Human Anatomy Vol 1

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Fig.8.22:' Testing triceps brachii against resistance

abducted position of the arm. Gravity extends the elbow

passively.

Electromyography has shown that the medial head

of the triceps is active in all forms of extension, and the

actions of the long and lateral heads are minimal, except

when acting against resistance.

RADIAT NERVE OR MUSCUTOSPIRAL NERVE

Radial nerve is the largest branch of the posterior cord

of the brachial plexus with a root value of C5-C8, TL

(see Fig.4.l4).

Oligin, Course ond Terminotion

Radial nerve is given off from the posterior cord in the

Iower part of axilla.

L It runs behind third part of axillary artery.

2 In the arm it lies behind the brachial artery.

3 Leaves the brachial artery to enter the lower

triangular space to reach the oblique radial sulcus

on the back of humerus.

4 The nerve reaches the lateral side of arm^5 cm below

deltoid tuberosity, pierces lateral intermuscular

septum to enter the anterior compartment of arm on

its lateral aspect.

5 It descends down across the lateral epicondyle into

cubital fossa.

Radial nerve terminates by dividing into a superficial

and a deep branch just below the level of lateral

epicondyle. These are seen in the cubital fossa.

Relolions

a. In the lower part of the axilla, radial nerve Passes

downwards and has the following relations.

Ant rly:Thrdpart of the axillary artery @eeFig. 4.8).

Posteriorly: Subscapularis, latissimus dorsi and teres

major.

Laterally : Axillary nerve and coracobrachialis.

dially: Axillary vein (see Fig. a.9).

b. In the upper part of the arm, it continues behind the

brachial artery, and passes posterolaterally (with the

profunda brachii vessels) through the lower

triangular space, below the teres major, and between

the long head of the tricepsbrachii and the humerus.

It then enters the radial groove with the profunda

vessels (see Fig. 6.12).

c. In the radial groove, the nerve runs downwards and

of the

8.13).

eltoid

tuberosity, the nerve pierces the lateral intermuscular

septum and passes into the anterior compartment of

the arm (Fig.8.23) to reach the cubital fossa where it

ends by dividing into superficial and deep branches.

Bronches ond Distribution

Various branches of radial nerve are shown in Fi g. 8.23.

Jt4*serufcr

1 Before entering the spiral groove, radial nerve supplies

the long and medial heads of the triceps brachii.

2 In the spiral groove, it supplies the lateral and medial

heads of the triceps brachii and the anconeus.

3 Below the radial groove, on the front of the arm, it

supplies the brachialis with proprioceptive fibres.

The brachioradialis and extensor carpi radialis

longus are supplied with motor fibres.

Cerfsneous Srcncfiss

1 In the axilla, radial nerve gives off the posterior

cutaneous nerve of the arm which supplies the skin

on the back of the arm.

2 In the radial groove, the radial nerve gives off the

lower lateral cutaneous nerves of the arm and the

posterior cutaneous nerve of the forearm.

Articular branches: The articular branches near the

elbow supply the elbow joint.

The radial nerve is very commonly damaged in

the region of the radial (spiral) groove. The

common causes of injury are as follows.

a. Sleeping in an armchair with the limb hanging

by the side of the chair (saturday night palsy),

or even the pressures of the crutch (crutch

paralysis) (Fig. 8.2a).

b. Fractures of the shaft of the humerus. This

results in the weakness and loss of power of

extension at the wrist (wrist drop) (Fig. 8.25)

and sensory loss over a narrow strip on the back

of forearm, and on the lateral side of the dorsum

of the hand (Fig. 8.26).

Wrist drop is quite disabling, because the patient

cannot grip any object firmly in the hand without

the synergistic action of the extensors.