physio lecture 3 Flashcards
(126 cards)
1
Q
What is the basic structural unit of skeletal muscles?
A
The basic structural unit of skeletal muscles is the muscle fiber.
1
Q
What are the two types of myofilaments found in muscle fibers, and what are their functions?
A
Actin and myosin are the two types of myofilaments in muscle fibers. Actin is a thin filament, while myosin is a thick filament. They work together to facilitate muscle contraction.
2
Q
What is the function of the sarcolemma in muscle fibers?
A
The sarcolemma is the cell membrane of skeletal muscle fibers, and it plays a crucial role in storing calcium ions (Ca2+) necessary for muscle contraction.
3
Q
How does the T-tubule system contribute to muscle contraction?
A
T-tubules are invaginations of the sarcolemma that extend deep into the muscle fiber. They allow action potentials to penetrate deep into the muscle fiber, ensuring uniform muscle contraction.
4
Q
What is the significance of the triad in muscle fibers?
A
The triad consists of two sarcoplasmic reticulum structures and a T-tubule. It helps store and release calcium ions (Ca2+), which are essential for muscle contraction.
5
Q
How does the sarcoplasmic reticulum contribute to muscle contraction?
A
The sarcoplasmic reticulum stores calcium ions (Ca2+) needed for muscle contraction. When stimulated, it releases Ca2+ into the muscle fiber, initiating the contraction process.
6
Q
What type of nerve fiber connects to the middle of a muscle fiber to transmit signals?
A
Aα motor neurons connect to the middle of a muscle fiber to transmit signals.
7
Q
What is the point where the nerve and muscle meet called?
A
The point where the nerve and muscle meet is known as the neuromuscular junction.
8
Q
How do individual muscle fibers receive signals from motor neurons?
A
Each individual muscle fiber receives signals from only one branch of the motor neuron.
9
Q
Can one motor neuron control multiple muscle fibers?
A
Yes, one motor neuron can connect to and control many muscle fibers.
10
Q
What is a motor unit, and how does it function?
A
A motor unit consists of one motor neuron and all the muscle fibers it controls. This team works together to make the muscle contract.
11
Q
What are the primary functions of skeletal muscles?
A
The primary functions of skeletal muscles include enabling movement, maintaining posture, providing sensory feedback, generating heat, offering protection, assisting in venous return, and serving specific roles in bodily functions based on their location.
12
Q
How do skeletal muscles contribute to movement and posture control?
A
Skeletal muscles, connected to bones, contract and change the shape of bones to create motion. They also play a role in maintaining posture by counteracting the pull of gravity on bones.
13
Q
What is the role of skeletal muscle receptors in the central nervous system?
A
Skeletal muscles have receptors that provide sensory information to the central nervous system (CNS) about muscle length and tension. This feedback helps the body understand the position of body parts.
14
Q
How do skeletal muscles contribute to heat production in the body?
A
Muscle contractions generate heat as a byproduct of energy use. When the body is cold, muscles may contract involuntarily (shiver) to produce more heat and maintain body temperature.
15
Q
In what ways do skeletal muscles offer protection to the body?
A
Skeletal muscles act as a layer of defense against external mechanical damage in areas where bones don’t provide adequate protection. They can also help prevent dislocations and fractures by increasing muscle tone when excessive force is applied to an extremity.
16
Q
How do skeletal muscles assist in venous return, and when is this particularly important?
A
Skeletal muscles assist in the return of blood to the heart, especially in areas below the heart’s level. This helps prevent blood from flowing in the wrong direction in veins, particularly when standing or sitting for extended periods.
17
Q
Give examples of specific functions of skeletal muscles based on their location.
A
Skeletal muscles have specific roles based on their location, such as respiratory muscles for breathing, limb muscles for controlling flexion and extension, speech-related muscles for vocalization, and muscles that regulate the position of the urinary bladder.
18
Q
What is excitability in the context of skeletal muscles?
A
Excitability in skeletal muscles refers to their ability to respond to electrical stimuli, meaning they react when an electrical signal is applied to them.
19
Q
What is the significance of conductivity in skeletal muscles?
A
Conductivity allows skeletal muscles to carry impulses from nerve-muscle synapses, enabling them to contract from both ends simultaneously. The speed of impulse conduction in skeletal muscles is typically around 3-5 meters per second.
