It is fibers. The bundles of fibers are surrounded by a tissue inside the cell.
Hope I helped
The immune system doent take it as a threat but other systems would take it as a threath
Answer: The things that are listed .
Explanation: The circulatory system is made up of blood vessels that carry blood away from and towards the heart : Arteries carry blood away from the heart and veins carry blood back to the heart .
The 650 skeletal muscles in the human body contract when they receive signals from motor neurons, which are triggered from a part of the cell called the sarcoplasmic reticulum. Motor neurons tell your muscles to contract and the better you become at having those signals tell your muscles to contract, the stronger you can get.
