Chapter 10 Flashcards
Muscle tissue is one of the four major tissue types.
A) True
B) False
A) True
Explanation: Muscle tissue is indeed one of the four major tissue types, alongside epithelial, connective, and nervous tissues.
The plasma membrane of a muscle cell is called the sarcoplasmic reticulum.
A) True
B) False
B) False
Explanation: The plasma membrane of a muscle cell is called the sarcolemma. The sarcoplasmic reticulum is a specialized type of smooth endoplasmic reticulum that stores and releases calcium ions.
Another name for a muscle cell is a muscle fiber.
A) True
B) False
A) True
Explanation: Muscle cells are also known as muscle fibers due to their elongated shape.
Skeletal muscle requires nervous system stimulation to contract.
A) True
B) False
A) True
Explanation: Skeletal muscles are under voluntary control and require stimulation from the nervous system to initiate contraction.
The epimysium is the connective tissue covering the exterior of a muscle.
A) True
B) False
A) True
Explanation: The epimysium is a dense layer of connective tissue that surrounds the entire muscle, providing structural support and protection.
Which of the following statements about the microscopic structure of muscle fibers is not correct:
A) The sarcoplasmic reticulum surrounds each myofibril in a muscle fiber.
B) At each A band-I band junction, the sarcolemma dives deep into the cells interior forming an elongated tube called the T tubule.
C) The T tubule is integrated with two terminal cisterns of the sarcoplasmic reticulum to form triads.
D) At the triad, T tubule proteins act as voltage sensors and change shape in response to voltage changes.
E) All are true statements
E) All are true statements
During repolarization, Sodium (Na+) channels close and voltage-gated Potassium (K+) channels open – the K+ efflux rapidly restores negatively charged conditions inside cell.
A) True
B) False
A) True
Explanation: During repolarization, the closing of Sodium (Na+) channels and the opening of Potassium (K+) channels result in the efflux of K+ ions, which restores the negative membrane potential.
In a relaxed state, the thick and thin filaments overlap only in the I band.
A) True
B) False
B) False
Explanation: In a relaxed state, the thick and thin filaments overlap in the A band. The I band contains only thin filaments and is where the filaments do not overlap.
Once an AP is initiated, it is unstoppable and leads to a muscle fiber contraction.
A) True
B) False
A) True
Explanation: Once an action potential (AP) is initiated, it propagates along the muscle fiber and triggers contraction, making it an all-or-nothing event.
Each muscle fiber is individually innervated by its own axon terminal.
A) True
B) False
A) True
Explanation: Each muscle fiber is connected to a single motor neuron at the neuromuscular junction, where it receives signals to contract.
During repolarization Sodium (Na+) channels close and Potassium (K+) channels open.
A) True
B) False
A) True
Explanation: During repolarization, voltage-gated Na+ channels close, and K+ channels open to restore the resting membrane potential by allowing K+ to exit the cell.
Which of the following statements about the generation and propagation of action potentials initiated at the neuromuscular junction is not true:
A) The binding of neurotransmitters to receptors at the neuromuscular junction (NMJ) opens chemically (ligand) gated ion channels.
B) The opening of ligand gated channels at the NMJ allows the simultaneous diffusion of Sodium (Na+) inward and Potassium (K+) outward causing interior of cell to becomes less negative (a local depolarization).
C) Local depolarization spreads to adjacent membrane areas and causes additional voltage-gated Na+ channels to open.
D) Increasing Na+ influx further decreases membrane voltage toward critical voltage called threshold.
E) All are true statements.
E) All are true statements.
Which is the correct sequence of events for the generation of an action potential?
A)
1. Neurotransmitters are received at the neuromuscular junction
2. Neurotransmitter binding opens Sodium (Na+)/Potassium (K+) channels
3. Na+ influx causes local depolarization of the cell membrane causing an end-plate potential
4. The end-plate potential spreads to adjacent membrane areas causing additional voltage gated Na+ channels to open
5. Action potential is generated
B)
1. Neurotransmitters are received at the neuromuscular junction
2. Neurotransmitter binding opens Na+/K+ channels
3. Na+ influx causes local depolarization of the cell membrane causing an end-plate potential
4. Action potential is generated
5. The end-plate potential spreads to adjacent membrane areas causing additional voltage gated Na+ channels to open
C)
1. Neurotransmitters are received at the neuromuscular junction
2. Action potential is generated
3. Neurotransmitter binding opens Na+/K+ channels
4. The end-plate potential spreads to adjacent membrane areas causing additional voltage gated Na+ channels to open
5. Na+ influx causes local depolarization of the cell membrane causing an end-plate potential
A)
1. Neurotransmitters are received at the neuromuscular junction
2. Neurotransmitter binding opens Na+/K+ channels
3. Na+ influx causes local depolarization of the cell membrane causing an end-plate potential
4. The end-plate potential spreads to adjacent membrane areas causing additional voltage gated Na+ channels to open
5. Action potential is generated
What is the correct sequence of events that occur at the neuromuscular junction?
A)
1. An action potential arrives at the axon terminal of a motor neuron.
2. Ach binding opens ions channels allowing Na+ in and K+ out of the muscle fiber.
3. Ach diffuses across the synaptic cleft and binds to receptors on the sarcolemma.
4. Voltage-gated Ca++ channels in the axon terminal open and Ca++ moves in
5. Ca++ entry causes the neurotransmitter acetylcholine (Ach) to be released by exocytosis.
B)
1. An action potential arrives at the axon terminal of a motor neuron.
2. Voltage-gated Ca++ channels in the axon terminal open and Ca++ moves in
3. Ca++ entry causes the neurotransmitter acetylcholine (Ach) to be released by exocytosis.
4. Ach diffuses across the synaptic cleft and binds to receptors on the sarcolemma.
5. Ach binding opens ions channels allowing Na+ in and K+ out of the muscle fiber.
C)
1. An action potential arrives at the axon terminal of a motor neuron.
2. Ca++ entry causes the neurotransmitter acetylcholine (Ach) to be released by exocytosis.
3. Ach diffuses across the synaptic cleft and binds to receptors on the sarcolemma.
4. Voltage-gated Ca++ channels in the axon terminal open and Ca++ moves in.
5. Ach binding opens ions channels allowing Na+ in and K+ out of the muscle fiber.
B)
1. An action potential arrives at the axon terminal of a motor neuron.
2. Voltage-gated Ca++ channels in the axon terminal open and Ca++ moves in
3. Ca++ entry causes the neurotransmitter acetylcholine (Ach) to be released by exocytosis.
4. Ach diffuses across the synaptic cleft and binds to receptors on the sarcolemma.
5. Ach binding opens ions channels allowing Na+ in and K+ out of the muscle fiber.
Which of the following statements about resting membrane potential is not correct:
A) The resting sarcolemma is polarized; that is the inside of the plasma membrane is negative relative to the outside.
B) There is more Potassium (K+) inside the cell than outside the cell.