20
Q
How do skeletal muscles demonstrate contractility?
A
Contractility in skeletal muscles refers to their ability to contract, meaning they can shorten and generate force during muscle contraction.
21
Q
What is stretchability, and how do skeletal muscles exhibit this property?
A
Stretchability in skeletal muscles means they can be stretched when an external stretching force is applied to them, elongating the muscle.
22
Q
Explain the concept of elasticity in skeletal muscles.
A
Elasticity in skeletal muscles refers to their ability to return to their original shape after being stretched when the stretching force is removed. They “bounce back” like an elastic band.
23
Q
What is plasticity in the context of skeletal muscles?
A
Plasticity in muscles means they can retain some deformation even after the stretching force is eliminated. This deformation can persist until the next muscle contraction.
24
What are the two main types of contractile filaments in skeletal muscles?
The two main types of contractile filaments in skeletal muscles are actin filaments and myosin filaments.
25
What is the function of myosin binding sites on the actin filament?
Myosin binding sites on the actin filament are where myosin heads bind during muscle contraction, enabling the sliding filament theory of muscle contraction.
26
How does titin contribute to muscle function in skeletal muscles?
Titin is an elastic filament that helps maintain the position of the myosin filament, ensuring it stays close to the center of the sarcomere and preventing it from moving too close to the Z-line. This contributes to the structural integrity of the sarcomere.
27
Describe the sliding filament theory of muscle contraction briefly.
The sliding filament theory of muscle contraction involves the interaction between myosin heads (from myosin filaments) and actin filaments, resulting in muscle contraction. Myosin heads bind to actin filaments at specific sites, leading to the sliding of actin filaments past myosin filaments and shortening of the sarcomere.
28
What is the role of tropomyosin in muscle contraction?
Tropomyosin acts as a barrier, covering the active sites on the actin filament and preventing myosin from binding to actin during muscle contraction.
29
How does troponin contribute to muscle contraction regulation?
Troponin plays a crucial role in muscle contraction regulation by binding to tropomyosin, actin, and calcium ions (Ca2+). It helps position tropomyosin over the active sites on actin and inhibits ATPase activity while allowing calcium ions to bind and trigger muscle contraction.
30
What are the three subunits of troponin, and what are their functions?
Troponin consists of three subunits:
T (Tropomyosin-binding): Binds with tropomyosin, positioning it over the active sites on actin.
I (Inhibitory): Binds with actin and inhibits ATPase activity, which is responsible for using ATP as an energy source for muscle contraction.
C (Calcium-binding): Has a high affinity for calcium ions and can bind to calcium ions released from the sarcoplasmic reticulum.
31
Where are tropomyosin and troponin typically located in muscle fibers?
Tropomyosin and troponin are located close to the T-tubules, where they play a vital role in regulating muscle contraction in coordination with the sarcoplasmic reticulum.
32
What initiates the mechanism of muscle contraction?
The mechanism of muscle contraction is initiated by an action potential that travels along the muscle fiber cell membrane and into the T-system.
33
What is the role of calcium in muscle contraction?
Calcium plays a critical role in muscle contraction by binding to troponin C, which results in a conformational change and the movement of tropomyosin away from the active sites on actin. This allows myosin heads to bind to actin, forming cross-bridges and initiating the sliding of myofilaments.
34
How does the sliding of myofilaments lead to muscle contraction?
As myosin heads pull on actin filaments and slide them alongside myosin filaments, the sarcomere shortens in length. This sliding of myofilaments within the sarcomere causes changes in the positions of actin and myosin filaments, resulting in muscle contraction.
35
Do the individual actin and myosin filaments change in length during muscle contraction?
No, the individual actin and myosin filaments themselves do not change in length during muscle contraction. Instead, they slide alongside each other, causing the sarcomere to shorten.
36
What role do Dihydropyridine receptors play in muscle cells?
Dihydropyridine receptors act as calcium gatekeepers in muscle cell membranes, mainly functioning as voltage sensors in skeletal muscle. In smooth and cardiac muscle, they can also work as voltage-gated calcium channels.
37
What is the mechanism of calcium release in skeletal muscle cells?
