Chapter 13
The Peripheral Nervous System and Reflex Activity
505
13
Table 13.4
Branches of the Brachial Plexus
(See Figure 13.10 and Appendix G)
NERVES
CORD AND VENTRAL RAMI
STRUCTURES SERVED
Musculocutaneous
Lateral cord (C
5
–C
7
)
Muscular branches: flexor muscles in anterior arm (biceps brachii, brachialis,
coracobrachialis)
Cutaneous branches: skin on lateral forearm (extremely variable)
Median
By two branches, one from
medial cord (C
8
, T
1
) and one
from the lateral cord (C
5
–C
7
)
Muscular branches to flexor group of anterior forearm (palmaris longus, flexor carpi
radialis, flexor digitorum superficialis, flexor pollicis longus, lateral half of flexor
digitorum profundus, and pronator muscles); intrinsic muscles of lateral palm and
digital branches to the fingers
Cutaneous branches: skin of lateral two-thirds of hand on ventral side and dorsum of
fingers 2 and 3
Ulnar
Medial cord (C
8
, T
1
)
Muscular branches: flexor muscles in anterior forearm (flexor carpi ulnaris and medial
half of flexor digitorum profundus); most intrinsic muscles of hand
Cutaneous branches: skin of medial third of hand, both anterior and posterior aspects
Radial
Posterior cord (C
5
–C
8
, T
1
)
Muscular branches: posterior muscles of arm and forearm (triceps brachii, anconeus,
supinator, brachioradialis, extensors carpi radialis longus and brevis, extensor carpi
ulnaris, and several muscles that extend the fingers)
Cutaneous branches: skin of posterolateral surface of entire limb (except dorsum of
fingers 2 and 3)
Axillary
Posterior cord (C
5
, C
6
)
Muscular branches: deltoid and teres minor muscles
Cutaneous branches: some skin of shoulder region
Dorsal scapular
Branches of C
5
rami
Rhomboid muscles and levator scapulae
Long thoracic
Branches of C
5
–C
7
rami
Serratus anterior muscle
Subscapular
Posterior cord; branches of C
5
and C
6
rami
Teres major and subscapularis muscles
Suprascapular
Upper trunk (C
5
, C
6
)
Shoulder joint; supraspinatus and infraspinatus muscles
Pectoral (lateral and
medial)
Branches of lateral and medial
cords (C
5
–T
1
)
Pectoralis major and minor muscles
Tey transmit sensory impulses from the skin of the neck, the
ear area, the back of the head, and the shoulder. Other branches
innervate muscles of the anterior neck.
Te single most important nerve from this plexus is the
phrenic nerve
(fren
9
ik), which receives fibers from C
3
, C
4
, and
C
5
. Te phrenic nerve runs inferiorly through the thorax and
supplies both motor and sensory fibers to the diaphragm (
phren
5
diaphragm), which is the chief muscle causing breathing
movements.
Homeostatic Imbalance
13.2
Irritation of the phrenic nerve causes spasms of the diaphragm, or
hiccups. If both phrenic nerves are severed, or if the C
3
–C
5
region of
the spinal cord is crushed or destroyed, the diaphragm is paralyzed
and respiratory arrest occurs. Mechanical respirators keep victims
alive by forcing air into their lungs—literally breathing for them.
Brachial Plexus and Upper Limb
Te large, important
brachial plexus
, situated partly in the neck
and partly in the axilla, gives rise to virtually all the nerves that
innervate the upper limb
(Table 13.4)
. It can be palpated (felt)
in a living person just superior to the clavicle at the lateral bor-
der of the sternocleidomastoid muscle. Ventral rami of C
5
–C
8
and most of the ±
1
ramus intermix to form the brachial plexus.
Additionally, it oFen receives fibers from C
4
or ±
2
or both.
Te brachial plexus is very complex (some consider it the
anatomy student’s nightmare). Perhaps the simplest approach is
to master the terms used for its four major groups of branches
(Figure 13.10a, b)
. ²rom medial to lateral, these are (1) the
ventral rami, misleadingly called
roots
, which form (2)
trunks
,
which form (3)
divisions
, which form (4)
cords
. You might want
to use the saying “
R
eally
t
ired?
D
rink
c
offee” to help you re-
member this branching sequence.
Te five
roots
(ventral rami C
5
–±
1
) of the brachial plexus lie
deep to the sternocleidomastoid muscle. At the lateral border
of that muscle, these roots unite to form
upper
,
middle
, and
lower trunks
, each of which divides almost immediately into an
anterior division
and a
posterior division
.
Te anterior and posterior divisions, which generally indi-
cate which fibers serve the front or back of the limb, pass deep
to the clavicle and enter the axilla. Tere they give rise to three
large fiber bundles called the
lateral
,
medial
, and
posterior
cords
. (Te cords are named for their relationship to the axil-
lary artery, which runs through the axilla; see ²igure 19.23.)
All along the plexus, small nerves branch off. Tese supply the
muscles and skin of the shoulder and superior thorax.
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