C) There is more Sodium (Na+) outside the cell than inside the cell.
D) The presence of negatively charged proteins inside the cell contribute to the negative charge inside the cell.
E) All are true statements.
E) All are true statements.
What are the three types of muscle tissue in the body?
A) Skeletal, Nervous, Cardiac
B) Cardiac, Skeletal, Smooth
C) Smooth, Connective, Cardiac
D) Nervous, Connective, Skeletal
B) Cardiac, Skeletal, Smooth
Explanation: The body contains three types of muscle tissue: skeletal muscle, cardiac muscle, and smooth muscle. Each type has distinct properties and functions within the body.
All muscle tissues exhibit excitability.
A) True
B) False
A) True
Explanation: All three muscle tissues exhibit excitability as their plasma membranes can change their electrical states and send an action potential along the entire length of the membrane.
Fill in the blank: Skeletal muscle completely depends on signaling from the ______ to work properly.
Nervous system
Explanation: Skeletal muscle completely depends on signaling from the nervous system to work properly, unlike cardiac and smooth muscle which can respond to other stimuli such as hormones and local stimuli.
What quality allows muscle tissue to stretch or extend?
A) Contractility
B) Excitability
C) Extensibility
D) Elasticity
C) Extensibility
Explanation: Extensibility allows muscle tissue to stretch or extend. This is an important quality that enables muscles to lengthen in response to stretching.
Which muscle type has a striated appearance and is multinucleated?
A) Cardiac muscle
B) Skeletal muscle
C) Smooth muscle
D) All of the above
B) Skeletal muscle
Explanation: Skeletal muscle fibers are multinucleated and have a striated appearance due to the regular arrangement of actin and myosin proteins.
Cardiac muscle fibers are connected to each other so that the entire heart contracts as one unit.
A) True
B) False
A) True
Cardiac muscle fibers are physically and electrically connected to each other so that the entire heart contracts as a single unit, known as a syncytium.
Fill in the blank: ______ muscle regulates blood pressure necessary to push blood through the circulatory system.
Smooth
Explanation: Smooth muscle in the walls of arteries is crucial for regulating the blood pressure necessary to push blood through the circulatory system.
What feature is absent in smooth muscle but present in skeletal and cardiac muscles?
A) Actin and Myosin
B) Striations
C) Nuclei
D) Elasticity
B) Striations
Explanation: Smooth muscle lacks the striated appearance seen in skeletal and cardiac muscles because its actin and myosin are not arranged in a regular pattern.
All muscles require adenosine triphosphate (ATP) to contract.
A) True
B) False
A) True
Explanation: All muscles require adenosine triphosphate (ATP) to continue the process of contracting and relaxing.
Which type of muscle can respond to hormones and local stimuli?
A) Skeletal muscle
B) Cardiac muscle
C) Smooth muscle
D) Both B and C
D) Both B and C
Explanation: Both cardiac muscle and smooth muscle can respond to other stimuli, such as hormones and local stimuli, in addition to signals from the nervous system.
What property allows muscle tissue to recoil back to its original length?
A) Contractility
B) Excitability
C) Extensibility
D) Elasticity
D) Elasticity
Explanation: Elasticity allows muscle tissue to return to its original length when relaxed due to the presence of elastic fibers.
Skeletal muscle can contract without nervous system input.
A) True
B) False
B) False
Explanation: Skeletal muscle completely depends on signaling from the nervous system to contract, unlike cardiac and smooth muscles which can respond to other stimuli.
Fill in the blank: The process of contracting in muscles begins when a protein called ______ is pulled by a protein called myosin.
Actin
Explanation: Muscle contraction begins when the actin protein is pulled by the myosin protein, which is a key interaction in the contraction process.
Which type of muscle fiber has a single nucleus and lacks striations?
A) Skeletal muscle
B) Cardiac muscle
C) Smooth muscle
D) All of the above
C) Smooth muscle
Explanation: Smooth muscle fibers have a single nucleus and lack the striated appearance seen in skeletal and cardiac muscle fibers.
Calcium ions (Ca++) play a role in the contraction of all types of muscle tissue.
A) True
B) False
A) True
Explanation: Calcium ions (Ca++) are essential for muscle contraction in all types of muscle tissue. In skeletal and cardiac muscles, Ca++ binds to proteins that expose actin-binding sites, while in smooth muscle, Ca++ activates enzymes that lead to muscle contraction.
Fill in the blank: ______ muscle fibers each have one to two nuclei and are connected to ensure the heart contracts as one unit.
Cardiac
Explanation: Cardiac muscle fibers each have one to two nuclei and are physically and electrically connected to each other so that the entire heart contracts as one unit.
Which type of muscle tissue is critical for moving materials through internal passageways?
A) Skeletal muscle
B) Cardiac muscle
C) Smooth muscle
D) None of the above
C) Smooth muscle
Explanation: Smooth muscle is essential for moving materials through internal passageways, such as the digestive tract and blood vessels.
The striations in skeletal muscle are due to the regular arrangement of actin and myosin proteins.
A) True
B) False
A) True
Explanation: The striations in skeletal muscle are caused by the regular, organized arrangement of actin and myosin proteins within the muscle fibers.
Fill in the blank: ______ muscle is found in the walls of arteries and helps regulate blood pressure.
Smooth
Explanation: Smooth muscle is found in the walls of arteries and plays a critical role in regulating blood pressure by contracting and relaxing.
Which muscle type has fibers referred to as syncytium?
A) Skeletal muscle
B) Cardiac muscle
C) Smooth muscle
D) All of the above
B) Cardiac muscle
Explanation: Cardiac muscle fibers are connected to form a functional syncytium, allowing the heart to contract as a single unit.
Skeletal muscles are under voluntary control.
A) True
B) False
A) True
Explanation: Skeletal muscles are controlled voluntarily, allowing conscious movement and coordination of the body.
Fill in the blank: Skeletal muscles are enclosed in three layers of connective tissue called ______.
Mysia
Explanation: Each skeletal muscle is enclosed in three layers of connective tissue known as the mysia, which provide structure and compartmentalize the muscle fibers.
Which layer of connective tissue surrounds each muscle fiber?
A) Epimysium
B) Perimysium
C) Endomysium
D) Sarcolemma
C) Endomysium
Explanation: The endomysium is the connective tissue that encases each muscle fiber, providing extracellular fluid and nutrients to support the muscle fiber.
Muscle contraction generates heat which contributes to maintaining homeostasis.
A) True
B) False
A) True
Explanation: Muscle contraction requires energy, and when ATP is broken down, heat is produced. This heat generation helps maintain homeostasis by regulating body temperature.
Fill in the blank: The plasma membrane of a muscle fiber is called the ______.
Sarcolemma
Explanation: The plasma membrane of a muscle fiber is known as the sarcolemma. It plays a key role in conducting electrical impulses necessary for muscle contraction.
Which type of tissue is primarily responsible for the contractile function of skeletal muscle?
