Tissues And Functions Of The Muscular System

The attachment of a muscle's tendon to the stationary bone is called the origin, while the attachment of the muscle's other tendon to the movable bone is called insertion.

Myofibrils are the contractile organelles of the muscle fiber. They are responsible for the contraction and relaxation of muscles. Made up of repeating units called sarcomeres, myofibrils contain thick and thin filaments that slide past each other during muscle contraction, resulting in muscle movement. These structures play a crucial role in generating force and enabling muscle contraction. Myofibrils are essential for muscle function and are therefore the correct answer in this context.

The number of cells is not one of the descriptive ways to name a muscle. Descriptive ways to name a muscle typically include characteristics such as size, shape, number of origins, and sites of origins. The number of cells is not a commonly used characteristic for naming muscles, as it does not provide specific information about the muscle's physical attributes or function.

The different types of muscle tissue differ from each other by their microscopic anatomy, location, and type of control. Microscopic anatomy refers to the structural characteristics of the muscle tissue, such as the arrangement of muscle fibers and the presence of specific proteins. Location refers to where the muscle tissue is found in the body, such as skeletal muscles attached to bones or smooth muscles in the walls of organs. Type of control refers to whether the muscle tissue is under voluntary control (skeletal muscles) or involuntary control (smooth and cardiac muscles). Therefore, all of these choices contribute to the differences between the types of muscle tissue.

Motion will occur in a muscle when the effort supplied exceeds the load. In other words, when the force applied by the muscle is greater than the resistance it is trying to move, motion will occur.

Tropomyosin and troponin are regulatory proteins that can be found associated with an actin molecule. Tropomyosin is a long, filamentous protein that wraps around the actin filament, regulating access to the myosin binding sites on actin. Troponin is a complex of three subunits that binds to tropomyosin and actin. It plays a crucial role in regulating muscle contraction by controlling the position of tropomyosin on the actin filament. Together, tropomyosin and troponin work to regulate the interaction between actin and myosin during muscle contraction.

The signal to excite a muscle cell must cross the synaptic cleft. The synaptic cleft is the small gap between the motor neuron axon and the muscle cell, where the neuromuscular junction is located. Acetylcholine, a neurotransmitter, is released from the synaptic vesicles in the motor neuron axon and diffuses across the synaptic cleft. It then binds to receptors on the sarcolemma of the muscle cell, initiating a series of events that lead to muscle contraction. Therefore, the diffusion of acetylcholine across the synaptic cleft is necessary for the signal to excite a muscle cell.

Axon terminal clusters at the ends of motor neurons are referred to as synaptic end bulbs. These bulbs play a crucial role in the transmission of signals from the motor neurons to the muscles at the neuromuscular junction. They contain neurotransmitters that are released into the synaptic cleft, allowing the signal to be transmitted to the muscle fibers and causing them to contract.

Muscles produce ATP through a combination of processes. Creatine phosphate is used as a quick source of energy during short bursts of intense activity. Anaerobic cellular respiration occurs when there is not enough oxygen available, and glucose is broken down to produce ATP. Aerobic cellular respiration takes place when there is sufficient oxygen, and glucose is fully broken down in the presence of oxygen to produce ATP. Therefore, all of these choices contribute to the production of ATP in muscles.

Slow oxidative fibers found in skeletal muscle contract slowly, but are resistant to fatigue. This means that they are designed for endurance activities that require prolonged contraction without tiring easily. These fibers are smaller in diameter compared to fast-twitch fibers, which are adapted for intense bursts of anaerobically fueled movement. Slow oxidative fibers also have a high capacity for oxidative metabolism, enabling them to generate ATP aerobically and sustain contractions for longer periods. They do not contain vast stores of glycogen like fast-twitch fibers, which rely more on anaerobic metabolism. Additionally, slow oxidative fibers are typically recruited early on during activities that require low to moderate force.

The sarcoplasmic reticulum is a specialized organelle found in muscle cells that is responsible for storing and releasing calcium ions (Ca2+). Calcium ions play a crucial role in muscle contraction by binding to proteins within the muscle fibers and initiating the sliding of the actin and myosin filaments. This allows for the generation of force and movement. Therefore, the sarcoplasmic reticulum is used for storing Ca2+ ions, which are essential for muscle function.