In skeletal muscle, calcium release occurs through electro-mechanical coupling. When an action potential depolarizes the Dihydropyridine receptors on the cell membrane, it causes the Ryanodine receptors on the sarcoplasmic reticulum to change shape and release calcium (Ca2+) into the cell's cytoplasm.
38
How is calcium release different in smooth and cardiac muscle compared to skeletal muscle?
In smooth and cardiac muscle, calcium release involves calcium-gated calcium release. The action potential triggers the release of Ca2+ ions from the T-tubule (influx) through the Dihydropyridine receptors. These ions then bind to the Ryanodine receptors, assisting in the release of Ca2+ into the cytoplasm. Unlike in skeletal muscle, these two types of channels are not located close to each other.
39
What are Dihydropyridines, and how do they affect muscle cells?
Dihydropyridines are substances known as calcium channel blockers. They act like locks on calcium channels, affecting mainly smooth and cardiac muscle cells. They can block the influx of calcium ions into these cells, thereby influencing muscle activity.
40
How do Ryanodine receptor antagonists impact calcium release in muscle cells?
Ryanodine receptor antagonists block the ryanodine receptors responsible for releasing calcium (Ca2+) into muscle cells. This blocking effect predominantly affects skeletal muscle cells, as they rely more on the sarcoplasmic reticulum as a source of Ca2+. In contrast, smooth and cardiac muscle cells obtain their Ca2+ from the cell membrane and the external environment. Ryanodine receptor antagonists can be used to control calcium release and muscle activity, especially in situations where overheating is a concern.
41
How does the process of skeletal muscle relaxation begin?
The process of skeletal muscle relaxation begins with the action of special calcium pumps that transport calcium (Ca2+) out of the muscle cell, using ATP as an energy source.
42
What is the role of troponin and tropomyosin in muscle relaxation?
Troponin and tropomyosin play crucial roles in muscle relaxation. Troponin regains its initial conformation, and tropomyosin moves back to cover the active sites on actin, preventing myosin heads from binding to actin.
43
How do elastic forces and the protein titin contribute to muscle relaxation?
Elastic forces exerted by the protein titin help the sarcomere, the basic contractile unit of muscle, return to its initial length, moving away from the Z-line. This contributes to muscle relaxation.
44
What role does ATP play in the mechanism of muscle relaxation?
ATP is essential for muscle relaxation. It is used to power the calcium pumps that transport calcium out of the muscle cell, as well as for the sodium-calcium channel. Additionally, ATP is required for the sodium-potassium pump, which indirectly supports the sodium-calcium pump's activity.
45
How does the type of muscle fiber influence the process of muscle relaxation?
The type of muscle fiber influences muscle relaxation by affecting the number of cross-bridges formed during contraction and relaxation. Fast fibers like type IIa and IIb can create more cross-bridges, resulting in stronger contractions and more attachment between myosin and actin, which can influence the speed and efficiency of relaxation.
46
What is the "all-or-none" principle in muscle contraction?
The "all-or-none" principle in muscle contraction states that muscle fibers follow the principle of either fully contracting or remaining relaxed when stimulated. There is no partial contraction of a muscle fiber.
47
Can you control the force of contraction in a single motor unit by adjusting stimulus strength?
No, you cannot control the force of contraction in a single motor unit by adjusting stimulus strength. When a motor unit contracts, it does so fully, and stimulus strength does not change the degree of contraction for a single motor unit.
48
How is the overall strength of contraction in skeletal muscles regulated?
The overall strength of contraction in skeletal muscles is regulated by varying the excitability of different motor units within the muscle. By activating different motor units with varying thresholds, the muscle can achieve a range of contraction strengths.
49
What happens when stimulus strength is too strong during muscle contraction?
When the stimulus strength is too strong, the force of contraction may decrease because some motor units may not respond to the excessive stimulation.
50
How does muscle fiber excitability relate to motor unit activation?
Muscle fiber excitability determines how readily a motor unit responds to a stimulus. Motor units with higher excitability have lower thresholds and require less stimulus strength to activate, while those with lower excitability require stronger stimuli for activation. This variation in excitability allows for fine-tuned control of muscle contraction.