A) Nervous tissue
B) Connective tissue
C) Muscle tissue
D) Epithelial tissue
C) Muscle tissue
Explanation: Muscle tissue is primarily responsible for the contractile function of skeletal muscles, allowing them to produce movement.
The sarcoplasmic reticulum is responsible for storing and releasing calcium ions in muscle fibers.
A) True
B) False
A) True
Explanation: The sarcoplasmic reticulum stores and releases calcium ions (Ca++), which are essential for muscle contraction.
Fill in the blank: Each skeletal muscle fiber contains bundles of myofibrils, which are composed of ______ and ______ filaments.
Actin, Myosin
Explanation: Each skeletal muscle fiber contains bundles of myofibrils, which are composed of actin (thin filament) and myosin (thick filament) filaments, essential for muscle contraction.
Which connective tissue layer surrounds an entire skeletal muscle?
A) Epimysium
B) Perimysium
C) Endomysium
D) Sarcolemma
A) Epimysium
Explanation: The epimysium is the outermost layer of dense, irregular connective tissue that surrounds the entire skeletal muscle, helping to protect and support the muscle.
What is the functional unit of a skeletal muscle fiber?
A) Myofibril
B) Sarcomere
C) Myosin
D) Actin
B) Sarcomere
Explanation: The sarcomere is the functional unit of a skeletal muscle fiber, responsible for its striated appearance and contractile function.
The sarcomere is bordered by structures called Z-discs.
A) True
B) False
A) True
Explanation: The sarcomere is bordered by Z-discs, which anchor the actin filaments and mark the boundaries of each sarcomere.
Which of the following bands in the sarcomere contains only thin filaments?
A) A band
B) I band
C) H zone
D) M line
B) I band
Explanation: The I band contains only thin filaments (actin) and is the lighter region of the sarcomere.
Think: I Band - “I” for invisible
Fill in the blank: The thick filament in the sarcomere is composed of ______.
Myosin
Explanation:
The thick filament in the sarcomere is composed of myosin, which interacts with actin filaments during muscle contraction.
The neuromuscular junction (NMJ) is the site where a motor neuron’s terminal meets a muscle fiber.
A) True
B) False
A) True
Explanation: The neuromuscular junction (NMJ) is the site where the terminal of a motor neuron meets a muscle fiber, allowing for the transmission of excitation signals to the muscle.
Fill in the blank: An action potential in a muscle fiber is initiated by the release of the neurotransmitter ______.
Acetylcholine
Explanation: The neurotransmitter acetylcholine is released at the neuromuscular junction, initiating an action potential in the muscle fiber.
What is the primary role of the sarcoplasmic reticulum in muscle contraction?
A) Storing ATP
B) Conducting action potentials
C) Storing and releasing calcium ions
D) Producing acetylcholine
C) Storing and releasing calcium ions
Explanation: The sarcoplasmic reticulum stores and releases calcium ions, which are crucial for triggering muscle contraction.
Excitation-contraction coupling refers to the process by which an action potential triggers muscle contraction.
A) True
B) False
A) True
Explanation: Excitation-contraction coupling is the process by which an action potential in the muscle fiber leads to the release of calcium ions and subsequent muscle contraction.
The ______ is the region of the sarcomere that contains both thick and thin filaments.
A band
Explanation: The A band is the region of the sarcomere that contains overlapping thick (myosin) and thin (actin) filaments.
Which structure in the sarcomere anchors the thin filaments and marks the boundary between sarcomeres?
A) M line
B) Z disc
C) H zone
D) A band
B) Z disc
Explanation: The Z disc anchors the thin filaments and marks the boundary between adjacent sarcomeres.
What is the role of acetylcholine (ACh) at the neuromuscular junction?
A) To release calcium ions
B) To initiate an action potential in the muscle fiber
C) To store energy in the form of ATP
D) To break down acetylcholinesterase
B) To initiate an action potential in the muscle fiber
Explanation: Acetylcholine (ACh) is released by the motor neuron’s axon terminal at the neuromuscular junction and binds to receptors on the muscle fiber, initiating an action potential.
The sarcolemma is the plasma membrane of a muscle fiber.
A) True
B) False
A) True
Explanation: The sarcolemma is the plasma membrane that surrounds each muscle fiber, playing a crucial role in conducting action potentials.
Fill in the blank: The ______ releases calcium ions in response to an action potential in the muscle fiber.
Sarcoplasmic reticulum
Explanation: The sarcoplasmic reticulum releases calcium ions when an action potential travels along the sarcolemma and into the T-tubules.
What structure carries the action potential into the interior of the muscle fiber?
A) Sarcoplasmic reticulum
B) T-tubules
C) Myofibrils
D) Motor end-plate
B) T-tubules
Explanation: T-tubules carry the action potential deep into the muscle fiber, ensuring the entire fiber is activated simultaneously.
The neuromuscular junction is where the terminal of a motor neuron meets a muscle fiber.
A) True
B) False
A) True
Explanation: The neuromuscular junction (NMJ) is the site where a motor neuron’s terminal meets a muscle fiber, facilitating the transmission of nerve signals to the muscle.
Fill in the blank: The enzyme ______ degrades acetylcholine in the synaptic cleft.
Acetylcholinesterase
Explanation: Acetylcholinesterase breaks down acetylcholine in the synaptic cleft, terminating the signal and allowing the muscle to relax.
Which ion channel opens in response to acetylcholine binding at the motor end-plate?
A) Potassium channels
B) Calcium channels
C) Sodium channels
D) Chloride channels
C) Sodium channels
Explanation: Acetylcholine binding to receptors on the motor end-plate opens sodium channels, leading to depolarization and initiation of an action potential in the muscle fiber.
The triad in a muscle fiber consists of a T-tubule and two terminal cisternae.
A) True
B) False
A) True
Explanation: The triad is formed by a T-tubule flanked by two terminal cisternae of the sarcoplasmic reticulum, facilitating the efficient release of calcium ions during muscle contraction.
Fill in the blank: The depolarization of the muscle fiber membrane leads to the opening of ______ channels, which propagate the action potential.
Voltage-gated sodium
Explanation: Depolarization of the muscle fiber membrane opens voltage-gated sodium channels, allowing sodium ions to enter and propagate the action potential along the sarcolemma.
What happens immediately after the action potential travels along the sarcolemma and T-tubules?
A) ATP is synthesized
B) Calcium is released from the sarcoplasmic reticulum
C) Acetylcholine is broken down
D) Myosin binds to actin
B) Calcium is released from the sarcoplasmic reticulum
Explanation: After the action potential travels along the sarcolemma and T-tubules, calcium is released from the sarcoplasmic reticulum into the sarcoplasm, initiating muscle contraction.
What neurotransmitter is released from the motor neuron to initiate muscle contraction?
A) Dopamine
B) Acetylcholine (ACh)
C) Serotonin
D) Norepinephrine
B) Acetylcholine (ACh)
Explanation: Acetylcholine (ACh) is the neurotransmitter released from the motor neuron that binds to receptors on the muscle fiber membrane, leading to depolarization and muscle contraction.
