Quick Facts
Origin: Usually from the lateral root of median nerve.
Course: Interconnects the median and the ulnar nerves.
Branches: None.
Supply: Motor innervation to the flexor carpi ulnaris.
Origin
The lateral root of ulnar nerve refers to a communicating ramus which originates from the lateral root of median nerve and interconnects median and ulnar nerves. The communicating ramus may also arise more proximally from the lateral cord or anterior division of middle trunk or even the middle trunk itself (Hollinshead, 1958; Chaudhary et al., 2013).
Course
The ulnar nerve normally originates from the medial cord of brachial plexus, with its components derived from spinal segments C8, T1. These traverse the lower trunk of brachial plexus, its anterior division, and finally enter the medial cord. However, in a considerable number of cases, the ulnar nerve receives fibers from the seventh cervical segment. These fibers reach the ulnar nerve via the middle trunk, its anterior division, the lateral cord, the lateral root of median nerve, and then a communicating ramus from the lateral root of the median nerve to ulnar nerve. The communicating ramus is also called the lateral root of ulnar nerve. It passes distomedially in the axilla, posterior to the medial root, and usually anterior to the axillary artery, to join with the ulnar nerve.
The site of origin of the lateral root of ulnar nerve varies. For instance, instead of arising from the lateral root of median nerve it could originate more proximally from the lateral cord or the anterior division of middle trunk or even middle trunk itself.
Branches
There are no named branches.
Supplied Structures
The lateral root of ulnar nerve contains neuronal fibers from the C7 anterior ramus which reach the ulnar nerve mostly from the lateral root of median nerve via this intercommunicating ramus. It joins the ulnar nerve at or distal to the inferior border of the subscapularis muscle and is believed to provide motor innervation to the flexor carpi ulnaris muscle.
References
Chaudhary, P., R., S., Arora, K. and Kalsey, G. (2013) 'Communicating ramus from lateral root of median nerve to ulnar nerve and fusion of musculocutaneous nerve and median nerve – aconjunction of co-incidence? ', International Journal of Anatomy and Research, 1(2), pp. 93-99.Hollinshead, W. H. (1958) Anatomy for surgeons. Anatomy for Surgeons: Hoeber-Harper.
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Ulnar Nerve
The ulnar nerve is a mixed nerve that originates from the C8 and T1 nerve roots and exits the brachial plexus as a terminal branch of the medial cord.
