Cervical Spinal Nerves
The neck anatomy contains a complex array of cervical nerves innervating the upper body including the face, shoulders, chest, arms, and hands. Nerves give us our sense of temperature, sensation, and allow us to respond to heat, cold, and touch by moving muscles, opening and closing pores, raising the hairs on our skin, amongst other actions. The structure of the cervical vertebrae allow these nerves to exit the spinal column through tiny gaps called the neural foramen between each pair of vertebrae. This neural foramen proved a protective channel for the nerves but is subject to impingement and compression if pathology occurs in the cervical spine. Damage to the cervical spinal nerves may result in pain, paraesthesia, weakness, numbness, and paralysis of the upper body.
In lower spinal regions the nerves generally have more space as they exit the spinal cord, which progresses to the bottom of the thoracic spine before the nerves come off like a horse’s tail – hence, cauda equina – in the lumbar and sacral regions. This means that a herniated disc or other compression in the lower spine is less likely to cause pinched nerves and resulting symptoms of nerve impingement. The cervical spine has much smaller vertebrae and any osteophyte growth or disc herniation or bulging can cause symptoms much more quickly.
Cervical Nerve Names
There are thirty-three nerves exiting the spinal column comprising: eight cervical nerves; twelve thoracic nerves; five lumbar nerves; five sacral nerves, and three coccygeal segments. The nerves are named according to the lower vertebral segment that they run between in the cervical spine, hence C4 nerve root at the C3-C4 segment. The exception to this rule is the eighth cervical nerve which emerges below the C7 vertebra instead. In the lumbar spine it is the upper vertebrae that they are named after, hence L3 at the L3-L4 vertebrae. Although there are seven cervical vertebra, there are eight cervical nerves, which can cause some confusion when discussing the location of neck pain and the nerve causing it. The first cervical nerve (C1) emerges from between the Atlas and the occipital bone and is, therefore, called the suboccipital nerve.
Nerves are protected by insulation in the majority of cases, and have the capacity to transmit or receive an electrical charge from the brain or from parts of the spinal cord. If the insulation or membrane becomes damaged or unhealthy due to lack of nutrition or injury then these electrical signals can be interrupted, become faulty or cease entirely. In conditions such as Multiple Sclerosis, it is this myelin sheath, or nerve insulation, that is affected, with the degeneration resulting in dysfunctional nerve signalling, pain, numbness, weakness, and possible paralysis.
Muscles Innervated by Cervical Nerves
The suboccipital nerve (C1) innervates the following muscles:
- rectus capitis anterior
- rectus capitis lateralis
- longus capitis
- splenius cervicis
- rectus capitis posterior major
- levator scapulae
The first and second cervical nerves are responsible for innervation of the head, face, inner middle ear, sinuses, eyes, upper neck, auditory nerves and other areas. The cervical nerves C3-C7 bear the responsibility of innervating the neck, shoulders, thyroid, teeth, tonsils, outer ear, nose, mouth, vocal cords, and more, with some of their individual responsibilities outlined below. The fourth cervical nerve innervates the thoracic diaphragm, leading to the creation of the surgical mnemonic “Cut C4, breathe no more.” The fifth cervical nerve has a more limited responsibility for muscle innervation than some of the others as it is associated with the Pectoralis major and minor through both the medial and lateral pectoral nerves.
The sixth cervical nerve shares a common branch from C5 and can, like any nerve become dysfunctional due to trauma, tumors, and degradation causing problems with muscle atrophy and tendinitis. C6 is involved in the innervation of a number of muscles in the rotator cuff and distal arm including the :
- Biceps Brachii
- Teres Minor
- Serratus Anterior
- Pectoralis Major
- Teres Major
- Extensor Carpi Radialis Brevis
- Extensor Carpi Radialis Longus
- Latissimus Dorsi
The seventh cervical nerve emerges from the spinal column above the seventh cervical vertebra and innervates the following muscles:
- Pectoralis major
- Pectoralis minor
- Latissimus dorsi
- Triceps brachii
- Flexor carpi ulnaris
- Palmaris longus
- Flexor pollicis longus
- Pronator quadratus
- Extensor carpi radialis brevis
- Extensor digitorum
- Extensor digiti minimi
- Extensor carpi ulnaris
- Abductor pollicis longus
- Extensor pollicis brevis
- Extensor pollicis longus
- Extensor indicis
The eighth cervical nerve is involved in the brachial plexus, a complex region of nerves and blood vessels which can become compressed and cause functional problems. C8 constitutes part of the radial and ulnar nerves and is responsible for a large part of innervation of the upper limbs. The primary function of C8 is the flexion of the fingers, with pathology of this nerve often tested by assessing function in the little finger or side of the hand. Numerous muscles are innervated by C8 including, but not limited to:
- Pectoralis minor – Medial pectoral nerve (C5, C6, C7,C8, T1)
- Flexor carpi ulnaris – Ulnar nerve (C7, C8, T1)
- Palmaris longus – Median nerve (C7,C8)
- Flexor digitorum superficialis – Median nerve (C8, T1)
- Flexor digitorum profundus – Median and Ulnar nerves (C8, T1)
- Flexor pollicis longus – Median nerve (C7,C8)
- Pronator quadratus – Median nerve (C7,C8)
C8 also innervates a number of other muscles, in part, along with the other cervical nerves.
