Chapter 8 Flashcards

Question

What are gap junctions and their function in unitary smooth muscle?

Answer 1

Gap junctions are specialized connections between muscle cells that allow ions and action potentials to flow freely from one fiber to another ensuring coordinated contraction.

Answer 2

Unitary smooth muscle is known as syncytial smooth muscle due to its interconnections among fibers that function together as a syncytium facilitating coordinated contraction.

Answer 3

Physiological responses involving these muscles include thermoregulation (piloerection in cold) emotional reactions (fear) and other involuntary actions tied to the sympathetic nervous system.

Answer 4

Coordinated contraction is crucial for the effective function of organs such as the gastrointestinal tract where mass contractions help in processes like peristalsis.

Answer 5

Visceral smooth muscle is also called visceral smooth muscle because it is found in the walls of most viscera of the body including the gastrointestinal tract bile ducts ureters uterus and many blood vessels.

Answer 6

Visceral smooth muscle is primarily located in the walls of the gastrointestinal tract bile ducts ureters uterus and many blood vessels.

Answer 7

Smooth muscle contains both actin and myosin filaments that have chemical characteristics similar to those of actin and myosin filaments in skeletal muscle.

Answer 8

Smooth muscle does not contain the troponin complex which is required for the control of skeletal muscle contraction.

Answer 9

The mechanism for controlling contraction in smooth muscle differs from that in skeletal muscle primarily due to the absence of the troponin complex in smooth muscle.

Answer 10

The contractile process in smooth muscle is activated by calcium ions.

Answer 11

Adenosine triphosphate (ATP) is degraded to adenosine diphosphate (ADP) to provide the energy for smooth muscle contraction.

Answer 12

Actin and myosin filaments derived from smooth muscle interact with each other in much the same way that they do in skeletal muscle.

Answer 13

Yes the contractile mechanism in smooth muscle is discussed in more detail later in the chapter.

Answer 14

Calcium ions are crucial as they activate the contractile process in smooth muscle.

Answer 15

During the contraction process in smooth muscle ATP is degraded to adenosine diphosphate (ADP) to provide energy.

Answer 16

The main differences include: 1) Smooth muscle lacks the troponin complex found in skeletal muscle. 2) The actin and myosin filaments in smooth muscle are not arranged in a striated pattern. 3) Smooth muscle features dense bodies to which actin filaments are attached in contrast to the organized sarcomeres of skeletal muscle.

Answer 17

The two types of smooth muscle are: A) Multi-unit smooth muscle which consists of individual muscle fibers that operate independently; and B) Unitary smooth muscle which consists of sheets of muscle fibers that contract as a single unit due to gap junctions.

Answer 18

In skeletal muscle excitation-contraction coupling is heavily reliant on the troponin-tropomyosin complex and action potentials traveling along T-tubules. In contrast smooth muscle relies on the influx of calcium ions which bind to calmodulin instead of troponin leading to contraction.

Answer 19

Calcium ions initiate contraction in smooth muscle by binding to calmodulin. This calcium-calmodulin complex activates myosin light-chain kinase (MLCK) which phosphorylates myosin light chains enabling myosin to interact with actin filaments.

Answer 20

Smooth muscle contractions are generally slower and can be sustained for longer periods compared to the quick and short contractions typically observed in skeletal muscle.

Answer 21

Dense bodies serve as anchoring points for actin filaments in smooth muscle similar to Z-discs in skeletal muscle. They are crucial for the transmission of force during contraction and can be located on the cell membrane or within the cytoplasm.

Answer 22

Smooth muscle requires less energy for contraction compared to skeletal muscle. This is partly because smooth muscle can maintain tension with less frequent calcium influxes and has a lower metabolic rate.

Answer 23

Smooth muscle achieves contraction through the sliding filament mechanism as actin filaments slide over myosin filaments without the need for the organized sarcomere structure present in skeletal muscle.

Answer 24

Myosin light-chain kinase (MLCK) is an enzyme that is activated by the calcium-calmodulin complex in smooth muscle. Once activated MLCK phosphorylates myosin light chains allowing myosin to bind to actin and facilitate contraction.

Answer 25

Electron micrographic techniques are used to visualize and study the organization of actin and myosin filaments in smooth muscle. These techniques allow for the observation of structures such as dense bodies and the arrangement of filaments.

Answer 26

Intercellular protein bridges bond together membrane-dense bodies of adjacent cells allowing the force of contraction to be transmitted from one cell to the next.

Answer 27

Myosin filaments are interspersed among the actin filaments in a muscle fiber.

Answer 28

Myosin filaments have a diameter that is more than twice that of actin filaments.

Answer 29

Electron micrographs typically show 5 to 10 times as many actin filaments as myosin filaments.

Answer 30

The postulated structure consists of a large number of actin filaments radiating from two dense bodies with the ends of these filaments overlapping a myosin filament located midway between the dense bodies.

Answer 31

The contractile unit of smooth muscle is similar to that of skeletal muscle but lacks the regularity of skeletal muscle structure.

Answer 32

Dense bodies serve the same role as Z disks in skeletal muscle.

Answer 33

The arrangement allows for contraction without the ordered structure seen in skeletal muscle enabling more flexibility in contraction.

Answer 34

Understanding filament arrangement is critical for comprehension of muscle contraction mechanisms and how muscles generate force.

Answer 35

Both smooth and skeletal muscle have contractile units that involve the interaction between actin and myosin filaments.

Answer 36

'Side polar' cross-bridges are structures of myosin filaments arranged such that the cross-bridges on one side hinge in one direction while those on the opposite side hinge in the opposite direction. This configuration allows the myosin to effectively pull actin filaments in two opposite directions simultaneously.

Answer 37

The 'side polar' cross-bridge arrangement allows smooth muscle cells to contract much more efficiently enabling them to contract up to 80% of their length compared to less than 30% contraction in skeletal muscle. This allows for greater flexibility and range in movement.

Answer 38

Figure 8-2 illustrates the physical structure of smooth muscle showing actin filaments emanating from dense bodies on the upper left side while the lower portions demonstrate the interaction between myosin filaments and actin filaments. The arrangement highlights the complex structural relationship that allows for effective muscle contraction.

Answer 39

Smooth muscle contraction facilitated by side polar cross-bridges allows for greater contraction (up to 80% of their length) while skeletal muscle is limited to less than 30%. This difference is largely due to the organization and structure of the myosin and actin filaments.

Answer 40

Dense bodies serve as anchor points for actin filaments in smooth muscle similar to the Z-lines in skeletal muscle. They help organize the actin filaments to facilitate contraction.

Answer 41

Actin filaments in smooth muscle are arranged to emanate from dense bodies allowing for efficient contraction and maximizing the range of motion during muscle activity. This arrangement is critical for smooth muscle's ability to function effectively in different physiological contexts.

Answer 42

Smooth muscle can contract in a sustained manner and to a much greater extent than skeletal muscle due to its unique structure and cross-bridge formation. While skeletal muscle contracts rapidly and is restricted in its length contraction smooth muscle allows for sustained and varied contraction enabling it to fulfill a range of roles in the body.

Answer 43

A cross-bridge is formed when the myosin heads attach to actin filaments during muscle contraction facilitating the sliding of the filaments past one another leading to contraction.

Answer 44

Smooth muscles are responsible for involuntary movements such as those in the digestive tract blood vessels and respiratory passages allowing for functions like peristalsis regulation of blood flow and control of airway diameter.

