Chapter 10 Flashcards
(176 cards)
1
Q
What is the primary function of skeletal muscles in terms of movement?
A
keletal muscles move the body by moving bones, enabling actions like facial expressions, speaking, breathing, and swallowing
2
Q
How do skeletal muscles help with posture?
A
Skeletal muscles stabilize joints and maintain body position to help keep posture.
3
Q
What role do skeletal muscles play in protecting and supporting the body?
A
Skeletal muscles package internal organs and hold them in place, offering protection and support.
4
Q
How do skeletal muscles regulate elimination of materials from the body?
A
Circular sphincters in skeletal muscles control the passage of material at body orifices, such as the anus and urethra.
5
Q
How do skeletal muscles contribute to maintaining body temperature?
A
Skeletal muscles produce heat during contraction, helping to regulate body temperature.
6
Q
Elasticity
A
ability to return to original length following a
lengthening or shortening
3
7
Q
Extensibility
A
ability to be stretched
8
Q
Contractility
A
exhibited when filaments slide past each other
9
Q
what Enables muscle to cause movement
A
Contractility
10
Q
conductivity
A
involves sending an electrical change down
the length of the cell membrane
11
Q
excitability
A
ability to respond to a stimulus by changing
electrical membrane potential
12
Q
What is the skeletal muscle considered in terms of anatomy?
A
A skeletal muscle is considered an organ made up of multiple tissue types working together: muscle fibers, connective tissue, blood vessels, and nerves
13
Q
How are muscle fibers arranged within a muscle?
A
Muscle fibers are bundled together within a fascicle.
14
Q
What is a fascicle in the context of skeletal muscle?
A
A fascicle is a bundle of muscle fibers, and a whole muscle contains many fascicles.
15
Q
What is a muscle fiber?
A
A muscle fiber is a single muscle cell, which makes up the fascicles within a skeletal muscle.
16
Q
What are the three concentric layers of connective tissue in skeletal muscle?
A
The three layers are the epimysium, perimysium, and endomysium
17
Q
What is the epimysium?
A
The epimysium is a dense irregular connective tissue that wraps the entire skeletal muscle.
18
Q
What is the perimysium and its function?
A
The perimysium is a dense irregular connective tissue that wraps each fascicle (bundle of muscle fibers). It houses many blood vessels and nerves.
19
Q
What is the endomysium and its function?
A
The endomysium is a delicate layer of areolar connective tissue that wraps individual muscle fibers. It provides electrical insulation, supports capillaries, and binds neighboring muscle cells together.
20
Q
What are the two types of muscle attachments to bone, skin, or other muscles?
A
Tendons and aponeuroses
21
Q
What is a tendon?
A
A tendon is a cordlike structure made of dense regular connective tissue that attaches muscle to bone, skin, or other muscles.
22
Q
What is an aponeurosis?
A
An aponeurosis is a thin, flattened sheet of dense irregular connective tissue that attaches muscle to bone, skin, or other muscles.
23
Q
What is deep fascia and its function?
A
Deep fascia is dense irregular connective tissue located superficial to the epimysium. It separates individual muscles and binds muscles with similar functions together.
24
Q
What is superficial fascia and its function?
A
Superficial fascia is made of areolar and adipose connective tissue, located superficial to the deep fascia. It separates muscles from the skin.
25
How are skeletal muscles vascularized?
Skeletal muscles are highly vascularized, with extensive blood vessels that deliver oxygen and nutrients while removing waste products
26
What type of neurons innervate skeletal muscles?
Skeletal muscles are innervated by somatic motor neurons.
27
How do somatic motor neurons communicate with skeletal muscle fibers?
The axons of somatic motor neurons branch and terminate at neuromuscular junctions, where they transmit signals to muscle fibers.
28
Why is skeletal muscle considered voluntary?
Skeletal muscle is considered voluntary because its contraction is consciously controlled.
29
What is the sarcoplasm of a muscle cell, and what does it contain?
