Page 380 - Fundamentals of anatomy physiology

The buccinator (BUK-si-na. -tor) muscle on the face com-
presses the cheeks—when, for example, you purse your lips and
blow forcefully. Buccinator translates as “trumpet player.”
Another facial muscle, the risorius (ri-SOR-e. -us) muscle,
was supposedly named after the mood expressed. However, the
Latin word risor means “one who laughs.” A more appropriate
description for the effect would be “a grimace.”
Axial and Appendicular Muscles
The separation of the skeletal system into axial and appendicu-
lar divisions serves as a useful guideline for subdividing the
muscular system as well:
1. The axial muscles arise on the axial skeleton. This category
includes approximately 60 percent of the skeletal muscles
in the body. They position the head and spinal column
and also move the rib cage, assisting in the movements that
make breathing possible. They do not play a role in move-
ment or support of either the pectoral or pelvic girdle or the
limbs.
2. The appendicular muscles stabilize or move components
of the appendicular skeleton. These muscles include the
remaining 40 percent of all skeletal muscles.
Figure 11–4 provides an overview of the major axial and
appendicular muscles of the human body. These are superficial
muscles, which tend to be rather large. The superficial muscles
cover deeper, smaller muscles that we cannot see unless the
overlying muscles are removed or reflected—that is, cut and
pulled out of the way. Later figures that show deep muscles in
specific regions will indicate whether superficial muscles have
been removed or reflected.
Next we will study examples of both muscular divisions.
Pay attention to patterns of origin, insertion, and action. In the
figures in this chapter, you will find that some bony and carti-
laginous landmarks are labeled to provide orientation. Should
you need further review of skeletal anatomy, figure captions in
this chapter indicate the relevant figures in Martini’s Atlas of the
Human Body.
The tables that follow also contain information about the
innervation of the individual muscles. Innervation is the dis-
tribution of nerves to a region or organ. The tables indicate the
nerves that control each muscle. Many of the muscles of the
head and neck are innervated by cranial nerves, which originate
at the brain and pass through the foramina of the skull. In ad-
dition, spinal nerves are connected to the spinal cord and pass
through the intervertebral foramina. For example, spinal nerve
L1 passes between vertebrae L1 and L2. Spinal nerves may form
a complex network called a plexus after exiting the spinal cord.
One branch of this network may contain axons from several
spinal nerves. Many tables identify the spinal nerves involved
as well as the names of their specific branches.
Chapter 11 The Muscular System 367
Checkpoint
9. Identify the kinds of descriptive information used to
name skeletal muscles.
1 0. What does the name flexor carpi radialis longus tell you
about this muscle?
See the blue Answers tab at the back of the book.
11-5 Axial muscles are muscles of
the head and neck, vertebral column,
trunk, and pelvic floor
11
Learning Outcome Identify the principal axial muscles of the body, plus
their origins, insertions, actions, and innervation.
The axial muscles fall into logical groups on the basis of loca-
tion, function, or both. The groups do not always have distinct
anatomical boundaries. For example, a function such as exten-
sion of the vertebral column involves muscles along its entire
length and movement at each of the intervertebral joints. We
will discuss the axial muscles in four groups:
1. The Muscles of the Head and Neck. This group includes
muscles that move the face, tongue, and larynx. They are
responsible for verbal and nonverbal communication—
laughing, talking, frowning, smiling, whistling, and so on.
You also use these muscles while eating—especially in
sucking and chewing—and even while looking for food,
as some of them control your eye movements. The group
does not include muscles of the neck that are involved with
movements of the vertebral column.
2. The Muscles of the Vertebral Column. This group includes
numerous flexors, extensors, and rotators of the vertebral
column.
3. The Oblique and Rectus Muscles. This group forms the mus-
cular walls of the trunk between the first thoracic vertebra
and the pelvis. In the thoracic area the ribs separate these
muscles, but over the abdominal surface the muscles form
broad muscular sheets. The neck also has oblique and rec-
tus muscles. They do not form a complete muscular wall,
but they share a common developmental origin with the
oblique and rectus muscles of the trunk.
4. The Muscles of the Pelvic Floor. These muscles extend be-
tween the sacrum and pelvic girdle. The group forms the
perineum, a muscular sheet that closes the pelvic outlet.
Muscles of the Head and Neck
We can divide the muscles of the head and neck into several
functional groups. The muscles of facial expression, the muscles of
mastication (chewing), the muscles of the tongue, and the muscles
of the pharynx originate on the skull or hyoid bone.