Physical Therapy Aide DEMO


Demo Lesson

Chapter 1

Anatomy of Skeletal Muscles

Chapter 2

Contraction of Skeletal Muscles

Chapter 3

Common Injuries to the Muscular System

Chapter 4



Anatomy of Skeletal Muscles


Let's first talk about the way skeletal muscles are organized. You already know that muscles attach to bones via structures called tendons or aponeurosis. Take a look at Figure 6-2 on page 97 in your textbook Human Diseases to see what I mean.


First, look at the gastrocnemius muscle in the posterior (back) view. You can see that it's attached to the heel bone by the Achilles tendon. The artist colored the muscle tissue brown and the tissue of the tendon white. You can see similar bands of other tendons in both the anterior and posterior views shown in this figure.


Now look at the back of the skull. Notice that the occipitalis muscle is attached to a white band of connective tissue that covers the skull. That is an aponeurosis. You can see another aponeurosis connected to the rectus abdominis muscle in the anterior view. In fact, the artist labeled it for you.


This graphic shows you how skeletal muscle, attached by tendons to bones, is organized.


Organization of skeletal muscle

Organization of skeletal muscle


The main part of the muscle, the muscle belly, contains thousands of individual muscle fibers, the muscle's cells. Each individual muscle fiber is wrapped in a layer of connective tissue called the endomysium. Groups of muscle fibers are bundled together in fascicles. Another layer of connective tissue, called the perimysium, surrounds each individual fascicle. The entire muscle belly is surrounded by a sheath of connective tissue called the epimysium.


The fascia (more connective tissue) lies on top of the epimysium and thickens on both ends to form tendons, which attach to the bones. Tendons are encased in a sheath that secretes synovial fluid to reduce friction, allowing the tendon to glide smoothly as muscles shorten and lengthen.


You should also know that muscle fibers consist of many smaller fibers called myofibrils. These myofibrils run parallel to each other and are made of alternating myofilaments of the proteins actin and myosin. Your body actually makes more of these myofibrils when you consistently put stress on your muscles through activities like weight lifting. That's what makes your muscles get bigger when you exercise on a regular basis.


Structure of a muscle fiber

Structure of a muscle fiber


If you become very inactive, however, your body will actually lose myofibrils. That's why muscles that have been in a cast for any length of time look smaller than the same muscles in the other limb. It will take time and exercise for the body to replace the myofibrils that have been lost. PTs use this knowledge about myofibrils to plan exercise programs for people whose muscles have weakened because of disuse.


Activity 2


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