The sarcoplasm is the cytoplasm of a muscle cell. It contains typical organelles as well as contractile proteins and other special structures necessary for muscle function.
30
what is unique about the nuclei of muscle cells?
Muscle cells (fibers) are multinucleated, meaning they contain multiple nuclei, which form when individual myoblasts fuse during embryonic development.
31
What are satellite cells, and what is their function?
Satellite cells are undifferentiated myoblasts located near muscle fibers. They provide support and repair muscle fibers after injury.
32
What is the sarcolemma, and what role does it play in muscle cell function?
The sarcolemma is the plasma membrane of a muscle cell. It contains voltage-gated ion channels that help conduct electrical signals necessary for muscle contraction.
33
What are T-tubules, and what is their function in muscle cells?
T-tubules (transverse tubules) are extensions of the sarcolemma that penetrate deep into the muscle cell. They contain voltage-sensitive calcium channels, which play a key role in muscle contraction by allowing calcium to enter the cell.
34
What are myofibrils in a muscle cell?
Myofibrils are bundles of myofilaments (actin and myosin) that are enclosed in the sarcoplasmic reticulum. A muscle cell can contain hundreds to thousands of myofibrils.
35
What is the function of the sarcoplasmic reticulum in muscle cells?
The sarcoplasmic reticulum is an internal membrane complex similar to the smooth endoplasmic reticulum. It stores and regulates calcium ions, which are crucial for muscle contraction.
36
What are myofilaments in muscle cells?
Myofilaments are contractile proteins within myofibrils that enable muscle contraction. There are two types: thick filaments and thin filaments.
37
What are thick filaments made of?
Thick filaments are made up of bundles of many myosin protein molecules. The myosin heads point toward the ends of the filament
38
What are thin filaments made of?
Thin filaments are twisted strands of actin. Each F-actin strand is composed of G-actin monomers.
39
What is the role of G-actin in muscle contraction
: G-actin has myosin-binding sites where the myosin heads attach during muscle contraction.
40
What regulatory proteins are associated with thin filaments?
Tropomyosin and troponin are regulatory proteins present on the thin filaments. They help control the interaction between actin and myosin during contraction.
41
What is a sarcomere?
A sarcomere is the repeating unit of a muscle fiber that contains overlapping thick and thin myofilaments.
42
What structure delineates the ends of a sarcomere?
The ends of a sarcomere are delineated by Z discs, which are specialized proteins that anchor the thin filaments
43
What is the function of the Z discs in a sarcomere?
The Z discs serve as anchors for the thin filaments and help define the boundaries of a sarcomere.
44
What do the positions of thin and thick filaments create in a sarcomere?
The arrangement of thin and thick filaments creates alternating light I-bands and dark A-bands in the sarcomere.
45
What do the I bands represent in a sarcomere?
The I bands are light-appearing regions that contain only thin filaments. They are bisected by the Z disc.
46
How do the I bands change during muscle contraction?
The I bands get smaller during muscle contraction and can disappear completely during maximal contraction.
47
What is the A band in a sarcomere?
The A band is the dark-appearing region of the sarcomere that contains thick filaments and overlapping thin filaments. It makes up the central region of the sarcomere.
48
What structures are found within the A band?
The A band contains the H zone (region with only thick filaments) and the M line (middle of the sarcomere where thick filaments are anchored).
49
What is the H zone in a sarcomere?
The H zone is the central portion of the A band, where only thick filaments are present, and there is no overlap with thin filaments.
50
how does the H zone change during muscle contraction?
The H zone disappears during maximal muscle contraction as the thin filaments slide over the thick filaments and overlap more.
51
What is the M line in a sarcomere?
The M line is located in the middle of the H zone and serves as the attachment site for thick filaments. It is composed of a protein meshwork structure.
52
Why do muscle fibers have abundant mitochondria?
Muscle fibers have abundant mitochondria to support aerobic ATP production, which is essential for sustained muscle contraction.
