Careful! Only The Best Of Biology Students Can Pass This Test!

Muscle fatigue sets in due to the non-availability of ATP. ATP, or adenosine triphosphate, is the main source of energy for muscle contractions. During exercise or any physical activity, ATP is broken down into ADP (adenosine diphosphate) and inorganic phosphate, releasing energy that is used for muscle contraction. However, ATP stores in the muscles are limited and can be quickly depleted. When ATP levels decrease, muscle contractions become weaker and less efficient, leading to muscle fatigue.

During muscle contraction, ATP (adenosine triphosphate) is the primary source of energy. ATP is a molecule that stores and releases energy when needed. When a muscle contracts, ATP molecules are broken down, releasing energy that is used for muscle contraction. This energy is necessary for the myosin heads to interact with actin filaments, causing muscle fibers to contract. Oxygen and glucose are also important for energy production, but they are not the direct source of energy for muscle contraction. Calcium is involved in the process of muscle contraction, but it does not directly provide the energy needed for the contraction.

Calcium ions are responsible for the formation of transverse links in muscle. These ions play a crucial role in muscle contraction by binding to proteins like troponin and allowing the interaction between actin and myosin filaments. This interaction leads to the sliding of filaments and muscle contraction. Sodium, potassium, and chlorine ions are important for maintaining the resting membrane potential and transmitting nerve impulses, but they are not directly involved in the formation of transverse links in muscle.

When a muscle gets shorter and thicker, it is contracting. Muscle contraction occurs when the muscle fibers generate force by pulling on the tendons, resulting in movement. This process involves the sliding of actin and myosin filaments within the muscle fibers, causing the muscle to shorten and thicken. Therefore, the correct answer is contracting.

Shortage of oxygen in the muscle leads to anaerobic respiration, where glycogen is converted to glucose for energy production. This process produces lactic acid as a byproduct, which accumulates in the muscle and causes muscle fatigue.

During muscle contraction, the fiber membrane becomes permeable to Na+ ions. This allows the Na+ ions to enter the muscle fiber, which triggers a series of events leading to muscle contraction. This change in permeability is due to the opening of ion channels in the fiber membrane, specifically sodium channels. The influx of Na+ ions leads to depolarization of the muscle fiber, which ultimately results in the contraction of the muscle.

Skeletal muscles are responsible for the voluntary movement of the body. Eye movement is controlled by skeletal muscles, allowing us to move our eyes in different directions. The other options, such as heart beats, dilatation of the eye pupil, and dilatation of blood vessels, are controlled by smooth muscles or involuntary muscles, not skeletal muscles.

The disappearance of potential difference on the muscle fiber membrane is due to the entry of sodium ions. When a muscle fiber is at rest, the inside of the cell is negatively charged compared to the outside. This is maintained by the sodium-potassium pump, which actively transports sodium ions out of the cell and potassium ions into the cell. However, when a muscle is stimulated, sodium channels open, allowing sodium ions to rush into the cell. This causes a change in the electrical potential of the membrane, leading to the disappearance of the potential difference.

For the contraction of skeletal muscles to occur, both ATP and calcium ions are necessary. ATP provides the energy needed for muscle contraction, while calcium ions are responsible for triggering the contraction process by binding to specific proteins in the muscle fibers. Without ATP, the muscles would not have the energy required to contract, and without calcium ions, the contraction process would not be initiated. Therefore, both ATP and calcium ions are essential for skeletal muscle contraction.

If a muscle fiber contains six Z-lines and five H-zones, then there must be five sarcomeres in that fiber. Each sarcomere is defined by the presence of a Z-line at each end and an H-zone in the middle. Since there are six Z-lines and each sarcomere has two Z-lines, there must be a total of three sarcomeres. However, since there are only five H-zones, this means that one of the sarcomeres does not have an H-zone, resulting in a total of five sarcomeres in the fiber.

Each muscle fiber is innervated by a single motor neuron. Therefore, the least number of motor neurons that can supply 300 muscle fibers is 300.

In a muscle consisting of 5 muscle bundles, each containing 40 muscle fibers, the number of neuromuscular junctions can be calculated by multiplying the number of muscle bundles (5) by the number of muscle fibers in each bundle (40). Therefore, the total number of neuromuscular junctions in the muscle is 5 x 40 = 200.