Sodium ions (Na+) enter the muscle fiber to initiate an action potential.
A) True
B) False
A) True
Explanation: Sodium ions (Na+) entering the muscle fiber membrane cause depolarization, which triggers an action potential necessary for muscle contraction.
Fill in the Blank: The release of calcium ions (Ca++) from the __________ triggers muscle contraction.
sarcoplasmic reticulum (SR)
Explanation: The sarcoplasmic reticulum (SR) releases calcium ions (Ca++) that bind to troponin, allowing the interaction between actin and myosin necessary for muscle contraction.
What protein does calcium bind to in order to initiate muscle contraction?
A) Tropomyosin
B) Myosin
C) Troponin
D) Actin
C) Troponin
Explanation: Calcium binds to troponin, which causes a conformational change that moves tropomyosin, exposing the binding sites on actin for myosin to attach.
ATP is required for both muscle contraction and relaxation.
A) True
B) False
A) True
Explanation: ATP is needed to sustain muscle contraction by energizing the cross-bridge cycling and also for muscle relaxation by pumping calcium ions back into the sarcoplasmic reticulum.
Fill in the Blank: The interaction between thick and thin filaments that leads to muscle contraction is known as the __________.
sliding filament model
Explanation: The sliding filament model describes how actin (thin) and myosin (thick) filaments slide past each other to shorten the muscle fiber, resulting in contraction.
Which ion is pumped back into the sarcoplasmic reticulum to initiate muscle relaxation?
A) Sodium (Na+)
B) Potassium (K+)
C) Calcium (Ca++)
D) Magnesium (Mg++)
C) Calcium (Ca++)
Explanation: Calcium ions (Ca++) are pumped back into the sarcoplasmic reticulum to reduce their concentration in the sarcoplasm, leading to muscle relaxation.
Muscle contraction stops when the motor neuron stops signaling.
A) True
B) False
A) True
Explanation: Muscle contraction stops when the motor neuron ends its signal, causing repolarization of the sarcolemma and T-tubules, and closing the calcium channels in the sarcoplasmic reticulum.
Fill in the Blank: The initial depolarization of the muscle fiber membrane is caused by the entry of __________ ions.
sodium (Na+)
Explanation: The entry of positively charged sodium ions (Na+) into the muscle fiber membrane initiates depolarization, leading to an action potential and subsequent muscle contraction.
What structure in the muscle fiber stores calcium ions?
A) T-tubules
B) Mitochondria
C) Sarcoplasmic reticulum (SR)
D) Golgi apparatus
C) Sarcoplasmic reticulum (SR)
Explanation: The sarcoplasmic reticulum (SR) is responsible for storing and releasing calcium ions, which are crucial for muscle contraction.
Which of the following structures shortens during muscle contraction?
A) Actin filament
B) Myosin filament
C) Sarcomere
D) Z-disc
C) Sarcomere
Explanation: The sarcomere shortens during muscle contraction as the thin (actin) and thick (myosin) filaments slide past each other, bringing the Z-discs closer together.
The A band of a sarcomere becomes narrower during contraction.
A) True
B) False
B) False
Explanation: The A band remains the same width during contraction. It is the I band and the H zone that become narrower.
Fill in the Blank: During muscle contraction, the myosin heads form cross-bridges by binding to __________.
actin
Explanation: Myosin heads bind to the actin filaments to form cross-bridges, which are essential for muscle contraction.
What protein covers the myosin-binding sites on actin filaments when a muscle is relaxed?
A) Troponin
B) Tropomyosin
C) Myosin
D) Titin
B) Tropomyosin
Explanation: Tropomyosin covers the myosin-binding sites on actin filaments, preventing myosin from binding to actin when the muscle is relaxed.
ATP is necessary for both the attachment and detachment of myosin heads during muscle contraction.
A) True
B) False
A) True
Explanation: ATP is required for the myosin heads to attach to actin and form cross-bridges, and also for the detachment of myosin heads from actin, allowing the cycle to continue.
Fill in the Blank: The power stroke in muscle contraction is the movement of the __________ heads that pulls the actin filaments toward the center of the sarcomere.
myosin
Explanation: The power stroke refers to the action of the myosin heads pivoting and pulling the actin filaments toward the center of the sarcomere, which shortens the muscle.
The sliding filament model explains how muscles can contract without the sarcomere shortening.
A) True
B) False
B) False
Explanation: The sliding filament model explains muscle contraction as a process where the sarcomere shortens due to the sliding of actin and myosin filaments past each other.
Which of the following steps occurs first in the sliding filament model of muscle contraction?
A) Cross-bridge formation
B) Power stroke
C) Calcium ion binding to troponin
D) ATP hydrolysis
C) Calcium ion binding to troponin
Explanation: The first step is the binding of calcium ions to troponin, which causes a conformational change that moves tropomyosin away from the myosin-binding sites on actin.
Fill in the Blank: The release of __________ ions from the sarcoplasmic reticulum initiates the contraction cycle.
calcium (Ca++)
Explanation: The release of calcium ions from the sarcoplasmic reticulum into the sarcoplasm initiates the contraction cycle by binding to troponin.
What is the role of ATP in the muscle contraction cycle?
A) To bind to actin filaments
B) To detach myosin heads from actin
C) To cover the myosin-binding sites on actin
D) To store calcium ions
B) To detach myosin heads from actin
Explanation: ATP binds to the myosin heads, causing them to detach from the actin filaments, which is necessary for the cross-bridge cycle to continue.
Which of the following is NOT a source of ATP for muscle contraction?
A) Creatine phosphate
B) Anaerobic glycolysis
C) Aerobic respiration
D) Protein synthesis
D) Protein synthesis
Explanation: ATP for muscle contraction comes from creatine phosphate, anaerobic glycolysis, and aerobic respiration. Protein synthesis is not a source of ATP for muscle contraction.
Creatine phosphate can provide energy for muscle contraction for up to 15 seconds.
A) True
B) False
A) True
Explanation: Creatine phosphate can quickly donate a phosphate group to ADP to form ATP, providing energy for muscle contraction for approximately 15 seconds.
During aerobic respiration, where does the majority of ATP production occur?
A) Cytoplasm
B) Sarcoplasmic reticulum
C) Mitochondria
D) Nucleus
C) Mitochondria
Explanation: The majority of ATP production during aerobic respiration occurs in the mitochondria, where glucose and other nutrients are oxidized to produce ATP.
Fill in the Blank: The process that breaks down glucose without oxygen to produce ATP is called __________.
anaerobic glycolysis
Explanation: Anaerobic glycolysis is the process of breaking down glucose without oxygen to produce ATP, resulting in the formation of lactic acid.
Aerobic respiration is less efficient than anaerobic glycolysis.
A) True
B) False
B) False
Explanation: Aerobic respiration is more efficient than anaerobic glycolysis, producing approximately 36 ATP molecules per glucose molecule compared to only 2 ATP molecules from anaerobic glycolysis.