53
What role does myoglobin play in muscle cells?
Myoglobin within muscle cells stores oxygen, which is used for aerobic ATP production during muscle contraction.
54
What is glycogen, and how is it used by muscle cells?
Glycogen is a stored form of glucose in muscle cells. It provides a rapid source of fuel for ATP production when needed quickly during intense activity.
55
What is creatine phosphate, and how does it help muscle cells?
Creatine phosphate is a molecule that can quickly donate its phosphate group to replenish ATP supplies, providing an immediate source of energy for muscle contraction.
56
What is a motor unit in skeletal muscle?
A motor unit consists of a motor neuron and all the muscle fibers it controls.
57
How do motor neurons innervate skeletal muscle fibers?
Axons of motor neurons from the spinal cord (or brain) innervate multiple muscle fibers, forming motor units.
58
How does the number of muscle fibers innervated by a motor neuron vary?
The number of muscle fibers a motor neuron innervates can vary: small motor units innervate fewer fibers, while large motor units innervate thousands of fibers
59
What is the function of small motor units?
Small motor units, with fewer than five muscle fibers, allow for precise control of muscle force output.
60
What is the function of large motor units?
Large motor units, with thousands of muscle fibers, allow for the production of a large amount of force, but they do not provide precise control
61
How are the muscle fibers of a motor unit arranged in a muscle?
The muscle fibers of a motor unit are dispersed throughout the muscle, not located in a single, clustered compartment.
62
What is the neuromuscular junction?
The neuromuscular junction is the location where a motor neuron innervates a muscle fiber, allowing communication for muscle contraction.
63
Where is the neuromuscular junction typically located on a muscle fiber?
The neuromuscular junction is usually located at the mid-region of the muscle fiber.
64
What are the main components of the neuromuscular junction?
The neuromuscular junction consists of three main parts: the synaptic knob, the synaptic cleft, and the motor end plate.
65
What is the synaptic knob?
The synaptic knob is the expanded tip of the motor neuron axon at the neuromuscular junction. It plays a key role in transmitting signals to the muscle fiber.
66
What do synaptic vesicles in the synaptic knob contain?
Synaptic vesicles contain the neurotransmitter acetylcholine (ACh), which is released to communicate with the muscle fiber.
67
What role do Ca2+ pumps in the synaptic knob play?
Ca2+ pumps in the plasma membrane of the synaptic knob establish a calcium gradient, with a higher concentration of Ca2+ outside the neuron compared to inside.
68
What are voltage-gated Ca2+ channels, and what happens when they open?
Voltage-gated Ca2+ channels are located in the membrane of the synaptic knob. When these channels open, Ca2+ flows into the neuron, down its concentration gradient.
69
What is the motor end plate?
The motor end plate is a specialized region of the sarcolemma (muscle cell membrane) with numerous folds. It contains many acetylcholine (ACh) receptors.
70
What is the function of ACh receptors on the motor end plate?
The ACh receptors are plasma membrane protein channels that open when acetylcholine binds to them. This allows Na+ ions to enter the muscle cell and K+ ions to exit.
71
What is the synaptic cleft?
The synaptic cleft is a narrow, fluid-filled space that separates the synaptic knob of the motor neuron from the motor end plate of the muscle fiber.
72
What enzyme is found in the synaptic cleft, and what is its function?
Acetylcholinesterase is an enzyme found in the synaptic cleft. Its function is to break down acetylcholine (ACh) molecules after they have stimulated the ACh receptors, terminating the signal.
73
What is the first event that occurs at the neuromuscular junction in muscle contraction?
The motor neuron releases acetylcholine (ACh) into the synaptic cleft, which binds to receptors on the motor end plate of the muscle fiber.
74
What happens after acetylcholine binds to receptors on the motor end plate?
Binding of ACh opens ion channels in the motor end plate, allowing Na+ to enter the muscle fiber and K+ to exit, causing a change in membrane potential and initiating an action potential in the muscle fiber
75
How is the action potential propagated in the muscle fiber?
