Lesson Overview 32.2 The Muscular System

Muscle Tissue There are three different types of muscle tissue, each specialized for a specific function in the body: skeletal, smooth, and cardiac.

Skeletal Muscles Skeletal muscles are usually attached to bones. Most skeletal muscle movements are voluntary (you control them) Skeletal muscle cells are large, have many nuclei, vary in length, and are long and slender When viewed under a microscope, skeletal muscle appears to have alternating light and dark bands called “striations.” For this reason, it is said to be striated.

Smooth Muscles Smooth muscle cells don’t have striations and therefore look “smooth” under the microscope.  Smooth muscle cells are spindle-shaped and have one nucleus. Smooth muscles form part of the walls of hollow structures such as the stomach, blood vessels, and intestines.

Smooth Muscles Smooth muscle movements are involuntary and perform functions such as moving food through the digestive tract, controlling the flow of blood through the circulatory system, and even decreasing pupil size in bright light.

Cardiac Muscle Cardiac muscle is found in the heart. It is striated like skeletal muscle but has smaller cells and usually have just one or two nuclei. Involuntary muscle control and have their own “pace maker” cells that tell it when to contract

Muscle Fiber Structure Skeletal muscle cells, or fibers, are filled with tightly-packed filament bundles called myofibrils. Each myofibril contains thick filaments of a protein called myosin and thin filaments of a protein called actin.

Muscle Fiber Structure The actin filaments are bound together in areas called Z lines. Two Z lines and the filaments between them make up a unit called a sarcomere (the unit of muscle contraction)

The Sliding-Filament Theory During a muscle contraction, myosin filaments form cross-bridges with actin filaments. The cross-bridges then change shape, pulling the actin filaments toward the center of the sarcomere. This action decreases the distance between the Z lines, and the muscle fiber shortens.

The Sliding-Filament Theory Then the cross-bridge detaches from actin, and repeats the cycle by binding to another site on the actin filament. As thick and thin filaments slide past each other, the length of the fiber shortens, hence the name “sliding-filament theory” of muscle contraction.

Muscles and Movement How do muscle contractions produce movement? Skeletal muscles generate force and produce movement by pulling on body parts as they contract. [muscles NEVER push, they only pull]

How Muscles and Bones Interact Skeletal muscles are joined to bones by tough connective tissues called tendons. Tendons pull on the bones to produce movement

A = Deltoid B= Biceps C= Quadriceps D= Pectoralis E= Abdominals F= Triceps G = Hamstring H= Gastrocnemius I= Trapezius J= Latissimus dorsi K= Gluteus maximus