The Human Shoulder - Nervous system anatomy

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Nervous system

The easiest way to think of a nerve is as a collection of fibers. These fibers are neurons. A neuron runs from the spine and affects one muscle1. The nerve may be a collection of fibers coming from different spinal levels and may affect several muscles.

From the third to the eigth cervical vertebrae (C3-C8) and the first thoracic vertebrae (T1) nerves exit the spine and come together forming the brachial plexus. The brachial plexus has a pretty complicated set of divisions.

  • The Roots - these come off the spine as mentioned above
  • The Trunks - the trunks are clusters of roots. The Superior is from C5-6, the Middle is C7, and the Inferior is C8-T1
  • The Divisions - each of the Trunks has an anterior and posterior division
  • The Cords - The lateral cord comes from the anterior division of the superior and middle trunks; the posterior cord comes from all three posterior divisions; the medial cord comes from the anterior divison of the inferior trunk

From every level, roots to the cords, nerves exit the plexus and run toward their target muscles. The nerves are often referred to by the level of the spine that contributes to them. The spinal level is especially important when there is damage to the spine. A tumor on the right side of C5 could affect any nerve leaving at that space. Any nerve that is created from a C5 root could be affected. Remember though that there are a number of differnt fibers. In this way one root can affect several muscles, even though one fiber can only effect one muscle, because one root contains many fibers and several nerves.

The table below is created as a reference for anyone needing to know about a specific nerve.

Here is the complete list of branches of the brachial plexus:

Supraclavicular branches
Dorsal scapularC5 with contributions from C4Innervates rhomboid muscles and levator scapulae
Long thoracicC5-C7Innervates serratus anterior
Nerve to subclaviusSuperior trunk, C4-C6Innervates subclavius and sternoclviaular joint
SuprascapularSuperior trunk, C4-C6Innervates supraspinatus, infraspinatus and glenuhumeral joint
Infraclavicular branches
Lateral pectoralLateral, C5-C7Innervates pec. maj., but supplies a loop to med. pect. nerve
MusculocutaneousLateral, C5-C7innervates coracobrachilais, biceps, brachialis; continues as lateral antebrachial cutaneous nerve
MedianLater from C6-C7, medial from C8-T1Innervates the flexor muscles in forearm (except flexor carpi ulnaris, ulnar half of flexor digitorum profundus) and five hand muscles
Medial pectoralMedial cord, from C8-T1Innervates the pec. min. and part of pec. maj.
Medial brachial cutaneousMedial cord, from C8-T1Supplies the skin on the medial side of the arm
Medial antebrachial cutaneousMedial cord, from C8-T1Supplies the skin on the medial side of the forearm
Ulnarterminal branch of the medial cord, C7-T1Innervates one and one half flexor muscles in the forearm, most small muscles of the hand and skin of the hand medial to a line bissecting the 4th digit
Upper subscapularPost cord C5-C6Innervates top of subscapularis
ThoracodorsalPost cord C6-C8Innervates latissimus dorsi
Lower subscapularpost cord C5-C6innervates bottom of subscapularis and teres major
Axillaryterminal brach of post cord C5-C6innervates teres mino and deltoid, shoulder joint and skin over inferior part of deltoid
RadialTerminal branch post C5-T1Innervates triceps, anconeus, brachoradialis, extensors of forearm; supplies skin on posterior aspect of arm and forearm via posterior cutaneous nerves
Useful anatomical nomenclature
The Skeletal and Muscular Anatomy
The Nervous Anatomy
Common causes of shoulder pain and weakness
Shoulder rehabilitation following surgery
Therapies and interventions
Links and references
1Actually it can affect any organ, but we're focused on the muscles here.

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