Answer 45

Smooth muscle contraction is characterized by prolonged tonic contractions that can last hours or even days whereas skeletal muscles typically contract and relax rapidly.

Answer 46

The cycling speed of myosin cross-bridges in smooth muscle is much slower than in skeletal muscle with a frequency of attachment and release being as little as 1/10 to 1/300 that in skeletal muscle.

Answer 47

The fraction of time that the myosin cross-bridges remain attached to actin filaments is believed to be greatly increased in smooth muscle which plays a major role in determining the force of contraction.

Answer 48

Despite the slower cycling of myosin cross-bridges in smooth muscle the increased duration of attachment to actin filaments enhances the overall force of contraction.

Answer 49

The primary structural difference is that smooth muscle has a slower cycling mechanism for myosin cross-bridges compared to the rapid cycling seen in skeletal muscle.

Answer 50

Prolonged contraction in smooth muscle allows it to maintain tonicity and support functions such as peristalsis in the digestive tract and regulation of blood vessel diameter.

Answer 51

Factors that could affect prolonged tonic contraction in smooth muscle include calcium ion concentration neurotransmitter release and various hormonal signals.

Answer 52

Smooth muscle's prolonged tonic contraction is particularly important in contexts such as vascular tone regulation gastrointestinal motility and maintaining bladder pressure.

Answer 53

The phosphorylation of the myosin light chain is crucial in initiating the contraction process in smooth muscle regulating the interaction between myosin and actin.

Answer 54

Slow myosin cross-bridge cycling in smooth muscle typically results in lower energy expenditure compared to the rapid cycling in skeletal muscle allowing smooth muscle to sustain contractions with less ATP consumption.

Answer 55

The cross-bridge heads in smooth muscle have far less ATPase activity than in skeletal muscle.

Answer 56

The lower ATPase activity in smooth muscle results in a significantly reduced degradation of ATP which energizes the cross-bridge movements leading to a slower rate of cycling.

Answer 57

Smooth muscle requires only 110 to 1300 times less energy to sustain the same tension of contraction compared to skeletal muscle.

Answer 58

The low energy utilization by smooth muscle is crucial for the energy economy of the body allowing organs like the intestines urinary bladder and gallbladder to maintain tonic muscle contraction for extended periods.

Answer 59

The low energy requirement in smooth muscle is primarily due to the slow attachment and detachment cycling of the cross-bridges with only one molecule of ATP needed for each cycling regardless of its duration.

Answer 60

Tonic muscle contraction refers to the sustained contraction of smooth muscle which can be maintained almost indefinitely enabling organs to function continuously.

Answer 61

Smooth muscle tissue demonstrates a slowness in both the onset of contraction and relaxation which is distinct from the rapid contractions seen in skeletal muscle.

Answer 62

Examples of viscera that utilize smooth muscle contraction include the intestines urinary bladder and gallbladder.

Answer 63

The cycling rate of cross-bridges in smooth muscle is slower than in skeletal muscle due to lower ATPase activity.

Answer 64

ATP is required for the energization of cross-bridge movements in smooth muscle with only one molecule of ATP being needed for each contraction cycle.

Answer 65

The design of smooth muscle which emphasizes slower cycling and lower energy needs allows organs to maintain prolonged contraction with minimal energy expenditure.

Answer 66

Prolonged contraction of smooth muscle contributes positively to the overall energy efficiency and economy of the body as it allows for sustained functions of various organs without the need for excessive energy input.

Answer 67

The contraction time for smooth muscle ranges from 1 to 3 seconds.

Answer 68

Tissue begins to contract 50 to 100 milliseconds after it is excited.

Answer 69

Smooth muscle reaches full contraction about 0.5 seconds after the initial contraction begins.

Answer 70

The decline in contractile force for smooth muscle occurs over 1 to 2 seconds.

Answer 71

The contraction time of smooth muscle is about 30 times longer than a single contraction of an average skeletal muscle fiber.

Answer 72

The slow onset and prolonged contraction of smooth muscle are due to the slowness of attachment and detachment of the cross-bridges with actin filaments.

Answer 73

The initiation of contraction in smooth muscle in response to calcium ions is much slower than in skeletal muscle.

Answer 74

Despite the relatively few myosin filaments the maximum force of contraction can often be greater in smooth muscle than in skeletal muscle.

Answer 75

Some types of smooth muscle can have a contraction time as short as 0.2 seconds.

Answer 76

Some types of smooth muscle can have a contraction time as long as 30 seconds.

Answer 77

Cross-bridges refer to the interactions between myosin heads and actin filaments during muscle contraction. In smooth muscle these interactions allow for the generation of force and contraction.

Answer 78

The maximum force of contraction of smooth muscle is often greater than that of skeletal muscle with smooth muscle achieving 4 to 6 kg/cm2 of cross-sectional area compared to 3 to 4 kg/cm2 for skeletal muscle.

Answer 79

The greater force of contraction in smooth muscle results from the prolonged attachment of myosin cross-bridges to the actin filaments allowing for sustained tension.

Answer 80

The latch mechanism is a physiological process that allows smooth muscle to maintain prolonged contractions with minimal energy consumption by reducing the amount of stimulation needed to sustain the contraction once it is achieved.

Answer 81

Smooth muscle can maintain contractions using significantly less energy sometimes as little as 1/300th of the energy required for a comparable sustained contraction in skeletal muscle.

Answer 82

The latch mechanism is important for maintaining prolonged tonic contraction without requiring a continuous high level of excitation which allows for efficient energy use and sustained muscle tone.

Answer 83

Once smooth muscle achieves full contraction the level of continuing excitation can often be reduced to much less than the initial level while still maintaining the full force of contraction due to the latch mechanism.

Answer 84

Smooth muscle can maintain contraction using the latch mechanism for extended periods facilitating functions such as holding organs in place with low energy expenditure.

Answer 85

The latch mechanism benefits functions such as maintaining tone in blood vessels allowing for steady blood flow and reduced energy demand on the circulatory system.

Answer 86

Examples of smooth muscle include the muscles in the walls of blood vessels the gastrointestinal tract the urinary bladder and the uterus.

Answer 87

Smooth muscle can maintain contraction for extended periods with minimal energy use and requires little continued excitatory signaling from nerve fibers or hormones.

Answer 88

Stress-relaxation refers to the ability of visceral unitary smooth muscle in hollow organs to return to nearly its original contraction force within seconds or minutes after being elongated or shortened.

Answer 89

When fluid volume suddenly increases in the urinary bladder it stretches the smooth muscle in the bladder wall causing an immediate large increase in pressure. However after about 15 to 60 seconds despite continued stretch the pressure returns nearly to the original level.

Answer 90

When the volume in the bladder is suddenly decreased the pressure drops drastically at first but then it gradually rises again after a few seconds.

Answer 91

The stress-relaxation ability of smooth muscle allows for the accommodation of changes in volume such as that in the urinary bladder without requiring constant nerve or hormonal stimulation thereby improving organ function and efficiency.

Answer 92

Visceral unitary smooth muscle is primarily found in hollow organs such as the urinary bladder intestines and uterus.

Answer 93

Sustained contraction in smooth muscle benefits the body by enabling organs to hold contents (like urine in the bladder) without continuous energy expenditure allowing for effective and efficient bodily functions.

Answer 94

The phenomena are called stress-relaxation and reverse stress-relaxation.

