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The
Musculocutaneous, Axillary and Spinal Accessory Nerves
Musculocutaneous Nerve
This nerve can be studied when lesions involve the nerve itself, a C5
or C6 root or the upper trunk or lateral cord of the brachial plexus. In
routine nerve conduction, however, it is mainly used in repetitive stimulation.
The motor fibers can be stimulated at the axilla and supraclavicular
fossa and the motor response recorded from the belly of the biceps. Use
a small ground electrode for active electrode because of the size of the
muscle. Place the reference electrode over the elbow and the ground between
the active electrode and the axilla.
The sensory fibers (the lateral antebrachial cutaneous nerve) can be
stimulated at the elbow, just lateral to the biceps tendon and the sensory
response recorded 12 cm distal to the cathode over the lateral aspect of
the forearm.
Musculocutaneous
Entrapment, Compression or Injury Sites
The musculocutaneous nerve is seldom involved by injury alone. When
it is, trauma is the cause and can occur at any point along the nerve.
Axillary Nerve
This nerve is studied when lesions involve the nerve itself, a C5 root,
or the posterior cord or upper trunk of the brachial plexus. Its most coomon
use, however, is in performing repetitive stimulation.
Record the motor response from the deltoid by means of a small ground
electrode as the active electrode. Place the reference over the elbow and
the ground between the active electrode and the stimulator. This nerve
can be stimulated in the supraclavicular fossa.
Axillary
Entrapment, Compression or Injury Sites
The axillary nerve is especially vulnerable to injury as it winds around
the lateral aspect of the humerus where it can be involved either by fractures
of the humerus or shoulder dislocation.
Spinal Accessory Nerve
Stimulate the nerve in the neck halfway between the mastoid process
and the clavicle behind the belly of the sternocleidomastoid muscle. Record
the motor response from the belly of the upper trapezius, easily located
by asking the subject to shrug their shoulders. Use a ground electrode
as the active electrode and place the reference over the shoulder. Place
the ground between the active and stimulating electrodes. This nerve is
most commonly used for repetitive stimulation.
Spinal
Accessory Entrapment, Compression or Injury Sites
The spinal accessory nerve is most susceptible to injury in its superficial
course through the posterior cervical triangle (causing trapezius palsy)
and less frequently above the sternomastoid branch (with resulting trapezius
and sternomastoid weakness).
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