Fill in the Blank: The end product of anaerobic glycolysis that can cause muscle fatigue is __________.
lactic acid
Explanation: Lactic acid is the end product of anaerobic glycolysis, and its accumulation in the muscle can contribute to muscle fatigue.
Which molecule acts as an immediate energy reserve that can be quickly converted to ATP in muscle cells?
A) Glucose
B) Fatty acids
C) Creatine phosphate
D) Glycogen
C) Creatine phosphate
Explanation: Creatine phosphate acts as an immediate energy reserve, quickly donating a phosphate group to ADP to form ATP, providing a rapid source of energy for muscle contraction.
Muscle fatigue occurs when ATP production cannot keep up with ATP demand.
A) True
B) False
A) True
Explanation: Muscle fatigue occurs when ATP production is insufficient to meet the energy demands of muscle contraction, leading to decreased muscle performance.
Fill in the Blank: During intense muscle activity, the buildup of __________ leads to oxygen debt.
lactic acid
Explanation: The buildup of lactic acid during intense muscle activity leads to oxygen debt, which is the amount of oxygen required to restore ATP and creatine phosphate levels and convert lactic acid back to pyruvic acid.
What role does myoglobin play in muscle cells?
A) Storing glucose
B) Carrying oxygen
C) Breaking down ATP
D) Synthesizing proteins
B) Carrying oxygen
Explanation: Myoglobin is a protein in muscle cells that binds and stores oxygen, allowing for more efficient muscle contractions and less fatigue during aerobic respiration.
Which enzyme catalyzes the transfer of a phosphate group from creatine phosphate to ADP to form ATP?
A) Hexokinase
B) Phosphofructokinase
C) Creatine kinase
D) Lactate dehydrogenase
C) Creatine kinase
Explanation: Creatine kinase is the enzyme that catalyzes the transfer of a phosphate group from creatine phosphate to ADP to form ATP, providing quick energy for muscle contraction.
Glycolysis can sustain muscle activity for long periods of time without oxygen.
A) True
B) False
B) False
Explanation: Glycolysis can only sustain muscle activity for short periods of time (approximately 1 minute) without oxygen, as it produces ATP less efficiently and leads to the accumulation of lactic acid.
Fill in the Blank: Aerobic respiration produces approximately __________ ATP molecules per glucose molecule.
36
Explanation: Aerobic respiration produces approximately 36 ATP molecules per glucose molecule, making it a highly efficient process for generating energy.
What happens to the pyruvic acid produced during anaerobic glycolysis when oxygen is available?
A) It is converted into lactic acid
B) It is converted into glucose
C) It enters the Krebs cycle for further breakdown
D) It is stored as glycogen
C) It enters the Krebs cycle for further breakdown
Explanation: When oxygen is available, pyruvic acid produced during glycolysis enters the Krebs cycle (citric acid cycle) in the mitochondria for further breakdown and ATP production.
Myoglobin in muscle cells helps delay the onset of muscle fatigue.
A) True
B) False
A) True
Explanation: Myoglobin binds and stores oxygen in muscle cells, which helps provide a steady supply of oxygen during aerobic respiration, thereby delaying the onset of muscle fatigue.
Fill in the Blank: The energy released from the hydrolysis of __________ powers the myosin head’s movement during muscle contraction.
ATP
Explanation: The hydrolysis of ATP releases energy, which powers the movement of the myosin head during muscle contraction, enabling the power stroke and sliding of actin filaments.
Which of the following processes is responsible for the largest amount of ATP production in muscle cells?
A) Creatine phosphate metabolism
B) Anaerobic glycolysis
C) Aerobic respiration
D) Fermentation
C) Aerobic respiration
Explanation: Aerobic respiration is responsible for the largest amount of ATP production in muscle cells, producing approximately 36 ATP molecules per glucose molecule.
Oxygen debt is the amount of oxygen required to restore normal metabolic conditions in muscle cells after intense exercise.
A) True
B) False
A) True
Explanation: Oxygen debt refers to the amount of oxygen required to restore ATP and creatine phosphate levels, convert lactic acid back to pyruvic acid, and return muscle cells to their normal metabolic conditions after intense exercise.
Fill in the Blank: During muscle contraction, the __________ filaments slide past the __________ filaments to shorten the sarcomere.
actin, myosin
Explanation: During muscle contraction, the thin actin filaments slide past the thick myosin filaments, resulting in the shortening of the sarcomere and overall muscle contraction.
Which process generates lactic acid as a byproduct?
A) Aerobic respiration
B) Glycolysis with oxygen
C) Anaerobic glycolysis
D) Creatine phosphate metabolism
C) Anaerobic glycolysis
Explanation: Anaerobic glycolysis generates lactic acid as a byproduct when glucose is broken down without the presence of oxygen, leading to the production of ATP and lactic acid.
Which type of muscle contraction involves the muscle lengthening while maintaining tension?
A) Concentric contraction
B) Isometric contraction
C) Eccentric contraction
D) Isotonic contraction
C) Eccentric contraction
Explanation: An eccentric contraction occurs when the muscle lengthens while maintaining tension, such as lowering a weight in a controlled manner.
Isometric contractions occur when the muscle changes length to move a load.
A) True
B) False
B) False
Explanation: Isometric contractions occur when the muscle produces tension without changing its length, meaning the muscle does not move the load.
Fill in the Blank: The force generated by the contraction of a muscle, or the shortening of sarcomeres, is called __________.
muscle tension
Explanation: Muscle tension refers to the force generated by muscle contraction, which is essential for moving loads.
Which of the following best describes a concentric contraction?
A) Muscle lengthens while maintaining tension
B) Muscle maintains constant length and tension
C) Muscle shortens while generating force
D) Muscle generates force without shortening
C) Muscle shortens while generating force
Explanation: A concentric contraction involves the muscle shortening while generating force, such as lifting a weight.
Isotonic contractions involve a change in muscle length while maintaining constant tension.
A) True
B) False
A) True
Explanation: Isotonic contractions involve a change in muscle length while the tension remains constant, allowing for movement of a load.
Fill in the Blank: The group of muscle fibers innervated by a single motor neuron is called a __________.
motor unit
Explanation: A motor unit consists of all the muscle fibers innervated by a single motor neuron, allowing for coordinated muscle contraction.
What is the primary role of motor units in muscle contraction?
A) Storing calcium ions
B) Generating ATP
C) Controlling muscle fiber recruitment
D) Synthesizing proteins
C) Controlling muscle fiber recruitment
Explanation: Motor units control the recruitment of muscle fibers during contraction, allowing for fine or gross motor control depending on the size and type of motor units.
Recruitment of larger motor units produces weaker muscle contractions.
A) True
B) False
B) False
Explanation: Recruitment of larger motor units produces stronger muscle contractions because larger motor units innervate more muscle fibers, generating greater force.