Answer 95

The initiating stimulus for most smooth muscle contraction is an increase in intracellular calcium ions.

Answer 96

An increase in intracellular calcium ions can be caused by nerve stimulation of the smooth muscle fiber hormonal stimulation stretch of the fiber or changes in the chemical environment of the fiber.

Answer 97

Smooth muscle does not contain troponin the regulatory protein that is activated by calcium ions to cause skeletal muscle contraction.

Answer 98

Smooth muscle contraction is activated by a different mechanism compared to skeletal muscle contraction since it lacks troponin.

Answer 99

Smooth muscle uses stress-relaxation and reverse stress-relaxation phenomena to maintain pressure.

Answer 100

These phenomena allow the organ to maintain approximately the same amount of pressure inside its lumen despite sustained large changes in volume.

Answer 101

Skeletal muscle contraction is regulated by troponin and calcium ions while smooth muscle contraction is regulated by a different mechanism that does not involve troponin.

Answer 102

It refers to the various ways through which smooth muscle contractions are initiated and maintained primarily through the modulation of calcium ion levels.

Answer 103

Intracellular calcium ion (Ca2+) concentration increases when Ca2+ enters the cell through calcium channels in the cell membrane or is released from the sarcoplasmic reticulum.

Answer 104

Calmodulin (CaM) binds to calcium ions (Ca2+) to form a Ca2+-CaM complex which then activates myosin light chain kinase (MLCK).

Answer 105

Active MLCK phosphorylates the myosin light chain which leads to the attachment of the myosin head to the actin filament causing contraction of the smooth muscle.

Answer 106

Smooth muscle cells contain a regulatory protein called calmodulin which is similar to troponin but functions differently in initiating contraction.

Answer 107

Calmodulin activates myosin cross-bridges by binding calcium ions and forming a complex that activates myosin light chain kinase (MLCK) leading to phosphorylation of myosin.

Answer 108

The myosin light chain once phosphorylated by MLCK interacts with actin filaments to initiate muscle contraction.

Answer 109

ADP (adenosine diphosphate) and ATP (adenosine triphosphate) are energy-carrying molecules. During muscle contraction ATP is hydrolyzed to ADP and phosphate (P) providing the energy necessary for myosin-head movement and muscle contraction.

Answer 110

The end result of the calcium ion signal pathway is the contraction of smooth muscle due to the interaction between phosphorylated myosin and actin filaments.

Answer 111

Calcium ions enter the cell through calcium channels or are released from the sarcoplasmic reticulum increasing Ca2+ concentration. These ions bind to calmodulin to form a Ca2+-CaM complex which activates MLCK. MLCK phosphorylates the myosin light chain allowing myosin heads to bind to actin ultimately resulting in contraction.

Answer 112

Smooth muscle contraction is regulated by the calcium-calmodulin-MLCK pathway in contrast to skeletal muscle which utilizes the troponin-tropomyosin complex for regulation.

Answer 113

Calcium ion levels are crucial for the activation of myosin light chain kinase and the subsequent phosphorylation that leads to muscle contraction thus playing a vital role in smooth muscle physiology and function.

Answer 114

Contraction in smooth muscle cells is initiated by an increase in calcium concentration in the cytosolic fluid. This increase can occur due to the influx of calcium from the extracellular fluid through calcium channels or the release of calcium from the sarcoplasmic reticulum.

Answer 115

Calmodulin binds reversibly with calcium ions. When calcium concentration increases the calcium ions bind to calmodulin forming a calmodulin-calcium complex which then activates myosin light chain kinase.

Answer 116

Myosin light chain kinase is a phosphorylating enzyme that is activated by the calmodulin-calcium complex. Its role is to phosphorylate one of the light chains of each myosin head specifically the regulatory chain which is crucial for the contraction process.

Answer 117

When phosphorylated by myosin light chain kinase the regulatory chain allows the myosin head to bind repetitively with actin filaments facilitating contraction. If the regulatory chain is not phosphorylated the binding and detachment cycling of the myosin head with actin does not occur.

Answer 118

The sarcoplasmic reticulum releases calcium ions into the cytosolic fluid when stimulated contributing to the increase in calcium concentration necessary for smooth muscle contraction.

Answer 119

Caveolae are invaginations in the cell membrane of smooth muscle fibers that facilitate the influx of calcium ions from the extracellular fluid.

Answer 120

The phosphorylation state of the myosin regulatory chain determines whether the myosin head can effectively bind to actin. When phosphorylated the head can bind and cycle with actin leading to muscle contraction. When it is not phosphorylated this binding and cycling does not occur.

Answer 121

The calcium concentration in the cytosol is critical for smooth muscle contraction; it triggers binding to calmodulin which leads to the activation of myosin light chain kinase and ultimately facilitates the phosphorylation of myosin allowing for muscle contraction.

Answer 122

During muscle contraction phosphorylated myosin heads can bind to actin filaments and proceed with attachment-detachment cycling which generates force and causes muscle contraction. This cycling is essential for the physical shortening of the muscle.

Answer 123

If calmodulin does not bind to calcium ions the calmodulin-calcium complex will not form resulting in the inactivation of myosin light chain kinase. This means that the myosin regulatory light chain will not be phosphorylated preventing contraction from occurring.

Answer 124

The primary source of calcium ions for skeletal muscle contraction is the sarcoplasmic reticulum which provides virtually all the calcium ions required for the process.

Answer 125

In smooth muscle the source of calcium ions for contraction predominantly comes from the extracellular fluid instead of the sarcoplasmic reticulum as in skeletal muscle.

Answer 126

Calcium ions from the extracellular fluid enter the muscle cell during an action potential or stimulus causing the muscle contraction process.

Answer 127

The sarcoplasmic reticulum is only slightly developed in most smooth muscle whereas it is well-developed in skeletal muscle.

Answer 128

The concentration of calcium ions in the extracellular fluid is greater than 10^(-3) molar while inside smooth muscle cells it is less than 10^(-7) molar.

Answer 129

When calcium channels open rapid diffusion of calcium ions occurs into the smooth muscle cell from the extracellular fluid.

Answer 130

The contraction of smooth muscle is initiated when calcium ions enter the cell either during an action potential or in response to other stimuli.

Answer 131

The significant difference in calcium ion concentration between the extracellular fluid and inside smooth muscle cells creates a gradient that allows calcium ions to rapidly diffuse into the cell when channels open thus triggering contraction.

Answer 132

Calcium ions enter smooth muscle cells primarily from the extracellular fluid when calcium channels are activated leading to a rise in intracellular calcium concentration which initiates muscle contraction.

Answer 133

The lesser development of the sarcoplasmic reticulum in smooth muscle means that it relies more on extracellular calcium influx for contraction compared to skeletal muscle that utilizes stored calcium from the sarcoplasmic reticulum.

Answer 134

The latent period is the time it takes for diffusion to occur before muscle contraction begins averaging 200 to 300 milliseconds.

Answer 135

The latent period for smooth muscle contraction is about 50 times greater than that for skeletal muscle contraction.

Answer 136

The smooth muscle sarcoplasmic reticulum releases calcium ions needed for muscle contraction when an action potential is transmitted.

Answer 137

Caveolae are small invaginations of the cell membrane that abut the surfaces of sarcoplasmic tubules in some smooth muscle cells.

Answer 138

Caveolae are involved in exciting calcium ion release from abutting sarcoplasmic tubules upon receiving an action potential.