51
What are the distinct phases of a single muscle contraction when stimulated by low-frequency stimuli?
A single muscle contraction stimulated by low-frequency stimuli consists of three distinct phases:
Latent Period: This phase lasts for about 5-7 milliseconds and involves the preparation of the muscle for contraction. It includes events such as the influx of calcium ions, binding to troponin, removal of tropomyosin, and an increase in ATPase activity.
Contraction Phase: During this phase, which lasts for 10-100 milliseconds, the force of muscle contraction increases, and the muscle may shorten. Myosin heads repeatedly bind to actin filaments and rotate, driving muscle contraction.
Relaxation Period: Following contraction, the muscle returns to its initial length during this phase, which lasts for 50-100 milliseconds.
52
What is complete tetanic contraction, and when does it typically occur?
Complete tetanic contraction is a continuous and uninterrupted muscle contraction where the muscle remains contracted without any breaks. It typically occurs at higher frequencies of stimulation, around 20 Hz for slower muscles and even faster, like 40-60 Hz, for faster muscles. This type of contraction can lead to cramps or be observed in conditions like epilepsy.
53
What is summation of contraction, and how does it affect muscle contractions?
Summation of contraction is the stacking of one muscle contraction on top of another, making each subsequent contraction stronger until a certain limit is reached. It occurs when muscle contractions happen in rapid succession without allowing the muscle to fully relax. Summation of contraction is facilitated by the accumulation of calcium ions in muscle cells during repeated contractions, resulting in stronger and more forceful contractions. However, there is a limit to how much calcium can accumulate, and once that limit is reached, further summation is not possible.
54
What is the primary characteristic of isometric contractions?
Isometric contractions involve a type of muscle contraction where the length of the muscle doesn't change.
55
What is the main purpose of isometric contractions in the body?
Isometric contractions are crucial for maintaining posture and holding objects in a fixed position.
56
Which type of contraction involves a muscle shortening while maintaining constant tension?
Isotonic contractions involve a muscle shortening while maintaining constant tension.
57
What are the two subtypes of auxotonic contractions, and how do they differ?
Auxotonic contractions include concentric and eccentric contractions. In concentric contraction, the muscle shortens while producing positive work, whereas in eccentric contraction, the muscle lengthens while producing negative work.
58
At what length is a muscle capable of generating maximum force during contraction?
A muscle generates maximum force at its optimal resting length, which is typically around 2.1 to 2.2 micrometers for sarcomeres within muscle fibers.
59
What is the primary energy source used for both muscle contraction and relaxation in skeletal muscles?
The primary energy source for both muscle contraction and relaxation in skeletal muscles is ATP (adenosine triphosphate).
60
How does phosphocreatine contribute to muscle energy?
Phosphocreatine provides rapid energy to muscles by transferring phosphate groups to ADP (adenosine diphosphate) to regenerate ATP.
61
What is the role of ATP in maintaining the resting membrane potential during muscle relaxation?
ATP powers ion pumps across the cell membrane, including the calcium pump, which returns calcium ions (Ca2+) to the sarcoplasmic reticulum during muscle relaxation and helps maintain the resting membrane potential.
62
Describe the steps involved in the energy cycle during muscle contraction.
During muscle contraction, ATP initially binds to the myosin head, is partially cleaved into ADP and inorganic phosphate (P), and then powers the cross-bridge formation between myosin and actin filaments. After the power stroke, ATP binds to the myosin head again, leading to the release from actin and repeating the cycle.
63
What is the "rigor state" in muscle contraction, and when is it commonly observed?
The "rigor state" occurs when myosin heads remain attached to actin filaments, preventing muscle relaxation. It is commonly observed in rigor mortis, which occurs after death when ATP levels decrease and myosin heads get stuck to actin filaments, leading to muscle rigidity.
64
What is the primary energy source for immediate muscle contraction?
The primary energy source for immediate muscle contraction is ATP (Adenosine Triphosphate).
65
How does phosphocreatine (PCr) contribute to muscle energy production?
Phosphocreatine (PCr) rapidly transfers a phosphate group to ADP (Adenosine Diphosphate) to regenerate ATP, providing quick energy for short bursts of high-intensity muscle activity.
66
What is anaerobic glycolysis, and what is its role in muscle energy production?
