Study GuideBiology–Support and Movement in Animals1. Human MuscleMuscles allow the body tomove, maintain posture, and produce force. Each muscle is made up ofthousands of muscle fibers, and each fiber is actually asingle muscle cell.These cells arespecially designed to shorten and relax, which is what creates movement.Let’s explore how muscles are built, how they contract, where their energy comes from, and thedifferent types of muscles in the human body.1.1 Structure of a Muscle FiberInside every muscle cell are tiny structures calledmyofibrils. These are long, threadlike units that fillmost of the cell.•Each myofibril is divided into repeating sections calledsarcomeres.•Sarcomeres are thebasic functional units ofmuscle contraction.Actin and Myosin FilamentsEach sarcomere contains two types of protein filaments:•Myosin–thick filaments with small “heads”•Actin–thin filamentsThese filaments lieparallel to each other, and the myosin heads point toward the actin filaments. Inskeletal muscle, the overlapping pattern of actin and myosin creates astriped (banded)appearance, calledstriations. This is why skeletal muscle is also known asstriated muscle.Preview Mode
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