Answer 139

In smooth muscle action potentials in caveolae cause calcium release from adjacent sarcoplasmic tubules similar to how action potentials in skeletal muscle transverse tubules release calcium from longitudinal sarcoplasmic tubules.

Answer 140

Figure 8-4 illustrates the slightly developed sarcoplasmic tubules and caveolae in smooth muscle cells.

Answer 141

The sarcoplasmic reticulum in smooth muscle is less developed and has a different arrangement with caveolae present unlike the more organized transverse tubule system in skeletal muscle.

Answer 142

The composition and arrangement of the smooth muscle sarcoplasmic reticulum facilitate the rapid release of calcium ions which is crucial for initiating contraction.

Answer 143

Generally the more extensive the sarcoplasmic reticulum the more efficient the release of calcium ions leading to a more effective muscle contraction.

Answer 144

The sarcoplasmic reticulum in smooth muscle fibers is responsible for storing calcium ions which are crucial for muscle contraction. The presence of sarcoplasmic reticulum allows for a more rapid contraction in smooth muscle.

Answer 145

Smooth muscle contraction is highly dependent on the concentration of extracellular calcium ions. Unlike skeletal muscle where changes in extracellular calcium concentration have little effect on contraction a significant decrease in extracellular calcium concentration (to about 13-110% of normal) can lead to cessation of contraction in smooth muscle.

Answer 146

When extracellular fluid calcium ion concentration decreases significantly typically to about 13-110% of normal smooth muscle contraction usually ceases. This highlights the critical role extracellular calcium plays in smooth muscle function.

Answer 147

To relax smooth muscle after contraction calcium ions must be removed from the intracellular fluids. This is achieved by a calcium pump that actively transports calcium ions out of the smooth muscle fiber either back into the extracellular fluid or into the sarcoplasmic reticulum if available.

Answer 148

The calcium pump in smooth muscle fibers is essential for relaxation. It removes calcium ions from the intracellular environment thereby reducing calcium concentration and allowing the muscle fiber to relax after contraction.

Answer 149

The contraction mechanism of smooth muscle is more dependent on extracellular calcium concentrations while the contraction of skeletal muscle is less affected by changes in extracellular calcium levels. This difference is crucial in understanding how each muscle type responds to stimuli and regulates contraction.

Answer 150

Extracellular calcium ion concentration is critical for smooth muscle function as it directly influences the ability of the muscle to contract. A decrease in extracellular calcium can lead to a significant decrease or cessation of contraction unlike skeletal muscle where such changes have little impact.

Answer 151

ATP is the primary energy source required for the pump that regulates smooth muscle contraction.

Answer 152

Smooth muscle contractions often last for seconds while skeletal muscle contractions last for hundredths to tenths of a second.

Answer 153

Calcium channels closing leads to the transport of calcium ions out of the cytosolic fluid which is critical for the relaxation of smooth muscle.

Answer 154

The calcium ion concentration falls below a critical level allowing for the reversal of contraction processes.

Answer 155

Myosin phosphatase is responsible for the cessation of contraction. It splits the phosphate from the regulatory light chain of myosin stopping the cycling and ceasing contraction.

Answer 156

Myosin phosphatase is located in the cytosol of the smooth muscle cell and is essential for reversing the phosphorylation of the myosin head allowing relaxation of the muscle.

Answer 157

The calcium pump's activity transports calcium ions out of the cell contributing to muscle relaxation.

Answer 158

A critical level of calcium ion concentration is necessary for maintaining contraction; falling below this level initiates relaxation.

Answer 159

Smooth muscle contraction is slower than skeletal muscle contraction due to the slower action of the calcium pump and the regulatory mechanisms involved.

Answer 160

Muscle relaxation in smooth muscle involves the closure of calcium channels the action of the calcium pump to remove calcium ions and the activity of myosin phosphatase to dephosphorylate myosin halting contraction.

Answer 161

The extent of the latch phenomenon in smooth muscle cells is determined to a great extent by the amount of active myosin phosphatase present in the cell.

Answer 162

The latch phenomenon in smooth muscle allows for the long-term maintenance of muscle tone with minimal energy expenditure.

Answer 163

Key components involved in the relaxation process of smooth muscle include extracellular fluid sarcoplasmic reticulum calcium ions (Ca2+) ATP calmodulin (CaM) myosin myosin phosphatase phosphorylated myosin ADP (adenosine diphosphate) ATP (adenosine triphosphate) Na+ and phosphate.

Answer 164

Calcium ions (Ca2+) play a crucial role in smooth muscle relaxation as they are involved in enzymatic reactions that help reduce the phosphorylation of myosin leading to muscle relaxation.

Answer 165

Myosin phosphatase is responsible for dephosphorylating myosin which contributes to the maintenance of the latch phenomenon facilitating sustained muscle tone with low energy expenditure.

Answer 166

Calmodulin (CaM) acts as a calcium-binding protein that upon binding to Ca2+ activates myosin light chain kinase which phosphorylates myosin initiating muscle contraction.

Answer 167

Increased myosin phosphatase activity leads to a decrease in phosphorylated myosin levels promoting relaxation of the smooth muscle and potentially reducing the tone of the muscle.

Answer 168

The latch phenomenon is important for the function of many smooth muscle organs as it allows for sustained contraction and tone without the need for continuous energy consumption optimizing metabolic efficiency.

Answer 169

The components involved in excitation-contraction coupling in smooth muscle include calcium ions (Ca2+) calmodulin (CaM) myosin light chain kinase (MLCK) myosin phosphatase phosphorylated myosin ATP ADP and the sarcoplasmic reticulum.

Answer 170

Figure 8-5 which shows components such as extracellular fluid sarcoplasmic reticulum calcium ions calmodulin myosin myosin phosphatase and phosphorylated myosin along with arrows indicating the flow of ions and reactions.

Answer 171

Smooth muscle can be stimulated to contract by nervous signals hormonal stimulation stretch of the muscle and several other mechanisms.

Answer 172

Skeletal muscle fibers are stimulated exclusively by the nervous system whereas smooth muscle can be stimulated by various methods including nervous signals hormones stretch and others.

Answer 173

Autonomic neuron varicosities branch diffusely and secrete neurotransmitters from multiple sites which can stimulate smooth muscle contraction.

Answer 174

Gap junctions are connections between unitary visceral smooth muscle cells that allow depolarization to rapidly spread from one cell to another enabling the muscle to contract as a single unit.

Answer 175

Unitary visceral smooth muscle cells contract as a single unit due to gap junctions while multi-unit smooth muscle is comprised of cells that are stimulated independently by neurotransmitters released from nearby autonomic nerve varicosities.

Answer 176

Multi-unit smooth muscle is a type of smooth muscle in which each cell is stimulated independently by a neurotransmitter released from closely associated autonomic nerve varicosities.

Answer 177

Neurotransmitter receptors on smooth muscle membranes play a key role in facilitating the contraction process by responding to signals from autonomic neurons.

Answer 178

The ability of smooth muscle to respond to multiple types of stimuli allows for more complex and varied control of bodily functions including digestion blood flow and respiratory processes.

Answer 179

Hormonal stimulation can initiate or modify the contraction of smooth muscle impacting processes like digestion hormonal regulation and vascular changes.

Answer 180

Various neurotransmitters including acetylcholine and norepinephrine are involved in stimulating smooth muscle contraction through their specific receptors on the smooth muscle cells.

