BRACHIAL PLEXUS
DISSECTION
After cleaning the branches of the axillary artery . proceed to wash the plexus brachialis . it's formed by the ventral primary rami of the lower four cervical (C5-C8) and therefore the first thoracic (T1) nerves. the primary and second parts of the axillary artery are associated with the cords; and third part is related to the branches of the plexus.
The plexus consists of roots, trunks, divisions, cords and branches.
Roots
These are constituted by the anterior primary rami of spinal nerves C5-C8 and T1, with contributions from the anterior primary rami of C4 and T2.
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 which from T2 is usually 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:
Roots and Trunks-Supraclavicular Part
Roots C5 and C6 join to form the upper trunk. Root C7 forms the middle trunk. Roots C8 and T1 join to form the lower trunk.
Divisions of the Trunks-Retroclavicular Part
Each trunk (3 in number) divides into ventral and dorsal divisions (which ultimately supply the anterior and posterior aspects of the limb). These divisions join to form cords.
Cords and Branches--Infraclavicular Part
i. The lateral cord is formed by the union of ventral divisions of the upper and middle trunks (two divisions).
ii. The medial cord is formed by the ventral division of the lower trunk (one division).
iii. The Posterior cord is formed by union of the dorsal divisions of all the three trunks (three divisions).
Sympathetic Innervation
1. Sympathetic nerves for the upper limb are derived from spinal segments T2 to T6. Most of the vasoconstrictor fibres supplying the arteries emerge from segments T2 and T3.
2. The preganglionic fibres arise from lateral horn cells and emerge from the spinal cord through ventral nerve roots.
3. Passing through white rami communicantes, they reach the sympathetic chain.
4. They ascend within the chain and end in the middle cervical, inferior cervical and first thoracic ganglia.
5. Postganglionic fibres from middle cervical ganglion pass through grey rami communicantes to reach C5, C6 nerve roots.
6. Postganglionic fibres from inferior cervical ganglion pass through grey rami communicantes to reach C7, and C8 nerve roots.
7. Postganglionic fibres from first thoracic sympathetic ganglion pass through grey rami communicantes to reach T1 nerve roots.
8. The arteries of skeletal muscles are dilated by sympathetic activity. For the skin, however, these nerves are vasomotor, sudomotor and pilomotor.
Vasomotor: Constricts the arterioles of skin.
Sudomotor: Increases the sweat secretion.
Pilomotor: Contracts the arrector pilorum muscle to cause erection of the hair.
Branches
The roots value of each branch is given in brackets.
Branches of the Roots
1. Nerve to serratus anterior (long thoracic nerve) (C5- C7). It only supplies serratus anterior muscle, one of the key muscles, for overhead abduction.
2. Nerve to rhomboids (dorsal scapular nerve) (C5). This nerve supplies rhomboid minor and rhomboid major muscles, responsible for retraction of the shoulder girdle.
3. Branches to longus colli and scaleni muscles (C5-C8) and branch to phrenic nerve (C4). The root of phrenic nerve from C5 is small one, the main root is from C4. Phrenic nerve is the sole motor nerve supply of thoracoabdominal diaphragm. In addition, it carries afferent fibres from mediastinal pleura, fibrous pericardium and part of the parietal peritoneum.
Branches of The Trunks
These arise only from the upper trunk which gives two branches:
1 Suprascapular (C5, C6). This nerve supplies Supraspinatus and infraspinatus muscles.
2 Nerve to Subclavius (C5, C6). It supplies the small Subclavius muscles. It may give a root for phrenic nerve.
Branches of the Cords
Branches of lateral cord
1 Lateral pectoral (C5-C7). This nerve supplies both pectoralis major and pectoralis minor muscles.
2 Musculocutaneous (C5-C7 ).This is the nerve of muscles of front of arm, i.e. coracobrachialis both the long and short heads of biceps brachii and the brachialis muscles.
3 Lateral root of median (C5-C7). It joins the medial root of median nerve. Median nerve is the chief nerve of the muscles of front of forearm and of muscles of thenar eminence
Branches of medial cord
1 Medial pectoral (C8, TI). It also supplies both the pectoralis minor and pectoralis major muscles.
2 Medial cutaneous nerve of arm (C8, TI).Carries Sensory impulses from a small area of medial side of arm.
3 Medial cutaneous nerve of forearm (C8, T1) carries sensory impulses from large area of medial side of the forearm.
4 Ulnar (C7, C8, T1). C7 fibres reach by a Communicating branch from lateral root of median nerve. This is the nerve of one and a half muscles of front of forearm and 15 intrinsic muscles of the palm.