Motor unit recruitment refers to the process of increasing the number of active motor units in a muscle. When a muscle needs to generate more force, the nervous system activates additional motor units to contract. This recruitment allows for a greater number of muscle fibers to be stimulated, resulting in a stronger contraction. It is an important mechanism for increasing muscle strength and is commonly seen during activities that require more force, such as lifting heavy weights or performing intense exercise.

The epimysium is a band of connective tissue that surrounds whole muscles. It provides support and protection to the muscle fibers and helps to maintain the shape and integrity of the muscle. It is the outermost layer of connective tissue in the muscle and is responsible for connecting the muscle to the surrounding structures.

The terminal cisterns of the sarcoplasmic reticulum are responsible for releasing calcium when stimulated by the T tubules. Calcium is a crucial ion in muscle contraction, as it binds to the protein troponin, allowing the myosin heads to interact with actin and initiate the sliding of the sarcomeres, which ultimately leads to muscle contraction. The terminal cisterns are specialized regions of the sarcoplasmic reticulum that are located near the T tubules, allowing for efficient communication and coordination between the two structures during muscle contraction.

Most muscles in the human body cross at least one joint. A joint is a point where two or more bones meet, allowing movement and flexibility. Muscles attach to bones via tendons, which are strong, fibrous tissues that connect muscle to bone. When a muscle contracts, it pulls on the tendon, causing movement at the joint. Therefore, it is accurate to say that most muscles cross at least one joint in order to facilitate movement.

An agonist is a muscle that is primarily responsible for producing a specific movement or action. It is the main muscle involved in generating force and initiating a movement. Therefore, it can be considered as the prime mover. The other options listed are not synonyms for a prime mover and do not accurately describe the function of an agonist muscle.

The contraction cycle in muscle cells requires the presence of calcium ions and ATP. Calcium ions are necessary for the binding of myosin and actin, which initiates muscle contraction. ATP is needed for the detachment of myosin from actin and the re-energizing of the myosin heads, allowing for repeated muscle contractions. Therefore, both calcium ions and ATP are essential for the contraction cycle to continue.

Creatine phosphate is a high-energy molecule found in muscle cells that can rapidly regenerate ATP, the main source of energy for muscle contractions. When muscles contract, ATP is broken down into ADP and a phosphate group, releasing energy. Creatine phosphate can then donate its phosphate group to ADP, converting it back into ATP. This process allows for the rapid replenishment of ATP, providing enough energy for a muscle to contract for approximately 15 seconds.

For every nerve that penetrates a skeletal muscle, there is generally one artery and one or two veins. This means that the muscle receives a supply of oxygenated blood through the artery and the deoxygenated blood is drained away through the veins. The number of veins can vary, but there is always at least one artery and one vein present.

Slow Oxidative muscle fibers are characterized by their ability to sustain contractions for long periods of time without fatiguing. This is due to their high capacity for aerobic metabolism, which allows them to generate ATP efficiently through oxidative phosphorylation. These muscle fibers have a rich supply of mitochondria, which are responsible for producing ATP, and they also contain high levels of myoglobin, a protein that stores oxygen and facilitates its delivery to the muscle. As a result, Slow Oxidative muscle fibers have a high resistance to fatigue compared to other types of muscle fibers.

A twitch contraction refers to the brief contraction of all muscle fibers in a motor unit in response to a single action potential. This contraction is a result of the motor neuron stimulating the muscle fibers, causing them to contract simultaneously. It is called a twitch because it is a quick and involuntary contraction that lasts for a very short duration. This term is commonly used in the context of studying muscle physiology and understanding muscle contractions.

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Extensibility is the property of muscle that allows it to stretch without causing damage. This means that muscles can be elongated or stretched beyond their normal resting length without tearing or breaking. This is crucial for muscle function as it allows for a greater range of motion and flexibility. It also enables muscles to adapt and grow in response to exercise and physical activity.

Slow oxidative fibers are the least powerful type of muscle fiber. These fibers have a high capacity for aerobic metabolism and are resistant to fatigue. They are primarily used for endurance activities such as long-distance running or cycling. Slow oxidative fibers have a slower contraction speed and lower force production compared to other types of muscle fibers.

Intercalated discs are a unique characteristic of cardiac muscle tissue. These specialized structures connect individual cardiac muscle cells, allowing for coordinated contraction of the entire heart. Intercalated discs contain gap junctions, which facilitate the rapid spread of electrical signals between cells, ensuring synchronous contraction. This unique feature is essential for the efficient pumping action of the heart and distinguishes cardiac muscle from other types of muscle tissue.

