Lesson 5
The Human Muscular System

5.1 The Skeletal Muscle

MUSCLE TISSUES

The cellular elements of muscle tissues are specialized to produce motion by contraction. They also produce body heat.

a. Smooth muscle tissue is utilized to make up the muscular portion of the various visceral organs (stomach, blood vessels, etc.).

b. Cardiac muscle tissue makes up the muscular wall of the heart--the myocardium.

c. Striated muscle tissue is used in the makeup of several types of muscles. The main type of muscle is the skeletal muscle. Other types of muscles made with striated muscle tissue are the facial or integumentary muscles and muscles of the jaw apparatus.

THE SKELETAL MUSCLE

Each skeletal muscle is an individual organ of the human body. Each is made up of several types of tissues--mainly, striated muscle fibers and FCT (fibrous connective tissue). Each is attached to and moves bones. Bones are parts of the skeleton serving as levers.

a. General Construction of a Skeletal Muscle. The large portion of a muscle is known as its belly or fleshy belly. This muscle is attached to bones by tendons or aponeuroses. Tendons and aponeuroses are similar to each other. However, tendons are cord-like and aponeuroses are broad and flat. The fleshy portion may be directly connected to the bone. If so, it is called a "fleshy attachment."

b. Muscular NAVL (Nerves, Arteries, Veins, Lymphatics).

(1) From the main NAVL (nerve, artery, vein, lymphatic), there are branches going to each muscle. These muscular branches are bound together by an FCT sheath to form a neurovascular bundle.

(2) The motor point is that specific location on the surface of the muscle where the neurovascular bundle enters.

(3) A motor unit is the single motor neuron and the number of striated muscle fibers activated by it (innervation). The importance of the motor unit is that its fibers work in unison. Either all fibers within a unit contract or none contract. When a certain amount of force is needed, one unit after another is recruited until just enough units are available to produce the desired action.

NAMING SKELETAL MUSCLES

The name of a muscle may appear with the abbreviation M., meaning Musculus or muscle. We abbreviate muscles (plural) with the symbol Mm. Skeletal muscles are named according to their physical attributes (shape, size, length, etc.), their location, or their function.

ARRANGEMENT OF HUMAN SKELETAL MUSCLES

See figures 5-1 and 5-2 for some of the skeletal muscles.

Figure 5-1. Skeletal and facial muscles, anterior view.

Figure 5-2. Skeletal and facial muscles, posterior view.

a. Trunk Musculature. The trunk musculature is arranged in two ways--longitudinal muscles and oblique muscles. Together, they:

(1) Maintain trunk posture.

(2) Move the parts of the trunk.

(3) Adjust the internal pressures of the trunk to perform certain functions such as breathing.

b. Limb Musculature. The limb musculature is arranged around the joints to produce the appropriate motions of the limbs. Elementary mechanics are described in the next section to help you to understand typical arrangements of limb musculature.