Fill in the Blank: The gradual activation of more motor units to increase the strength of muscle contraction is known as __________.
recruitment
Explanation: Recruitment is the process of gradually activating more motor units to increase the strength of muscle contraction, allowing for precise control of muscle force.
Which type of contraction is involved in maintaining posture and joint stability without movement?
A) Concentric contraction
B) Eccentric contraction
C) Isometric contraction
D) Isotonic contraction
C) Isometric contraction
Explanation: Isometric contractions maintain posture and joint stability without causing movement, as the muscle tension matches the load without changing muscle length.
What is the ideal sarcomere length to produce maximal tension?
A) 60-80% of resting length
B) 80-120% of resting length
C) 100-140% of resting length
D) 120-160% of resting length
B) 80-120% of resting length
Explanation: The ideal sarcomere length to produce maximal tension is between 80-120% of its resting length, where there is optimal overlap between actin and myosin filaments.
A sarcomere stretched beyond 120% of its resting length will generate maximal tension.
A) True
B) False
B) False
Explanation: A sarcomere stretched beyond 120% of its resting length will generate less tension due to insufficient overlap between the actin and myosin filaments.
Fill in the Blank: The graph depicting the relationship between sarcomere length and tension is known as the __________.
length-tension relationship
Explanation: The length-tension relationship graph shows how the length of the sarcomere affects the tension it can generate during contraction.
During a muscle twitch, which phase is characterized by the propagation of the action potential and release of Ca++ ions?
A) Latent period
B) Contraction phase
C) Relaxation phase
D) Refractory period
A) Latent period
Explanation: The latent period is the phase during which the action potential is being propagated along the sarcolemma, and Ca++ ions are released from the sarcoplasmic reticulum.
The contraction phase of a muscle twitch involves the binding of Ca++ to troponin and the formation of cross-bridges.
A) True
B) False
A) True
Explanation: During the contraction phase, Ca++ binds to troponin, causing a shift in tropomyosin and allowing myosin heads to form cross-bridges with actin, leading to sarcomere shortening.
Fill in the Blank: The phase during which muscle tension decreases as Ca++ ions are pumped back into the sarcoplasmic reticulum is called the __________.
relaxation phase
Explanation: The relaxation phase is when muscle tension decreases as Ca++ ions are pumped back into the sarcoplasmic reticulum, ending cross-bridge cycling.
What term describes the process where successive action potentials increase muscle tension by summing their effects?
A) Tetanus
B) Wave summation
C) Treppe
D) Twitch
B) Wave summation
Explanation: Wave summation occurs when successive action potentials increase muscle tension by summing their effects, leading to greater contraction.
Tetanus is the state of continuous muscle contraction without relaxation.
A) True
B) False
A) True
Explanation: Tetanus is the state of continuous muscle contraction without relaxation, achieved by high-frequency stimulation that prevents the muscle from relaxing.
Fill in the Blank: A single contraction in response to a single action potential from a motor neuron is called a __________.
twitch
Explanation: A twitch is a single contraction of a muscle fiber in response to a single action potential from a motor neuron.
Which instrument is used to measure the tension produced over time by a muscle contraction?
A) Myograph
B) Electromyograph
C) Oscilloscope
D) Dynamometer
A) Myograph
Explanation: A myograph is an instrument used to measure the tension produced over time by a muscle contraction, often displayed as a myogram.
What is the phenomenon called where muscle contractions become more efficient after repeated stimulation?
A) Tetanus
B) Treppe
C) Wave summation
D) Hypertonia
B) Treppe
Explanation: Treppe, also known as the staircase effect, occurs when muscle contractions become more efficient and stronger after repeated stimulation.
Treppe can only be maintained with adequate ATP supply.
A) True
B) False
A) True
Explanation: Treppe results from an increase in muscle efficiency and requires a continuous supply of ATP to sustain the increased tension.
Fill in the Blank: The continuous partial contraction of muscles to maintain posture and stability is referred to as __________.
muscle tone
Explanation: Muscle tone is the continuous partial contraction of muscles, which helps maintain posture and stability even when muscles are not actively producing movement.
Which condition is characterized by a lack of muscle tone, resulting in a flaccid appearance and weak reflexes?
A) Hypertonia
B) Hypotonia
C) Treppe
D) Tetanus
B) Hypotonia
Explanation: Hypotonia is a condition characterized by a lack of muscle tone, resulting in a flaccid appearance and weak reflexes, often due to damage to the central nervous system or loss of innervation to muscles.
Hypertonia is characterized by reduced reflex responses and muscle rigidity.
A) True
B) False
B) False
Explanation: Hypertonia is characterized by increased muscle tone, often accompanied by hyperreflexia (excessive reflex responses) and muscle rigidity.
Fill in the Blank: The condition where muscle tone is excessively high, often resulting in muscle rigidity, is called __________.
hypertonia
Explanation: Hypertonia is a condition where muscle tone is excessively high, leading to muscle rigidity and often resulting from damage to the upper motor neurons in the central nervous system.
Which of the following best describes the muscle tone required for maintaining posture and joint stability without producing movement?
A) Complete relaxation
B) Flaccid tone
C) Continuous partial contraction
D) Maximal contraction
C) Continuous partial contraction
Explanation: Muscle tone involves continuous partial contraction of muscles to maintain posture and joint stability without producing noticeable movement.
Muscle tone is achieved through the cyclic activation of motor units.
A) True
B) False
A) True
Explanation: Muscle tone is maintained by the cyclic activation of motor units, which ensures that some motor units are always active while others rest, preventing complete muscle fatigue.
Fill in the Blank: The absence of muscle tone, often due to damage to the central nervous system, is known as __________.
hypotonia
Explanation: Hypotonia refers to the absence of muscle tone, which can result from damage to parts of the central nervous system or loss of innervation to the muscles.
What is the primary cause of hypertonia in muscles?
A) Decreased ATP production
B) Damage to lower motor neurons
C) Damage to upper motor neurons
D) Lack of calcium ions
C) Damage to upper motor neurons
Explanation: Hypertonia is primarily caused by damage to upper motor neurons in the central nervous system, leading to increased muscle tone and often muscle rigidity.
What is the alternate name for the phenomenon of treppe?
A) Summation effect
B) Staircase effect
C) Plateau effect
D) Tetanus effect
B) Staircase effect
Explanation: Treppe is also known as the staircase effect because the increase in muscle tension with repeated contractions resembles a staircase pattern.
Muscle tone is only important during active movement.
A) True
B) False
B) False
Explanation: Muscle tone is important not only during active movement but also for maintaining posture, joint stability, and readiness for action.
Fill in the Blank: Muscle tone allows muscles to continually stabilize joints and maintain __________.
posture
Explanation: Muscle tone helps to stabilize joints and maintain posture by providing a continuous level of low-level muscle contraction.
Which of the following is a condition characterized by a lack of muscle tone and can result from damage to the central nervous system?