The least number of myofibrils that the muscle contains can be calculated by multiplying the number of muscle bundles, muscle fibers per bundle, and myofibrils per fiber. In this case, the muscle has 10 bundles, each containing 50 muscle fibers, and each fiber has 1000-2000 myofibrils. To find the least number, we can assume that each fiber has the minimum number of myofibrils, which is 1000. Therefore, the total number of myofibrils in the muscle would be 10 x 50 x 1000 = 500,000.

During the movement of limbs in humans, all of the above mentioned statements are true. The limbs are supported by the skeletal system, which provides a framework for movement. The muscles of the limbs contract and relax in response to signals from the nervous system, allowing for movement. Therefore, the movement of limbs is indeed accomplished through the contraction and relaxation of muscles, which are supported by the skeletal system and controlled by the nervous system.

The correct answer is Epimysium. The epimysium is the connective tissue layer that surrounds the entire skeletal muscle. It provides support and protection to the muscle fibers and helps to maintain the shape and structure of the muscle.

The correct answer is Sarcomere. The sarcomere is the functional unit of the contractile system in a striated muscle. It is the basic unit of muscle contraction and is composed of overlapping thick and thin filaments. The sarcomere is responsible for the muscle's ability to generate force and produce movement.

Intercostal muscles are found in the ribs. These muscles are located between the ribs and play a crucial role in the process of breathing. They help in expanding and contracting the ribcage, allowing for the movement of the chest during inhalation and exhalation.

Z-lines are the dark bands that define the two ends of each sarcomere. They are made up of specialized proteins and act as anchoring points for the thin filaments of actin. The Z-lines help to maintain the structural integrity of the sarcomere and play a crucial role in muscle contraction.

During skeletal muscle contraction, calcium binds to troponin, not myosin heads. Calcium binding to troponin causes a conformational change that allows myosin heads to bind to actin, leading to muscle contraction. ATP is hydrolyzed to provide energy for the myosin heads to move along the actin filaments. As a result of muscle contraction, the I-bands shorten and the H-zones disappear.

Each skeletal muscle fiber is controlled by a neuron at a single neuromuscular junction. This is where the neuron releases neurotransmitters that bind to receptors on the muscle fiber, initiating muscle contraction. The synaptic cleft is the small gap between the neuron and the muscle fiber, while the synaptic knob is the swollen end of the neuron that contains vesicles with neurotransmitters. The sarcomere is the basic unit of muscle contraction.

The correct answer is "Skeletal muscles are responsible for the pumping action of the heart." This statement is incorrect because the heart is primarily composed of cardiac muscle, not skeletal muscle. Cardiac muscle is a specialized type of muscle that is responsible for the pumping action of the heart, while skeletal muscles are responsible for voluntary movements and support the skeleton.

During muscle contraction, the transverse links, also known as cross-bridges, pull the actin filaments towards the center of the sarcomere. Actin and myosin are the two main proteins involved in muscle contraction. Actin is the thin filament that forms the backbone of the sarcomere, while myosin is the thick filament that contains the heads which interact with actin to generate force and cause muscle contraction. Acetyl choline is a neurotransmitter that is released at the neuromuscular junction to initiate muscle contraction, and sarcoplasm is the cytoplasm of muscle cells.

When the neuro-chemical transmitters reach the muscle fiber through the synaptic cleft, they bind to receptors on the muscle fiber membrane. This binding causes a change in the electrical charge of the membrane, leading to the opening of ion channels. The opening of these ion channels allows the flow of positively charged ions into the muscle fiber, which depolarizes the membrane. Depolarization is a necessary step for the muscle fiber to generate an action potential and ultimately contract. Therefore, the correct answer is depolarized.

The region which its length does not change when the muscle fiber contracts is A.

Calcium ions are responsible for the transmission of the impulse across synapse to the muscle fiber. When an action potential arrives at the presynaptic terminal, it triggers the release of calcium ions into the synaptic cleft. These calcium ions then bind to proteins on the presynaptic membrane, causing the synaptic vesicles to fuse with the membrane and release neurotransmitters into the synaptic cleft. The neurotransmitters then bind to receptors on the postsynaptic membrane, initiating a new action potential in the muscle fiber.

