Chapter 2. Prehension

214 THE PHASES OF PREHENSION
focusing or sharpening mechanism, operating prior to
mechanoreceptor transduction. From papillary ridges emerge the
ducts of a form of exocrine glands, called eccrine glands. Thus the
skin surface contacting objects is a lubricated surface, not a dry one.
As well, the increased surface area due to the papillary ridges also
provides room for more tactile sensory organs (Montagna & Parakkal,
1974). We now consider eccrine sweat glands, then cutaneous
mechanoreceptors.
6.1.2 Eccrine glands and efferent control by the
autonomic nervous system
Found on all body skin of higher primates, but only the non-hairy
skin of other mammals, the eccrine glands are believed to be more
important and phylogenetically more recent than the rudimentary
apocrine glands. Eccrine glands develop from the epidermis (unlike
apacrine glands and sebaceous glands which develop from the follicles
of hairy skin, and are not discussed here), coiling downward through
the dermis to subdermal fat. Half the coil is secretory epithelium and
half of it is duct (see Figure 6.1). There may be 100-400/cm2 and 2-5
million over the entire body surface (Rothman, 1954). In friction
surfaces, these eccrine ducts open at the apex of papillary ridges,
rarely in the furrows. Note the regularity of spacing of the pores in
the center of the epidermal ridge lines of the palm in Figure 6.3.
The sweat glands of the friction surfaces of the body may be
distinguished from other eccrine sweat glands on the basis of regional
distribution, response to stimuli activating them, and on the basis of
the composition of the aqueous sweat. Table 6.1 shows that the palms
Table 6.1 Distribution of Eccrine Glands in Humans (number of
sweat glandskquare inch of surface area) (from Krause, 1844, cited
palms 2,736
soles 2,685
dorsa of hands 1,490
forehead 1,258
chest and abdomen 1,136
forearm
- flexor aspect 1,123
- extensor aspect 1,093
dorsa of feet 924
thigh and leg, 576
medial
thigh, lateral 554
cheek 548
nape of neck 417