A) Hypertonia
B) Tetany
C) Hypotonia
D) Isotonia
C) Hypotonia
Explanation: Hypotonia is characterized by a lack of muscle tone, often resulting from damage to the central nervous system or loss of muscle innervation.
Muscle tone results from the simultaneous activation of all motor units in a muscle.
A) True
B) False
B) False
Explanation: Muscle tone results from the cyclic activation of a few motor units at a time, not the simultaneous activation of all motor units, allowing for sustained muscle readiness without fatigue.
Fill in the Blank: The gradual increase in muscle tension due to repeated stimulation, which results in increased efficiency of contractions, is known as __________.
treppe
Explanation: Treppe refers to the gradual increase in muscle tension with repeated stimulation, leading to more efficient contractions over time.
What happens to muscle tension during the phenomenon of treppe?
A) It decreases gradually
B) It remains constant
C) It increases in a graded manner
D) It fluctuates randomly
C) It increases in a graded manner
Explanation: During treppe, muscle tension increases in a graded manner with each successive contraction, becoming more efficient over time.
Hypotonic muscles have weak reflexes and a flaccid appearance.
A) True
B) False
A) True
Explanation: Hypotonic muscles are characterized by weak reflexes and a flaccid appearance, indicating a lack of normal muscle tone.
Fill in the Blank: Excessive muscle tone, often accompanied by excessive reflex responses, is referred to as __________.
hypertonia
Explanation: Hypertonia is the condition of excessive muscle tone, often accompanied by hyperreflexia and muscle rigidity.
Which of the following best describes the condition of hypertonia?
A) Low muscle tone and weak reflexes
B) Normal muscle tone with efficient contractions
C) Excessive muscle tone and increased reflexes
D) Muscle tone without any reflex activity
C) Excessive muscle tone and increased reflexes
Explanation: Hypertonia is characterized by excessive muscle tone and increased reflex responses, often resulting in muscle rigidity and spasticity.
Excitation-contraction coupling is the connection between the electrical events of an action potential and mechanical events of a muscle contraction.
A) True
B) False
A) True
Explanation: excitation-contraction coupling describes the process by which an electrical signal (excitation) is converted into a mechanical response (contraction) in muscle cells.
During cross bridge cycling, cross bridge attachments form and break several times during a contraction.
A) True
B) False
A) True
Explanation: During cross-bridge cycling, the myosin heads attach to actin, perform a power stroke to pull the actin filaments towards the center of the sarcomere, release, and then reattach to a new position on the actin filament. This process repeats multiple times during a muscle contraction, allowing for the sliding of actin and myosin filaments past each other, which results in muscle shortening and generation of force.
Contraction is ultimately stimulated by the binding of calcium to troponin which then changes shape and removes the blocking action of tropomyosin.
A) True
B) False
A) True
Explanation: Contraction is ultimately stimulated by the binding of calcium to troponin. When calcium ions bind to troponin, it causes a conformational change in the troponin-tropomyosin complex. This change moves tropomyosin away from the myosin-binding sites on actin, allowing myosin heads to attach to actin and initiate contraction.
The electrical signals of the action potential do not dirctly act upon myofilaments, instead a rise in intracellular Na+ concentrations trigger the actual muscle contraction.
A) True
B) False
B) False
Explanation: The electrical signals of the action potential do not directly act upon myofilaments. Instead, it is a rise in intracellular calcium (Ca²⁺) concentrations that triggers the actual muscle contraction, not sodium (Na⁺). The action potential travels along the sarcolemma and down the T-tubules, leading to the release of Ca²⁺ from the sarcoplasmic reticulum, which then binds to troponin and initiates the contraction process.
ATP supplies the only energy for muscle contractions.
A) True
B) False
A) True
Explanation: ATP supplies the primary and immediate energy source for muscle contractions. ATP is required for the myosin heads to detach from actin, to re-cock the myosin heads into a position to form new cross-bridges, and to pump calcium back into the sarcoplasmic reticulum during muscle relaxation. While other molecules like creatine phosphate and glycogen can be metabolized to regenerate ATP, the direct energy for muscle contraction is provided by ATP.
Which of the following is the correct sequence of events for excitation-contraction coupling:
A)
1. An action potential is generated at the NMJ and propagated down the sarcolemma
2. The action potential travels down the T tubules
3. Myosin binding to actin forms cross bridges and contraction (cross bridge cycling) begins
4. Ca++ binds to troponin and removes the blocking action of tropomyosin on actin
5. Change in voltage gated channels at the triad causes Ca++ release from the SR
B)
1. An action potential is generated at the NMJ and propagated down the sarcolemma
2. Myosin binding to actin forms cross bridges and contraction (cross bridge cycling) begins
3. Ca++ binds to troponin and removes the blocking action of tropomyosin on actin
4. The action potential travels down the T tubules
5. Change in voltage gated channels at the triad causes Ca++ release from the SR
C)
1. An action potential is generated at the NMJ and propagated down the sarcolemma
2. The action potential travels down the T tubules
3. Change in voltage gated channels at the triad causes Ca++ release from the SR
4. Ca++ binds to troponin and removes the blocking action of tropomyosin on actin
5. Myosin binding to actin forms cross bridges and contraction (cross bridge cycling) begins
C)
1. An action potential is generated at the NMJ and propagated down the sarcolemma
2. The action potential travels down the T tubules
3. Change in voltage gated channels at the triad causes Ca++ release from the SR
4. Ca++ binds to troponin and removes the blocking action of tropomyosin on actin
5. Myosin binding to actin forms cross bridges and contraction (cross bridge cycling) begins
Which of the following statements about excitation/contraction coupling is not true?
A) Excitation-contraction links the electrical events of an action potential to the mechanical events of a muscle contraction.
B) The electrical signal of the action potential does not directly act upon the actin and myosin proteins, instead it causes a rise in intracellular Ca++.
C) During excitation-contraction coupling, an action potential is transmitted across the sarcolemma and down the T tubules.
D) Changes in the shape of voltage-sensitive proteins in the T tubules stimulate Ca++ release from SR.
E) All are true statements
E) All are true statements
Which of the following statements about the cessation of an action potential is not correct:
A) When the action potential ceases, the voltage-sensitive tubule proteins return to their original shape, stopping the release of Ca+ into the sarcoplasm.
B) Ca+ levels in the sarcoplasm fall as Ca+ is pumped back into the extracellular space.
C) In the absence of Ca++, the blocking action of tropomyosin is restored.
D) When actin and myosin can’t bind, relaxation of the myofibrils occurs.
B) Ca+ levels in the sarcoplasm fall as Ca+ is pumped back into the extracellular space.
Explanation: This statement is not correct because, after the cessation of an action potential, Ca++ is pumped back into the sarcoplasmic reticulum, not the extracellular space. The sarcoplasmic reticulum is responsible for sequestering Ca++ ions within the muscle cell to decrease the cytoplasmic concentration and facilitate muscle relaxation.
What opens in response to the action potential traveling down the T tubule?
