The Muscular System 36-2 BIO 1004 Flora

Types of Muscle Tissue 3 Different Types of muscle tissue: o Skeletal o Smooth o Cardiac o Each type of muscle is specialized for a specific function

Skeletal Muscle Usually attached to bones Responsible for voluntary movements Have alternating light bands and dark bands o This is the reason for the name “striated” muscle Large and vary in length o 1-30 cm Muscle cells are called muscle fibers Consist of fibers, connective tissues, blood vessels, and nerves

Smooth Muscle Not under voluntary control Spindle shaped, one nucleus, and not striated Found in stomach, intestines, and blood vessels Forms digestive tract and controls the blood flow through circulatory system Most can function without the CNS Connected through “gap junctions” that allow muscle cells to communicate with each other.

Cardiac Muscle Found in the heart Much like a combination of skeletal and smooth muscle o Striated, but smaller cells than skeletal o One or two nuclei Under control of the CNS

Muscle Contraction Muscle fibers in skeletal muscle are composed of small structures called myofibrils Striations in skeletal muscle and cardiac muscle is composed of protein filaments called actin and myosin Filaments are arranged in clusters called “sarcomeres” o Sarcomeres are separated from each other by “z-lines”

Myofibril

Muscle Contraction Cont. Actin and myosin are responsible for muscle contraction Muscles contract when the thin filaments in the muscle fiber slide over the thick filaments Myosin must form a “cross-bridge” with actin filament As the cross-bridge changes shape, it pulls on the actin filament which decreases the distance between z-lines When thousands of myosin bridges change shape, the muscle fiber shortens and the muscle contracts

Muscle Contraction Cont. Muscle contraction energy is supplied by ATP Controlled by the CNS – motor neurons connect to muscle cells The point at which the motor neuron comes in contact with the muscle cell is known as the neuromuscular junction The neurotransmitter involved in muscle contraction is acetylcholine Muscle cells remain contracted until the release of acetylcholine stops Max contraction vs. weak contraction o Few cells vs. all muscle cells

Interaction Between Muscles and Bones Skeletal muscles are joined to bone by connective tissue called tendons