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Structure of the cervical plexus, including the cutaneous and muscular branches.
Hello everyone! This is Megan from Kenhub, and welcome to another anatomy tutorial. In today's tutorial, we’re going to be looking at the cervical plexus and some of the nerves arising from this plexus. The cervical plexus is a cluster of nerves formed by the ventral rami of the first 4 cervical spinal nerves – C1 to C4. In some textbooks, you may find that the fifth cervical nerve is included in the cervical plexus due to the fact that it contributes to the formation of the phrenic nerve, which is one of the motor branches of the cervical plexus.
The cervical plexus gives off both muscular branches which are the anterior branches and cutaneous branches which are the posterior branches. It is formed in the neck and lies deep to sternocleidomastoid and anterolateral to levator scapulae and the middle scalene muscles. Right below the cervical plexus, there is another important plexus, the brachial plexus, which is responsible for cutaneous and muscular innervation of the entire upper limb. But, in today's tutorial, we're going to focus on the cervical plexus. We will look at some of the branches of the cervical plexus as well as the spinal nerves that contribute to its formation.
I'm going to begin the description of this plexus by first looking at the muscular or deep branches of the cervical plexus. The nerve seen here is a very important nerve known as the phrenic nerve. In this image, we can see the phrenic nerve running across the surface of the anterior scalene muscle. The phrenic nerve arises from the fourth cervical spinal nerve – C4 – but also receives contributions from the third cervical spinal nerve – C3 – and the fifth cervical spinal nerve – C5. Therefore, we can say, that the phrenic nerve receives innervation not only from the cervical plexus but also from the brachial plexus.
The phrenic nerve contains motor, sensory and sympathetic nerve fibers. As I said earlier, the phrenic nerve crosses the anterior scalene muscle entering into the superior thoracic aperture in front of the subclavian artery and travels to the middle mediastinum to reach the diaphragm. Here, we can see an inferior view of the diaphragm. We can see the xiphoid process here and the inferior costal margin. The phrenic nerve, which is highlighted in green here, is supplying motor innervation to the diaphragm and sensory innervation to the central tendon. The central tendon is the white area seen here.
The phrenic nerve also gives off sensory branches that supply the pericardium. They are known as the pericardial (2:50) branches and are highlighted in green in this image. Another important muscular branch of the cervical plexus is this structure seen here known as ansa cervicalis. The term, ansa cervicalis, is Latin for the handle of the neck. It is a loop of nerves formed by the anterior rami of the cervical spinal nerves C1 to C3. The ansa cervicalis is formed by a combination of the superior root of the ansa cervicalis and the inferior root of the ansa cervicalis.
The superior root which is also known as the anterior root is formed from the cervical spinal nerve – C1 – whereas the inferior root, also referred to as the posterior root, is formed from the second and third cervical spinal nerves – C2 and C3. The branches of ansa cervicalis mainly supply innervation to the infrahyoid muscles in the anterior cervical triangle.
Here, I just want to show you a list of the motor branches of ansa cervicalis. One of the branches is the geniohyoid nerve from C1. Geniohyoid is the only suprahyoid muscle that ansa cervicalis supplies. The other branches supply infrahyoid muscles such as thyrohyoid from C1, omohyoid from C1 to C3, sternohyoid also from C1 to C3, and sternothyroid from C1 to C3. These nerve branches supply motor innervation to their corresponding muscles.
Now that we covered ansa cervicalis, let's look at this nerve which is not part of the cervical plexus but is closely associated to it. The nerve we're talking about is the hypoglossal nerve. The hypoglossal nerve is cranial nerve twelve. It exits the skull via the hypoglossal canal and courses downwards. As it completes this descent and begins to pass forward across the internal and external carotid arteries, some fibers join with the fibers of the C1 nerve and form the superior root of the ansa cervicalis we saw previously. These fibers finally innervate the geniohyoid and thyrohyoid muscles. In this way, the hypoglossal nerve is related to and forms anastomosis with the cervical plexus.
So, here, we can see the hypoglossal nerve highlighted in green. We can see its fibers joining with C1 which is highlighted in yellow. Keep in mind that the main branch of the hypoglossal nerve continues and innervates the thyroid muscle with fibers from the first cervical spinal nerve C1. This is before it goes on to innervate some of the extrinsic and intrinsic muscles of the tongue.
