Neuroanatomy Draw It To Know It

44 Neuroanatomy: Draw It to Know It

Ulnar Nerve (Cont.)

First, indicate that the deep branch innervates the
hypothenar group, which comprises abductor digiti
minimi, opponens digiti minimi, and fl exor digiti
minimi. Abductor digiti minimi abducts the fi ft h digit
in the plane of the palm. In regards to opponens digiti
minimi, both the median and ulnar nerves produce the
action of thumb to little fi nger opposition: the median
nerve supplies the opponens pollicis muscle, which
directs the thumb to the little fi nger, and the ulnar nerve
innervates the opponens digiti minimi muscle, which
directs the little fi nger to the thumb. Flexor digiti minimi
fl exes the fi ft h digit toward the palm.
Now, show that the deep branch innervates the intrin-
sic hand group, which comprises lumbricals 3 and 4, the
palmar interossei, and dorsal interossei muscles. Th e
third and fourth lumbricals have dual actions on digits 4
and 5: they extend their proximal interphalangeal joints
and fl ex their metacarpal–phalangeal joints. Th e palmar
interossei bring the fi ngers together (they provide fi nger

closure) whereas the dorsal interossei spread them apart.

We focus on the fi rst dorsal interosseous muscle because

it is commonly clinically tested; it provides fi nger abduc-

tion of the second digit.

Lastly, show that the deep branch innervates the

thenar group, which comprises fl exor pollicis brevis and

adductor pollicis. Flexor pollicis brevis fl exes the thumb

against the palm; the median nerve also innervates it.

Adductor pollicis adducts the thumb against the side of

the palm. It is the In component of the Up, In, Out triad,

which is as follows. Th e median-innervated abductor

pollicis brevis moves the thumb perpendicular to the

plane of the palm: with the palm up, it raises the thumb

up toward the ceiling. Th e ulnar-innervated adductor

pollicis and the radial-innervated abductor pollicis

longus move the thumb in the plane of the palm: adduc-

tor pollicis draws the thumb in toward the side of the

palm and abductor pollicis longus moves the thumb out

away from the side of the palm.^1 – 4 , 9 , 11 , 12

FIGURE 3-29 Abductor digiti minimi. FIGURE 3-30 Palmar interossei.

FIGURE 3-31 First dorsal interosseous. FIGURE 3-32 Adductor pollicis.