Chapter 2. Prehension

226 THE PHASES OF PREHENSION
for FA1 unit, a buzzing, wobbling or fluttery sensation was
experienced (Johansson, 1978).
In addition to mechanoreceptors in the skin and subcutaneous
tissues, joint, muscle and tendon receptors are providing
proprioceptive information during contact and manipulation. In
examination of the deep ulnar nerve, Devanandan and colleagues, in
bonnet monkeys (Macaca radiata) found that myelinated sensory fibers
comprised 70% of the total nerve fibers, that 50% of myelinated fibers
in nerves to the intrinsic muscles of the hand are sensory, and further
that 25 - 50% of the fibers in the deep ulnar nerve innervate the joints
of the hand (Devanandan, Ghosh & Simoes, 1980). Followup
anatomical studies demonstrated a paucity of tendon organs in the
intrinsic hand musculature, in contrast to the rich number and density
of muscle spindles (Devanandan, Ghosh & John, 1983). Thus, there
is a large quantum of feedback concerning movement parameters, not
of evolving tension in the intrinsic muscles. They consider the role of
spindles in intrinsic muscles to be, in part, providing rapid feedback in
evolving manipulation so that the intrinsic muscles of the hands can be
appropriately altering the resultant force vectors that act on the
respective digital joints. The muscle spindle afferents in the lumbrical
nerve have been implicated also in perception of direction, distinct
from the perception of movement, given the loss of perception of
direction with injury or administration of local anesthetic
(Devanandan, personal communication, November, 1989).
It appears that there are substantial differences beween
mechanoreceptors in digital joints and more proximal joints, such that
digital joints are specialized particularly for detection of dynamic
mechanical changes, rather than static joint position. In examining the
receptors in the metacarpophalangeal joints of bonnet monkeys and
one male human, Sathian and Devanandan (1983) found a dominance
of dynamic mechanoreceptors: paciniform corpuscles (Type II), a
smaller number of Ruffini endings (Type I) and their restriction to
palmar ligaments, and a complete absence of the static receptors, Golgi
endings (Type 111). Free nerve endings (Type IV) and paciniform
corpuscles were also found close to blood vessels, perhaps to detect
mechanical changes associated with vasodilation. In the
interphalangeal joints, as shown in Figure 6.8, there are some free
nerve endings; however, pacinifondpacinian corpuscles are almost the
exclusive encapsulated mechanoreceptors in the joints. With 3 - 50
lamellae, these were situated in groups, and exclusively in the lateral
and ventral (palmar) aspects of the joint capsule (Babu 8z Devanandan,
1991). A single parent axon may branch and supply endings with