Table of contents

1. Introduction to Biology2h 42m
2. Chemistry3h 37m
3. Water1h 26m
4. Biomolecules2h 23m
5. Cell Components2h 26m
6. The Membrane2h 31m
7. Energy and Metabolism2h 0m
8. Respiration2h 40m
9. Photosynthesis2h 49m
10. Cell Signaling59m
11. Cell Division2h 47m
12. Meiosis2h 0m
13. Mendelian Genetics4h 44m
14. DNA Synthesis2h 27m
15. Gene Expression3h 6m
16. Regulation of Expression3h 31m
17. Viruses37m
- Viruses
  37m
18. Biotechnology2h 58m
19. Genomics17m
- Genomes
  17m
20. Development1h 5m
21. Evolution3h 1m
22. Evolution of Populations3h 53m
23. Speciation1h 37m
24. History of Life on Earth2h 6m
25. Phylogeny2h 31m
26. Prokaryotes4h 59m
27. Protists1h 12m
28. Plants1h 22m
29. Fungi36m
- Fungi
  19m
- Fungi Reproduction
  17m
30. Overview of Animals34m
- Overview of Animals
  34m
31. Invertebrates1h 2m
32. Vertebrates50m
33. Plant Anatomy1h 3m
34. Vascular Plant Transport1h 2m
- Water Potential
  1h 2m
35. Soil37m
- Soil and Nutrients
  20m
- Nitrogen Fixation
  16m
36. Plant Reproduction47m
- Flowers
  33m
- Seeds
  14m
37. Plant Sensation and Response1h 9m
38. Animal Form and Function1h 19m
39. Digestive System1h 10m
- Digestion
  1h 3m
- Blood Sugar Homeostasis
  7m
40. Circulatory System1h 49m
41. Immune System1h 12m
42. Osmoregulation and Excretion50m
- Osmoregulation and Excretion
  50m
43. Endocrine System1h 4m
- Endocrine System
  1h 4m
44. Animal Reproduction1h 2m
- Animal Reproduction
  1h 2m
45. Nervous System1h 55m
- Neurons and Action Potentials
  1h 8m
- Central and Peripheral Nervous System
  46m
46. Sensory Systems46m
- Sensory System
  46m
47. Muscle Systems23m
- Musculoskeletal System
  23m
48. Ecology3h 11m
49. Animal Behavior28m
- Animal Behavior
  28m
50. Population Ecology3h 41m
51. Community Ecology2h 46m
52. Ecosystems2h 36m
53. Conservation Biology24m
- Conservation Biology
  24m

47. Muscle Systems

Musculoskeletal System

General Biology

47. Muscle Systems

Musculoskeletal System

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3:21 minutes

Problem 6

Textbook Question

Rigor mortis is the stiffening of a body after death that occurs when myosin binds to actin but cannot unbind. What prevents myosin from unbinding?

Verified step by step guidance

Understand the role of ATP: ATP (adenosine triphosphate) is necessary for muscle contraction and relaxation. During life, ATP binds to myosin, causing it to release from actin filaments.

Recognize the effect of death on ATP production: After death, cellular respiration ceases, leading to a depletion of ATP within the muscle cells.

Identify the consequence of ATP depletion: Without ATP, myosin heads that are attached to actin during the last contraction remain bound. This is because ATP is required to detach myosin from actin.

Link to rigor mortis: The continued attachment of myosin to actin without the presence of ATP results in the stiffening of muscles, a condition known as rigor mortis.

Understand the timeline: Rigor mortis typically begins within a few hours after death and can last up to 72 hours, depending on various factors such as ambient temperature and the condition of the body prior to death.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Muscle Contraction Mechanism

Muscle contraction occurs through the sliding filament theory, where myosin heads bind to actin filaments, forming cross-bridges. This process requires ATP, which provides the energy for myosin to pull actin and subsequently release. In rigor mortis, the lack of ATP prevents myosin from detaching from actin, leading to sustained muscle contraction and stiffness.

Role of ATP in Muscle Function

Adenosine triphosphate (ATP) is crucial for muscle function, as it supplies the energy needed for muscle contraction and relaxation. During contraction, ATP is hydrolyzed to ADP and inorganic phosphate, allowing myosin to release from actin. After death, ATP production ceases, resulting in myosin remaining bound to actin, which is a key factor in the development of rigor mortis.

Biochemical Changes Post-Mortem

After death, the body undergoes various biochemical changes, including the depletion of ATP and the accumulation of calcium ions. The lack of ATP prevents muscle fibers from relaxing, while increased calcium levels promote continued binding of myosin to actin. These changes contribute to the onset of rigor mortis, which typically begins a few hours after death and can last for several days.

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What is the role of calcium in muscle contraction?

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