296
296
chapter
10
Control
of Body
Movement
Motor Control Hierarchy
Voluntary and Involuntary Actions
Local Control of Motor Neurons
Interneurons
Local Afferent Input
The Brain Motor Centers and the
Descending Pathways They Control
Cerebral Cortex
Subcortical and Brainstem Nuclei
Cerebellum
Descending Pathways
Muscle Tone
Abnormal Muscle Tone
Maintenance of Upright Posture and
Balance
Walking
Additional Clinical Examples
Tetanus
c
arrying out a
coordinated movement
is a complicated process
involving nerves, muscles, and
bones. Consider the events
associated with reaching out
and grasping an object. The
fi ngers are fi rst extended
(straightened) to reach around
the object, and then fl exed
(bent) to grasp it. The degree
of extension will depend upon
the size of the object (Is it a
golf ball or a soccer ball?),
and the force of fl exion will
depend upon its weight and
consistency (a bowling ball or
a balloon?). Simultaneously,
the wrist, elbow, and shoulder
are extended, and the trunk
is inclined toward the object.
The shoulder, elbow, and
wrist are stabilized to support
fi rst the weight of the arm
and hand and then the added
weight of the object. Through
all this, the body maintains
upright posture and balance
despite its continuously
shifting position.
previous page 324 Vander's Human Physiology The Mechanisms of Body Function read online next page 326 Vander's Human Physiology The Mechanisms of Body Function read online Home Toggle text on/off