The action potential travels along the sarcolemma (muscle cell membrane) and into the T-tubules (transverse tubules), which transmit the signal deep into the muscle fiber.
76
What happens when the action potential reaches the sarcoplasmic reticulum?
The action potential triggers the release of calcium ions (Ca2+) from the sarcoplasmic reticulum into the cytoplasm of the muscle fiber.
77
What role do calcium ions play in muscle contraction
Calcium ions bind to troponin, a regulatory protein on the thin filaments of the sarcomere. This causes a conformational change that moves tropomyosin, exposing the myosin-binding sites on actin.
78
How do thick and thin filaments interact to cause muscle contraction?
A
Myosin heads on the thick filaments bind to the exposed myosin-binding sites on actin (thin filaments) and pull, using ATP to generate force, which shortens the sarcomere and results in muscle contraction.
79
What happens when the action potential stops?
Acetylcholine in the synaptic cleft is broken down by acetylcholinesterase, stopping the signal to the muscle. Calcium ions are pumped back into the sarcoplasmic reticulum, and the muscle relaxes as troponin and tropomyosin block the myosin-binding sites on actin.
80
calcium entry at
synaptic knob
81
nerve signal travels down
axon, opens voltage gated Ca2 channels. diffuses into synaptic knob, and binds to proteins on surface of synaptic vessicles.
82
calcium helps release_____ from synaptic knob
ACh
83
vesscles merge with cell membrane at ___
synaptic knob:exocytosis
84
thousand sof ACh molecules released from about ___ vesicles
300
85
What happens when acetylcholine (ACh) binds to receptors at the motor end plate
ACh diffuses across the synaptic cleft and binds to receptors on the motor end plate, which excites the muscle fiber and initiates an action potential in the muscle cell.
86
What is the first step in the neuromuscular junction process?
The action potential travels down the motor neuron, reaching the synaptic knob (axon terminal) at the neuromuscular junction.
87
How does calcium (Ca²⁺) play a role in neurotransmitter release at the neuromuscular junction?
The action potential causes voltage-gated calcium (Ca²⁺) channels in the synaptic knob to open, allowing Ca²⁺ to enter the neuron.
88
What happens when calcium enters the synaptic knob?
The influx of Ca²⁺ triggers synaptic vesicles filled with acetylcholine (ACh) to fuse with the presynaptic membrane, releasing ACh into the synaptic cleft.
89
What happens after acetylcholine (ACh) is released into the synaptic cleft?
ACh binds to receptors on the motor end plate (the muscle fiber’s membrane), opening ion channels and causing an influx of Na⁺ and a small amount of K⁺ to exit. This leads to a change in the membrane potential, initiating an action potential in the muscle fiber.
90
What is the role of calcium (Ca²⁺) inside the muscle fiber during contraction?
When the action potential travels down the T-tubules, it triggers the release of Ca²⁺ from the sarcoplasmic reticulum into the cytoplasm of the muscle fiber, which is crucial for muscle contraction.
91
How does calcium (Ca²⁺) trigger muscle contraction?
Calcium binds to the protein troponin on the thin filaments (actin), causing a conformational change that moves tropomyosin, exposing the myosin-binding sites on actin. This allows myosin heads to bind to actin, initiating the sliding filament mechanism of contraction.
92
What happens after muscle contraction?
After contraction, calcium ions are actively pumped back into the sarcoplasmic reticulum, and troponin and tropomyosin return to their resting positions, blocking myosin-binding sites and causing muscle relaxation.
93
What is the first event in the action potential at the sarcolemma?
An action potential arrives at the motor end plate, causing ACh to bind to receptors and open ion channels.
94
What happens when ion channels open at the motor end plate?
Sodium (Na⁺) enters the muscle fiber, causing depolarization of the sarcolemma.
95
How does the action potential spread along the sarcolemma?
The depolarization spreads along the sarcolemma and down the T-tubules, initiating an action potential in the muscle fiber
96
What is the result of the action potential reaching the T-tubules?
