Drag the appropriate labels to their respective targets. Reset Help T tubule Terminal cisternae A band Sarcolemma I band Triad Myofibrils Submit Request Answer
The Correct Answer and Explanation is:
Here is the correct labeling for the image:
- Sarcolemma – The outermost label pointing to the outer membrane.
- Myofibrils – The label pointing to the long, cylindrical structures inside the muscle fiber.
- A band – The dark, thick region within a sarcomere (middle label inside the myofibril).
- I band – The lighter area that does not overlap with thick filaments (lighter region beside the A band).
- T tubule – The structure that invaginates into the muscle fiber (middle tube running transverse).
- Terminal cisternae – The enlarged areas of the sarcoplasmic reticulum near the T tubule.
- Triad – A T tubule with two terminal cisternae on each side.
Explanation
This diagram represents a cross-section of a skeletal muscle fiber, highlighting various internal structures crucial to muscle contraction.
Sarcolemma is the plasma membrane of the muscle fiber. It plays a key role in conducting electrical signals (action potentials) from the neuromuscular junction into the muscle cell’s interior.
Myofibrils are rod-like units within muscle fibers composed of repeating sections of sarcomeres, the basic functional units of muscle contraction. Sarcomeres are formed by the alignment of thick (myosin) and thin (actin) filaments.
A bands are dark bands that contain the entire length of thick filaments (myosin), including overlapping thin filaments. I bands are lighter areas that contain only thin filaments and appear lighter under a microscope. The alternating A and I bands give skeletal muscle its striated appearance.
T tubules (transverse tubules) are invaginations of the sarcolemma that penetrate deep into the muscle fiber. They conduct action potentials from the surface to the interior of the cell, ensuring that the entire fiber contracts simultaneously.
Terminal cisternae are enlarged sections of the sarcoplasmic reticulum that border the T tubules. They store calcium ions and release them upon stimulation, which is critical for triggering muscle contraction.
Triads are formed by one T tubule flanked by two terminal cisternae. This arrangement ensures efficient communication between the excitation (from the action potential) and contraction mechanisms, a process known as excitation-contraction coupling.
Understanding these components and their functions is fundamental to grasping how muscle fibers contract and how electrical signals are translated into mechanical force.
