Brachial Plexus Anatomy PDF

Anatomy 534 Brachial Plexus 35 pinus of ventralArterialRami Dorsal.fi How is a Plexus Formed?...

Anatomy 534 Brachial Plexus 35 pinus of ventralArterialRami Dorsal.fi How is a Plexus Formed? By union f.d A "typical" spinal nerve exhibits bifurcation into a dorsal and ventral ramus. The dorsal ramus at each vertebral level passes segmentally to the back. The pattern exhibited by the ventral so if rami however may differ: segmfental - in the thoracic levels T2-T11 they remain "segmental"; - in other regions, they may fuse, bifurcate and rejoin in a complex fashion forming Phrenic n a "plexus" The dorsal and ventral rami of each spinal nerve 13 1 G 5 any are responsible for innervating (sensory/cutaneous innervation) a strip of skin referred to as a dermatome. in add t c f 7 iirind 4 L f I see Anatomy 534 Brachial Plexus 36 Structural Formation of the Brachial Plexus The brachial plexus is responsible for the motor and sensory innervation of the upper limb and its associated muscles. It is a vulnerable structure prone to injury during obstetric delivery, in accidents and gunshot wounds. It's organization needs to be known in some detail. The basic pattern of the plexus exhibits roots, trunks, divisions and cords. The branches (nerves emanating from the plexus) are added to this arrangement. The plexus is formed from a series of roots which are in fact the ventral rami of C5 to T1. The subsequent plexiform arrangement allows neurons from several segmental levels of the cord to be distributed to the periphery in a single nerve. 1. the roots, 5 in number (C5 through T1), lie within the prevertebral musculature of the neck and emerge into the posterior triangle between the anterior and middle scalene muscles. 2. the roots then unite to form trunks - named after their anatomical relationship to one another: - the upper two roots unite to form the superior trunk, - the lower two roots unite and form the inferior trunk, - the root from C7 continues on to become the middle trunk. Anatomy 534 Brachial Plexus 37 3. behind the clavicle, each trunk divides into an anterior and posterior division. 4. in the axilla the cords of the brachial plexus are formed by the union of the anterior and posterior divisions of the trunks. The cords are named after their relationship to the axillary artery: - the posterior divisions of all 3 trunks unite to form the posterior cord. This structure supplies the extensor mm. of the posterior aspect of the upper limb. - the upper two anterior divisions unite to form the lateral cord. - the remaining anterior division (of the lower trunk) forms the medial cord. The two cords formed by the anterior divisions supply flexor mm. on the anterior aspect of the upper limb. Branches from the Roots - C5 gives off the last contribution to the phrenic n. (C3,4,5) Branches from the Upper Trunk - none of importance Branches from the Cords - Lateral cord - the musculocutaneous n. (C5,6,7) and the lateral root of the median n. (C6,7). - Medial cord - the medial root of the median n. (C8, T1) and the ulnar n. (C8, T1). - Posterior cord - the axillary n. (C5,6) and the radial n. (C5-8, T1). Anatomy 534 Brachial Plexus 38 Relationship of Nerves and Vessels in the Axilla Within the axillary sheath in the axilla lie the axillary artery and axillary vein. Wrapped around the axillary a. are the cords of the branchial plexus. Five main nerves arise from the plexus: Musculocutaneous n. Median n. Ulnar n. Axillary n. Radial n. Anatomy 534 Brachial Plexus 39 Regional Summary Roots of the brachial plexus in the prevertebral muscular floor of the posterior triangle. The trunks pass through the posterior triangle. Divisions are located behind the clavicle (removed) while the cords are positioned around the axillary artery in the axilla. 1. dorsal scapular n. 2. suprascapular n. 3. axillary n. 4. musculocutaneous n. 5. median n. 6. ulnar n. 7. phrenic n.