Human Anatomy Vol 1

(mdmrcog) #1
UPPER LIMB

Fi1.4.12: Lymph above umbilicus drains into axillary lymph
nodes while below umbilicus drains into inguinal group

Spinol Nerve
Each spinal nerve is formed by union of dorsal root
and ventral root. Dorsal root is sensory and is
characterised by the presence of spinal or dorsal root
ganglion and enters the dorsal horn and posterior
funiculus of spinal cord. Ventral root is motor, arises
from anterior horn cells of spinal cord.
The motor and sensory fibres get united in the
spinal nerve which divides into short dorsal ramus and
long ventral ramus. Both the rami thus contain motor
and sensory fibres. In addition, these also manage to
obtain sympathetic fibres via grey ramus communicans
(Fig. a.13).

Only the ventral primary rami form plexuses.
Brachial plexus is formed by ventral primary rami or
ventral rami of C5, C6,C7,C8 and T1 segments of spinal
cord.

Dissection

After cleaning the branches of the axillary artery,
proceed to clean the brachial plexus. lt is formed by
the ventral primary rami of the lower four cervical
(C5-C8) and the first thoracic (T1) nerves. The first
and second parts of the axillary artery are related to
the cords; and third part is related to the branches of
the plexus. Study the description of the brachial plexus
before proceeding further.

The plexus consists of roots, trunks, divisions, cords
and branches (Fig. 4.14).

Rools
These are constituted by the anterior primary rami of
spinal nerves C5, C6, C7, Cg and T1, with contributions
from the anterior primary rami of C4 and T2 (Fig. a.8).
The origin of the plexus may shift by one segment
either upward or downward, resulting in a prefixed or
postfixed plexus respectively.
In a prefixed plexus, the contribution by C4 is large
and that from T2 is often absent.
In a postfixed plexus, the contribution by T1 is large,
T2 is always present, C4 is absent, and C5 is reduced in
size. The roots join to form trunks as follows:

Dorsal ramus

Dorsal root ganglion

Sensory fibres

Motor fibres
Spinal cord at T1 level

Preganglionic sympathetic fibres

.ct
E


=o
CL
CL


tr
.o
(.)
U)o

Ventral ramus Sensory
fibres

Postganglionic
sympathetic fibre

White ramus communicans

Grey ramus
communtcans

Fig.4.13: Mixed fibres of root of brachial plexus
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