sarcomere and sarcolemma are two different things.
a sarcomere is between two d zisks of a myofiber (muscle fiber).
a sarcolemma is a plasma membrane. there are many sections of
sarcomere under the layer of sarcolemma.
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The outer boundaries of the sarcomere are defined by the Z-discs or Z-lines, which mark the ends of the sarcomere unit. These Z-discs separate one sarcomere from the next and provide attachment points for actin filaments.