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Describe Formation and Parts of brachial plexus.
Formation : Brachial plexus is formed by the ventral rami of C5- C8 and T1 spinal nerves in the posterior triangle of the neck.
- Prefixed plexus : if there is contribution from C4 spinal nerve to the brachial plexus.
- Postfixed plexus : if there is contribution from T2 spinal nerve to the brachial plexus.
Course: Brachial plexus extends from the posterior triangle in the neck, through the cervico-axillary canal into the axilla.
Parts: Following are the parts of brachial plexus:
- Roots – Ventral/anterior rami of C5-C8 & T1 spinal nerves form the roots of brachial plexus.
- Trunks – The roots form three trunks:
- Upper trunk – C5 & C6 roots join to form upper trunk
- Middle trunk – C7 root forms middle trunk
- Lower trunk – C8 & T1 roots join to form lower trunk
- Divisions : Each trunk divides into anterior (ventral) and posterior (dorsal) divisions.
- Cords : Divisions form three cords
- Lateral cord – anterior divisions of upper and middle trunk join to form lateral cord.
- Medial cord – anterior division of lower trunk forms medial cord.
- Posterior cord – posterior divisions of all the three trunks join to form posterior cord.
Location of Brachial Plexus
Location: Brachial plexus is divided into two parts: supraclavicular and infraclavicular parts.
- Supraclavicular Part lies in the posterior triangle of neck. It comprises of roots and trunks of brachial plexus.
- Infraclavicular Part lies in the axilla. It comprises of cords of brachial plexus.
Enumerate the Branches of Brachial Plexus.
Branches of brachial plexus are:
From the roots:
- Dorsal scapular nerve (C5)
- Long thoracic nerve ( C5,C6,C7)
From the upper trunk:
- Suprascapular nerve ( C5, C6)
- Nerve to subclavius (C5,C6)
From the three cords of brachial plexus.
Branches of lateral cord – Three
- Lateral pectoral nerve ( C5-7)
- Lateral root of median nerve (C5-7)
- Musculocutaneous nerve (C5-7)
Branches of medial cord – Five
- Medial pectoral nerve (C8,T1)
- Medial cutaneous nerve of arm (C8,T1)
- Medial cutaneous nerve of forearm (C8,T1)
- Medial root of median nerve (C8,T1)
- Ulnar nerve (C8,T1)
Branches of posterior cord – Five
- Upper subscapular nerve (C5,C6)
- Lower subscapular nerve (C5,C6)
- Thoracodorsal nerve (C6-8)
- Axillary nerve (C5,C6)
- Radial nerve (C5-T1)
What is Erb’s Point?
Erb’s point is the region on upper trunk of brachial plexus where :
- There is union two roots – ventral rami of C5 & C6
- It divides into two divisions – anterior and posterior divisions
- It provides origin to two nerves – suprascapular and nerve to subclavius.
Applied Aspects
Erb’s paralysis (Erb-Duchenne Palsy)
- Site of lesion is Erb’s point i.e. upper trunk of brachial plexus(C5,C6).
- Cause is undue separation of head from the shoulder which may occur in the following conditions.
- An abnormal or difficult childbirth ( forceps delivery).
- When a person falls on shoulder.
- Position of the upper limb: It appears like a Policeman’s or Waiter taking tip.
- The arm is adducted and medially rotated.
- The forearm is extended and pronated.
- Motor loss :The muscles paralyzed are supraspinatus,deltoid,infraspinatus,teres minor biceps brachii, brachialis, brachioradialis and supinator.
- paralysis of supraspinatus and deltoid results in loss of abduction of arm.
- paralysis of infraspinatus and teres minor results in loss of lateral rotation of arm.
- paralysis of biceps brachii, brachialis, brachioradialis results in loss of flexion of forearm.
- paralysis of biceps brachii and supinator results in loss of supination of forearm.
- Sensory loss :There is loss of sensations from the skin over the lower part of the deltoid (supplied by axillary nerve -root value C5,C6).
Klumpke’s paralysis
- Site of lesion is lower trunk of brachial plexus (C8,T1).
- Cause is undue separation of arm from the trunk (abduction injury) which may occur in the following conditions.
- Birth injury
- Clutching something while falling from the height.
- Position of the hand is complete claw hand i.e.
- hyperextension at metacarpophalangeal joints
- flexion at interphalangeal joints.
- Motor loss: Intrinsic muscles of the hand are paralyzed.
- Sensory loss: Loss of sensations from a narrow zone along the medial side of hand and forearm.
- Horner’s syndrome : occurs due to involvement of sympathetic fibers of T1 spinal nerve.
- Characteristic features of Horner syndrome are:
- Partial Ptosis – drooping of eyelid (due to paralysis of a part of levator palpabrae superioris that is supplied by sympathetic fibers).
- Miosis – constriction of pupil (due to paralysis of dilator pupillae that is supplied by sympathetic fibers).
- Anhidrosis – decreased sweating.
- Enophthalmos – posterior displacement of the eye.
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