Answer 181

Receptor proteins in smooth muscle can initiate contraction or inhibit contraction distinguishing them from skeletal muscle.

Answer 182

Smooth muscle contraction is controlled by nervous hormonal and other factors which can initiate or inhibit the contraction process.

Answer 183

Smooth muscle does not have the structured neuromuscular junctions found in skeletal muscle. Instead autonomic nerve fibers branch diffusely over the muscle fiber surface.

Answer 184

Autonomic nerve fibers generally do not make direct contact with smooth muscle fiber cell membranes; they form diffuse junctions that release neurotransmitters into the surrounding matrix.

Answer 185

Neurotransmitters released by the autonomic nerve fibers act at a distance of a few nanometers to a few micrometers away from the actual muscle cells.

Answer 186

The matrix coating of smooth muscle plays a role in transmitting the signals from the autonomic nerve fibers to the smooth muscle cells facilitating contraction or inhibition.

Answer 187

Smooth muscle contraction can be influenced by neural control hormonal control and other non-hormonal mechanisms.

Answer 188

Smooth muscle fibers are organized in sheets or layers with autonomic nerve fibers branching diffusely over them unlike the structured arrangement in skeletal muscle.

Answer 189

Stimulation of receptor proteins in smooth muscle initiates a contraction or relaxation response depending on the type of receptor and the neurotransmitter involved.

Answer 190

Understanding the mechanisms of smooth muscle contraction is crucial for comprehend physiological processes like digestion blood vessel regulation and respiratory function.

Answer 191

Diffusion is the process where a substance moves from an area of higher concentration to an area of lower concentration until equilibrium is reached.

Answer 192

In muscle tissues with several layers of muscle cells the nerve fibers typically innervate only the outer layer. Muscle excitation then travels from the outer layer to the inner layers through action potential conduction or by the diffusion of the neurotransmitter.

Answer 193

Action potential conduction refers to the propagation of electrical signals or action potentials across the muscle tissue enabling muscle contraction and communication between muscle cells.

Answer 194

Axons that innervate smooth muscle fibers lack the typical branching end feet seen in the motor end plates of skeletal muscle fibers. Instead they feature fine terminal axons with multiple varicosities along their length.

Answer 195

Varicosities are bulbous swellings or enlargements along the terminal axons of autonomic nerve fibers. They facilitate the release of neurotransmitter substances to nearby smooth muscle fibers.

Answer 196

Schwann cells envelop the axons innervating smooth muscle fibers but at the varicosities their presence is interrupted to allow for the secretion of neurotransmitters.

Answer 197

The varicosities contain vesicles similar to those in skeletal muscle end plates which store neurotransmitter substances. However while skeletal muscle vesicles always contain acetylcholine the vesicles in autonomic nerve fibers may contain various neurotransmitters.

Answer 198

Acetylcholine is the primary neurotransmitter associated with skeletal muscle junctions.

Answer 199

Communication occurs through the varicosities where neurotransmitter release occurs. This allows the axons to influence smooth muscle contraction over a wider area due to the multiple varicosities that can interact with various muscle cells.

Answer 200

The innervation of smooth muscle fibers is less precise because the axons have multiple varicosities that can release neurotransmitter over a broad area rather than targeting a specific muscle cell unlike the direct transmission seen in skeletal muscle at the motor end plate.

Answer 201

Fiber endings in smooth muscle fibers can contain acetylcholine in some fibers and norepinephrine in others along with occasionally other substances.

Answer 202

Contact junctions are specialized sites in multi-unit types of smooth muscle where varicosities are separated from the muscle cell membrane by 20 to 30 nanometers similar in width to the synaptic cleft found in skeletal muscle junctions. They function similarly to the skeletal muscle neuromuscular junction.

Answer 203

The rapidity of contraction in smooth muscle fibers connected to contact junctions is considerably faster than that of fibers stimulated by diffuse junctions.

Answer 204

The two primary transmitters secreted by autonomic nerves innervating smooth muscle are acetylcholine and norepinephrine.

Answer 205

No acetylcholine and norepinephrine are never secreted by the same nerve fibers in smooth muscle.

Answer 206

Acetylcholine acts as an excitatory transmitter substance for smooth muscle.

Answer 207

The 20 to 30 nanometer gap found in contact junctions of smooth muscle is significant because it allows for a rapid transmission of signals similar to the synaptic cleft in skeletal muscle facilitating quicker muscle contractions.

Answer 208

Rapid contraction is observed in the multi-unit types of smooth muscle particularly those utilizing contact junctions.

Answer 209

Other substances may occasionally be present at smooth muscle fiber endings although they are not as commonly identified as acetylcholine and norepinephrine.

Answer 210

The primary function of neurotransmitter substances at the smooth muscle neuromuscular junction is to facilitate communication between nerve fibers and smooth muscle cells regulating contraction and muscle tone.

Answer 211

When acetylcholine excites a muscle fiber norepinephrine ordinarily inhibits it.

Answer 212

The relationship is that when acetylcholine excites a muscle fiber norepinephrine inhibits it; conversely when acetylcholine inhibits a fiber norepinephrine usually excites it.

Answer 213

The different responses are due to the types of receptor proteins on the muscle cell membrane; some receptors are excitatory while others are inhibitory.

Answer 214

Acetylcholine and norepinephrine affect smooth muscle by binding to receptor proteins on the muscle cell membrane which can be either excitatory or inhibitory determining the muscle's response.

Answer 215

The type of receptor protein on the muscle cell membrane determines whether smooth muscle is inhibited or excited.

Answer 216

More information about the receptor proteins and their functions can be found in Chapter 61 regarding the function of the autonomic nervous system.

Answer 217

The two main neurotransmitters discussed are acetylcholine and norepinephrine.

Answer 218

Excitatory receptors cause muscle contraction when activated while inhibitory receptors prevent contraction or cause relaxation when activated.

Answer 219

The significance of receptor type is that it determines the physiological response of smooth muscle to neurotransmitters which can either be contraction or relaxation.

Answer 220

Membrane potentials in smooth muscle refer to the electrical charge difference across the cell membrane that affects muscle contraction and relaxation.

Answer 221

Excitatory responses lead to muscle contraction while inhibitory responses lead to muscle relaxation.

Answer 222

Neurotransmitters like acetylcholine and norepinephrine bind to receptor proteins on muscle cells which then trigger either excitation or inhibition depending on the receptor type.

Answer 223

A neurotransmitter binds to a receptor protein on the smooth muscle cell membrane triggering a biochemical response that results in either muscle contraction (if excitatory) or relaxation (if inhibitory).

Answer 224

The membrane potential of smooth muscle in the normal resting state is usually about -50 to -60 millivolts.

Answer 225

The membrane potential of smooth muscle is about 30 millivolts less negative than that of skeletal muscle.

Answer 226

The type of action potential observed in cardiac muscle fibers is characterized by a prolonged period of contraction.

Answer 227

Smooth muscle cells have far more voltage-gated calcium channels than skeletal muscle cells but few voltage-gated sodium channels.

Answer 228

Sodium does not participate much in the generation of the action potential in most smooth muscle; the action potential is mainly generated by calcium ion flow.

Answer 229

The flow of calcium ions into the interior of the smooth muscle fiber is mainly responsible for generating the action potential.

Answer 230

The action potential in smooth muscle is significant as it leads to contraction and is crucial for functions such as vascular tone and motility in hollow organs.