The action potential triggers the release of calcium (Ca²⁺) from the sarcoplasmic reticulum into the muscle fiber.
97
ow does the sarcolemma return to its resting state after depolarization?
Potassium (K⁺) exits the cell, repolarizing the sarcolemma and returning it to its resting membrane potential.
98
What happens during repolarization?
Potassium (K⁺) ions exit the muscle fiber, restoring the negative resting membrane potential
99
What happens when the action potential travels down the T-tubules?
The action potential causes voltage-sensitive calcium channels in the T-tubule membrane to open, triggering the release of calcium from the sarcoplasmic reticulum (SR).
100
How does calcium (Ca²⁺) release from the sarcoplasmic reticulum affect muscle contraction?
Calcium binds to myofilaments, specifically troponin, triggering a conformational change that leads to muscle contraction.
101
What happens when calcium (Ca²⁺) binds to troponin?
Calcium binding to troponin triggers the movement of troponin and tropomyosin, exposing the myosin-binding sites on actin.
102
How does the exposure of myosin-binding sites on actin affect muscle contraction?
The exposure of the myosin-binding sites allows the myosin heads to bind to actin, initiating crossbridge cycling and muscle contraction.
103
What happens during the first step of crossbridge cycling, crossbridge formation?
The myosin head attaches to the exposed binding site on actin, forming a crossbridge.
104
What occurs during the power stroke in crossbridge cycling?
The myosin head pulls the thin filament toward the center of the sarcomere, releasing ADP and Pi.
105
What happens during the release of the myosin head in crossbridge cycling?
ATP binds to the myosin head, causing it to release from the actin filament
106
How is the myosin head reset during crossbridge cycling?
ATP is split into ADP and Pi by myosin ATPase, providing energy to "cock" the myosin head for the next cycle.
107
How long does crossbridge cycling continue?
Crossbridge cycling continues as long as calcium (Ca²⁺) and ATP are present.
108
What is the result of continuous crossbridge cycling?
Sarcomere shortening occurs as the Z discs move closer together.
109
What happens to the H zone and I band during crossbridge cycling?
The H zone and I band narrow or disappear as the thick and thin filaments slide past each other.
110
Do the thick and thin filaments change length during crossbridge cycling?
No, the thick and thin filaments remain the same length but slide past each other.
111
What is the first step in muscle relaxation?
The nerve signal terminates, and acetylcholine (ACh) release from the motor neuron stops.
112
What happens to acetylcholine (ACh) after the nerve signal stops?
Acetylcholine is broken down by acetylcholinesterase, which halts its activity at the motor end plate.
113
What occurs after the ACh receptor closes?
The end plate potential ceases, and no further action potentials are generated in the muscle fiber.
114
What happens to the calcium channels in the sarcoplasmic reticulum during relaxation?
The calcium channels in the sarcoplasmic reticulum close, and calcium ions are pumped back into the SR.
115
How does the return of calcium to the sarcoplasmic reticulum affect muscle relaxation?
The return of calcium to the SR causes troponin to return to its original shape, blocking the myosin-binding sites on actin.
116
What happens to the muscle after relaxation?
The muscle returns to its original position due to its inherent elasticity.
117
How much ATP is stored in muscle cells?
Muscle cells have only a small amount of ATP stored, which is used up after about 5 seconds of intense exertion.
118
How is ATP rapidly produced after stored ATP is depleted?
Myokinase transfers a phosphate group from one ADP to another, rapidly generating more ATP.
119
What are the three ways to generate additional ATP in skeletal muscle fibers?
ATP is generated through creatine phosphate, glycolysis, and aerobic cellular respiration.
120
What type of bond does creatine phosphate contain?
Creatine phosphate contains a high-energy bond between creatine and phosphate.
121
How is ATP generated using creatine phosphate?
The phosphate from creatine phosphate is transferred to ADP to form ATP, a process catalyzed by creatine kinase.