Myofibrils contain all of these choices: contractile proteins, regulatory proteins, and structural proteins. Contractile proteins, such as actin and myosin, are responsible for muscle contraction. Regulatory proteins, such as tropomyosin and troponin, regulate the interaction between actin and myosin. Structural proteins, such as titin and dystrophin, provide support and stability to the myofibrils. Therefore, all three types of proteins are present in myofibrils.

The fascicle arrangement refers to the pattern in which muscle fibers are organized within a muscle. In a pennate arrangement, the muscle fibers are obliquely attached to a central tendon, giving a feather-like appearance. Triangular, parallel, and fusiform arrangements are all types of fascicle arrangements commonly found in muscles. However, an oval arrangement is not a recognized fascicle arrangement. This suggests that oval is the correct answer as it does not fit the criteria of a fascicle arrangement.

Fast Glycolytic fibers found in skeletal muscle are adapted for intense bursts of anaerobically fueled movement. This means that they are designed to produce quick and powerful contractions without the need for oxygen. These fibers rely on the breakdown of glucose through glycolysis to generate energy rapidly. This allows for short bursts of high-intensity activity, such as sprinting or weightlifting.

In a lever system, the effort is the force applied to move the lever, while the load is the resistance or weight being lifted or moved. The fulcrum is the pivot point of the lever, and the resistance refers to the force opposing the effort. Therefore, the correct answer is "effort and load" as they accurately represent the forces acting on the lever.

Calcium ions play a crucial role in muscle contraction. In skeletal muscle cells, calcium ions bind to the troponin molecule. Troponin is a regulatory protein that is part of the thin filament in muscle cells. When calcium ions bind to troponin, it causes a conformational change that allows the myosin heads to interact with actin, leading to muscle contraction. Therefore, troponin is directly involved in the regulation of muscle contraction in skeletal muscle cells.

Hypertrophy refers to the increase in the size of muscle fibers. This occurs when the muscle is subjected to repetitive and intense exercise, causing the muscle fibers to adapt and grow in size. This increase in size is accompanied by an increase in strength and is a common goal for individuals engaged in resistance training. Conversely, a decrease in the size of muscle fibers is known as atrophy, which can occur due to disuse or certain medical conditions.

A motor unit is comprised of a single motor neuron and all the muscle fibers that it innervates. This means that a motor neuron is responsible for activating multiple muscle fibers within a specific area. When the motor neuron sends a signal, all the muscle fibers it innervates contract together, allowing for coordinated movement. This organization allows for precise control of muscle contraction and ensures that all the muscle fibers in a specific area are activated simultaneously.

In an isometric contraction, the muscle develops tension but does not lengthen. This means that the muscle remains at a constant length while still generating force. The contraction is characterized by the muscle fibers pulling on each other without any visible movement or change in length. Therefore, the correct answer is "shorten."

The sarcoplasmic reticulum is responsible for storing and releasing calcium ions, which are crucial for muscle contractions. When a muscle is stimulated to contract, the sarcoplasmic reticulum releases calcium ions into the cytosol, which then bind to specific proteins called troponin. This binding allows the muscle fibers to slide past each other, resulting in muscle contraction. Therefore, the correct answer is that the sarcoplasmic reticulum releases calcium ions at the beginning of a contraction.

Muscle tissue is responsible for various functions in the body, including moving blood throughout the body, generating heat through contractions, stabilizing joints, and promoting movement of body structures. However, storing energy is not a major function of muscle tissue. Energy storage is primarily carried out by adipose tissue, which is specialized for storing excess energy in the form of fat.

The myosin head is energized by the hydrolysis of ATP. During muscle contraction, ATP is broken down into ADP and inorganic phosphate, releasing energy that is used to power the movement of the myosin head. This energy allows the myosin head to bind to actin filaments and undergo a conformational change, resulting in muscle contraction. Calcium ions are involved in the regulation of muscle contraction, but they do not directly energize the myosin head. Potassium ions and phosphorylation of ADP are not directly involved in the energization of the myosin head.

