Question

What happens to the I bar and H zone during contraction? Do the lengths of the thick and thin filaments change?

Answer 1

Hint: During muscle contraction, the filaments of the H zone and the I bar are shortened. The central region of A zone is referred to as the H zone. It consists of only thick filaments and gets shortened at the time of muscle contraction. The I band shortens and consists of only thin filaments

Complete answer:
In the human body muscles are the structures responsible for motion, and also help to facilitate body processes like respiration and digestion. Our body contains three different types of muscle structures such as skeletal muscles, cardiac muscles, and smooth muscles.

Considering the skeletal muscle fiber structure, their cells are large with length up to 30 cm and with a diameter up to 100 micrometers. The sarcolemma is the plasma membrane of the skeletal muscle fiber, which is responsible for triggering muscle contraction. Within each muscle fiber, there occurs a long cylindrical structure called Myofibril lying parallel to the muscle fiber. Hundreds and thousands of muscle fibers are present within the single muscle fiber.

When entire muscle contracts, the myofibrils are shortened which are present at the end of the sarcolemma. The skeletal muscle tissue consists of repeated bands of Actin and Myosin protein filaments with dark A and light I bands present along the length of the myofibrils.

There are two main filaments that occur in the myofibrils. Thick filaments in A band and the thin filaments in z disc. When the thick and thin filaments overlap, there occurs a space which is in dense appearance called H-zone.

During Muscle contraction, the sarcomere shortens, some of the regions also shorten while the other regions remain the same. When muscle contracts, the H zone (central region of Azone) which consists of thick filaments is shortened and the I band which contains only thin filaments is also shortened during the time of contraction.

Note: Based on two variables the muscle contraction can be described such as length and tensions. There are four types of muscle contractions which include isometric, isotonic, eccentric, and concentric.