Anaerobic glycolysis is a process that converts glucose into ATP without the need for oxygen. It provides moderate energy and sustains muscle contractions for several minutes, making it important for short bursts of intense exercise.
67
How does aerobic energy production differ from anaerobic glycolysis in terms of efficiency and sustainability?
Aerobic energy production is more efficient and sustainable than anaerobic glycolysis. It occurs in the presence of oxygen, yielding more ATP molecules (36 ATP per glucose molecule) and providing a continuous supply of energy for extended periods during activities like endurance running or cycling.
68
What are the speed and limitations of ATP and phosphocreatine as energy sources for muscle activity?
ATP provides immediate but limited energy for the first few seconds of intense muscle activity. Phosphocreatine (PCr) can rapidly regenerate ATP and sustain muscle contractions for about 10-15 seconds, offering a quick energy reserve within muscle cells.
69
What percentage of the total energy used by skeletal muscles is typically converted into mechanical work during muscle contraction?
Only about 25-30% of the total energy used by skeletal muscles is converted into mechanical work during muscle contraction, with the rest being lost as heat.
70
What are the three main types of muscle fibers in skeletal muscles, and how do they differ in terms of energy production and fatigue resistance?
The three main types of muscle fibers are Type I (Slow Oxidative), Type IIa (Fast Oxidative-Glycolytic), and Type IIb (Fast Glycolytic). Type I fibers rely primarily on aerobic metabolism, are fatigue-resistant, and are suited for endurance activities. Type IIa fibers use a combination of aerobic and anaerobic metabolism, while Type IIb fibers primarily rely on anaerobic metabolism, making them well-suited for short bursts of high-intensity activity but more prone to fatigue.
71
How does the myoglobin content differ among the three types of muscle fibers, and what role does myoglobin play in muscle function?
Type I fibers have a high myoglobin content, which helps store oxygen for sustained energy production. Type IIa fibers have a moderate myoglobin content, while Type IIb fibers have a low myoglobin content. Myoglobin plays a crucial role in facilitating oxygen transport and storage within muscle cells.
72
What factors influence the choice of muscle fiber type used in a particular activity or sport?
The choice of muscle fiber type used in a particular activity depends on the demands of that activity. Endurance activities favor Type I fibers, while high-intensity, short-duration activities rely on Type IIb fibers. Many muscles contain a mixture of these fiber types to adapt to various functional requirements.
73
How can genetics and training influence an individual's muscle fiber composition?
Muscle fiber types are determined by genetics, but training can influence the proportion of different fiber types in a muscle. While training can modify some muscle characteristics, the inherent composition of muscle fibers still plays a significant role in an individual's athletic performance and predisposition to excel in certain sports.
74
What percentage of the total energy used by skeletal muscles is typically converted into mechanical work during muscle contraction?
Only about 25-30% of the total energy used by skeletal muscles is converted into mechanical work during muscle contraction, with the rest being lost as heat.
75
What are the three main types of muscle fibers in skeletal muscles, and how do they differ in terms of energy production and fatigue resistance?
The three main types of muscle fibers are Type I (Slow Oxidative), Type IIa (Fast Oxidative-Glycolytic), and Type IIb (Fast Glycolytic). Type I fibers rely primarily on aerobic metabolism, are fatigue-resistant, and are suited for endurance activities. Type IIa fibers use a combination of aerobic and anaerobic metabolism, while Type IIb fibers primarily rely on anaerobic metabolism, making them well-suited for short bursts of high-intensity activity but more prone to fatigue.
76
How does the myoglobin content differ among the three types of muscle fibers, and what role does myoglobin play in muscle function?
Type I fibers have a high myoglobin content, which helps store oxygen for sustained energy production. Type IIa fibers have a moderate myoglobin content, while Type IIb fibers have a low myoglobin content. Myoglobin plays a crucial role in facilitating oxygen transport and storage within muscle cells.
77
What factors influence the choice of muscle fiber type used in a particular activity or sport?
The choice of muscle fiber type used in a particular activity depends on the demands of that activity. Endurance activities favor Type I fibers, while high-intensity, short-duration activities rely on Type IIb fibers. Many muscles contain a mixture of these fiber types to adapt to various functional requirements.