122
ow long does creatine phosphate provide additional energy?
Creatine phosphate provides an additional 10-15 seconds of energy.
123
Does glycolysis require oxygen?
No, glycolysis does not require oxygen.
124
What is the end product of glycolysis?
Glycolysis converts glucose into two pyruvate molecules.
125
How much ATP is produced during glycolysis?
Glycolysis produces 2 ATP molecules per glucose molecule.
126
Where does glycolysis occur in the cell?
Glycolysis occurs in the cytosol of the cell
127
Does aerobic cellular respiration require oxygen?
Yes, aerobic cellular respiration requires oxygen.
128
Where does aerobic cellular respiration occur?
Aerobic cellular respiration occurs within the mitochondria.
129
What happens to pyruvate during aerobic cellular respiration?
Pyruvate is oxidized to carbon dioxide during aerobic cellular respiration.
130
What molecules are involved in the transfer of energy during aerobic respiration?
Energy is transferred to NADH and FADH₂ during aerobic respiration.
131
How is ATP generated in aerobic cellular respiration?
ATP is generated by oxidative phosphorylation, using the energy from NADH and FADH₂
132
How much ATP is produced through aerobic cellular respiration?
Aerobic cellular respiration produces a net of 30 ATP molecules.
133
Can triglycerides be used as a fuel for ATP production?
Yes, triglycerides can be used as fuel to produce ATP, especially when they have longer fatty acid chains.
134
When does lactate formation from pyruvate occur?
Lactate formation from pyruvate occurs under conditions of low oxygen availability.
135
How is lactate formed from pyruvate?
Pyruvate is converted to lactate by the enzyme lactate dehydrogenase.
136
Where can lactate be used as fuel?
Lactate can be used as fuel by skeletal muscle fibers or can enter the blood and be taken up by cardiac muscle or the liver.
137
What is the lactic acid cycle?
The lactic acid cycle involves the cycling of lactate to the liver, where it is converted to glucose, which is then transported back to the muscle.
138
What is oxygen debt?
Oxygen debt is the amount of additional oxygen needed after exercise to restore pre-exercise conditions.
139
What are the main purposes of the additional oxygen required during oxygen debt?
The additional oxygen is needed to replace oxygen on hemoglobin and myoglobin, replenish glycogen, convert lactic acid back to glucose, and replenish ATP and creatine phosphate.
140
What is the effect of endurance exercise on muscle?
Endurance exercise leads to better ATP production, including an increase in the number of mitochondria.
141
What is the effect of resistance exercise on muscle?
Resistance exercise leads to hypertrophy, which is an increase in muscle size due to the synthesis of contractile proteins.
142
How does resistance exercise affect glycogen and mitochondria?
Resistance exercise increases glycogen reserves and the number of mitochondria in muscle fibers.
143
What is the effect of exercise on muscle fibers' number?
There is limited hyperplasia, or an increase in the number of muscle fibers, with exercise.
144
What is muscle atrophy?
Atrophy is the decrease in muscle size due to lack of use, such as when a person wears a cast.
145
Is muscle atrophy reversible?
Muscle atrophy is initially reversible, but it can become permanent if the lack of use is extreme or prolonged.
146
what is the shape and structure of cardiac muscle cells?
Cardiac muscle cells are short, branching fibers with one or two nuclei.
147
Are cardiac muscle cells striated?
Yes, cardiac muscle cells are striated, containing sarcomeres
148
What is the role of mitochondria in cardiac muscle cells?
Cardiac muscle cells have many mitochondria and primarily use aerobic respiration to generate ATP.
149
What are intercalated discs and their function in cardiac muscle?
Intercalated discs join the ends of neighboring cardiac muscle fibers and contain desmosomes and gap junctions, allowing for synchronized contraction.
150
How are cardiac muscle contractions initiated?
Contractions are initiated by the heart's autorhythmic pacemaker cells.
151
How is heart rate and contraction force regulated?
