Chapter 2. Prehension

Chapter 4 - Planning of Prehension 71
s
Somatic sensory Visual I
cortex
cortex
Visual
afferent
afferent
pathway
Location and
Input from
muscles. movement
skin and joints
Sensory I periphery Eye
I '
I
Direct
system
1
Of
hand and
arm
I Motivational
I
systems flimbicl
Motor cortex
1 Indirect
system
1 I
ord Spinal cord
Motor systems
I
Reflexes and
postural
adlustments
Sensory stimulus Motor performance
Figure 4.3 Three major brain systems - the motivational systems,
the sensory systems and the motor systems must interact during an
act like reaching to grasp an object. The motor cortex receives
inputs from the motivational systems, and sensory systems. In
parallel, descending systems from the cortex include the direct
corticospinal system, which makes monosynaptic connections to
the motoneurons of the hand muscles, and also connections to the
motoneurons of the shoulder and arm muscles. Indirect pathways
descend from the motor cortex and multiple brainstem structures to
make connections with postural muscles. All of these systems are
reflected in the delay between a 'GO' signal, and the first EMG
burst observed prior to initiation of the grasping movement (from
Kandel and Schwartz, 1985; reprinted by permission).
and the complexity of the upcoming grasping task. To date, no
research has shown reaction time to vary with object properties.
What is happening during this time delay? Evidence suggests that
the CNS is engaged in preparatory processes related to the