150 The Muscular System
MUSCLES OF THE HEAD AND NECK
Three general groups of muscles are found in the head
and neck: those that move the head or neck, the mus-
cles of facial expression, and the muscles for chewing.
The muscles that turn or bend the head, such as the
sternocleidomastoids (flexion) and the pair of splenius
capitis muscles (extension), are anchored to the skull
and to the clavicle and sternum anteriorly or the ver-
tebrae posteriorly. The muscles for smiling or frown-
ing or raising our eyebrows in disbelief are anchored
to the bones of the head or to the undersurface of the
skin of the face. The masseter is an important chewing
muscle in that it raises the mandible (closes the jaw).
FlexionFlexionExtensionExtensionAbductionAdductionAbductionAdduction
Figure 7–7. Actions of muscles.
QUESTION:Crossing the arm in front of the chest would
be which of these actions?Table 7–2 ACTIONS OF MUSCLESAction Definition
Flexion
Extension
Adduction
Abduction
Pronation
Supination
Dorsiflexion
Plantar flexion
RotationMost are grouped in pairs of antagonistic functions.- To decrease the angle of a joint
- To increase the angle of a joint
- To move closer to the midline
- To move away from the midline
- To turn the palm down
- To turn the palm up
- To elevate the foot
- To lower the foot (point the toes)
- To move a bone around its
longitudinal axis