Nerve Pain and Pathology
Neck pain can be caused by the nerve roots being irritated, compressed, or cut by pathology of the cervical spine. Acute trauma, such as whiplash, a penetrative stab-wound, or severe blow to the neck can inflict this damage. Chronic, repetitive, trauma may also cause nerves to be compromised, such as in the case of cervical arthritis, osteophyte growth, disc bulging, or disc herniation. The nerves pass through a weak spot in the intervertebral disc as they progress downward through the spine – this means that disc herniation commonly occurs right underneath the nerve root. In the neck it is commonly the nerve exiting the spinal column that is impacted by disc herniation, whereas in the lower spine it is the nerve passing through that level that is affected. Disc herniation may only cause symptoms in the arm (or leg if in the lower spine), meaning that the nerve root is not immediately obvious as the cause of the problem. Arm pain is usually accompanied by numbness and tingling that extends into the fingers in the event of a herniated disc in neck. Progressive weakness is often seen, with eventual muscle wasting, if the condition remains untreated, as the muscles are no longer correctly innervated by the nerves.
In most cases a pinched nerve in neck occurs at C6 or C7, although other nerves can be affected. The position of the nerve impingement can often be located due to the resulting symptoms, which helps focus X-rays, MRI and CT scans on the area thought to be affected. A pinched nerve at C5, for example, is likely to result in shoulder pain, slight numbness in the shoulder, and a progressive weakness in the deltoids and bicep muscles. In contrast, an injury to the nerve at C6 may instead cause weakness in the wrist extensors, and numbness and pain that travels down the arm and into the thumb. Pain and numbness in the arm and middle finger, with associated tricep weakness is likely if the nerve is pinched at C7, and pain and numbness in the outside of the hand (particularly the little finger) is connected to pathology at C8.
Damage to the myelin that insulates the nerves can also cause problems with nerve signal transmission. Similar to the insulation around electrical wire, myelin maintains nerve signal strength and where gaps develop in this insulation the signal can become weak, intermittent, or lost altogether. This is what occurs in Multiple Sclerosis, where lesions in the nerves degrade the myelin and prevent correct nerve signal transmission resulting in the weakness, numbness, pain, and poor mobility that is associated with this condition.
Cervical Nerve Recovery
Nerve pain is caused by the presence of both inflammation and pressure, so removing one of these triggers can relieve the pain and allow the nerve to heal. In most cases this is achieved through systemic anti-inflammatory drugs, such as NSAIDs, or through epidural steroid injections, oral steroids, or dietary and lifestyle modifications. Surgery in which the spine is decompressed to relieve the pressure on the nerves is usually a last resort, unless symptoms are progressing quickly and relief is no achieved through the use of pharmaceutical intervention. Keeping the joints mobile, through such things as physical therapy, can help with recovery as, even if a nerve heals, stiffness in the joints may make it harder to regain mobility.
Nerves, as they exit the spine and reach into the arm, hand, and fingers, consist of one long cell which makes them particularly susceptible to injury and, accordingly, slow to heal. Nerves heal from the root downward and can take weeks, months, or even years to heal if they do so at all after being injured. Short-term nerve compression, provided it is not severe, rarely causes permanent nerve damage, although symptoms may take a long time to recover from. Long-term, persistent, or severe compression can result in permanent dysfunction of the nerve; surgical decompression is indicated in these circumstances.
Nerves can also be overstretched if having to accommodate a herniated disc or bony growth. The symptoms will be the same as for pinched nerves, with transmission problems. If a nerve is stretched and breaks then the nerve may be able to grow back, assuming that the insulation remains intact. If a nerve is cut then the end farthest from the spinal cord dies. The nerve may, in some cases, grow back very slowly from the root end down the intact insulation until it reaches a receptor again. This can take years and will only occur if the insulation has not also been cut. If a nerve and the insulation are cut then the nerve fibers can sometimes grow into a ball at the severed end forming scar tissue referred to as a neuroma. Neuromas can be extremely painful as this sensitive ball of nerve fibers can cause an electrical sensation when the area is touched.
Nerve Transplant and Regrowth
A cut nerve may be stitched back together in a surgical procedure, along with its insulation. As nerve fibers are so tiny, this is a very delicate operation. On some occasions a nerve transplant may occur, where nerve tissue from elsewhere in the body, such as the leg, may be inserted to replace a cut nerve in order to allow innervation of the arms, or hands, for example. With millions of nerve fibers present in the nerve bundle it is extremely difficult to match them all back together so the emphasis is on repairing the insulation and helping the nerve to grow back down the tube.
Nerve transplants can result in loss of sensation in the area where the nerve was removed. Instead of using nerve tissue, a small gap may be bridged by a ‘conduit’ formed from a vein or special cylinder instead. Nerves grow at a rate of approximately an inch every month, making it a long process to restore connection to a peripheral limb or extremity. Pins and needles, paraesthesia, are common during the recovery process and are usually taken as a good sign that the nerve is restoring itself. Retraining of the brain and nervous system may be necessary after a long healing process as the brain can become ‘lazy’ and no longer respond to signals from a damaged nerve now healed.
Currently, there is no treatment for conditions such as Multiple Sclerosis, which actually restore the lost myelin that insulates healthy nerves. There are some treatments which appear to slow down the degeneration, however, which concentrate on suppressing the auto-immune destruction of myelin. Research on stem cell treatment to restore this myelin is underway, with hope that an effective restorative treatment can be found soon.
Jha, A(2010), MS could be reversed by activating stem cells in brain, new study suggests, The Guardian, Sunday 5 December 2010, http://www.guardian.co.uk/science/2010/dec/05/ms-activating-stem-cells-brain