The myofibril is the correct answer because it is a specialized organelle found in muscle cells that contains actin and myosin. Actin and myosin are proteins that are responsible for muscle contraction and movement. The myofibril is composed of repeating units called sarcomeres, which are the functional units of muscle contraction. Therefore, the myofibril is the organelle that contains actin and myosin.

The given question asks which statement is correct for different degrees of muscle tension shown in the figure. The correct answer states that all of the given statements are correct. This means that at maximum muscle tension (A), there is maximum binding of myosin and actin, allowing for contraction. At minimum muscle tension (B), the binding between myosin and actin is blocked, preventing contraction. And at an intermediate level of muscle tension (C), the actin filaments do not overlap the myosin ones, preventing the formation of cross bridges and therefore contraction.

When a contracted skeletal muscle is relaxed, the two regions H and I increase in length.

Each muscle fiber is innervated by one motor neuron. Therefore, the maximum number of motor neurons that can supply the muscle is equal to the number of muscle fibers, which is 300.

During muscle contraction, the length of the A-band remains constant. The A-band represents the dark region in the middle of the sarcomere that contains overlapping thick and thin filaments. As the muscle contracts, the thin filaments slide over the thick filaments, causing the sarcomere to shorten. However, the length of the A-band remains constant because the thick filaments do not change in length during contraction.

The sarcomere is the functional unit of the contractile system in striated muscles. It is the basic structural and functional unit of a muscle fiber, consisting of overlapping actin and myosin filaments. When a muscle contracts, the sarcomeres within the muscle fibers shorten, resulting in muscle contraction. The Z-bands, myofibrils, and cross bridges are all components of the sarcomere, but the sarcomere itself is the specific unit responsible for muscle contraction.

Smooth muscle is not cross striated because myosin and actin fibers are arranged at angles to each other as they run through the cell. In cross-striated muscles, such as skeletal muscle, the myosin and actin filaments are organized into well-ordered sarcomeres and myofibrils. However, in smooth muscle, the arrangement is more irregular, with the fibers running in different directions. This lack of regular arrangement is what gives smooth muscle its characteristic smooth appearance under a microscope.

Intercalated discs are specialized cell junctions found in cardiac muscle tissue. These discs play a crucial role in connecting individual cardiac muscle cells, allowing them to function as a coordinated unit. Intercalated discs are most likely to be observed in a longitudinal section of cardiac muscle because this section provides a view of the muscle fibers running parallel to the long axis of the heart. In contrast, a transverse section of cardiac muscle would provide a cross-sectional view of the muscle fibers, which may not clearly show the intercalated discs.

During skeletal muscle contraction, the A-bands, which are the dark bands, will remain a constant length. The H-zone, which is the space occupied by only thick filaments, will actually shorten as the thin filaments slide over the thick filaments. The I-bands, which are the light bands, will also shorten as the thin filaments overlap with the thick filaments. Additionally, the z-lines, which mark the boundaries of sarcomeres, will come closer together as the sarcomeres shorten. Therefore, the statement that is not correct is that the space occupied by the H-zone will not change.

ATP (adenosine triphosphate) is the direct energy store for muscles. It is a molecule that provides the necessary energy for muscle contraction. When ATP is broken down, it releases energy that is used by the muscles for various activities. ATP is constantly being produced and used in muscle cells to support their function. Glycogen and glucose are energy sources that can be converted into ATP, but they are not the direct energy stores. Lactic acid is a byproduct of anaerobic metabolism and is not directly involved in providing energy for muscle contraction.

Skeletal muscle contraction is characterized by its rapidity, voluntary control, and ability to exert tremendous power. However, it cannot contract for long periods of time without tiring. Skeletal muscles rely on the breakdown of ATP for energy, and prolonged contraction leads to the depletion of ATP and the buildup of metabolic waste products, causing fatigue.

The correct answer is "A motor unit is made up of one neuron that supplies a single muscle fiber." This statement is not correct because a motor unit is actually made up of one motor neuron and multiple muscle fibers. Each motor neuron branches out and forms connections with multiple muscle fibers, allowing for coordinated contractions of a single muscle.

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The sliding filament theory is a widely accepted explanation for muscle contraction, but it does not fully explain the mechanism of contraction in the muscles of the small intestine. The muscles of the small intestine exhibit a unique pattern of contraction known as peristalsis, which involves coordinated waves of contraction and relaxation to propel food through the digestive system. This mechanism is not fully accounted for by the sliding filament theory, which primarily focuses on the interaction between actin and myosin filaments in muscle fibers.

