Fundamentals of Anatomy and Physiology

104

5. Movement: Muscles through tendons pull on
   bones, and bones move our bodies through our

environment.^

6. Protection: Bones protect vital organs of the body
   like the heart, lungs, brain, and spinal cord. Blood
   cells, especially the white blood cells, protect us

from foreign microorganisms and tissue injury.^

7. Insulation: Adipose tissue (fat) insulates us from exces-

sive heat loss and excessive increases in temperature.^

8. Storage: Bone stores the mineral salts calcium and
   phosphorous. Adipose tissue stores the high-energy
   molecules of fat to be used and converted to ad-

enosine triphosphate when necessary.^

9. Attachment and separation: Connective tissue at-
   taches skin to underlying muscle. It also forms lay-
   ers around and between organs.

Muscle Tone.

The basic characteristic of muscle tissue is its ability to
shorten and thicken or contract. This is due to the in-
teraction of two proteins in the muscle cell: actin and
myosin. Muscle cell contractility is discussed in greater
detail in Chapter 9. Because a muscle cell’s length is much
greater than its width, muscle cells are frequently referred
to as muscle fibers. The three types of muscle tis-sue are
smooth, striated or skeletal, and cardiac.

Chapter 5

Smooth muscle cells are spindle-shaped with a sin-

gle nucleus (Figure 5-14). They are not striated (STRYE-

ate-ed), that is, you do not see alternating dark and light

bands when viewed under the microscope. This muscle

tissue is involuntary, meaning we do not control its con-

traction. It is controlled by the autonomic nervous system.

We find smooth muscle in the walls of hollow organs like

those of the digestive tract, arteries, and veins. The mus-cle

cells are arranged in layers: an outer longitudinal layer and

an inner circular layer. Simultaneous contraction of the two

layers pushes materials inside the hollow organs in one

direction. Hence, food is pushed by contraction of the

smooth muscles along the digestive tract, called

peristalsis- (pair-ih-STALL-sis), and blood is pushed

along in arteries and veins. Urine is also pushed down the

ure - ters from the kidneys by contraction of smooth muscle.

Striated or skeletal muscle is the muscle we

normally think about when we mention muscle (Figure 5-

15). It is the tissue that causes movement of our body by

pulling on bones, hence the name skeletal muscle. The long

thin cells of skeletal muscle are multinucleated and striated.

We can see alternating light bands of the thin protein

filaments of actin and dark bands of the thick protein

filaments of myosin. When we eat “meat” of animals and

fish, it is usually muscle that we are consuming. Muscle

makes up about 40% of our total weight and mass. Stri-ated

muscle is voluntary and is under the control of the central

nervous system.

Function Characteristics and Location Morphology

Smooth

(nonstriated involuntary)

These provide for involuntary

movement. Examples include the

movement of materials along the

digestive tract, controlling the

diameter of blood vessels and

the pupil of the eyes.

Smooth muscle is nonstriated

because it lacks the obvious

striations (bands) of skeletal

muscles; its movement is

involuntary. It makes up the

walls of the digestive,

genitourinary, respiratory

tracts, blood vessels, and

lymphatic vessels.

(^)
Spindle-shaped Cells separated^
Nucleus cell (^) from each other (^)

(A)

Source

Associates/Science Biophoto ©

(B) Photo

(^) ,
® Learning
(B)
Cengage
© (A)
Figure 5- 14 Views of smooth muscle
cells.