Skeletal Muscles Are Grouped
Based on Location and Action
LEARNING OBJECTIVES
1.
explain
how skeletal muscles make bones
move.
2.
identify
major muscle groups of the upper body.
3.
Describe
major muscle groups of the lower
body.
he body consists of around 700 skeletal mus-
cles that are grouped based on their locations
and actions. Muscles of the upper body con-
trol functions of the head and neck, shoulder,
and arms, thorax, and abdomen. Muscles of the lower body
move the legs and pelvis.
Skeletal Muscles Work in Groups
Skeletal muscles attach to bones via bands of connective
tissue called
tendons.
Two bones are usually involved in the
movement of a joint: one is stationary, and the other one
moves. The location where a muscle attaches to a station-
ary bone via a tendon is called the
origin
. The other end
of the muscle is attached by means of a tendon to the mov-
able bone at a point called the
insertion
. The fleshy por-
tion of the muscle, between the tendons of the origin and
insertion, is called the
belly
(
Figure 6.12
).
A good analogy is a spring on a door. The part of the
spring attached to the door represents the insertion, the
part attached to the frame is the origin, and the coils of
the spring are the belly.
R elationships o f m uscles to b o n e s • Figure 6.12
The ends of muscles have different names,
depending on where they are attached.
They work in groups or pairs that have
opposing actions. For movements of the
elbow, the biceps and triceps are a muscle
pair with opposing actions.
Shoulder joint
Scapula
ORIGIN of triceps brachii
from scapula and humerus
BELLY
of triceps
brachii
muscle
Tendon
INSERTION of triceps
brachii on ulna
Elbow joint
Ulna
ORIGIN of biceps brachii
from scapula
Tendons
BELLY
of biceps
brachii
muscle
STATIONARY BONE -
For movement of the arm,
this is the humerus.
Tendon
INSERTION of biceps
brachii on radius
Radius
168 CHAPTER 6
The Muscular System
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