Answer 231

Chapters 9 and 10 discuss the prolonged contraction period of cardiac muscle fibers.

Answer 232

The membrane potential of smooth muscle can be influenced by various physiological conditions such as hormonal signals stretch and specific neurotransmitters.

Answer 233

Calcium channels open much more slowly than sodium channels and remain open much longer.

Answer 234

These characteristics contribute to the prolonged plateau action potentials seen in some smooth muscle fibers.

Answer 235

Calcium ions not only enter the cells during the action potential but also act directly on the smooth muscle contractile mechanism to cause contraction.

Answer 236

Self-excitatory smooth muscle generates action potentials internally without any external stimulus often related to a basic slow wave rhythm of the membrane potential.

Answer 237

A slow wave potential refers to a basic rhythmic fluctuation of the membrane potential observed in visceral smooth muscle which can lead to the spontaneous generation of action potentials.

Answer 238

Slow wave potentials can be depicted as a typical waveform graph demonstrating the rhythmic oscillation of membrane potential over time.

Answer 239

The slow wave rhythm in gut smooth muscle can facilitate spontaneous action potentials leading to coordinated contractions necessary for gut motility.

Answer 240

Calcium ions upon entering the smooth muscle cells during an action potential directly initiate contraction by interacting with the contractile mechanism within the fibers.

Answer 241

A slow wave is a local property of smooth muscle fibers that is not an action potential; it represents a rhythmic variation in membrane potential but does not spread progressively like an action potential.

Answer 242

The slow wave is not a self-regenerative process and does not propagate over the membranes of muscle fibers like an action potential does.

Answer 243

1. Waxing and waning of the pumping of positive ions (presumably sodium ions) outward through the muscle fiber membrane leading to fluctuations in membrane potential. 2. Rhythmic increases and decreases in the conductances of ion channels.

Answer 244

When sodium pumps are rapidly active the membrane potential becomes more negative; when their activity decreases the membrane potential becomes less negative contributing to the generation of slow waves.

Answer 245

No slow waves themselves cannot cause muscle contraction. They must be strong enough to initiate action potentials which then lead to muscle contraction.

Answer 246

When the peak of the negative slow wave potential rises towards the positive direction it can trigger action potentials in the smooth muscle fibers.

Answer 247

The significance of slow waves is that they can lead to the generation of action potentials when they reach a certain threshold which can ultimately result in muscle contraction.

Answer 248

The approximate threshold for eliciting action potentials in most visceral smooth muscle is from -60 to about -35 millivolts.

Answer 249

When the threshold is reached an action potential develops and spreads over the muscle mass resulting in contraction.

Answer 250

Figure 8-7A illustrates a graph showing a typical smooth muscle action potential spike potential demonstrating a spike potential elicited by an external stimulus.

Answer 251

Figure 8-7B represents a graph of a slow wave potential in the visceral smooth muscle of the gut.

Answer 252

Figure 8-7C depicts a graph of a smooth muscle action potential with a plateau.

Answer 253

Panel A shows a spike potential elicited by an external stimulus while Panel B shows repetitive spike potentials due to slow rhythmical electrical waves.

Answer 254

The plateau phase of action potentials is significant because it prolongs the duration of the contraction allowing for a sustained contraction which is important for the function of various visceral smooth muscles.

Answer 255

Figure 8-7 depicts spike potentials slow wave potentials and action potentials with a plateau highlighting different types of electrical activity that can occur in smooth muscle.

Answer 256

Slow rhythmical electrical waves lead to repetitive spike potentials which can trigger wave-like contractions in the visceral smooth muscle.

Answer 257

Understanding action potentials in visceral smooth muscle is crucial for medical students as it relates to the function of various organs within the digestive system and their regulation as well as implications in conditions that affect smooth muscle activity.

Answer 258

Slow wave potentials are rhythmic fluctuations in membrane potential that occur in visceral smooth muscle. They can trigger one or more action potentials at each peak resulting in the rhythmic contraction of the smooth muscle mass. These slow waves are often referred to as pacemaker waves.

Answer 259

Slow waves control the rhythmical contractions of the gut by generating action potentials in visceral smooth muscle. The rhythmic nature of these contractions is essential for gut motility and gut health.

Answer 260

During a peak of a slow wave one or more action potentials can occur leading to the contraction of the smooth muscle. This process allows the muscle to respond rhythmically to stimuli.

Answer 261

When visceral unitary smooth muscle is stretched sufficiently it generates spontaneous action potentials. This response is due to a combination of the normal slow wave potentials and a decrease in overall negativity of the membrane potential due to the stretch.

Answer 262

The stretching of the gut wall leads to automatic and rhythmic contractions that help in moving contents along the digestive tract. This mechanism allows the gut to respond to overfilling effectively.

Answer 263

Peristaltic waves are contractions that move contents through the intestines. They are often initiated by local automatic contractions that occur when the gut is excessively stretched by intestinal contents.

Answer 264

Action potentials in smooth muscle result from slow wave potentials triggering rhythmic contractions that are essential for the functioning of various smooth muscle tissues particularly in the gut.

Answer 265

Pacemaker waves refer to slow wave potentials in visceral smooth muscle that initiate action potentials leading to rhythmic contractions necessary for processes like gut motility.

Answer 266

During muscle stretch the membrane potential becomes less negative which combined with normal slow wave activity can enhance the generation of action potentials leading to contraction.

Answer 267

Rhythmic contractions of smooth muscle controlled by pacemaker activity are essential for functions such as peristalsis in the gut facilitating the movement of contents digestion and absorption.

Answer 268

The gut responds to excessive stretching by initiating local automatic contractions that create peristaltic waves aiding in moving the contents away from the overfilled area.

Answer 269

When the gut wall is overfilled the stretching leads to a generation of spontaneous action potentials due to the combined effects of slow waves and the change in membrane potential resulting in rhythmic contractions that push the contents forward.

Answer 270

The primary function of multi-unit smooth muscle is to contract mainly in response to nerve stimuli enabling fine control over activities such as the adjustment of pupil size in the iris of the eye and hair standing up due to piloerection.

Answer 271

Acetylcholine and norepinephrine are the neurotransmitters involved in the contraction of multi-unit smooth muscle. Acetylcholine is secreted by nerve endings in some multi-unit smooth muscles while norepinephrine is secreted in others.

Answer 272

During depolarization the smooth muscle membrane experiences a change in electrical potential which causes the muscle to contract. This depolarization occurs due to the action of neurotransmitters like acetylcholine and norepinephrine.

Answer 273

Action potentials usually do not develop in multi-unit smooth muscle because the muscle fibers are too small to generate an action potential. Instead contraction occurs in response to local depolarization.

Answer 274

In visceral unitary smooth muscle approximately 30 to 40 smooth muscle fibers must depolarize simultaneously to elicit a self-propagating action potential.

Answer 275

The localized depolarization in small smooth muscle cells even without an action potential is called the junctional depolarization.

Answer 276

Examples of multi-unit smooth muscles include the iris of the eye which controls pupil size and the piloerector muscles associated with hair follicles that cause hair to stand upright.

Answer 277

Multi-unit smooth muscle responds mainly to nerve stimuli with localized contractions and typically does not generate action potentials while visceral unitary smooth muscle can generate action potentials when a sufficient number of fibers depolarize simultaneously.