A) ligand gated Na+/K+ channels
B) voltage-gated Na+ channels
C) voltage-sensitive Ca++ gates
C) voltage-sensitive Ca++ gates
When the action potential travels down the T tubule, it triggers the opening of voltage-sensitive Ca++ gates (also known as voltage-gated calcium channels) in the sarcoplasmic reticulum. This leads to the release of Ca++ ions into the sarcoplasm, which is essential for muscle contraction.
By which method is ATP regenerated during exercise?
A) Direct phosphorylation of ADP by creatinine phosphate
B) anaerobic respiration
C) aerobic respiration
D) All of the above
D) All of the above
Explanation: All three methods contribute to ATP regeneration during different phases and intensities of exercise.
Smooth muscle fibers do not exhibit myofibrils or sarcomeres, but do have T tubules.
A) True
B) False
B) False
Explanation: Smooth muscle fibers do not have T tubules. They also lack myofibrils and sarcomeres, which are characteristic of striated muscles such as skeletal and cardiac muscle. Instead, smooth muscle cells have a different organization of actin and myosin filaments, which allows them to contract in a more sustained and controlled manner.
Smooth muscle tissue usually has two layers – longitudinal and circular.
A) True
B) False
A) True
Explanation: Smooth muscle tissue typically has two layers: a longitudinal layer and a circular layer. These two layers work together to facilitate various types of movements and functions within organs, such as peristalsis in the digestive tract. The longitudinal layer runs parallel to the long axis of the organ, while the circular layer encircles the organ.
Skeletal muscle does not require nervous system stimulation to contract, whereas smooth muscle does.
A) True
B) False
B) False
Explanation: Skeletal muscle does require nervous system stimulation to contract. It is controlled by voluntary signals from the nervous system. On the other hand, smooth muscle can contract without direct nervous system stimulation. Smooth muscle contraction can be triggered by various factors, including hormonal signals, changes in pH, oxygen levels, carbon dioxide levels, and stretch, in addition to autonomic nervous system stimulation.
One of the unique features of smooth muscle is its ability to divide and increase its number of cells.
A) True
B) False
A) True
Explanation: One of the unique features of smooth muscle is its ability to undergo hyperplasia, which is the process of increasing the number of cells. Smooth muscle cells can divide and increase in number, especially in response to certain stimuli, such as injury or hormonal signals. This capability is not found in skeletal or cardiac muscle to the same extent.
During smooth muscle excitation-contraction coupling, the protein calmodulin binds Ca++ instead of troponin.
A) True
B) False
A) True
Explanation: During smooth muscle excitation-contraction coupling, the protein calmodulin binds Ca++ instead of troponin. Calmodulin then activates myosin light-chain kinase (MLCK), which phosphorylates myosin light chains, enabling myosin to interact with actin and initiate contraction. This is different from skeletal muscle, where Ca++ binds to troponin to initiate contraction.
Which of the following statements about smooth muscle innervation is not true:
A) Smooth muscle contains neuromuscular junctions.
B) Smooth muscle does not require nervous system stimulation to contract.
C) Autonomic (involuntary) nerve fibers innervate smooth muscle at diffuse junctions.
D) Bulbs of nerves called varicosities store and release neurotransmitters into synaptic clefts in the general area of the cells.
A) Smooth muscle contains neuromuscular junctions.
Explanation: This statement is not true. Smooth muscle does not contain neuromuscular junctions, which are characteristic of skeletal muscle. Instead, smooth muscle is innervated by autonomic nerve fibers that release neurotransmitters at diffuse junctions near the muscle cells, using varicosities to store and release these neurotransmitters.
Which of the following statements about smooth muscle contractions is not true:
A) The final trigger for contraction is an increase in intracellular Ca2+.
B) Actin and myosin filaments interact by sliding filament mechanism.
C) Smooth muscle cells are electrically isolated from one another.
D) Smooth muscles exhibit slow, synchronized contractions.
C) Smooth muscle cells are electrically isolated from one another.
Explanation: This statement is not true. Smooth muscle cells are not electrically isolated from one another; instead, they are often connected by gap junctions, which allow for the direct passage of ions and small molecules between cells. This connection facilitates slow, synchronized contractions, which is a characteristic feature of smooth muscle tissue.
Which of the following is unique to smooth muscle contraction? (i.e. does not also occur in skeletal muscle)
A) The trigger for contraction is a rise in intracellular calcium.
B) The protein calmodulin binds calcium.
C) ATP energizes the sliding process.
D) Actin and myosin interact by the sliding filament mechanism.
B) The protein calmodulin binds calcium.
Explanation: This is unique to smooth muscle contraction. In skeletal muscle, the protein troponin binds calcium to initiate contraction, whereas in smooth muscle, calmodulin binds calcium and activates myosin light-chain kinase (MLCK), which then phosphorylates myosin and allows contraction to occur.
Which of the following is a characteristic unique to smooth muscle cells?
A) The ability to not only increase in size, but to divide and increase in numbers as well.
B) The ability to stretch then adapt to new length, while retaining its ability to recoil.
C) The ability to contract when between half and twice its resting length which allows hollow organs to tolerate tremendous change in volume.
D) All of the above.
D) All of the above.
Which is the correct sequence of events in the excitation-contraction coupling of smooth muscle?
A)
1. Calcium ions (Ca2+) enter the cytosol from the ECF via Ca2+ channels, or from the scant SR.
2. The activated kinase enzymes catalyze transfer of phosphate to myosin, activating the myosin ATPases
3. Activated calmodulin activates the myosin light chain kinase enzymes
4. Ca2+ binds to and activates calmodulin
5. Activated myosin forms cross bridges with actin of the thin filaments. Muscle contraction begins.
B)
1. Calcium ions (Ca2+) enter the cytosol from the ECF via Ca2+ channels, or from the scant SR.
2. Ca2+ binds to and activates calmodulin.
3. Activated calmodulin activates the myosin light chain kinase enzymes.
4. Activated myosin forms cross bridges with actin of the thin filaments. Muscle contraction begins.
5. The activated kinase enzymes catalyze transfer of phosphate to myosin, activating the myosin ATPases.
C)
1. Calcium ions (Ca2+) enter the cytosol from the ECF via Ca2+ channels, or from the scant SR.
2. Ca2+ binds to and activates calmodulin
3. Activated calmodulin activates the myosin light chain kinase enzymes
4. The activated kinase enzymes catalyze transfer of phosphate to myosin, activating the myosin ATPases
5. Activated myosin forms cross bridges with actin of the thin filaments. Muscle contraction begins.
C)
1. Calcium ions (Ca2+) enter the cytosol from the ECF via Ca2+ channels, or from the scant SR.
2. Ca2+ binds to and activates calmodulin
3. Activated calmodulin activates the myosin light chain kinase enzymes
4. The activated kinase enzymes catalyze transfer of phosphate to myosin, activating the myosin ATPases
5. Activated myosin forms cross bridges with actin of the thin filaments. Muscle contraction begins.
