How does a muscle shorten during its con | Class 11 Biology Chapter Locomotion and Movement, Locomotion and Movement NCERT Solutions

Current NCERT chapter

Academic session 2026-27, Chapter 17 in the current curriculum.

Welcome to the NCERT Solutions for Class 11 Biology - Chapter Locomotion and Movement. This page offers a step-by-step solution to the specific question from Exercise 0, Question 4:

How does a muscle shorten during its contraction and return to its original form during relaxation?

. With detailed answers and explanations for each chapter, students can strengthen their understanding and prepare confidently for exams. Ideal for CBSE and other board students, this resource will simplify your study experience.

Question 4:

How does a muscle shorten during its contraction and return to its original form during relaxation?

Answer:

When a sarcomere contracts, myosin heads attach to actin to forms cross- bridges. Then, the thin filaments slide over the thick filaments as the heads pull the actin. Thus result in sarcomere shortening, creating the tension of muscle contraction. The steps followed during relaxation are:

  1. At the beginning when the neural signal reaches the neuromuscular junction then neurotransmitter acetylcholine which creates an action potential in the sarcolemma.
  2. Calcium ions are released and spread through muscle fibres due to this action potential.
  3. Calcium ions bind to the subunit of troponin on the actin filament due to the increase in the concentration of the calcium ions which further remove the active sites in the myosin.
  4. Cross- bridge formed when myosin bind with actin.
  5. This causes the attached actin filaments to move towards the center of A- band. A concentration of the sarcomere occurs in the muscles as the Z- line moves inwards, the I- band gets reduced while the A- band retains its original length.  
  6. ADP and Pi are released when the cross bridge breaks and myosin goes back to its relaxed state and new ATP binds which breaks the cross- bridge.
  7. The muscle relaxation occurs after contraction when the calcium ions are pumped back to the active sites on actin myofilaments. The Z- line returns to original position, i.e. relaxation.


Study Tips for Answering NCERT Questions:

NCERT questions are designed to test your understanding of the concepts and theories discussed in the chapter. Here are some tips to help you answer NCERT questions effectively:

  • Read the question carefully and focus on the core concept being asked.
  • Reference examples and data from the chapter when answering questions about Locomotion and Movement.
  • Review previous year question papers to get an idea of how such questions may be framed in exams.
  • Practice answering questions within the time limit to improve your speed and accuracy.
  • Discuss your answers with your teachers or peers to get feedback and improve your understanding.

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Welcome to the NCERT Solutions for Class 11 Biology - Chapter . This page offers a step-by-step solution to the specific question from Excercise 0 , Question 4: How does a muscle shorten during its contraction and return to its original form during relaxation?....

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