Chapter 2. Prehension

Appendix A - Human Upper Limb Anatomy 359
close to forty degrees of freedom in the upper limb, of which thirty or
more are in the wrist and hand. These motions have standard
anatomical labels, described above. The bones, joints, degrees of
freedom and motions about the joints are summarized in Table A.l.
A.4 Muscles of the Upper Limb
Motion about a joint is caused primarily by muscle contractions
(and in some instances, allowed by ligaments). There are about 58
muscles of the upper limb, and 9 may be considered as extrinsic to the
upper limb, since they attach on other than limb skeletal parts. The
rest are intrinsic to the upper limb, with attachments on the limb
skeleton. Note that the extrinsic hand muscles cross the wrist and
elbow, causing some motion at these joints as well as the joints in the
hand. These are to be distinguished from the 19 intrinsic hand
muscles, which do not cross the wrist joint. Table A.2 lists the upper
limb muscles, and the number of joints crossed on the same line as
their PRIMARY actions. Included are muscles which also have some
action at more proximal joints than the primary action.
A.5 Peripheral and Segmental Innervation of
Muscles of the Upper Limb
Table A.3 lists the upper limb muscles, their peripheral and
segmental innervation.
A.6 Sensations of the Upper Limb, and Spinal
Innervation
In Chapter 6, we consider cutaneous mechanoreceptors.
Cutaneous sensations are relayed to the spinal cord via dorsal root
ganglia at each segmental level. A dermatome is an area of skin
innervated by a single dorsal root. Figure AS shows the segmental
dermatome mapping of the upper limb, after Keegan et al. (1948),
adapted from Hollinshead (1982). The upper limb innervation is
derived primarily from C3 to C8 and T1. Dermatome boundaries are
not as clear-cut as indicated below because more than one peripheral
nerve sends afferents to each dorsal root, and fibers from serveral
dorsal roots mix in the peripheral nerves.