Terminal cisternae

Definition

Terminal cisternae are enlarged regions of the sarcoplasmic reticulum in muscle fibers that store calcium ions. These structures play a crucial role in muscle contraction by releasing calcium into the cytosol when stimulated, triggering the interaction between actin and myosin filaments, which leads to muscle shortening and force generation.

5 Must Know Facts For Your Next Test

1. Terminal cisternae are located adjacent to T-tubules, forming a triad structure essential for efficient calcium release during muscle contraction.
2. When an action potential travels down a T-tubule, it triggers voltage-sensitive receptors that open calcium channels in the terminal cisternae, releasing calcium ions into the cytosol.
3. The release of calcium from the terminal cisternae is critical for initiating the sliding filament mechanism, where actin and myosin filaments interact to cause muscle contraction.
4. After contraction, calcium ions are pumped back into the terminal cisternae by active transport, allowing for muscle relaxation.
5. Dysfunction or abnormalities in the terminal cisternae can lead to muscle diseases or impaired contraction and relaxation processes.

Review Questions

• How do terminal cisternae contribute to the process of muscle contraction?
  • Terminal cisternae play a vital role in muscle contraction by storing calcium ions that are released when an action potential stimulates the muscle fiber. The release of calcium ions into the cytosol triggers the interaction between actin and myosin filaments, which is essential for muscle shortening. This interaction leads to the sliding filament mechanism, ultimately resulting in muscle contraction and force generation.
• Discuss how terminal cisternae interact with T-tubules during muscle contraction and why this interaction is important.
  • Terminal cisternae interact closely with T-tubules to form triads, which are crucial for rapid communication within the muscle fiber. When an action potential travels down a T-tubule, it activates voltage-sensitive receptors that open calcium channels in the terminal cisternae. This close proximity ensures that calcium ions can be released quickly and efficiently into the cytosol, facilitating immediate contraction of the muscle fiber.
• Evaluate the implications of terminal cisternae dysfunction on overall muscle physiology and potential disease states.
  • Dysfunction in terminal cisternae can significantly impact overall muscle physiology by disrupting calcium homeostasis during contraction and relaxation. This may lead to decreased contractile strength or incomplete relaxation of muscles, potentially contributing to conditions such as myopathies or muscular dystrophies. Understanding these implications highlights the importance of terminal cisternae in maintaining normal muscle function and points towards potential therapeutic targets for treating related diseases.

Related terms

sarcoplasmic reticulum:

A specialized endoplasmic reticulum in muscle cells that stores calcium ions and helps regulate calcium levels during muscle contraction and relaxation.

calcium ions: Essential signaling molecules in muscle contraction that bind to troponin, leading to the exposure of binding sites on actin for myosin interaction.

T-tubules:

Transverse tubules that extend from the muscle fiber's surface into the interior, allowing action potentials to rapidly spread throughout the muscle cell and trigger calcium release from the terminal cisternae.