5 Medial root of median (C8, T1). It joins the lateral root and gets distributed with branches of median nerve.
Branches of posterior cord
1. Upper subscapular (C5, C6): This nerve supplies large multipennate subscapularis muscles.
2. Nerve to latissimus dorsi (C6-C8). Only supplies muscles of its name. It is also called thoracodorsal nerve
3. Lower subscapular (C5, C6). It helps upper subscapular nerve in supplying of the subscapularis muscles. In addition, it supplies the tares major muscles.
4 Axillary (circumflex) (C5, C6). It is responsible for Supplying one of the important muscles of the shoulder, the deltoid, It also supplies small tares minor muscle.
5 Radial (C5-C8, T1). This is the thickest branch of brachial plexus. It supplies all the three heads of triceps brachii muscle. Then it supplies 12 muscles on the back of forearm.
In addition to the branches of the brachial plexus, the upper limb is also supplied, near the trunk, by the supraclavicular branches of the cervical plexus, and by the intercostobrachial branch of the second intercostal nerve. Sympathetic nerves are distributed through the brachial plexus. The arrangement of the various nerves in the axilla was studied with the relations of the axillary artery.
Special Feature
The lateral cord, medial cord and their branches form the latter "M" with the three corners extended. Lateral cord gives Musculocutaneous and lateral root of median.
Medial cord gives ulnar and medial root of median.
The lateral root and medial root of median nerve join to form the median nerve.
Blood Supply of Brachial Plexus
Vertebral artery and thyrocervical trunk with its branches, the Suprascapular and transverse cervical arteries, Supply blood to the brachial plexus. These are the life line of this important plexus.
Brachial plexus injury :
ERB'S PARALYSI
Site of injury :
One region of the upper trunk of the brachial plexus is called Erb's point. Six nerves meet here. Injury to the upper trunk causes Erb's paralysis.
CAUSE OF INJURY :
Undue separation of the head from the shoulder, which is commonly encountered in the following.
i. BIRTH INJURY
ii. FALL ON THE SHOULDER
iii. DURING ANAESTHESIA
NERVE ROOT INVOLVED:
Mainly C5 and partly C6.
MUSCLE PARALYSED:
Mainly biceps brachii, deltoid, Brachialis and Brachioradialis. Partly Supraspinatus, Infraspinatus and Supinator.
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KLUMPKE'S PARALYSIS
Site of injury:
⚫ Lower trunk of the brachial plexus.
Cause of injury:
⚫ Undue abduction of the arm, as in clutching something with the hands after a fall from a height, or something in the birth injury.
Nerve roots involved:
⚫ Mainly T1 and partly C8
Muscles paralysed:
⚫ Intrinsic muscle of the hand(T1)
⚫ Ulnar flexors of the wrist and fingers (C8)
Deformity and POSITI0N of the hand: Claw hand due to the unopposed action of the long flexors and extensors of the fingers. In a claw hand, there is hyperextension at the metacarpophalangeal joints and flexion at the interphalangeal joints.
Disability:
⚫Biceps and supinator jerks are lost.
⚫Complete claw hand
⚫ Cutaneous anaesthesia and analgesia in a narrow Zone along the ulnar border of the forearm and hand.
⚫ Horner's syndrome: If T1 is injured proximal to white ramus communicans to first thoracic sympathetic ganglion, there is ptosis, miosis, anhydrosis, enophthalmos, and loss of cilio-spinal reflex-may be associated. This is because of injury to sympathetic fibres to the head and neck that leave the spinal cord through nerve T1.
⚫Vasomotor changes: The skin area with sensory loss is warmer due to arteriolar dilation. It is also drier due to the absence of sweating as there is loss of sympathetic activity.
⚫ Trophic changes: Long-standing case of paralysis leads to dry and scaly skin. The nails crack easily with atrophy of the pulp of fingers.
Injury to the Nerve to Serratus Anterior (Nerve of Bell)
Causes:
1. Sudden pressure on the shoulder from above.
2.Carrying heavy loads on the shoulder.