydrogen ion concentration, adenosine, lactic acid, increased potassium ions, decreased calcium ion concentration, and increased body temperature can all affect local vasodilatation.
Hormonal Effects on Smooth Muscle
- Many circulating hormones and neurotransmitters influence smooth muscle contraction:
- Norepinephrine
- Epinephrine
- Acetylcholine
- Angiotensin
- Endothelin
- Vasopressin
- Oxytocin
- Serotonin
- Histamine
Comparison of Smooth Muscle and Skeletal Muscle
| Feature | Smooth Muscle | Skeletal Muscle |
|---|---|---|
| Cell Structure | Small, spindle-shaped cells, no striations | Large, cylindrical, multinucleated cells, striated |
| Control | Involuntary, controlled by the autonomic nervous system, hormones, and local factors | Voluntary, controlled by the somatic nervous system |
| Speed of Contraction | Slow and sustained contractions. Can hold contractions for long periods | Fast contractions designed for rapid, short bursts of activity (e.g., movement of limbs). |
| Calcium Source | Calcium comes from both the extracellular fluid and the sarcoplasmic reticulum (SR) | Calcium is primarily released from the sarcoplasmic reticulum (SR) |
| Calcium-Binding Protein | Calmodulin binds calcium and activates myosin light chain kinase (MLCK), initiating contraction | Troponin binds calcium, causing a conformational change in tropomyosin that allows actin-myosin interaction |
| Initiation of Contraction | Contraction can be triggered by mechanical stretch, electrical signals, or chemical signals (e.g., hormones, neurotransmitters) | Contraction is triggered by an action potential from motor neurons leading to depolarization of the muscle fiber membrane |
| Energy Efficiency | Highly energy-efficient. Can maintain force with low ATP consumption, especially in the "latch state." | Less energy-efficient compared to smooth muscle, requires continuous ATP during contraction |
| Contraction Duration | Can maintain contraction for long periods without fatigue (e.g., bladder, blood vessels) | Contracts quickly but fatigues easily with prolonged activity |
| Regulation of Contraction | Regulated by phosphorylation of myosin light chains through MLCK and MLCP | Regulated by the interaction between actin and myosin, initiated by the removal of tropomyosin inhibition |
| Force Production | Produces less force than skeletal muscle but sustains force for longer periods | Produces high force in short bursts for rapid and strong movements |
| Resting Membrane Potential | More variable; slow wave potentials or depolarization can initiate contraction without a defined action potential | A stable resting membrane potential, action potentials are required for contraction |
| Types of Contraction | Typically tonic (maintaining tension over time) or phasic (rhythmic contractions) | Phasic, meaning it contracts quickly and then relaxes (e.g., twitch contraction) |
| Cell Communication | Cells are connected by gap junctions in single-unit smooth muscle, allowing synchronized contractions | Each muscle fiber is controlled individually by its own motor neuron (no gap junctions) |
| Fatigue Resistance | Extremely fatigue-resistant, can maintain contractions for long periods | Fatigues faster during extended periods of activity, though training can improve endurance |
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Description
Explore the fascinating world of smooth muscle physiology. This quiz covers its role in hollow organs, unique properties, and functions like peristalsis and vasoconstriction. Test your knowledge on how smooth muscle contributes to various bodily systems.