78
How can genetics and training influence an individual's muscle fiber composition?
Muscle fiber types are determined by genetics, but training can influence the proportion of different fiber types in a muscle. While training can modify some muscle characteristics, the inherent composition of muscle fibers still plays a significant role in an individual's athletic performance and predisposition to excel in certain sports.
79
What are the differences between smooth and skeletal muscles in terms of their structure and function?
Smooth muscles have gap junctions, can convert electrical signals to chemical signals, have a less developed sarcoplasmic reticulum, lack T-tubules, and do not contain troponin. In contrast, skeletal muscles do not have gap junctions for electrical communication between cells, rely primarily on electrical signals, have a well-developed sarcoplasmic reticulum, contain T-tubules for signal transmission, and include troponin in their regulation of muscle contraction.
80
How do unitary and multiunit smooth muscles differ in terms of their structure and function?
Unitary (single-unit) smooth muscle functions as a coordinated unit in the walls of hollow organs, allowing electrical signals to spread through gap junctions. Multiunit smooth muscle is composed of individual cells that contract independently and is found in structures like the iris and small blood vessels, lacking gap junctions for coordinated contractions.
81
What is automaticity, and how does it relate to unitary smooth muscle?
Automaticity refers to the property of unitary smooth muscle where a stimulus applied to one smooth muscle cell can lead to the activation of all the smooth muscle cells in a coordinated manner. In other words, unitary smooth muscle can initiate contractions spontaneously and propagate them throughout a tissue due to its interconnectedness through gap junctions.
82
What role do gap junctions play in unitary smooth muscle, and how do they contribute to its function?
Gap junctions are specialized connections between adjacent unitary smooth muscle cells. They allow for the direct transmission of electrical signals and ions between cells, enabling synchronized contractions. Gap junctions are essential for unitary smooth muscle to function as a single functional unit, responding to stimuli in a coordinated manner.
83
How is unitary smooth muscle typically regulated, and what physiological processes does it control?
Unitary smooth muscle is predominantly regulated by the autonomic nervous system, specifically the parasympathetic and sympathetic divisions. It plays a crucial role in various physiological processes, including peristalsis in the digestive tract, uterine contractions during childbirth, and the regulation of blood flow in small blood vessels (arterioles).
84
What distinguishes multiunit smooth muscle from unitary smooth muscle in terms of its cellular organization, innervation, and automaticity?
Multiunit smooth muscle is composed of individual smooth muscle cells that function as discrete units, rather than being interconnected like unitary smooth muscle cells. Each cell in multiunit smooth muscle is directly innervated by neurons, and it does not exhibit automaticity, meaning it requires neural stimulation to initiate contraction.
85
What are some specific locations in the body where multiunit smooth muscle is found, and why is it well-suited for these locations?
Multiunit smooth muscle is typically found in structures requiring fine control and precision. Examples include the iris (for controlling pupil size), ciliary muscles (for focusing the lens in the eye), and large arteries (for regulating blood pressure). Multiunit smooth muscle allows for precise control over individual cells in these locations, enabling fine-tuned responses to specific physiological demands.
86
How do action potentials in smooth muscle cells differ from those in skeletal muscle cells?
Action potentials in smooth muscle cells can exhibit various patterns, which may vary among different types of smooth muscle cells.
87
What are some characteristics of action potentials in certain smooth muscles?
Some smooth muscles display action potentials resembling a plateau phase, characterized by sustained depolarization and increased calcium ion influx.
88
What is the significance of slow waves in the membrane potential of visceral smooth muscle cells?
Slow waves in visceral smooth muscle cells, if reaching the threshold, can trigger multiple action potentials and potentially lead to tetanic contractions.
89
How does the influx of calcium ions affect the mechanism of contraction in smooth muscle cells?
The influx of calcium ions leads to an increase in intracellular calcium concentration, which is essential for smooth muscle contraction.
90
What role do potassium channels play in the process of smooth muscle contraction?
Potassium channels in smooth muscle cells are activated by elevated calcium levels and contribute to hyperpolarization, which affects calcium channels and the overall contraction process.
91
What allows smooth muscle cells to have fine control and regulation over contractile activity?
