The Cervical Plexus by Prof

Home , Ansa cervicalis, Cervical plexus, Lesser occipital nerve, Supraclavicular nerves

The Cervical Plexus By Prof. Dr. Imran Qureshi The Cervical Plexus is formed by the ventral rami of C1, C2, C3, and C4. It supplies: o Areas of the Skin o The Respiratory Diaphragm o The Strap muscles of the Anterior Triangle of the Neck, and o The nerves to The Sternocleidomastoid, Trapezius, Scalenes, Levator Scapulae, Longus Coli, Longus Capitis etc. I. Branches to the Skin: These appear in the posterior triangle at the midpoint of the posterior border of the sternocleidomastoid. They are: The Greater Auricular Nerve, which crosses the Sternocleidomastoid obliquely, posterior to the external jugular vein and ascends toward the lobe of the ear, Lesser Occipital Nerve, which parallels the posterior border of Sternocleidomastoid and ascends toward the occipital region, Anterior Cutaneous (Transverse Cervical) Nerve, which crosses transversely across the Sternocleidomastoid to reach the skin of the anterior triangle of the neck, The Supraclavicular trunk, which passes from under cover of the Sternocleidomastoid and divides into: The Lateral supraclavicular nerve, The Intermediate supraclavicular nerve, and The Medial supraclavicular nerve. The Lateral supraclavicular passes superficial to the trapezius to supply the skin of the shoulder tip. The Intermediate and Medial supraclavicular nerves pass superficial to the clavicle to the skin of the pectoral region.

II. Nerve to Respiratory Diaphragm (Phrenic Nerve): This nerve, which arises from the ventral rami of C3, C4, and C5, is the motor nerve of the diaphragm. It also supplies sensory fibers, including pain, to the central area. The contribution from C5 may join that from C3 and C4 directly, or secondarily as a branch from the nerve to the subclavius muscle. The contributions from C3 and C5 are small. C4 supplies most of the fibers. III. Nerves to Strap Muscles of the Anterior Triangle of the Neck: This element of the cervical plexus is often described as the "looped" segment of the plexus. From the loop between C1 and C2 a branch joins the Hypoglossal nerve (XII cranial nerve). Its fibers leave XII as the descending hypoglossal (dh); branches to the thyrohyoid (th); and geniohyoid (gh) muscles. The descending cervicalis (dc) is formed by branches from C2 and C3 and unites with the descending hypoglossi (dh) to form the ansa (loop) cervicalis (or ansa hypoglossi). From the ansa cervicalis arise the nerves to the sternothyroid (st), sternohyoid (sh), and both bellies of the omohyoid (oh) muscles. No nerve fibers from XII enter into the supply of the muscles mentioned. The nerve fibers which make up the branch to XII come from the loop between C I and C2 nerves, travel with XII, then leave it. IV. Branches of Anterior Rami of Cervical Nerves Which Supply Muscles MUSCLES BOUNDING THE POSTERIOR TRIANGLE The sternocleidomastoid from C2 (the motor nerve to this muscle is XI). Trapezius from C3 and C4 (the motor nerve is XI). MUSCLES FORMING THE FLOOR OF THE POSTERIOR TRIANGLE Anterior scalene C4 to C7. Middle scalene C3 to C7. Posterior scalene C3 to C5. Levator scapulae C3 to C5 NERVE DISTRIBUTION OF SPINAL CORD SEGMENT: There are 31 pairs of spinal nerves (8 cervical, 12 thoracic, 5 lumbar, 5 sacral and 1 coccygeal).

Each spinal nerve is formed by the union of a dorsal root (sensory) and a ventral root (motor) which stem from the spinal cord. The portion of the spinal cord from which a pair of spinal nerves arises is called a segment of the spinal cord. The distribution of nerves arising from a single spinal segment may be widespread, e.g. The Supraclavicular nerves are composed of nerve fibers from spinal cord segments C3 and C4. The Phrenic nerve is composed of nerve fibers from segments C3, C4, and C5. The Supraclavicular nerves supply sensory fibers to the skin of the neck, the upper pectoral region and the tip of the shoulder. The Phrenic nerve supplies sensory and motor fibers to the respiratory diaphragm. The area of skin served by the dorsal root of a spinal nerve is called a dermatome. Skin maps showing the distribution of spinal cord segments on the basis of dermatomes are more precise than those showing areas of distribution of a peripheral cutaneous nerve. The peripheral nerve usually contains fibers from more than one spinal cord segment. Referred Pain: Referred pain is defined as “Pain in a part other than that in which the cause that produced it is situated”. The anatomical basis for referred pain is that pain fibers from one or more segments of the spinal cord are distributed to widely separated parts of the body. The distribution of C3 and C4 spinal cord segment fibers that receive pain stimuli offers an excellent example. The position of the dermatomes for segments C3 and C4 are well known, as is the pathway by which pain fibers reach them, i.e. via the supraclavicular nerves. It is also known that, via the phrenic nerve, the same segments receive pain fibers from the diaphragm. Irritation of C3 and C4 nerve endings in the diaphragm results in pain at a conscious level and this pain is referred to the skin over the clavicle and especially over the tip of the shoulder, "shoulder tip pain." Apparently, the segment of most significance is C4 and its dermatome. The Phrenic nerve endings may be irritated through either the superior or inferior surface of the diaphragm; for example, an inflamed gall bladder producing an exudate which impinges on the diaphragm can trip off the reaction. Remember that these nerves are paired and that this reaction can occur on either side of the body. Also remember that the phrenic nerve not only supplies sensory fibers to the diaphragm, but it is also the sole motor supply to this important muscle.