Answer 278

Acetylcholine acts as a neurotransmitter that when secreted by nerve endings causes depolarization of the smooth muscle membrane which ultimately leads to contraction of the muscle.

Answer 279

In multi-unit smooth muscle contraction can be triggered by local depolarization due to neurotransmitter release even without the generation of action potentials.

Answer 280

The potential spreads 'electrotonically' over the entire fiber which is sufficient to induce muscle contraction.

Answer 281

1. Local tissue chemical factors acting directly on the smooth muscle contractile machinery. 2. Various hormones that influence smooth muscle contraction.

Answer 282

Approximately half of all smooth muscle contraction is likely initiated by stimulatory factors acting directly.

Answer 283

1. Local tissue chemical factors. 2. Various hormones.

Answer 284

The contraction of arterioles meta-arterioles and pre-capillary sphincters is discussed in relation to local tissue chemical factors.

Answer 285

The smallest blood vessels which have little or no nervous supply exhibit rapid smooth muscle contraction in response to alterations in local chemical conditions in the interstitial fluid.

Answer 286

Local tissue chemical factors are crucial in initiating the contraction of smooth muscle especially in the absence of nervous stimulation.

Answer 287

Potential examples include changes in pH oxygen concentration carbon dioxide levels and the presence of specific ions.

Answer 288

Hormones can modulate smooth muscle contractions in various contexts potentially enhancing or inhibiting contraction based on physiological demands.

Answer 289

Smooth muscle can quickly respond to changes in the local interstitial fluid conditions such as the concentration of certain ions or metabolites leading to contraction even without nerve stimulation.

Answer 290

In the normal resting state many small blood vessels remain contracted.

Answer 291

Multiple factors can relax the vessel wall allowing for increased blood flow.

Answer 292

A powerful local feedback control system regulates blood flow to the local tissue area.

Answer 293

Lack of oxygen in the local tissues causes smooth muscle relaxation resulting in vasodilation.

Answer 294

Excess carbon dioxide leads to vasodilation.

Answer 295

Increased hydrogen ion concentration causes vasodilation.

Answer 296

Adenosine lactic acid increased potassium ions nitric oxide and increased body temperature can all lead to local vasodilation.

Answer 297

Decreased blood pressure causes decreased stretch of the vascular smooth muscle which results in dilation of small blood vessels.

Answer 298

Many circulating hormones in the blood affect the contraction of smooth muscle.

Answer 299

When tissue oxygen levels are low blood vessels dilate to increase blood flow and deliver more oxygen.

Answer 300

Vasodilation is the widening of blood vessels which increases blood flow to tissues delivering necessary nutrients and oxygen while removing waste.

Answer 301

1. Lack of oxygen in tissues 2. Excess carbon dioxide 3. Increased hydrogen ion concentration.

Answer 302

Conditions that raise blood pressure can lead to smooth muscle contraction in blood vessels.

Answer 303

Increased body temperature generally leads to vasodilation enhancing blood flow.

Answer 304

Nitric oxide promotes vasodilation in blood vessels.

Answer 305

Important hormones that influence muscle contraction include norepinephrine epinephrine angiotensin II endothelin vasopressin oxytocin serotonin and histamine.

Answer 306

A hormone causes contraction of a smooth muscle when the muscle cell membrane has hormone-gated excitatory receptors specific to that hormone.

Answer 307

When a smooth muscle membrane contains inhibitory receptors for a hormone it causes inhibition rather than contraction.

Answer 308

Some hormone receptors in the smooth muscle membrane can open sodium or calcium ion channels leading to membrane depolarization similar to nerve stimulation. This can result in action potentials or enhance existing action potentials. In some situations depolarization may occur without action potentials allowing for calcium ion entry.

Answer 309

Calcium ions play a crucial role in smooth muscle contraction as their entry into the muscle cell facilitates the contraction process often triggered by depolarization of the membrane.

Answer 310

Yes smooth muscle contraction can occur without action potentials as depolarization can happen independently of action potentials allowing for calcium ion entry into the muscle cell.

Answer 311

Hormone-gated excitatory receptors are specific receptors on the muscle cell membrane that when activated by hormones open ion channels that depolarize the cell membrane leading to muscle contraction.

Answer 312

Nerve stimulation can depolarize the smooth muscle membrane similar to how certain hormones can depolarize the membrane potentially leading to muscle contraction.

Answer 313

Hormone receptors in smooth muscle are significant because they determine whether the muscle will contract or be inhibited depending on whether they are excitatory or inhibitory receptors.

Answer 314

Norepinephrine and epinephrine can cause smooth muscle contraction by binding to excitatory receptors on the muscle cell membrane leading to membrane depolarization and calcium ion influx.

Answer 315

Contraction in muscle cells is promoted by the opening of sodium and calcium channels allowing positive ions to enter the cell.

Answer 316

Inhibition occurs when hormones or tissue factors close sodium and calcium channels to prevent the entry of these positive ions. Additionally inhibition happens if normally closed potassium channels are opened allowing potassium ions to diffuse out of the cell.

Answer 317

Hyperpolarization is the state of increased negativity inside the muscle cell which occurs when potassium ions diffuse out and it strongly inhibits muscle contraction.

Answer 318

Hormones can initiate smooth muscle contraction or inhibition by activating membrane receptors that may not cause direct changes in the membrane potential leading to downstream effects.

Answer 319

Membrane receptors activated by hormones can influence smooth muscle contraction without directly altering the membrane potential.

Answer 320

The mechanisms involve the coordination of ion channel activities receptor activations and intracellular signaling pathways that lead to contraction or relaxation of smooth muscle.

Answer 321

The study discusses the mechanisms of vascular smooth muscle contraction and the pharmacologic treatment of smooth muscle disorders highlighting the molecular and cellular processes involved.

Answer 322

Understanding smooth muscle contraction is crucial in pharmacology because it underlies the development of treatments for various smooth muscle disorders allowing for targeted therapies.

Answer 323

Purinergic signaling involves the activation of purinergic receptors by nucleotides such as ATP and adenosine playing crucial roles in vasodilation modulation of vascular tone neurotransmission in the heart and regulation of platelet aggregation. It influences arterial contraction blood flow regulation and contributes to various physiological pathways including inflammation and cellular responses to stress.

Answer 324

The article 'Calcium sparks' was authored by Cheng H and Lederer WJ and focuses on the role of calcium sparks in cardiac and smooth muscle function how they are generated from ryanodine receptors and their significance in triggering muscle contractions and cellular signaling.

Answer 325

The vascular myogenic response is a mechanism where blood vessels react to changes in intraluminal pressure. It helps maintain consistent blood flow across various physiological conditions by inducing smooth muscle contraction in response to increased wall tension thereby regulating arterial diameter and resistance.

Answer 326

BK (Big Potassium) channels are calcium- and voltage-gated potassium channels that play a critical role in regulating vascular smooth muscle tone. They facilitate hyperpolarization and relaxation of the smooth muscle following calcium influx thus contributing to the regulation of blood vessel diameter and response to vascular stimuli.

Answer 327

Endothelial-smooth muscle cell interactions are crucial for the regulation of vascular tone particularly in skeletal muscle. These interactions involve the release of various signaling molecules such as nitric oxide from endothelial cells that relax smooth muscle cells modulating blood flow and pressure.

Answer 328

Epithelial Sodium Channels (ENaC) have been identified as potential mechanotransducers in vascular smooth muscle which means they can sense mechanical forces (like stretch) and convert them into biochemical signals that affect cellular function and vascular tone.