The presence of various action potential types and intracellular calcium dynamics contributes to the versatility of smooth muscle function, enabling it to respond to different physiological stimuli and perform diverse functions.
92
What are the two primary triggers of smooth muscle contraction?
The triggers of smooth muscle contraction involve both electrical and chemical mechanisms.
93
How are impulses transmitted in smooth muscle cells during the electrical trigger?
Impulses are transmitted along the cell membrane of smooth muscle cells.
94
What is the role of voltage-gated calcium channels in the electrical trigger?
Voltage-gated calcium channels, often referred to as Dihydropyridine receptors, open in response to electrical activity, allowing calcium ions to enter the smooth muscle cell.
95
After calcium ions enter the smooth muscle cell, what chemical process do they trigger?
The elevated intracellular calcium concentration triggers a chemical signaling process.
96
What are ryanodine receptors, and where are they located?
Ryanodine receptors are ligand-gated calcium channels located on the smooth endoplasmic reticulum (sER) within the smooth muscle cell.
97
How does the binding of calcium ions to ryanodine receptors affect intracellular calcium levels?
Binding of calcium ions to ryanodine receptors leads to the release of additional calcium from the sER into the cytoplasm of the smooth muscle cell.
98
What is the ultimate result of the combined electrical and chemical signaling cascade in smooth muscle cells?
The combined cascade leads to an increase in cytoplasmic calcium levels, initiating and sustaining smooth muscle contraction.
99
Why is the precise coordination of these signaling events important in smooth muscle function?
Precise coordination allows for fine-tuned regulation of smooth muscle activity in response to various physiological stimuli and signaling pathways.
100
What is the pharmacomechanical trigger of smooth muscle contraction, and how does it initiate muscle contraction?
The pharmacomechanical trigger involves hormones or neurotransmitters binding to specific receptors on smooth muscle cells, activating G-proteins, and opening ligand-gated calcium channels. This leads to an increase in cytoplasmic calcium ions (Ca2+), which initiates smooth muscle contraction.
101
What is the role of G-proteins in the pharmacomechanical trigger of smooth muscle contraction?
G-proteins are activated when hormones or neurotransmitters bind to their receptors on smooth muscle cells. These activated G-proteins can open ligand-gated calcium channels, allowing Ca2+ influx.
102
What are the second messengers generated by the activation of Phospholipase C (PLC), and how do they contribute to muscle contraction?
PLC generates two second messengers: Diacylglycerol (DAG) and Inositol trisphosphate (IP3). IP3 can bind to receptors on the smooth endoplasmic reticulum (sER), triggering the release of stored Ca2+ from the sER into the cytoplasm, further increasing cytoplasmic Ca2+ concentration and promoting muscle contraction.
103
What is myogenic deformation, and under what conditions does it occur?
Myogenic deformation is a mechanism that triggers smooth muscle contraction when the smooth muscle cell experiences stretching or deformation. It occurs in response to factors such as mechanical forces or pressure changes in the surrounding tissue.
104
How do deformation-gated calcium channels play a role in myogenic deformation?
Deformation-gated calcium channels are sensitive to changes in cell shape or mechanical stress. When the smooth muscle cell undergoes stretching or deformation, these channels open, allowing Ca2+ to enter the cell and increase cytoplasmic Ca2+ concentration.
105
What physiological processes involve myogenic deformation as a trigger for smooth muscle contraction?
Myogenic deformation plays a role in processes such as the stretch of the large intestine during food intake and the response of blood vessels to changes in pressure. In these cases, deformation of smooth muscle cells leads to muscle contraction and helps regulate various physiological functions.
106
What initiates smooth muscle contraction at the molecular level?
An increase in cytoplasmic calcium ions (Ca2+) initiates smooth muscle contraction.
107
What is the role of calmodulin (CaM) in smooth muscle contraction?
Calmodulin (CaM) binds to Ca2+ and forms a complex, which then activates myosin light chain kinase (MLCK).
108
How does myosin light chain kinase (MLCK) become active, and what is its role in muscle contraction?
MLCK becomes active when it binds to the Ca2+-CaM complex. Its role is to phosphorylate myosin, activating it for interaction with actin filaments.
109
What is the significance of caldesmon in smooth muscle contraction?
