Block 2 Pace Quiz Skeletal Muscle: Micro Anatomy

When the neurotransmitter is released and attached to the receptors on the sarcolemma, Na+ rushes into the cell causing depolarization, which subsequently leads to the contraction process.

The electrical signal of an action potential is conveyed into the interior of each muscle fiber by transverse tubules. Transverse tubules, also known as T-tubules, are invaginations of the muscle cell membrane that extend deep into the muscle fiber. They allow the action potential to quickly spread throughout the entire muscle fiber, ensuring synchronous muscle contraction. The T-tubules are in close proximity to the sarcoplasmic reticulum, which stores and releases calcium ions necessary for muscle contraction. Together, the T-tubules and sarcoplasmic reticulum play a crucial role in the excitation-contraction coupling process in muscle cells.

Mammalian skeletal muscle possesses triads. Triads are structures formed by the close association of a T tubule and two terminal cisternae of the sarcoplasmic reticulum. This arrangement allows for the efficient release and uptake of calcium ions during muscle contraction and relaxation.

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When an additional 5-pounds of dishes is placed on the tray, the muscles holding the tray need to generate more force to counteract the increased weight. This increase in force is achieved by activating more motor units in the muscles. Motor units consist of a motor neuron and the muscle fibers it innervates. By activating more motor units, more muscle fibers are recruited, resulting in a greater force of contraction. Therefore, the number of motor units activated is the correct answer in this scenario.

When a muscle is injured, satellite cells, which are a type of stem cell located on the surface of muscle fibers, are activated. These satellite cells have the ability to differentiate and fuse with existing muscle fibers to repair and regenerate the damaged muscle tissue. Therefore, the correct answer is differentiation of satellite cells.

The sarcoplasmic reticulum of skeletal muscle functions in cellular Ca++ storage. The sarcoplasmic reticulum is a specialized type of endoplasmic reticulum found in muscle cells. It plays a crucial role in regulating calcium ions within the muscle cell. During muscle contraction, calcium ions are released from the sarcoplasmic reticulum into the cytoplasm, which triggers the contraction. When the muscle relaxes, the sarcoplasmic reticulum actively pumps calcium ions back into its storage compartments, allowing the muscle to relax. Therefore, the sarcoplasmic reticulum functions as a storage site for calcium ions in the muscle cell.

Skeletal muscle myosin molecules have a head component that includes an actin-binding site. This means that the head of the myosin molecule can bind to actin filaments in the muscle fiber, forming cross-bridges. These cross-bridges are responsible for the sliding of actin filaments past myosin filaments, leading to muscle contraction.

Botulinum toxin is a neurotoxic protein produced by the bacterium Clostridium botulinum. It acts by blocking the release of acetylcholine, a neurotransmitter, at the neuromuscular junction synapse. By inhibiting the release of acetylcholine, botulinum toxin prevents the transmission of signals from nerve cells to muscle cells, leading to muscle paralysis. Therefore, it reduces neurotransmitter release at the neuromuscular junction synapse.

The correct order from smallest to largest is myofilament, myofibril, fiber, fascicle. Myofilaments are the smallest components of muscle fibers, followed by myofibrils, which are bundles of myofilaments. Fibers are groups of myofibrils, and fascicles are bundles of fibers.

Z-lines are structures found in skeletal muscle fibers that serve as attachment sites for thin filaments (actin). Thin filaments are composed of actin and other regulatory proteins and are responsible for muscle contraction. The Z-lines anchor the thin filaments and provide structural stability to the sarcomere, the basic unit of muscle contraction. Therefore, the correct answer is thin filaments (actin).

The perimysium is the correct answer because it is the connective tissue layer that surrounds a muscle fascicle. It is responsible for providing support and protection to the fascicle, as well as allowing for the transmission of blood vessels and nerves to the muscle fibers within the fascicle.

In skeletal muscle, the length of the fiber affects the shortening velocity during isotonic contraction. The longer fiber has a higher velocity because it has a greater distance to cover in the same amount of time. Isometric contraction, on the other hand, does not involve any change in length, so the length of the fiber does not affect the velocity. Therefore, the long fiber has a higher velocity during isotonic contraction than the short one.

Motor units consist of a motor neuron and all the muscles it supplies. This means that a single motor neuron can control multiple muscle fibers. When the motor neuron is activated, all the muscle fibers it innervates will contract simultaneously. This allows for coordinated and synchronized muscle movements.

The correct answer is spaced at irregular intervals along each muscle fiber. Skeletal muscle fibers are multinucleated, meaning they contain multiple nuclei. These nuclei are not evenly spaced along the length of the muscle fiber, but rather are located at irregular intervals. This arrangement allows for efficient control and coordination of muscle contraction, as different regions of the muscle fiber can be activated independently.

The endomysium is a connective tissue investment that surrounds individual muscle fibers. This connective tissue layer provides support and protection to the muscle fibers, allowing them to function properly. It also helps to maintain the structural integrity of the muscle and allows for efficient transmission of force during muscle contraction.

After acetylcholine crosses the synaptic cleft, it binds to receptors on the sarcolemma, which triggers the opening of sodium channels. This leads to the depolarization of the sarcolemma. The depolarization then spreads down the T tubules, which are invaginations of the sarcolemma. The T tubules are in close proximity to the terminal cisternae of the sarcoplasmic reticulum, which releases calcium ions in response to the depolarization. The calcium ions then bind to troponin, initiating muscle contraction. Therefore, the correct order of membrane depolarization in skeletal muscle fibers is sarcolemma, T tubule, terminal cisternae, sarcoplasmic reticulum.

Neuromuscular junctions are located midway along the length of the muscle fiber. This is because the neuromuscular junction is the point where the motor neuron meets the muscle fiber, and it is responsible for transmitting the nerve impulse from the neuron to the muscle fiber, causing muscle contraction. Placing the neuromuscular junction midway along the length of the muscle fiber allows for efficient transmission of the nerve impulse to all parts of the muscle, ensuring coordinated and synchronized muscle contractions.

To increase the activity of the Ca++/3Na+ exchanger would result in an increase in the exchange of calcium ions (Ca++) with sodium ions (Na+) across the cell membrane. This would lead to a decrease in the concentration of calcium ions within the cell, which would ultimately shorten the duration of a skeletal muscle contraction.

The correct answer is a mutation in the voltage-sensitive Ca2+ channel of skeletal muscle. This is because the patient's symptoms of extreme proximal muscle weakness, which are precipitated by rest following strenuous exercise, are consistent with a condition known as hypokalemic periodic paralysis. This condition is caused by mutations in the voltage-sensitive Ca2+ channel, which leads to abnormal muscle excitability and periodic episodes of muscle weakness.

T tubules are invaginations of the sarcolemma that extend deep into the muscle fiber. They play a crucial role in carrying the action potential from the sarcolemma to the interior of the muscle fiber, allowing for the depolarization and repolarization of the muscle cell during muscle contraction and relaxation. This helps to ensure synchronized and efficient muscle contraction. Therefore, the statement "Carry repolarization to the muscle fiber interior" is true of T tubules.