The brachial plexus ( Latin ; arm plexus ) is a network of the ventral branches of the spinal nerves of the last four neck and first thoracic segments (C5-Th1). In humans, smaller bundles of the fourth cervical vertebra segment (C4) and the second thoracic vertebra segment (Th2) are also involved in the formation of the brachial plexus. In some mammals, it begins with the sixth cervical nerve and extends to the second thoracic nerve (C6-Th2). The arm plexus belongs to the peripheral nervous system .
These spinal nerves unite after passing through the rear scalene (gap between the front and middle scalene ) to three main trunks ( trunks , more specifically, upper trunk , middle trunk and lower trunk ) and then a plurality of interconnected strands ( Fasciculi ; lateral cord , Fasciculus medialis and Fasciculus posterior ). These strands occur along the subclavian and axillary arteries in the axillary region . From these, in turn, nerves are formed which, due to the exchange of fibers in the plexus, always have parts of several (2–3) spinal nerves. These nerves innervate the entire upper (in animals, front) extremity and parts of the chest wall. The same principle is shown by the leg plexus ( lumbosacral plexus ).
Brachial plexus in humans
The human brachial plexus is formed from the spinal cord segments C5-Th1 and divides into a part above the clavicle (supraclavicular) and one below the clavicle (infraclavicular). The actual network for supplying the arm is formed by the infraclavicular part that pulls with the axillary artery .
Supraclavicular branches are:
- Nervus pectoralis medialis and lateralis (in animals Nervi pectorales craniales and caudales ) ( Fasciculus lateralis and medialis )
- Musculocutaneous nerve ( lateral fasciculus )
- Median nerve ( lateral and medial fasciculus )
- Ulnar nerve ( Fasciculus medialis )
- Nervus cutaneus brachii medialis ( Fasciculus medialis )
- Nervus cutaneus antebrachii medialis ( Fasciculus medialis )
- Axillary nerve ( posterior fasciculus )
- Radial nerve ( posterior fasciculus )
- Subscapular nerve ( posterior fasciculus )
- Thoracodorsal nerve ( posterior fasciculus )
Brachial plexus in pets
In domestic animals, the plexus behaves very similarly. The nervus cutaneus brachii medialis is not developed and the nervus cutaneus antebrachii medialis does not emerge from the plexus itself, but from the nervus musculocutaneus. The pectoral nerves run in several strands and are referred to as the pectoral nerves craniales and caudales . The subscapular nerve also consists of several branches ( nervi subscapulares ). In addition, a lateral thoracic nerve is isolated , which innervates the trunk skin muscle ( cutaneus trunci ) and is the efferent limb for the pannicular reflex .
Clinical significance of the brachial plexus
A conduction anesthesia can be used to temporarily switch off parts of the plexus and thus complete freedom from pain in the arm regions concerned can be achieved. Common methods are the interscalene block , the supraclavicular plexus block , the infraclavicular plexus block, and the axillary block .
In a demolition of the brachial plexus it comes to a complete paralysis ( paralysis ) of the muscles of the upper / front limb and a total failure of sensitivity . If individual fasciculi are partially torn off (or otherwise damaged), characteristic partial failures occur on the arm.
The passage of the brachial plexus through the posterior scalenus gap in the neck area can be narrowed, in which case what is known as a scalene syndrome may develop . The ulnar (little finger) side of the forearm and hand is painful and affected by abnormal sensations, which is increased when the arm is hanging down. Since the artery supplying the arm ( subclavian artery ) also passes through the scalenus gap, cyanosis (bluish discoloration due to lack of oxygen ) and edema (swelling due to impaired blood return) develop at the same time . The Adson test is then positive.
Damage to the brachial plexus with painful conditions is summarized under the collective term brachialgia .
As birth traumatic plexus palsy is defined as a paralysis ( paralysis ) of the arm, which is caused by train brachial plexus during birth. An unfavorable size ratio between the child and birth canal leads to what is known as shoulder dystocia . A distinction is made between stretching, tearing and tearing injuries (avulsion injuries). There is also the division into
- Erb-Duchenne type upper plexus paralysis (cervical nerves 4 to 6 (C4-6), affected). A flaccid arm palsy occurs (the hand can move) and phrenic nerve paresis .
- lower plexus paralysis type Klumpke (cervical nerve 7 to thoracic nerve 1 (C7-Th1) affected). The symptoms here are hand paralysis (paw pose) and Horner's syndrome . The prognosis is worse than that of upper plexus palsy.
Most injuries recover very well on their own. In the case of severe injuries (avulsion or avulsion injuries), direct surgery to restore the brachial plexus can be useful. Direct surgery only makes sense within the first nine months of life. It is therefore advisable to see a center for birth-trauma arm plexus palsy at an early stage. Later on, a further improvement can be achieved by loosening and relocating the tendons.
- TH Schiebler (Ed.): Textbook of the entire human anatomy. Cytology, histology, history of development, macroscopic and microscopic anatomy. 3. Edition. Springer-Verlag, Berlin / Heidelberg / New York / Tokyo 1983, ISBN 3-540-12400-4 , p. 231 f.
- Federative Committee on Anatomical Terminology (1998). Terminologia Anatomica . Stuttgart: Thieme