Caldesmon is a calcium-sensitive protein that normally holds tropomyosin over the active site of actin filaments, preventing myosin from binding. When the Ca2+-CaM complex binds to caldesmon, it releases tropomyosin, allowing myosin to bind to actin and facilitate muscle contraction.
110
How does calponin contribute to the regulation of smooth muscle contraction?
Calponin is another calcium-binding protein in smooth muscle cells. It can bind to the calcium-CaM complex, inhibiting calponin's normal inhibitory function. This inhibition helps decrease myosin ATPase activity, conserving energy during muscle contraction.
111
How do specialized calcium pumps contribute to smooth muscle relaxation?
Specialized calcium pumps actively transport calcium ions out of the cytoplasm, reducing the cytoplasmic calcium concentration.
112
What is the role of sodium-calcium exchange transport in reducing cytoplasmic calcium levels in smooth muscle cells?
Sodium-calcium exchange transport helps remove calcium from the cytoplasm by exchanging calcium ions for sodium ions, contributing to the decrease in cytoplasmic calcium.
113
How does the inactivation of calmodulin (CaM) play a role in smooth muscle relaxation?
When cytoplasmic Ca2+ decreases, the calcium-CaM complex is no longer formed, rendering CaM unable to activate myosin light chain kinase (MLCK), which leads to MLCK inactivation.
114
What is the function of myosin phosphatase in smooth muscle relaxation?
Myosin phosphatase is an enzyme that dephosphorylates myosin light chains, leading to the dephosphorylation of myosin heads and reduced ATPase activity, contributing to muscle relaxation.
115
How do caldesmon and calponin contribute to the prevention of cross-bridge formation during smooth muscle relaxation?
Caldesmon and calponin cover the active sites on actin filaments, preventing the interaction between actin and myosin, which is crucial for muscle relaxation.
116
How do the orientations of smooth muscle fibers differ from those of skeletal muscle?
Smooth muscle fibers are arranged in various directions, allowing for changes in cross-sectional area, while skeletal muscles are generally aligned in parallel.
116
What is the fundamental difference between the organization of smooth muscle and skeletal muscle fibers?
Smooth muscle often contracts in a coordinated manner as a single unit (unitary), while skeletal muscle fibers can contract independently.
117
What structural feature is lacking in smooth muscle when compared to skeletal muscle, resulting in a less organized appearance?
Smooth muscle lacks the highly organized sarcomere structure seen in skeletal muscle.
118
What serves as anchoring points for actin filaments in smooth muscle, and how does it compare to the anchoring of actin filaments in skeletal muscle?
In smooth muscle, actin filaments are anchored to dense bodies, similar to Z-discs in skeletal muscle.
119
How does the direction of contraction differ between smooth muscle and skeletal muscle?
Smooth muscle can contract in various dimensions, involving longitudinal and transverse length changes, while skeletal muscle typically contracts longitudinally along its length.
120
What distinguishes the arrangement of myosin filaments in smooth muscle cells from that in skeletal muscle during contraction?
Myosin filaments in smooth muscle cells are oriented in different directions from each other during contraction, whereas myosin filaments in skeletal muscle align in parallel with the actin filaments.
121
How does the reliance on calcium differ between smooth muscle and skeletal muscle during contraction?
Smooth muscle relies more on extracellular calcium, while skeletal muscle primarily uses intracellular calcium stored in the sarcoplasmic reticulum.
122
What are the various types of receptors that can activate smooth muscle, and how does this compare to the primary mode of activation for skeletal muscle?
Smooth muscle can be activated by mechanical, deformation, and chemical receptors. In contrast, skeletal muscle contraction is primarily initiated by neural stimulation at the neuromuscular junction.
123
What are some of the key regulatory proteins involved in smooth muscle contraction, and how do they differ from those found in skeletal muscle?
Smooth muscle employs proteins like calmodulin, caldesmon, and calponin for regulation, whereas skeletal muscle uses troponin and tropomyosin.
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What makes smooth muscle more versatile in responding to different stimuli compared to skeletal muscle?
Smooth muscle can be activated by changes in membrane potential, hormones, or mechanical stretching, allowing it to respond to a variety of stimuli. Skeletal muscle relies on neural input via motor neurons for activation.
