The actual contractile units of muscles extend from z disc to z disc. they are

There are four units of muscles extend from z disc to z disc. They are thick filaments,myofibrils, sarcoplasmic reticulum and sarcomeres. Cross sections of the sarcomere in areas where thick and thin filaments overlap show that thick filament is surrounded by 6 thin filaments - each thin is surrounded by 3 thin

Because the earth is not round ,but it may seem round when viewed from ,our planet but true some points earth is not round was an oblate spheroid -a square that it squashed as globe however is not even a perfect oblate spheroid.in fact isaac newton's first proposed that earth was not perfectly round but it was an oblate spheroid instead.that mean a square that is squashed as its poles and swollen at the