Heart rate and contraction force are influenced by the autonomic nervous system.
152
Where is smooth muscle found in the cardiovascular system, and what is its role?
Smooth muscle in blood vessels helps regulate blood pressure and blood flow
153
How does smooth muscle function in the respiratory system?
In the bronchioles, smooth muscle controls airflow to the alveoli.
154
What role does smooth muscle play in the digestive system?
In the intestines, smooth muscle mixes and propels materials through the digestive tract.
155
How does smooth muscle function in the urinary system?
Smooth muscle in the ureters propels urine from the kidneys to the bladd
156
What is the role of smooth muscle in the female reproductive system?
In the uterus, smooth muscle is involved in contractions, such as during childbirth.
157
What is the shape of smooth muscle cells?
Smooth muscle cells have a fusiform shape, wide in the middle with tapered ends.
158
How do smooth muscle cells compare in size to skeletal muscle fibers?
Smooth muscle cells are smaller than skeletal muscle fibers.
159
What is unique about the sarcolemma of smooth muscle cells?
The sarcolemma of smooth muscle cells has various types of calcium (Ca²⁺) channels, which are gated by chemicals, voltage, and other factors.
160
Do smooth muscle cells have transverse tubules (T-tubules)?
No, smooth muscle cells lack transverse tubules (T-tubules).
161
How is surface area increased in smooth muscle cells?
Surface area is increased by caveolae, which are flask-like invaginations in the sarcolemma.
162
How extensive is the sarcoplasmic reticulum in smooth muscle cells?
The sarcoplasmic reticulum in smooth muscle cells is sparse
163
Where does smooth muscle obtain calcium for contraction?
Calcium for smooth muscle contraction is primarily sourced from the extracellular fluid, as well as the sparse sarcoplasmic reticulum.
164
What types of filaments are present in smooth muscle?
Like skeletal muscle, smooth muscle filaments contain actin, myosin, and troponin.
165
How do the myosin filaments in smooth muscle differ from those in skeletal muscle?
Smooth muscle myosin filaments have myosin heads along their entire length, allowing for the formation of additional crossbridges.
166
What is the latchbridge mechanism in smooth muscle?
The latchbridge mechanism allows myosin to attach to actin for an extended period without using extra ATP, enabling sustained contractions.
167
What protein in smooth muscle binds calcium (Ca²⁺) to trigger contraction?
Calmodulin binds calcium (Ca²⁺) in smooth muscle to trigger contraction.
168
What is the role of myosin light-chain kinase (MLCK) in smooth muscle contraction?
Myosin light-chain kinase (MLCK) is an enzyme that phosphorylates myosin heads when activated by calmodulin, enabling contraction.
169
What enzyme is responsible for smooth muscle relaxation?
Myosin light-chain phosphatase dephosphorylates the myosin head, which is required for smooth muscle relaxation.
170
How are muscle fibers in multiunit smooth muscle arranged?
In multiunit smooth muscle, muscle fibers are arranged in units that receive stimulation to contract individually.
171
Where can multiunit smooth muscle be found?
Multiunit smooth muscle is found in the iris and ciliary muscles of the eye, arrector pili muscles in the skin, larger air passageways in the respiratory system, and the walls of larger arteries.
172
How is contraction in multiunit smooth muscle regulated?
The degree of contraction in multiunit smooth muscle depends on the number of motor units activated, similar to skeletal muscle.
173
What is the most common type of smooth muscle?
Single-unit (visceral) smooth muscle is the most common type
174
How do single-unit smooth muscle cells contract?
Single-unit smooth muscle cells contract in unison because they are linked by gap junctions.
175
How is single-unit smooth muscle organized in hollow organs?
Single-unit smooth muscle forms two or three sheets in the wall of hollow organs.
176
Where is single-unit (visceral) smooth muscle found?
Single-unit smooth muscle is found in the walls of the digestive, urinary, and reproductive tracts, portions of the respiratory tract, and most blood vessels.