The increase in permeability of the sarcolemma to sodium ions leads to the depolarization of the sarcolemma. When the sarcolemma becomes more permeable to sodium ions, they are able to enter the muscle cell more easily. This influx of sodium ions causes a change in the electrical charge of the sarcolemma, leading to depolarization. This depolarization is an important step in the generation of an action potential, which ultimately leads to muscle contraction.

When a muscle fiber contracts, the region that is no longer visible is called the H zone. The H zone is located in the center of the A band, which represents the length of the thick filaments in the sarcomere. During muscle contraction, the thin filaments slide over the thick filaments, causing the H zone to become shorter or disappear completely. Therefore, the correct answer is H.

Muscle fibers respond to stimuli by becoming depolarized, which means that the electrical charge inside the cell becomes more positive. This depolarization is caused by the movement of ions across the cell membrane. In this case, the correct answer is sodium because the movement of sodium ions into the cell is responsible for the initial depolarization of the muscle fiber. Sodium ions rush into the cell through channels in the cell membrane, causing an influx of positive charge and triggering a muscle contraction.

Calcium ions play a crucial role in muscle contraction by binding to tropomyosin, a protein that covers the myosin binding sites on the actin filament. When calcium ions bind to tropomyosin, it changes its shape and allows the myosin heads to attach to the actin filament, initiating muscle contraction. Therefore, the primary role of calcium ions in the sliding filament theory of muscle contraction is to bind to tropomyosin, changing its shape and moving it away from the myosin binding sites.

A muscle consists of many muscle fibers, and each muscle fiber is innervated by a motor neuron. The least number of motor neurons that can supply the muscle would be equal to the number of muscle fibers, which is 1000. However, a single motor neuron can innervate multiple muscle fibers, so the greatest number of motor neurons that can supply the muscle would be less than or equal to the number of muscle fibers. Therefore, the range of possible numbers of motor neurons is 10 to 200.

Red muscles are rich in myoglobin and cytochromes. Myoglobin is a protein that stores oxygen in muscle cells, allowing for sustained aerobic respiration. Cytochromes are proteins involved in the electron transport chain, which is essential for generating ATP, the energy currency of cells. These two substances are responsible for the red color of these muscles and their ability to sustain prolonged activity.

The sarcolemma is the membrane that covers the muscle fiber. It is a specialized plasma membrane that surrounds each individual muscle cell, allowing for the exchange of nutrients and waste products. The sarcolemma is essential for the proper functioning of the muscle fiber and plays a crucial role in muscle contraction and relaxation.

Cardiac muscle contains structures known as intercalated discs, which are specialized junctions between cardiac muscle cells. These discs play a crucial role in allowing the cells to communicate and contract together as a coordinated unit. Intercalated discs contain gap junctions, which allow for the rapid spread of electrical impulses between cells, and desmosomes, which provide structural support and prevent the cells from separating during contraction. This unique feature of intercalated discs is not present in skeletal muscle, making the statement accurate.

The area (R) in the figure represents the motor end plate. The motor end plate is a specialized region of the muscle fiber membrane that forms the synapse with the motor neuron. It is where the neurotransmitter acetylcholine is released from the motor neuron and binds to receptors on the motor end plate, initiating muscle contraction.

Calcium ions play a crucial role in muscular contraction by activating the binding of myosin to actin. Myosin is a protein that interacts with actin to generate the force required for muscle contraction. When calcium ions are released into the muscle cell, they bind to a protein called troponin, causing a conformational change that exposes the binding sites on actin. This allows myosin to bind to actin, forming cross-bridges and initiating the sliding of actin filaments over myosin filaments, leading to muscle contraction. Therefore, the activation of myosin binding to actin is an important step in the process of muscular contraction.

The correct answer is Z-line. The Z-line is a protein structure that anchors the actin filaments in a sarcomere, which is the basic unit of a muscle fiber. The actin filaments extend from the Z-line towards the center of the sarcomere, where they overlap with myosin filaments to generate muscle contraction. Therefore, the Z-line serves as an attachment point for the actin filaments and helps maintain the structural integrity of the sarcomere.