Another important communication of the cervical plexus is with the eleventh cranial nerve or the accessory nerve. This nerve is a motor nerve and is unique in the way that it has a cranial and spinal portion. The spinal portion arises from the ventral horn cells at the level of C1 to C5 spinal nerves. The fibers emerge from the cord laterally between the anterior and posterior nerve roots and form a trunk which ascends into the skull through the foramen magnum. It then exits the skull through the jugular foramen and runs towards the sternocleidomastoid muscle providing motor innervation to this muscle. It pierces sternocleidomastoid and courses obliquely to the end of the deep surface of the trapezius muscle innervating that as well. As it transverses the sternocleidomastoid muscle, it receives a branch which is known as the branch to trapezius and originates from the cervical plexus namely C2 and C3 cervical nerves. So, in this way, the cervical plexus anastomosis with the accessory nerve and contributes to the innervation of the trapezius muscle.
Before we move on to the cutaneous branches, I would like to mention here that the cervical plexus gives off several other muscular branches that supply some of the prevertebral and lateral vertebral muscles in the neck. These muscles include rectus capitis anterior, rectus capitis lateralis, longus colli, and longus capitis. So far, we've looked at the deep branches of the cervical plexus which are mainly motor branches.
Now, let's move on to look at the cutaneous branches of the cervical plexus that are sensory nerves. There are four sensory branches namely, the lesser occipital nerve, the great auricular nerve, the transverse cervical nerve, and the supraclavicular nerves. Here, we can see the lesser occipital nerve which is the uppermost of the sensory or cutaneous branches of the cervical plexus. It is formed from the loop of the ventral rami of the second cervical nerve – C2 – and it passes upwards at the posterior margin of sternocleidomastoid. In the next image, we can see that the lesser occipital nerve supplies the skin of the neck and the scalp posterior to the clavicle.
Another sensory or cutaneous branch of the cervical plexus is the nerve seen highlighted in green here. It's called the great auricular nerve. It originates from the second and third cervical spinal nerves and courses upwards crossing sternocleidomastoid onto the parotid gland. In the next image, we can see this. We can see the great auricular nerve highlighted in green superficial to the parotid gland. Here, the great auricular nerve divides to innervate the skin over the parotid gland, the posterior aspect of the auricle, and the mastoid area.
The transverse cervical nerve, or the anterior cervical cutaneous nerve, consists of branches from the cervical nerves C2 and C3. In the next image, we can see the transverse cervical nerve horizontally crossing the sternocleidomastoid to supply the anterior and lateral parts of the neck. The supraclavicular nerves are sensory branches of the cervical plexus. They arise from the loop between the third cervical spinal nerve and the fourth cervical spinal nerve as a common trunk under the cover of the sternocleidomastoid. The supraclavicular nerves are cutaneous branches and they spread out fanning around the shoulder and clavicular regions.
A good way to remember the names of the four sensory branches of the cervical plexus is by using the mnemonic OATS. The O comes from lesser occipital nerve, the A comes from great auricular nerve, the T comes from transverse cervical nerve, and the S comes the supraclavicular nerves.
So now that we've described all of the branches of the cervical plexus, let's go back and remember that the cervical plexus is made up of the ventral rami of the spinal nerves C1 to C4. Each of the cervical spinal nerves communicate with one another in a superior-inferior fashion close to their origins. Here we can see the first cervical spinal nerve – C1 – which, along with the second cervical spinal nerve and the third cervical spinal nerve, forms the ansa cervicalis as we have already seen.
We also have to mention that the first three cervical spinal nerves along with the fourth cervical spinal nerve receive communicating fibers that are contributions from the sympathetic trunk to the cervical plexus. It should be noted that each of these nerves except C1 divide into an ascending and descending branch and unite with branches of the adjacent cervical nerve to form loops.
Before we finish this tutorial, I'd like to briefly mention a clinical entity which is related to the cervical plexus. The phrenic nerve is one of the most important branches of the cervical plexus. It innervates the diaphragm and is crucial for the breathing process, so when the diaphragm contracts, the chest cavity expands and creates room for inhaled air.
There are several conditions which can cause damage to the phrenic nerve. These are a spinal cord injury at the level of C3 to C5 spinal nerves, a neck injury that affects the phrenic nerve, or a surgical complication in the area where the nerve passes through. These conditions may cause paralysis of the diaphragm and the symptoms vary depending on whether one or both phrenic nerves are affected. So, some patients may be asymptomatic while others will report dyspnea and orthopnea. If the symptoms are severe, the patient may need cardiopulmonary support.
And that brings us to the end of this tutorial. Thanks for listening.
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