Cervical plexus. Under the sternocleidomastoid muscle, the internal jugular vein is the element of the neck’s neurovascular bundle that is most intimately related to the output course of the anterior branches of spinal nerves C1, C2, C3, and C4

Cervical plexus. In a cross-section of the cervical region, it may be seen that the output of the anterior branches of the spinal nerves forming the cervical plexus is located in the boundary between the insertion of the prevertebral muscles anteriorly and the levator scapulae and scalene muscles posteriorly. On its way through the intervertebral foramen, each spinal nerve is located posterior to the ascending trajectory of the vertebral artery

Cervical plexus. The cervical plexus consists of three arches of nervous connection between the spinal nerves that integrate it. Each spinal nerve combines its axons with those of the adjacent spinal nerves, forming the C1–C2 loop, or arch of the atlas (arranged around the first cervical vertebra); the C2–C3 loop, or arch of the axis (surrounding the second cervical vertebra); and the C3–C4 loop

Cervical plexus. From the connections among the C1, C2, C3, and C4 nerves, specific nerves of this plexus are issued: motor nerves that innervate muscles in the region, sensory nerves (cut in this preparation) that will access the superficial plane to be distributed widely in the anterolateral region of the neck, and communicating branches to the sympathetic chain and cranial nerves XI and XII. Connections to the hypoglossal nerve (XII pc) provide part of the motor innervation of this plexus. Thus, the thyrohyoid nerve, the geniohyoid nerve, and the upper root of the cervical loop correspond to C1 and C2 nerve fibers that previously were incorporated into the path of this cranial nerve. Further, the upper root of the cervical loop joins the inferior root formed by branches from C2 and C3. Motor innervation of the sternothyroid, thyrohyoid, and omohyoid muscles is provided by this cervical loop

Cervical plexus. One of the main branches of the cervical plexus is the phrenic nerve, which provides motor innervation to the diaphragm and sensory branches to the pericardium and the diaphragmatic and mediastinal pleurae. This nerve originates from C4, with contributions from C3 and C5, and descends along the anterior scalene muscle belly to access the thorax. In the distribution area of the cervical plexus branches, also lies the path of the accessory nerve (cranial nerve XI). This trajectory may be found between the junction of the upper and middle third of the posterior sternocleidomastoid muscle border and the junction point of the lateral and middle third of the anterior border of the trapezius muscle

Cervical plexus. Sensory nerves originate in the cervical plexus. Before their subcutaneous distribution, they are gathered in a small area called the nervous neck point or Erb’s point. This point (circle) is an anatomic reference for anesthetic blockade of these nerve branches, and it is located at the midpoint of the posterior border of the sternocleidomastoid muscle. Another reference to its location is the path of the external jugular vein; the nerve point is cranial to the crossing point between this vein and the posterior border of the muscle

Cervical plexus. From the nervous neck point, the sensory nerves of the cervical plexus radiate to the anterior region of the neck, the supraclavicular area from the sternum to the acromion, the retroauricular occipital zone, the parotid region, and the ear

Brachial plexus. The brachial plexus is formed by the anterior branches of the spinal nerves from C5 to T1. From the brachial plexus, the peripheral nerves to the upper extremities originate. From the output of these spinal nerves in the paravertebral line of the lower cervical region, the brachial plexus passes through the interscalene space, the costoclavicular corridor, and the axillary cavity to reach the root of the upper extremity, where its terminal branches are constituted. In this trajectory, the plexus is accompanied by the axillary artery and the subclavian–axillary vein

Brachial plexus. The main trajectory of the brachial plexus is inferior, lateral, and posterior to the axillary cavity. It has an overall hourglass shape, expanded at the ends and clustered at its center, coinciding with its passage below the clavicle

Brachial plexus. The passage of the brachial plexus under the clavicle allows it to divide into two main segments: the supraclavicular plexus and the infraclavicular plexus. Each segment has characteristic anatomic references, specific topographic relations, collateral branches, and functional implications

Brachial plexus. The axonal recombination that occurs in the brachial plexus allows sensory and motor information from the spinal nerves that constitute it to be distributed to different peripheral nerves. This exchange follows a pattern that creates a series of defined and recognizable neural elements. Thus, the anterior rami of spinal nerves C5 to T1 combine to form trunks, each of which divides into an anterior and a posterior division. The combination of the anterior divisions on one hand and the posterior divisions on the other hand leads to the formation of brachial plexus fasciculi