Final answer:
Adjacent muscle fibers are organized into units called fascicles, surrounded by collagen and blood vessels, with perimysium and endomysium as connective tissues.
Step-by-step explanation:
Groups of adjacent fibers bundled together into units are called fascicles. These bundles are surrounded by the proteins collagen and elastin as well as blood vessels that deliver nutrients to the muscle cells. The fascicles are encased in a middle layer of connective tissue known as the perimysium, while each muscle fiber within a fascicle is encased in the endomysium. This arrangement supports and protects the muscle fibers, allowing them to withstand the forces of contraction, while also providing pathways for nerves and blood vessels.
Groups of adjacent fibers bundled together into units are called fascicles. These bundles are surrounded by the proteins endomysium and perimysium as well as blood vessels that deliver nutrients to the muscle cells.