Answer 329

In small artery mechanobiology cellular elements such as vascular smooth muscle cells endothelial cells and extracellular matrix components interact to sense and respond to mechanical forces like shear stress and pressure. Non-cellular elements such as the properties of the vessel wall itself and the surrounding tissue also play a role in modulating vascular responses to mechanical stimuli.

Answer 330

Gut peristalsis is governed by a multitude of cooperating mechanisms including the coordinated contraction of smooth muscle layers neural control and the complex interplay of various chemical signals and local reflexes that enable efficient movement of food through the gastrointestinal tract.

Answer 331

The emerging role of the vascular system includes the integration of complex signaling pathways involving purinergic signaling mechanotransduction and cell-cell interactions that collectively regulate blood flow vascular health and responses to physiological changes.

Answer 332

G protein-coupled receptors (GPCRs) play a crucial role in the regulation of microvascular myogenic tone by mediating signaling pathways that influence vascular smooth muscle contraction. They activate various intracellular signaling cascades in response to external stimuli which can lead to changes in intracellular calcium levels and muscle cell contraction.

Answer 333

Lacolley et al. discussed how vascular smooth muscle cells contribute to arterial stiffening particularly during development aging and in disease states. They highlighted the mechanisms by which smooth muscle cells adapt and change influencing the elasticity of blood vessels and how this is related to conditions such as hypertension.

Answer 334

Cross-bridge regulation in vascular smooth muscle involves the interaction of myosin heads with actin filaments mediated by calcium ions and regulatory proteins. The process is influenced by thin filament-associated proteins that modulate the activation state of myosin thus affecting the contraction strength and duration.

Answer 335

Ratz PH described the mechanics of vascular smooth muscle as involving the contraction and relaxation processes that regulate vascular tone. This includes elastic properties of the muscle fibers the viscoelastic behavior and how these factors collaborate to maintain vessel diameter and resistance.

Answer 336

Interstitial cells particularly interstitial cells of Cajal (ICC) play a pivotal role in gastrointestinal smooth muscle function by acting as pacemakers and modulating contractile activity. They generate spontaneous electrical activity which coordinates contractions and regulates peristalsis.

Answer 337

The sensitivity of smooth muscle and non-muscle myosin II to calcium ions (Ca2+) is crucial for muscle contraction. Somlyo AP and Somlyo AV indicated that this sensitivity can be modified by G proteins kinases and myosin phosphatase affecting contractile force and participating in various physiological responses.

Answer 338

Vascular tone in resistance arteries and arterioles is regulated by various types of ion channels including voltage-gated calcium channels potassium channels and transient receptor potential (TRP) channels. These channels facilitate the influx or efflux of ions thus modulating smooth muscle contraction and vascular resistance.

Answer 339

Webb RC identified several mechanisms that contribute to smooth muscle contraction and relaxation including the roles of calcium influx phosphorylation of myosin light chain by myosin light chain kinase (MLCK) and the action of myosin phosphatase that lowers tension by dephosphorylating myosin. Additionally various receptor activities influence these processes.

Answer 340

The heart consists of a right heart that pumps blood through the lungs and a left heart that pumps blood through the systemic circulation to provide blood flow to the organs and tissues of the body.

Answer 341

Each side of the heart has two chambers: an atrium and a ventricle.

Answer 342

The atria serve as weak primer pumps for the ventricles helping to move blood into the ventricles.

Answer 343

The ventricles provide the main pumping force to circulate blood throughout the body.

Answer 344

The article discusses the implications of spreading the signal for vasodilatation on skeletal muscle blood flow control and how aging affects this process.

Answer 345

The mechanisms involve how calcium ions activate smooth muscle cells contributing to muscle contraction.

Answer 346

The study explores sodium-calcium exchange and its physiological implications primarily looking at how this process regulates calcium levels in cardiac and smooth muscle.

Answer 347

The heart is structured as two pulsatile two-chamber pumps each consisting of an atrium and a ventricle.

Answer 348

Aging can impact the physiological mechanisms governing blood flow control leading to reduced efficiency in the vasodilatation process as discussed by Behringer and Segal.

Answer 349

Sodium-calcium exchange is crucial for maintaining calcium homeostasis in cardiac cells affecting the strength and timing of cardiac contractions.

Answer 350

Physiological implications refer to how specific biological processes or mechanisms affect overall bodily function such as how calcium levels influence muscle contraction or how vasodilatation affects blood flow.

Answer 351

1. Pulmonary circulation by the right ventricle. 2. Systemic circulation by the left ventricle.

Answer 352

The pericardium is a two-layer sac that surrounds the heart protecting it and holding it in place.

Answer 353

Cardiac rhythmicity refers to the continuous succession of contractions in the heart caused by the transmission of action potentials throughout the cardiac muscle leading to the heart's rhythmical beat.

Answer 354

The heart is composed of three major types of cardiac muscle: atrial muscle ventricular muscle and specialized excitatory and conductive muscle fibers.

Answer 355

While atrial and ventricular muscle contracts in a similar manner to skeletal muscle the duration of contraction in cardiac muscle is much longer.

Answer 356

These special mechanisms cause cardiac rhythmicity allowing for synchronized contractions that propel blood through the circulatory system.

Answer 357

The different types of cardiac muscle allow for specialized functions such as effective pumping (ventricular muscle) and coordination of electrical signals (conductive muscle fibers) which are critical for maintaining a steady heartbeat.

Answer 358

The rhythmical control system of the heart is discussed in Chapter 10.

Answer 359

Video 9-1 covers the physiology of cardiac muscle.

Answer 360

The specialized fibers of the heart responsible for automatic rhythmical electrical discharge are known as excitatory and conductive fibers which generate action potentials and conduct these potentials through the heart.

Answer 361

These specialized fibers contract feebly because they contain few contractile fibrils.

Answer 362

Action potentials provide an excitatory system that controls the rhythmical beating of the heart.

Answer 363

Cardiac muscle fibers are arranged in a latticework with the fibers dividing recombining and then spreading again. Cardiac muscle is striated similar to skeletal muscle.

Answer 364

Myofibrils are structures in cardiac muscle that contain actin and myosin filaments.

Answer 365

Actin and myosin filaments lie side by side and slide past each other during contraction similar to the mechanism in skeletal muscle.

Answer 366

Cardiac muscle is similar to skeletal muscle in that it is striated and contains typical myofibrils made up of actin and myosin.

Answer 367

Cardiac muscle differs from skeletal muscle in several ways such as its involuntary control intercalated discs for cell communication and a unique structure allowing for rhythmic contractions.

Answer 368

The latticework arrangement of cardiac muscle fibers allows for efficient contraction and communication between fibers ensuring coordinated heartbeats.

Answer 369

Intercalated discs are specialized structures that facilitate the rapid transmission of electrical signals between cardiac muscle cells and synchronize contractions.

Answer 370

The automatic rhythmical electrical discharge occurs through the generation of action potentials by sinoatrial (SA) node cells which then propagate through the heart via conduction pathways.

Answer 371

The rhythm of the heart is influenced by the excitatory and conductive fibers particularly the sinoatrial (SA) node and other pacemaker cells.

Answer 372

Understanding cardiac muscle physiology is crucial for diagnosing and treating heart diseases managing arrhythmias and performing interventions like pacemaker implantation.