The Muscular System

MUSCULAR SYSTEM

Types of Muscle Tissue: Skeletal, Smooth, and Cardiac

Skeletal, aka “striated” voluntary – attached to bones and

under conscious, willful control. Has the ability to contract (shorten)

and thereby bring about movement

Cardiac Muscle

Found only in the heart Striated Involuntary Cells connected by intercalated

disks

Smooth Muscle

Not striated Involuntary Walls of hollow organs such as:

Stomach, urinary bladder, respiratory passages

Arranged in sheets/layers

Muscle Functions

Producing Movement Maintaining Posture Stabilizing Joints Generating Heat

Maintaining body temperature

Muscle and Muscle Fiber Structure:

A muscle is composed of many muscle fibers (muscle fiber = muscle cell).

The individual muscles are separated from each other and held in place by a covering called the FASCIA.

This fascia also forms TENDONS connecting muscles to bones.

The muscle fiber membrane is called the SARCOLEMMA and the cytoplasm is called the SARCOPLASM.

Within the sarcoplasm are many parallel fibers known as MYOFIBRILS.

Each myofibril is made of many protein filaments called MYOFILAMENTS. There are two types: MYOSIN – thick filaments ACTIN – thin filaments

Actin and Myosin filaments are arranged in an overlapping pattern of light (“I” bands) and dark (“A” bands).

In the middle of each “I” band is a line called a “Z” line.

The section of a myofibril from one Z-line to the next Z-line is called a SARCOMERE.

The arrangement of these sarcomeres next to each other produces the STRIATIONS of the skeletal muscle fibers.

How do muscles contract?

Stimulated by nerve impulses to contract Sliding Filament Theory

Muscle cell becomes excited – action potential Flood of calcium Myosin heads bind to thin filaments Form “cross bridges” Heads bend and pull thin filaments together Muscle shortens – contracting! Video animation of muscle contraction