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Definition :

  • The Brachial plexus is a group or network of nerves in the shoulder.
  • Moreover the Brachial plexus carries movement and sensory signals from the spinal cord to the arms and hands.

Parts of Brachial plexus :

  • Roots
  • Trunks
  • Divisions
  • Cords and also
  • Branches

Roots :

  • The Brachial plexus constitutes the anterior primary rami of spinal nerves from C5 – C8 and T1.
  • This may be occasionally contributed by anterior primary rami of C4 and T2.
  • The origin of the plexus may either shift by one segment either upward or downward.
  • And this results in a prefixed or postfixed plexus respectively.
  • Most importantly in a prefixed plexus, the contribution by C4 plexus is maximum.
  • Whereas C5 is present, T1 is small and moreover T2 often absent.
  • In a postfixed plexus, the contribution by T1 is large and also T2 is always present.
  • Whereas C4 is absent and C5 is often reduced or smaller in size.
  • Finally the above mentioned roots join to form the Trunks.

Anatomy of brachial plexus or Erb's palsy

Supraclavicular part of Brachial plexus – Roots and Trunks :

  • The Roots of C5 and C6 join to form the Upper trunk.
  • Root C7 forms the Middle trunk.
  • Root C8 and T1 together form the Lower trunk.
  • Moreover the supraclavicular part lie in the neck between the Scalenus anterior and Scalenus medius muscles.
  • Further this supraclavicular part of the brachial plexus carries the axillary sheath from prevertebral fascia.

Retro clavicular part of Brachial plexus – Divisions of the trunks :

  • All three trunks divides into ventral and dorsal divisions.
  • Finally, they supply the anterior and posterior aspects of the limbs.
  • Further these divisions join to form the cords.

Infraclavicular part of Brachial plexus – Cords and Branches :

  • The union of Upper and the Middle trunks (two divisions) forms the Lateral cord.
  • Whereas the medial cord is formed by the ventral division of the lower trunk (One division).
  • The dorsal division of all three trunks forms the Posterior cord.
  • Above all these are named according to the relation of cords to the second part of the axillary artery.

Branches :

Branches of the roots :

  • Firstly, Nerve to Serratous anterior or Long thoracic nerve (C5-C7).
  • It supplies the serratous anterior muscle.
  • Moreover it is the key muscle for overhead abduction.
  • Secondly, Nerve to Rhomboids or Dorsal scapular nerve (C5).
  • This nerve supplies the rhomboid minor and the rhomboid major muscles.
  • In addition these muscles are responsible for the retraction of the shoulder girdle.
  • Further it gives a branch to Levator scapulae.
  • Thirdly, Branches to the Longus colli and scaleni muscles (C5-C8).
  • Finally, Branches to the phrenic nerve (C4).
  • The roots of phrenic nerve is from both C4 and C5.
  • Though the root from C5 is small whereas C4 is very large.
  • This supplies the Thoracoabdominal diaphragm.
  • In addition, it also carries the afferent fibres from mediastinal pleura, fibrous pericardium and also part of the Parietal peritoneum.

Branches of the Trunks :

  • These branches arises only from the Upper trunk.
  • One is the Suprascapular (C5, C6) which supplies the Supraspinatous and Infraspinatous muscles.
  • The second is the nerve to Subclavius (C5, C6) which supplies the subclavius muscle.
  • Moreover it may also give a root for phrenic nerve.

Branches of the cords :

Branches of the Lateral cord :

  • Lateral pectoral nerve (C5-C6) supplies both the Pectoralis major and also minor muscles.
  • Musculocutaneous nerve (C5-C7) nerve supplies the muscles of front of arm.
  • That is it supplies Coracobrachialis, both the long and short head of biceps brachii and also the Brachialis muscle.
  • Lateral root of Median nerve (C5-C7).
  • The above root joins the medial root of median nerve.
  • Moreover it is the chief nerve of muscles of front of forearm and also of the muscles of Thenar eminence.

Branches of the Medial cord :

  • Medial pectoral (C8,T1) nerve also supplies both the Pectoralis major and also minor muscles.
  • Medial cutaneous nerve of arm (C8 , T1) carries sensory impulses from a small area of the medial side of arm.
  • And also the Medial cutaneous nerve of forearm (C8,T1) carries sensory impulses from large area of medial side of the forearm.
  • Ulnar (C7,C8,T1) nerve supplies the one and half muscles of front of forearm and 15 intrinsic muscles of the palm.
  • The Medial root of median nerve (C8, T1) joins the lateral root and also gets distributed with branches of median nerve.

Branches of Posterior cord :

  • Upper subscapular nerve (C5,C6) supplies large multipennate subscapularis muscles.
  • Nerve to Latissimus dorsi (C6 – C8) supplies the muscle of its name.
  • Moreover it is also called Thoracodorsal nerve.
  • Lower subscapular nerve (C5,C6) helps upper subscapular nerve in supplying the Subscapularis muscle.
  • In addition, it also supplies the teres major muscle.
  • Axillary (Circumflex) (C5,C6) supplies the deltoid muscle.
  • And also it supplies the small portion of Teres minor muscle.
  • Radial (C5-C8,T1) nerve is the thickest branch of the brachial plexus.
  • It supplies all three heads of Triceps brachii muscle.
  • And also it supplies 12 muscles on the back of the forearm.

Special features :

  • The lateral cord, medial cord and their branches form the letter M with three corners extended.
  • Moreover the lateral cord gives the musculocutaneous and also the lateral root of median nerve.

Blood supply of Brachial plexus :

  • Firstly, Vertebral artery
  • Secondly, Thyrocervical trunk
  • Thirdly, Suprascapular arteries
  • Finally, transverse cervical arteries

Clinical features of Brachial plexus :

  • Erb’s paralysis
  • Klumpkes’s paralysis
  • And also Injury to the Nerve to Serratous anterior

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