Page 377 - Fundamentals of anatomy physiology

Spotlight Figure 11–3 Watch over 50 > ™ on Group Muscle Actions & Joints.
Muscle Action

The action produced by a muscle at any one joint is largely Abduction and Adduction
dependent upon the structure of the joint and the location of
the insertion of the muscle relative to the axis of movement at At joints that permit adduction and abduction, muscles whose lines
the joint. The direction, or geometric paths, of the action of action cross the medial side of a joint are adductors of that joint,
produced by a muscle—called lines of action—is often and muscles whose lines of action cross the lateral side of a joint are
represented by an arrow (or more than one arrow in abductors of that joint.
fan-shaped muscles).
LATERAL MEDIAL
Flexion and Extension
Abductor
At joints that permit flexion and extension, muscles whose lines of
action cross the anterior side of a joint are flexors of that joint, and The gluteus medius
muscles whose lines of action cross the posterior side of a joint are and minimus
extensors of that joint. muscles cross the
lateral side of the
ANTERIOR POSTERIOR hip joint. So they Hip joint
are abductors of
Flexor Extensors the hip joint. Adductor
The triceps brachii
The biceps brachii muscle crosses on The adductor
muscle crosses on the posterior side magnus muscle
the anterior side of of the elbow joint. crosses on the
the elbow joint. So So it is an extensor medial side of the
it is a flexor of the of the elbow joint. hip joint. So it is
elbow joint. an adductor of
Elbow joint the hip joint.
FLEXION

ABDUCTION

ADDUCTION

EXTENSION

Medial and Lateral Rotation

At joints that permit rotation, Shoulder joint ANTERIOR
movement or turning of the body
part occurs around its axis. The POSTERIOR Medial rotator
shoulder joint is a ball-and-socket The subscapularis
joint that permits rotation. The Lateral rotator muscle crosses on the
subscapularis muscle has lines of The teres minor muscle anterior side of the
action that cross the anterior aspect crosses the posterior shoulder joint. When it
of the shoulder joint. When the side of the shoulder contracts, it rotates the
subscapularis contracts it produces joint. When it contracts, shoulder medially.
medial rotation at the joint. The it rotates the shoulder
teres minor muscle has lines of laterally. Humerus
action that cross the posterior
aspect of the shoulder joint. When Scapula
the teres minor contracts, it
produces lateral rotation at the
shoulder.