Question 1 of 9intermediate🔧 ApplyDiagram5 marks

Draw the diagram of a sarcomere of skeletal muscle showing different regions.

Correct Answer

The diagram of a sarcomere should show the following labelled regions:

  1. 'A' band (dark band): This is the dark band in the sarcomere which retains its length during muscle contraction. It contains the thick filaments (myosin).

  2. 'I' band (light band): This is the light band which gets reduced during muscle contraction. It contains thin filaments (actin).

  3. 'H' zone: This is the central region of the 'A' band that represents the thick filaments only.

  4. 'Z' line: This line is present in the centre of the 'I' band and is attached to the actin filaments. The 'Z' lines are pulled inwards during contraction, causing shortening of the sarcomere.

  5. Thin filaments (Actin): These are present in the 'I' bands and extend into the 'A' bands. Actin is present in thin filament.

  6. Thick filaments (Myosin): These are present in the 'A' band and form cross-bridges with actin during contraction.

The sarcomere is the functional unit of muscle contraction, bounded by two 'Z' lines. During contraction, the actin filaments are pulled towards the centre of the 'A' band by the myosin head, causing the 'I' bands to reduce while the 'A' bands retain their length.

Exercise: EXERCISES | Q: 1 | (Page 312)
For More Understanding

Explanation

The question asks for a diagram of a sarcomere with labelled regions. From the textbook context, we learn that myofibrils have alternate dark and light bands. The 'A' band is the dark band containing thick filaments (myosin), while the 'I' band is the light band containing thin filaments (actin). The 'H' zone is the central region of the 'A' band, and the 'Z' line is present in the centre of the 'I' band. During contraction, the 'Z' line attached to actin is pulled inwards, causing shortening of the sarcomere. The 'I' bands get reduced while the 'A' bands retain their length during contraction.

Solution Steps

  1. Step 1: Draw a rectangular strip representing the sarcomere bounded by two 'Z' lines at the ends.

  2. Step 2: Draw the 'A' band (dark band) in the centre and label it.

  3. Step 3: Draw the 'I' bands (light bands) on either side of the 'A' band and label them.

  4. Step 4: Show the 'H' zone in the centre of the 'A' band and label it.

  5. Step 5: Draw thin filaments (actin) extending from 'Z' line into the 'A' band and label them.

  6. Step 6: Draw thick filaments (myosin) in the 'A' band and label them.

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