Page 137 - Anatomy and Physiology of Farm Animals, 8th Edition

122 / Anatomy and Physiology of Farm Animals

Anatomical Nomenclature As a consequence, skeletal muscle is also
of Muscles
called striated muscle.
VetBooks.ir A note on nomenclature is appropriate muscle is composed of muscle cells that
Smooth (involuntary or unstriated)
before undertaking this survey of the have no striations visible with a micro­
muscles of domestic animals. Traditionally, scope. Smooth muscle is found in systems
muscles are referred to by their Latin of the body with autonomic function.
names, and as these are foreign words, they Thus, smooth muscle is a major compo­
are italicized. The Latin names are usually nent of the wall of organs of the digestive
highly descriptive of the function and/or and urogenital systems and most blood
appearance of the muscle, and the student vessels. Contraction of smooth muscle is
is encouraged to use a medical dictionary an intrinsic property of the fibers them­
to explore their meaning. In Latin, as in selves, which means that contraction does
many Romance languages, the noun is not generally require stimulation by a
written first, followed by adjectives that nerve; however, the contractility of smooth
describe it. Hence, the musculus triceps muscle is regulated and coordinated by
brachii (literally, the three‐headed muscle the autonomic nervous system.
of the arm) begins with the noun, musculus, Cardiac muscle is characterized by
usually abbreviated as m., plural mm. In fibers with visible striations, so it is con­
English, nouns are generally preceded by sidered a type of striated muscle. However,
their descriptors, so the abbreviation for cardiac muscle, like smooth muscle, contracts
muscle is placed at the end of the string of intrinsically and is under autonomic – not
adjectives, for example, deep digital flexor voluntary – control. Cardiac muscle is
m. (Notice that the English name is not restricted to the heart, where it constitutes
italicized.) In Latin, the same muscle is the bulk of the organ’s walls.
m. flexor digitalis profundus. This text
uses English or Latin names, opting for
whichever is in wider use, but either should Skeletal Muscle Organization
be considered correct.
Vertebrate muscle has only one function:
contraction. “Relaxation” is a passive pro­
Types of Muscle Tissue cess, a lack of contraction. Thus, the varied
functions of the muscular system are all
The three types of muscle are skeletal, based on contraction (usually accompa­
smooth, and cardiac. The bulk of the nied by shortening) of muscle fibers. In the
muscle in the body is skeletal muscle, musculoskeletal system, this may result in
and it is responsible for producing the changes in angles at joints or stabilization
voluntary movements of the limbs, trunk, of joints at a particular angle in the face of
and head. It is also the muscle tissue with load (e.g., holding the limb straight when
which we are most familiar as the meat of bearing weight).
our food animals. Individual muscles are Muscle fibers are arranged in bundles
composed of aggregates of large, multi­ surrounded by fibrous connective tissue.
nucleated muscle cells (also called muscle The very thin layer of connective tissue
fibers) (see Chapter 9). These are usually investing individual muscle cells is called
attached to the bones of the skeleton (hence endomysium. The connective tissue sur­
the term “skeletal” muscle) and are under rounding bundles of muscle fibers forms a
voluntary control. Under the microscope, sheath called perimysium, and the robust
skeletal muscle fibers exhibit a charac­ connective tissue around an entire muscle
teristic striped pattern arising from the is known as epimysium. The epimysium
orderly arrangement of the contractile is also called the deep fascia of the
proteins within the cells (see Fig. 1‐10). muscle.