In the sliding filament mechanism, the thin filament is being pulled towards the M line. The M line is located in the center of the sarcomere and serves as the attachment point for the thick filaments. As the thick filaments slide past the thin filaments during muscle contraction, the thin filaments are pulled towards the M line. This movement causes the sarcomere to shorten, resulting in muscle contraction. Therefore, the correct answer is M line.

The correct answer is endomysium. The endomysium is a connective tissue layer that surrounds each individual muscle cell, providing support and protection. It also contains capillaries and nerves that supply the muscle cell with nutrients and signals for contraction. The perimysium surrounds bundles of muscle fibers called fascicles, the epimysium surrounds the entire muscle, and the deep fascia is a layer of connective tissue that surrounds groups of muscles.

A motor unit consists of a somatic motor neuron and all the skeletal muscle fibers it stimulates. This means that when the somatic motor neuron sends a signal, all the muscle fibers within that motor unit contract simultaneously. The motor unit is the functional unit responsible for generating movement in the skeletal muscles.

A triangular fascicle arrangement is characterized by fascicles that are spread over a broad area and converge at a thick central tendon. This arrangement resembles the shape of a triangle, with the fascicles radiating outwards from the central tendon.

An aponeurosis is a broad, flat tendon-like structure that connects muscles to other structures, such as bones or other muscles. It is formed when connective tissue extends as a broad flat layer. This allows for a wide distribution of forces and helps to provide strength and stability to the area. Therefore, the correct answer is aponeurosis.

Excitation refers to the phase where a muscle action potential propagates along the sarcolemma (cell membrane of a muscle fiber) and into the T tubules (invaginations of the sarcolemma). This phase is crucial for initiating muscle contraction. During excitation, the action potential triggers the release of calcium ions from the sarcoplasmic reticulum, which then binds to troponin and allows for the interaction between actin and myosin filaments, leading to muscle contraction.

Fused tetanus refers to a sustained contraction of a muscle where individual muscle twitches cannot be detected. This occurs when the muscle fibers are stimulated rapidly and do not have enough time to relax between contractions. As a result, the contractions blend together into a smooth, continuous contraction. This is in contrast to unfused tetanus, where individual muscle twitches can still be observed.

Smooth muscle tone is due to the prolonged presence of calcium ions in the cytosol. Calcium ions play a crucial role in regulating muscle contraction and relaxation. In smooth muscle, calcium ions bind to a protein called calmodulin, which activates an enzyme called myosin light chain kinase. This enzyme phosphorylates myosin, leading to the interaction between actin and myosin and subsequent muscle contraction. Therefore, the prolonged presence of calcium ions in the cytosol maintains smooth muscle tone. ATP, phosphate ions, and myoglobin do not directly contribute to smooth muscle tone.

Both the I band and A band contain thin filaments. The I band is a region of the sarcomere where only thin filaments are present. It is located between two A bands and represents the distance between two adjacent sarcomeres. The A band, on the other hand, contains both thin and thick filaments. It is the region where thick filaments overlap with thin filaments, giving it a darker appearance. Therefore, the correct answer is both I band and A band.

The statement that is FALSE is "Concentric isotonic contractions occur when the load equals or exceeds the tension produced in the muscle." In reality, concentric isotonic contractions occur when the tension produced in the muscle exceeds the load. In this type of contraction, the muscle shortens while generating force, such as when lifting a weight.

The correct answer is 2 because acetylcholine, a neurotransmitter, needs to bind with two molecules to open the ion channel of the ACh receptor. This binding triggers a conformational change in the receptor, allowing ions to flow through the channel and propagate the nerve signal.

A fixator muscle is a type of muscle that stabilizes the origin of a prime mover. It helps to keep the origin of the prime mover steady, allowing it to act more efficiently. This means that the fixator muscle supports and reinforces the action of the prime mover, enabling it to perform its function effectively.

The given statement "can be as much as a foot long" is the correct answer because skeletal muscle cells are known for their long and cylindrical shape. They can extend for a considerable length, often reaching up to a foot long. This characteristic allows them to generate the force necessary for movement and perform their primary function of contracting and relaxing to produce voluntary movements in the body.

The refractory period is a period of time during which a nerve or muscle cell is unable to respond to a stimulus, as it is still recovering from the previous stimulus. It is often referred to as the period of lost excitability because the cell is temporarily unresponsive. This period is crucial for ensuring that nerve and muscle cells do not become overstimulated and can properly recover before being able to respond again.