38 Neuroanatomy: Draw It to Know It
Median Nerve (Cont.)
FIGURE 3-19 Pronator quadratus. FIGURE 3-20 Flexor pollicis longus.
Th ere are two important proximal entrapment sites for
the median nerve, which we will indicate now. First,
show that proximal to the superfi cial forearm group, lies
the ligament of Struthers. All of the components of the
median nerve lie downstream of this ligament; therefore,
when the median nerve is entrapped in the ligament of
Struthers, all of the median nerve components are
aff ected. Next, indicate the heads of the pronator teres
muscles. When the median nerve becomes entrapped in
these muscle heads, everything downstream of them is
aff ected. Note, however, that the components of the
superfi cial forearm group, including the pronator teres
muscle, itself, are unaff ected when the nerve is entrapped
in the heads of the pronator teres muscles, because inner-
vation to the superfi cial forearm group lies proximal to
the entrapment site.
Now, draw the anterior interosseous nerve branch.
Show that it innervates the anterior interosseous group.
Indicate that the anterior interosseous group is derived
from roots C7–T1, which comprises pronator quadra-
tus, fl exor pollicis longus, and fl exor digitorum profun-
dus 2 and 3. Pronator quadratus pronates the forearm
with the elbow in fl exion. Flexor pollicis longus fl exes
the interphalangeal joint of the thumb; it is the “long”
fl exor of the thumb in that it passes the metacarpal–
phalangeal joint to fl ex the interphalangeal joint. Flexor
digitorum profundus 2 and 3 fl exes the distal interpha-
langeal joints of the second and third digits.
Now, draw the carpal tunnel at the wrist; this is the
most common entrapment site of the median nerve.
Show that the median sensory branch to the proximal
palm, the palmar cutaneous nerve, takes off proximal
to the carpal tunnel, and therefore it and everything
else we have drawn so far is unaff ected in carpal tunnel
syndrome.FIGURE 3-21 Flexor digitorum profundus 2 and 3.